USMLE 1 Q 12

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    1>A 25-year-old male presents to his family physician with the following
    statement: "Doctor, I can't urinate in public restrooms. I can if
    there is no one around, but if I go to the restroom in a movie, an
    airport, at the ball park or anywhere that someone else comes in,
    I can't urinate. Even if I have already started, it just stops and
    I can't get it going until the other person leaves. I am so
    embarrassed. What do they think of me if they see I can't
    do what every other man can do?" Which of the following
    is the most likely diagnosis?
    A. Anxiety disorder due to a general medical condition
    B. Panic disorder
    C. Social phobia
    D. Specific phobia
    E. Substance-induced anxiety disorder

    2>Autopsy of an elderly individual who died in a nursing home with no
    known genetic diseases reveals small amounts of amyloid deposition
    in the heart. Amyloid deposition is not seen in other organs. There
    is no history of long-standing inflammatory disease. This type of
    amyloid would be most likely to be composed of which of the
    following proteins?
    A. Amyloid-associated protein
    B. Amyloid light chain protein
    C. Beta-2-amyloid protein
    D. Beta-2-microglobulin
    E. Transthyretin

    3>A family is referred to a genetic specialist because of mild mental
    retardation in several of the school-age children. Laboratory evaluation
    demonstrates a specific chromosomal breakage site in metaphase studies
    of lymphocytes cultured with methotrexate. Which of the following
    chromosomes is most likely to be specifically affected?
    A. X
    B. Y
    C. 13
    D. 16
    E. 21

    4>A 5-year-old male with no previous medical history is brought to the
    ER by his mother because he accidentally ingested a large dose of rat
    poison. He is conscious but appears quite agitated. On physical exam,
    he is found to have a blood pressure of 110/70 and a heart rate of 90.
    Labs are significant for an elevated PT but a normal PTT. The patient
    should be immediately treated with
    A. atropine
    B. flumazenil
    C. N-acetylcysteine
    D. protamine
    E. vitamin K

    5>A 67-year-old man is evaluated for persistent shooting pains, lower
    limb ataxia, and bladder dysfunction. Physical examination demonstrates
    small irregular pupils that constrict with accommodation but not in
    response to light. A VDRL test is positive. A CT scan of the spinal
    cord would most likely demonstrate atrophy of which of the following
    A. Dorsal column
    B. Dorsal horn
    C. Lateral column
    D. Ventral column
    E. Ventral horn

    6>What is the earliest age at which toilet training is likely to be
    A. 10 months
    B. 13 months
    C. 16 months
    D. 19 months
    E. 22 months

    7>A 13-year-old boy is brought to a rural clinic because of poor school
    performance. His parents state that he did not begin talking until after
    three years of age, and still does not use language as effectively as
    his sister, who is 6-years-old. A careful family history reveals that
    a maternal grandfather was mildly retarded. The mother has two sisters,
    both of whom are apparently normal, but the mother admits that she did
    not do well in school, and dropped out at the age of 16. Physical
    examination of the child reveals large ears, a long, narrow face,
    and large testes. Which of the following genetic mechanisms most
    likely accounts for the observed findings in the son?
    A. Expanded trinucleotide repeat
    B. Genomic imprinting
    C. Robertsonian translocation
    D. Trisomy 13
    E. Trisomy 18

    8>A 15-year-old is brought to the emergency department in a coma. An alert
    ambulance attendant notes that the patient's breath smells like acetone.
    This would be most consistent with which of the following?
    A. Alcohol intoxication
    B. Diabetic hyperosmolar coma
    C. Diabetic ketoacidosis
    D. Heroin overdose
    E. Profound hypoglycemia

    9>A 28-year-old male with history of mood disorder presents with a decreased
    need for sleep, irritability, recklessness, and increased energy. Which of
    the following is the most likely additional presenting symptom?
    A. Depressed mood
    B. Fear of dying
    C. Insomnia
    D. Racing thoughts
    E. Recurrent thoughts and actions that relieve anxiety when
    carried out
    10 A 10-year-old girl who is a suspected victim of child abuse
    is referred to a psychologist for evaluation. As part of her
    workup, the patient is asked to construct a story based on pictures
    . Which of the following psychometric measures was utilized?
    A. Minnesota Multiphasic Personality Inventory
    B. Myers-Briggs Personality Inventory
    C. Rorschach Test
    D. Thematic Apperception Test
    E. Type A and B Behavior Patterns Test

    A 65-year-old woman has a long-standing dementing disorder characterized
    by deterioration in personality, neglect of personal hygiene, impaired
    judgment, and disinhibited behavior. MRI demonstrates severe cortical
    atrophy limited to the frontal lobes and anterior two thirds of the
    temporal lobes, while the remaining cortex is preserved. No evidence
    of recent or remote infarcts is found. Which of the following diagnoses
    is most consistent with these pathologic and clinical features?
    A. Alzheimer disease
    B. Creutzfeldt-Jacob disease
    C. Dementia with Lewy bodies
    D. Frontotemporal dementia
    E. Vascular dementia
    A 50-year-old woman who works as a paralegal in a law firm comes to her
    local doctor because of problems with sleep. The patient says that over
    the past several weeks, she hasn't slept well, feels tired, and has had
    headaches. She does not smoke or drink alcohol, except on special
    occasions, and does not take any medications. The patient's pupils
    are 5 mm in size, equal and reactive, with both the direct and
    consensual light reflexes intact. Accommodation is unimpaired.
    Examination of the visual fields and funduscopy are unremarkable.
    Extraocular movements reveal normal conjugate, oblique, and
    downward movement, but she is unable to look upwards. No other
    abnormalities are found on the neurological examination. Which
    of the following is the most likely diagnosis?
    A. Acoustic neuroma
    B. Astrocytoma in the cerebellum
    C. Craniopharyngioma
    D. Parasagittal meningioma
    E. Pinealoma

    13>A one-year-old baby presents with increasing flaccid paralysis, lack
    of coordination, and hyporeflexia. Over the next several years, the
    child's condition deteriorates to a bedridden vegetative state.
    Funduscopic examination reveals optic atrophy. Extensive enzymological
    studies document a deficiency of arylsulfatase A (cerebroside sulfatase)
    in leukocytes. Which of the following is the most likely diagnosis?
    A. Gaucher's disease
    B. Krabbe's disease
    C. Metachromatic leukodystrophy
    D. Niemann-Pick disease
    E. Tay-Sachs disease

    14>A 60-year-old male executive with a history of angina pectoris and
    depression had bypass surgery the previous day. His depression has
    responded well to selective serotonin reuptake inhibitors (SSRIs)
    and there is no history of psychosis in the past. He now presents
    with confusion, agitation, irritability, and tries to remove his
    IV lines. His level of consciousness fluctuates, and at times he
    forgets who he is. He is given a neuroleptic drug, and appears
    much improved. What is the most likely diagnosis?
    A. Adjustment disorder
    B. Delirium
    C. Dementia
    D. Exacerbation of depression with suicidal ideation and
    psychotic features
    E. Schizophrenia

    15>A 38-year-old woman with a history of multiple sexual partners is most
    at risk for which of the following?
    A. Bladder carcinoma
    B. Cervical carcinoma
    C. Endometrial carcinoma
    D. Ovarian carcinoma
    E. Rectal carcinoma

    16>Which of the following chemotherapeutic agents is specific for the M
    phase of the cell cycle?
    A. Cytarabine
    B. Daunorubicin
    C. Hydroxyurea
    D. Mechlorethamine
    E. Vincristine

    17>A 47-year-old man with a history of type 2 diabetes, depression, and
    hypertension presents to the emergency department with spontaneous
    priapism. Which of the following drugs is the most likely cause of
    his current condition?
    A. Atenolol
    B. Furosemide
    C. Glyburide
    D. Paroxetine
    E. Trazodone

    18>Tay-Sachs disease, an autosomal recessive disease caused by a deficiency
    of hexosaminidase A, is lethal in childhood. In a population of Ashkenazi
    Jews, blood testing shows the frequency of heterozygotes to be 0.1. What
    is the probability that the first child of two individuals from this
    population with no family history of the disease will have Tay-Sachs?
    A. 0.25
    B. 0.11
    C. 0.0625
    D. 0.0025
    E. Cannot be calculated from the information given

    19>A 44-year-old male with a history of polysubstance abuse presents with
    nausea, vomiting, increased heart rate, high blood pressure, sweating,
    agitation, and weakness. He also complains of seeing monsters on the
    wall during the interview. Which of the following best accounts for
    this presentation?
    A. Alcohol intoxication
    B. Alcohol intoxication or cocaine withdrawal
    C. Alcohol withdrawal
    D. Alcohol withdrawal or cocaine intoxication
    E. Cocaine intoxication
    F. Cocaine withdrawal

    20>In which of the following laboratory tests would you expect to find the
    greatest disparity in reference intervals between men and (non-pregnant)
    A. Mean corpuscular volume
    B. Serum alkaline phosphatase
    C. Serum ferritin
    D. Serum glucose
    E. Serum sodium

    21>A 7-year-old girl is walking across a vacant lot and steps on a nail. The
    next day, her foot is sore and the wound appears inflamed. During these
    early stages of infection, which of the following compounds exert the
    most powerful chemotactic effect on neutrophils, causing them to migrate
    into the inflamed area?
    A. C5a and IL-8
    B. IL-1 and tumor necrosis factor
    C. LTC4 and LTD4
    D. PGI2 and PGD2
    E. Thromboxane and platelet activating factor

    22>A 23-year-old woman with a history of sickle cell disease presents with
    fever and severe bone pain localized to her left tibia. X-ray reveals a
    lytic lesion and blood cultures reveal infection. A bone culture grows
    gram-negative rods. Which of the following best describes the infecting
    A. It is a facultative intracellular parasite
    B. It is a nonmotile facultative anaerobe
    C. It is comma-shaped and sensitive to acidic pH
    D. It is motile and does not ferment lactose
    E. It is motile and oxidase positive

    23>A 17-year-old girl loses her best friend in an automobile accident. After
    the death, she starts writing for hours daily in her diary. This would
    most likely be an example of which of the following defense mechanisms?
    A. Identification
    B. Projection
    C. Rationalization
    D. Regression
    E. Sublimation

    24>Physical examination of a neonate demonstrates abnormal facies with a
    small lower jaw, low-set ears, and a prominent occiput. The feet have a
    rocker-bottom deformation, and the infant is hypertonic. Cardiac
    evaluation demonstrates a ventricular septal defect. Which of the
    following is the average life-span for infants with this neonate's
    A. 2-3 months
    B. 1-2 years
    C. 4-7 years
    D. 15-25 years
    E. Normal life expectancy

    25>A biopsy of a brain tumor from a 42-year-old man reveals a glial neoplasm
    consisting of atypical astrocytes with scattered mitoses. Besides mitotic
    activity, which of the following markers can provide information about
    the neoplasm's proliferative activity?
    A. bcl-2
    B. Glial fibrillary acidic protein (GFAP)
    C. Ki-67
    D. p53
    E. Ubiquitin

    26>A pharmacologist is determining the pharmacokinetic parameters of a novel
    antibiotic in order to determine the proper dosage. The drug is a
    weak organic acid with a pKa of 3.0. Assuming a pH of 2.0 in the
    stomach, approximately what percent of the drug will be in a form
    that can be rapidly absorbed from the stomach?
    A. 0.1
    B. 1
    C. 10
    D. 50
    E. 90
    F. 99

    27>A 38-year-old woman vacationing in Connecticut is bitten by a tick.
    She does not seek medical treatment and eventually develops chronic
    arthritis of the knee and hip joints and paralysis of the left facial
    muscles. A physical examination during the early stages of the disorder
    would most likely have revealed
    A. aphthous ulcers in the mouth
    B. erythema chronicum migrans
    C. flaccid paralysis of limb flexors
    D. purpuric lesions in a bathing trunk distribution
    E. spastic paralysis of limb extensors

    28>A 20-year-old man with new onset of seizures and no history of hypertension
    is evaluated with a contrast-enhanced CT scan of the head, which
    demonstrates a mixed parenchymal and subarachnoid hemorrhage. The
    parenchymal hemorrhage is centered over one cerebral hemisphere.
    Which of the following is the most likely source of the hemorrhage?
    A. Arteriovenous malformation
    B. Berry aneurysm
    C. Bridging vein
    D. Charcot-Bouchard aneurysm
    E. Middle meningeal artery

    29>A baby is born with a small head, small eyes, and 6 fingers on each hand.
    Two dimensional echocardiography reveals congenital heart defects.
    Which of the following genetic conditions is most likely to be the
    cause of this child's presentation?
    A. Trisomy 13
    B. Trisomy 18
    C. Trisomy 21
    D. XXY
    E. XYY

    30>A 35-year-old male presents to an infectious disease specialist with
    recurrent infections with encapsulated bacterial organisms. The history
    indicates that these infections have become apparent in the last
    6 months. Laboratory findings indicates that the total immunoglobulin
    level exceeded 900 mg/dL with a low CH50 (hemolytic complement) level.
    Which of the following is the correct diagnosis?
    A. Acquired hypogammaglobulinemia (common variable hypogammaglobulinemia)
    B. C3 deficiency
    C. Hyper-IgM syndrome
    D. Wiskott-Aldrich syndrome
    E. X-linked infantile hypogammaglobulinemia

    31>A researcher develops a specific antibody to the complement component C3b
    . Assume that intravenous administration of the antibody prevents the
    biological effects of C3b. Administration of the antibody would be
    expected to interfere with which of the following biological functions?
    A. Decreased appetite
    B. Fever
    C. Increased collagen synthesis by fibroblasts
    D. Increased leukocyte adherence to endothelium
    E. Opsonization to facilitate phagocytosis

    32>A 42-year-old man previously diagnosed with kidney stones complains
    of gnawing, burning epigastric pain. On questioning, he also notes
    moderate to severe diarrhea. Measurement of the patient's basal gastric
    acid output reveals that it is markedly elevated. These symptoms are
    likely the result of which of the following neoplastic syndromes?
    A. Familial polyposis coli
    B. MEN I
    C. MEN IIA
    D. MEN IIB
    E. MEN III

    33>During the isolation of Met-enkephalin (Tyr-Gly-Gly-Phe-Met) from
    post-mortem human brain tissue, researchers find that the peptide
    is rapidly degraded by peptidases in 1 minute at 37 C. Detailed
    analysis of the peptide cleavage pattern of Met-enkephalin is
    investigated with two candidate enzymes. Using the drug bestatin,
    the investigators found no detectable Tyr-Gly-Gly-Phe-Met but did
    find significant concentrations of Tyr-Gly-Gly. Using thiorphan,
    there was no detectable Tyr-Gly-Gly-Phe-Met, but there was a
    high concentration of Tyr. Which of the following is the best
    conclusion about Met-enkephalin metabolism that can be drawn
    from these data?
    A. Bestatin inhibits an aminopeptidase, and thiorphan inhibits an endopeptidase in the degradative pathway
    B. Bestatin inhibits a carboxypeptidase in the degradative pathway
    C. Bestatin inhibits an endopeptidase in the degradative pathway
    D. Thiorphan inhibits an aminopeptidase, and bestatin inhibits an endopeptidase in the degradative pathway
    E. Thiorphan inhibits an aminopeptidase in the degradative pathway

    34>The pharmacokinetic properties of a new drug are being studied in
    normal volunteers during phase I clinical trials. The volume of
    distribution and clearance determined in the first subject are
    40 L and 2.0 L/hour, respectively. The half-life of the drug
    in this subject is approximately
    A. 2 hours
    B. 6 hours
    C. 14 hours
    D. 21 hours
    E. 40 hours

    35>The pregnant mother of a 6-year-old son with glucose-6-phosphate
    dehydrogenase deficiency is very worried that her female fetus
    will have the disease. The father and mother are clinically normal.
    Which of the following is true about her baby?
    A. The baby has a 25% chance of clinical disease
    B. The baby has a 50% chance of being a carrier
    C. The baby has a 50% chance of clinical disease
    D. The baby will be a carrier
    E. The baby will have clinical disease

    36>Medical students at a major teaching hospital are routinely assigned
    to observe obstetric patients and to assist during delivery. When a male
    medical student introduces himself to an obstetric patient, the patient
    becomes agitated and requests that no students be present during her
    delivery. The patient had been informed, prior to admission, that this
    was a teaching hospital and that a student would be assigned to her
    case. When informed of the patient's refusal, the attending physician
    in charge should
    A. ask the patient's husband for his consent
    B. assign a female medical student to observe
    C. not allow any medical students to observe this patient
    D. have the patient's nurse seek permission
    E. have the student approach the patient again and explain the necessity for student observation
    F. have the student observe in the background as a part of the health care team.
    G. meet with the patient and discuss the value of observation in medical training

    37>A 24-year-old migrant farm worker is rushed to a nearby emergency room
    after an accidental exposure to parathion. He is in respiratory distress
    and is bradycardic. Which of the following drugs can be given to increase
    the activity of his acetylcholinesterase?
    A. Atropine
    B. Deferoxamine
    C. Dimercaprol
    D. N-acetylcysteine
    E. Physostigmine
    F. Pralidoxime

    38>A 74-year-old woman with multiple myeloma is being treated with high
    doses of doxorubicin (Adriamycin). She has also received
    cyclophosphamide and prednisone recently. During his examination,
    the physician should check the patient for
    A. abdominal tenderness
    B. bladder distention
    C. limitation of movement
    D. papilledema
    E. pulmonary rales

    39>A 60-year-old man hospitalized with metastatic colon cancer signs a
    DNR order. This means that the medical staff treating him is required
    A. discontinue narcotic pain medication
    B. not attempt CPR in case of cardiac arrest
    C. refrain from prescribing future medications
    D. withhold parenteral nutrition and IV fluid hydration

    40>A 27-year-old swimmer who feels insecure about her athletic abilities
    harshly criticizes her teammates' techniques. Which of the following
    ego defense mechanisms is she displaying?
    A. Displacement
    B. Projection
    C. Reaction formation
    D. Repression
    E. Sublimation

    41>In a certain population, the frequency of color-blind males is 1 in 100.
    Assuming that the population is in Hardy-Weinberg equilibrium at this
    locus, the frequency of color-blind females is approximately
    A. 0.0001
    B. 0.0005
    C. 0.01
    D. 0.02
    E. 0.025

    42>A newborn presents with severe acidosis, vomiting, hypotonia, and
    neurologic deficits. Serum analysis reveals elevated levels of lactate
    and alanine. These observations suggest a deficiency in which of the
    following enzymes?
    A. Alanine aminotransferase
    B. Glutamate dehydrogenase
    C. Lactate dehydrogenase
    D. Pyruvate carboxylase
    E. Pyruvate dehydrogenase

    43>A 5-year-old boy who has been diagnosed with a mucopolysaccharidosis is
    given an IQ test and found to have nearly normal intellectual functioning.
    Which of the following are possible diagnoses for this patient?
    A. Hunter syndrome or Hurler syndrome
    B. Hunter syndrome or Scheie syndrome
    C. Hurler syndrome or Sanfilippo syndrome
    D. Morquio syndrome or Sanfilippo syndrome
    E. Morquio syndrome or Scheie syndrome

    44>A 72-year-old female patient with Alzheimer's disease, but no other
    medical problems, suddenly becomes comatose and dies due to an intracranial
    hemorrhage that caused severe damage to her entire left cerebral
    hemisphere. There was no evidence or history of trauma. What is the
    likely cause of this hemorrhage?
    A. Epidural hematoma
    B. Subdural hematoma
    C. Amyloid angiopathy
    D. Rupture of berry aneurysm
    E. Rupture of Charcot-Bouchard aneurysm

    45>A 23-year-old man living in a group home for the developmentally
    challenged has an IQ of 73. He does not read or write, and communicates
    with one or two word utterances. He will not interact with other group
    home members, and since birth he has "pulled back" and becomes agitated
    when others get physically close to him. In his room, everything is in
    a given place; if any of his belongings are moved, he becomes quite
    disturbed. Which of the following is the most likely diagnosis?
    A. Asperger's disorder
    B. Autistic disorder
    C. Childhood disintegrative disorder
    D. Obsessive compulsive disorder
    E. Schizophrenia, catatonic

    46>Which of the following amino acids is most responsible for the buffering
    capacity of hemoglobin and other proteins?
    A. Arginine
    B. Aspartic acid
    C. Glutamic acid
    D. Histidine
    E. Lysine

    47>Addition of which of the following exhaustively 14C labeled substrates
    would lead to evolution of 14CO2 from a cell-free suspension containing
    all the enzymes and substrates required for the synthesis of uridylic
    A. Aspartate
    B. Carbamoyl phosphate
    C. Glutamine
    D. Glycine
    E. N10-Formyltetrahydrofolate

    48>A 54-year-old college professor is diagnosed with colon cancer and has
    it resected. Tumor is found extending from the mucosa to the serosal
    surface of the colon and in three regional lymph nodes. Histological
    examination demonstrates that the tumor is composed of cells with
    ovoid, relatively small nuclei that form well-defined glands. Which
    of the following best describes this tumor?
    A. High stage, high grade
    B. High stage, low grade
    C. Low stage, high grade
    D. Low stage, low grade

    49> A 52-year-old man presents to his physician after a community health
    screening test reveals a fasting glucose of 170 mg/dL. Physical
    examination is remarkable for bronze skin pigmentation, hepatomegaly,
    splenomegaly, and limitation of motion in the second and third
    metacarpophalangeal joints of both hands. A liver biopsy obtained
    from the patient is shown above. The man has no known history of
    hemolytic anemia, and takes daily multivitamins without minerals.
    Which of the following pigments is most likely present in the
    man's liver?
    A. Bilirubin
    B. Carotene
    C. Ferritin
    D. Lipofuscin
    E. Melanin
    50> Which of the following enzymes is located at arrow 1 in
    the electron micrograph above?
    A. Carnitine acyltransferase II
    B. Fatty acyl CoA synthetase
    C. Glucose-6-phosphate dehydrogenase
    D. Hexokinase
    E. Pyruvate kinase



    1 The correct answer is C. In the condition described, a person is in a social situation and fears that he or she will not be able to perform in the same manner as most everyone else can. The two most common social phobias concern public speaking and restroom performance (sometimes called "shy bladder".)
    Anxiety disorder due to a general medical condition (choice A) is diagnosed when a medical condition precipitates anxiety, e.g., hypoglycemia.
    Panic disorder (choice B) is characterized by sudden paroxysms of anxiety. It can strike unexpectedly in uncued situations so it would not occur only when others are present.
    Specific phobias (choice D) are unreasonable fears of some identifiable thing, not situation (e.g., elevators).
    Substance-induced anxiety disorder (choice E) is diagnosed when anxiety is precipitated by ingestion of a psychoactive substance, e.g., hallucinogens.
    2The correct answer is E. This patient has senile cardiac amyloidosis, which is usually a clinically insignificant condition due to deposition of structurally normal transthyretin (formerly called prealbumin). The transthyretin is a normal serum protein used to transport thyroxin and retinal. In addition to causing senile cardiac amyloidosis, transthyretin, in a mutant rather than normal form, is deposited as amyloid in the familial amyloid polyneuropathies.
    Amyloid-associated protein (choice A) is a more common protein deposited as amyloid, and precipitates in secondary amyloidosis associated with underlying chronic inflammatory conditions.
    Amyloid light chain protein (choice B) is a common protein deposited as amyloid, and precipitates in amyloidosis related to multiple myeloma and other monoclonal B cell proliferations.
    Beta-2-amyloid protein (choice C) is deposited as amyloid in the brain (notably in blood vessels and cerebral plaques) of patients with Alzheimer's disease.
    Beta-2-microglobulin (choice D) is a normal serum protein that is deposited in amyloidosis complicating long-term hemodialysis.
    3The correct answer is A. The heritable mental retardation condition associated with chromosomal breakage is fragile X syndrome. The break point is at q27.3 on the X chromosome. The test for this condition involves culturing lymphocytes in either folate-deficient medium or with chemical agents such as methotrexate that tend to break chromosomes. To make the diagnosis, at least 4% of metaphase chromosomes must show the specific break-point on the X chromosome. The percentage of defective X-chromosomes above 4% does not correlate well with the degree of mental retardation. The breakage point is a site of CGG trinucleotide repeats, which tend to expand in successive generations, producing the clinical feature of worsening mental retardation in each generation.
    Y chromosome (choice B) damage is not part of fragile X syndrome, but loss of this chromosome is one mechanism of producing 45, X0 (Turner syndrome), characterized by mental retardation.
    Trisomy 13 (choice C, Patau syndrome), trisomy 16 (choice D, Edward's syndrome) and trisomy 21 (choice E, Down's syndrome) are all associated with mental retardation, but not chromosomal breakage syndromes.
    4The correct answer is E. As you might have guessed from his elevated PT level, the active ingredient in rat poison is warfarin. It acts as an anticoagulant by interfering with the normal hepatic synthesis of the vitamin K-dependent clotting factors II, VII, IX, and X. The most important adverse effect of warfarin is bleeding. The action of warfarin can be reversed with vitamin K.
    Atropine (choice A) is used as an antidote for anticholinesterase toxicity (e.g., ingestion of organophosphates).
    Flumazenil (choice B) is used as an antidote for benzodiazepine toxicity (e.g., Valium).
    N-acetylcysteine (choice C) is used as an antidote for acetaminophen toxicity.
    Protamine (choice D) is used as an antidote for heparin overdose. Note that heparin enhances the activity of antithrombin III, producing its anticoagulant effect. Heparin toxicity would have resulted in an elevated PTT.
    5The correct answer is A. The patient has tabes dorsalis, which is a form of neurosyphilis seen 10 to 25 years or longer after primary disease. The pupils described are Argyll Robertson pupils, and are considered diagnostic for neurosyphilis. Characteristically, the dorsal columns, which contain the ascending tracts for sensory information, become atrophic, probably as a result of damage to the dorsal root ganglion cells.
    The dorsal gray horn (choice B) contains neurons that respond to sensory input.
    The lateral column (choice C) contains both descending (e.g., lateral corticospinal, rubrospinal) and ascending (e.g., spinocerebellar, spinothalamic) tracts.
    The ventral column (choice D) contains both descending (e.g., anterior corticospinal, tectospinal) and ascending (e.g., spinothalamic) tracts.
    The ventral horn (choice E) contains lower motor neurons.
    6The correct answer is D. Toilet training is not possible before the age of 18 months because the long nerve fibers have not yet myelinated and sphincter control is not possible. Toilet training should be completed by 4 years of age.
    7The correct answer is A. The features described are typical of the familial form of mental retardation known as fragile X syndrome. This disorder is the second most common heritable cause of mental retardation, second only to Down syndrome. Striking features of this disease are that the clinical features tend to worsen with each successive generation, and that males are usually much more severely affected than females, although nearly 50% of carrier females are at least slightly mentally retarded. The explanation appears to involve a region of DNA on the X chromosome that normally contains 6-54 tandem repeats of the sequence CGG. Carrier females for fragile X syndrome may have up to 200 CGG repeats. Clinically affected individuals have 250-4,000 repeats of the CGG sequence. The greater the number of repeats, the more severe the retardation tends to be. Amplification of premutations to full mutations appears much more likely to occur during oogenesis than spermatogenesis.
    Genomic imprinting (choice B) is a phenomenon in which the phenotypic expression of a gene differs if the gene is inherited from the mother, rather than the father. An example of this effect is Angelman ("happy puppet") syndrome, caused by a deletion of band q12 in the maternal copy of chromosome 15. A similar deletion in the paternal chromosome 15 produces a different disease called Prader-Willi syndrome.
    A Robertsonian translocation (choice C) causes about 5% of cases of Down syndrome. Generally the mother [typically with genotype 45, XX, -14, -21, +t(14q; 21q)] has normal mentation, but some of her children may carry the translocation in addition to the normal maternal chromosome 21 and normal paternal chromosome 21, producing partial trisomy 21. This form of Down syndrome can appear to be a recessive genetic disease.
    Trisomy 13 (Patau syndrome; choice D) is characterized by microcephaly, mental retardation, cleft lip and palate, polydactyly, and rocker-bottom feet. Survival is rare beyond one year.
    Trisomy 18 (Edwards syndrome; choice E) is characterized by mental retardation, micrognathia, low-set ears, cardiac defects, renal defects, and rocker-bottom feet. Survival is rare beyond one year.
    8The correct answer is C. The smell of acetone on the breath of a comatose patient is an important, rapid diagnostic clue that strongly suggests ketoacidosis and is usually seen in patients with poorly controlled type 1 diabetes. Other features of diabetic ketoacidosis include high blood glucose, increased serum osmolality, hypovolemia, acidosis, and electrolyte imbalance.
    In alcohol intoxication (choice A), the breath will smell like alcohol.
    Diabetic hyperosmolar coma (choice B) usually is seen in older patients with type 2 diabetes and is not characterized by ketoacidosis. Since there is no acetone production, there is no specific scent to the breath.
    In heroin overdose (choice D), no acetone production occurs and there is no specific scent to the breath.
    In hypoglycemic coma (choice E), which can occur in diabetics with insulin overdose, no acetone production occurs and there is no specific scent to the breath.
    9The correct answer is D. The presentation suggests a manic or hypomanic episode of a mood disorder. Patients in a manic episode often have an elated or euphoric mood and racing thoughts. Other symptoms of mania include increased energy, hypersexuality, grandiosity, and increased talkativeness. In some patients, irritability, rather than euphoria, is characteristic.
    Depressed mood (choice A) can include anhedonia, decreased self-esteem, energy, concentration, appetite, and libido, as well as increased guilt and sucidality.
    An unreasonable fear that one might die (choice B) may be associated with panic disorder. Neurovegetative symptoms including severe anxiety, palpitation, shortness of breath, chest pain, trembling, and paresthesias may also occur.
    Despite poor sleep, manic patients do not complain of insomnia (choice C). Their need for sleep is decreased. During depressive episodes, patients complain of insomnia or hypersomnia.
    Obsessive-compulsive disorder is characterized by distressing recurrent thoughts (obsession) and actions (compulsion) (choice E) that relieve anxiety when carried out.
    11The correct answer is D. Not all dementing disorders manifest with the same clinical features. Although there is considerable overlap in clinical symptomatology among different types of dementias, making clinical diagnosis somewhat problematic, there are classic presentations that allow identification of a specific form of dementia with a high degree of confidence. In this case, the patient has symptoms due to frontal lobe damage, eg, disinhibition, impaired judgment, and personality changes. Furthermore, MRI demonstrates a specific pattern of cortical atrophy, restricted to the frontal lobes and anterior portion of the temporal lobes. This combination points toward a group of dementias called frontotemporal dementia, the most frequent form of which is Pick disease. Other forms of frontotemporal dementia are very infrequent. Remember: frontal symptoms in conjunction with frontotemporal atrophy = frontotemporal dementia/Pick disease.
    Alzheimer disease (choice A) is the most frequent form of dementia in industrialized countries. Although symptoms due to frontal damage may be present in Alzheimer disease, they are usually associated with a more generalized impairment of higher neurologic functions, eg, language, memory, and learned movements. In addition, cortical atrophy in Alzheimer disease is widespread and not limited to the frontal and anterior temporal lobes.
    Creutzfeldt-Jacob disease (choice B) represents the prototype of prion diseases. Cortical atrophy is not a prominent feature of Creutzfeldt-Jacob disease, which manifests with personality changes, memory loss, and seizures, leading to death after a rapid clinical course (a few months to 1 year).
    Dementia with Lewy bodies, also known as diffuse Lewy body disease (choice C), is one of the most common forms of dementia in Western countries, possibly more common than vascular dementia. It is characterized by widespread formation of Lewy bodies in the substantia nigra, limbic cortex, and subcortical nuclei, such as the basal nucleus of Meynert. Extrapyramidal symptoms similar to Parkinson disease manifest in this form of dementia as a result of degeneration of dopaminergic pathways.
    Vascular dementia (choice E) is an umbrella term encompassing dementing conditions that arise from pathology of large or small cerebral vessels. It manifests with memory loss associated with focal neurologic symptoms depending on the location of damage. MRI would identify old or recent infarcts, as well as white matter disease. Conditions associated with vascular dementia include the following:
    Multi-infarct dementia, which is caused by multiple, scattered brain infarcts secondary to atherosclerosis of large arteries of the circle of Willis and/or carotid arteries.
    Binswanger disease, which involves rarefaction of cerebral white matter and is caused by hypertension-related arteriolosclerosis.
    Lacunar infarcts, which consist of small (< 1 cm) infarcts in the striatum and thalamus; this condition is related to arteriolosclerosis.

    12The correct answer is E. This patient has a pinealoma. Tumors of the pineal gland compress the vertical gaze center in the tectum of the midbrain. The pineal gland manufactures melatonin from its precursor serotonin; an inadequate supply of melatonin results in insomnia. Tumors of the pineal gland will not compress the cerebral cortex or the rest of the brainstem. Frequently, the only physical sign noted is failure of upward gaze.
    An acoustic neuroma (choice A) is a schwannoma of the eighth cranial nerve. It results in deafness, ataxia, and dysarthria. Nystagmus may be present. The gaze centers are not affected.
    Astrocytomas of the cerebellum (choice B) are usually seen in children. These tumors present with headache, nausea, vomiting, papilledema, and cerebellar signs such as ataxia, dysarthria, nystagmus, and intention tremor. The gaze centers are not affected.
    Craniopharyngiomas (choice C) are usually seen in children. There is failure of growth, headaches, and bitemporal hemianopia.
    Parasagittal meningiomas (choice D) usually result in headache, spastic paresis, and urinary incontinence
    13The correct answer is C. There are a number of hereditary sphingolipidoses that have devastating clinical courses. In practice, these diseases may have a variable course and may be difficult to specifically diagnose reliably on clinical grounds alone. The most useful clue to the specific diagnosis in this case is the comment about the deficient arylsulfatase A. Deficiency of this enzyme produces metachromatic leukodystrophy, characterized by accumulation of cerebroside sulfates (galactosyl sulfatide). The cerebroside sulfates accumulate as intra- and extracellular spherical masses that stain metachromatically (purplish rather than bluish) with acid cresyl violet, particularly in the nervous system. The biochemical diagnosis can be made by evaluating cultured cells from a variety of sources, including leukocytes, fibroblasts, and hair bulbs. The most common presentation is that described in the question stem; adolescent and adult variants also occur.
    Gaucher's disease (choice A) is a sphingolipidosis caused by deficient beta-glucocerebrosidase.
    Krabbe's disease (choice B) is a sphingolipidosis caused by deficient beta-galactocerebrosidase.
    Niemann-Pick disease (choice D) is a sphingolipidosis caused by deficient sphingomyelinase.
    Tay-Sachs disease (choice E) is a sphingolipidosis caused by deficient hexosaminidase A (alpha subunit).
    14The correct answer is B. Delirium is a common complication of general anesthesia and surgery. It is manifested by acute changes in mental status with waxing and waning level of consciousness, agitation, irritability, and psychosis. Patients usually respond to low-dose neuroleptics to achieve sedation. The course is self-limited.
    Any psychosocial or biological stressor can lead to adjustment disorder (choice A). This patient's surgery will restrict his level of functioning, at least in the short term. This will be difficult for a high-functioning individual to accept. Adjustment disorder may present with depressive mood, anxiety, and irritability, but a fluctuating level of consciousness is not a feature of this disorder.
    Dementia (choice C) can present with irritability, confusion, and agitation, but usually has an insidious course and affects mainly cognition. In contrast to delirium, it does not have a fluctuating course.
    Severe depression can present with irritability, suicidal ideation, and psychotic features (choice D). The patient has a history of depression that responded well to SSRIs and he has no prior history of psychosis. He was motivated to undergo cardiac surgery, so removing his IV lines is unlikely to be a manifestation of suicidal ideation.
    Schizophrenia (choice E) presents with bizarre behavior, hallucinations, and delusions. It usually starts at a younger age than the acute symptoms in this patient, and is characterized by progressive deterioration in functioning. It is unlikely for a schizophrenic to achieve the functional level of an executive.
    15The correct answer is B. In a sense, cervical carcinoma can be considered a "sexually transmitted disease," since human papilloma virus (typically strains HPV-16 or HPV- 18) is transmitted venereally. In our culture, HPV-related dysplasia of the cervix is common, even in the 18-28 year old group, and carcinomas of the cervix (more rare now than in the past due to screening and aggressive therapy of dysplasia) can occur in the 35-45 age group. The other cancers listed typically occur in older age groups and are not as clearly related to venereal agents.
    16The correct answer is E. Vincristine (and vinblastine) are Vinca alkaloids that bind to tubulin, a component of cellular microtubules. This leads to disruption of the mitotic spindle apparatus and results in metaphase arrest since the chromosomes are unable to segregate. Since these drugs interfere with mitosis, they are considered cell-cycle specific for the M phase.
    Cytarabine (choice A) belongs to the class of antineoplastics that are antimetabolites. This drug class interferes with normal metabolic pathways by competing for enzymatic sites. Specifically, cytarabine (Ara-C) is a pyrimidine nucleoside analog. It interrupts DNA synthesis and function by inhibiting DNA polymerase and incorporating into the DNA or RNA of the cell. As you would expect, this drug is cell-cycle specific for the S phase.
    Daunorubicin (choice B) is one of the antibiotic antineoplastic agents (others include dactinomycin, doxorubicin, bleomycin, plicamycin, and mitomycin). These agents work by disrupting DNA functioning. Daunorubicin binds to DNA between base pairs on adjacent strands, resulting in uncoiling of the helix and destruction of the DNA template. While this drug has its maximum effect during the S phase, it is not cell-cycle specific. (Note: the only antibiotic that is cell-cycle specific is bleomycin.)
    Hydroxyurea (choice C) works by interfering with ribonucleoside diphosphate reductase, the enzyme responsible for generating the deoxyribonucleotides needed for DNA synthesis. It is S-phase specific.
    Mechlorethamine (choice D) is a nitrogen mustard. The nitrogen mustards (mechlorethamine, cyclophosphamide, melphalan, chlorambucil) belong to the larger class of alkylating agents. These agents work by alkylating DNA (along with RNA and proteins). The alkylating agents are generally NOT cell-cycle specific.
    17The correct answer is E. Priapism is characterized by the development of a painful erection for an extended period of time. When untreated, priapism can cause severe penile damage that can culminate in impotence. Administration of the antidepressant drug trazodone has been associated with priapism in a number of patients. In patients with prolonged or inappropriate penile erection, this medication should be discontinued and medical attention should be sought immediately. Injection of alpha-adrenergic stimulants, such as norepinephrine or epinephrine, may be successful in treating the priapism. Surgical intervention is necessary for the treatment of trazodone-induced priapism in many instances.
    Atenolol (choice A) is a beta-1 adrenergic antagonist indicated for the treatment of hypertension. This agent is commonly associated with impotence in males.
    Furosemide (choice B) is a loop diuretic indicated for the treatment of edema and hypertension; electrolyte abnormalities are the most common side effects seen with this agent.
    The sulfonylurea glyburide (choice C) is an oral hypoglycemic agent indicated for the treatment of type 2 diabetes; hypoglycemia is the most common side effect of this agent.
    Paroxetine (choice D) is a selective serotonin reuptake inhibitor (SSRI) used for the treatment of depression. This agent is commonly associated with impotence in males.
    18The correct answer is D. Since Tay-Sachs is lethal in childhood, the only adults carrying the gene are heterozygotes. The only mating that will produce progeny with the disease is the mating between two heterozygotes. Using the blood test data, the probability that a random individual is a heterozygote is 0.1. The probability that two heterozygotes will produce a child with Tay-Sachs disease is 0.25. So, the overall probability that two individuals in the population will produce a child with Tay-Sachs is (0.1)(0.1)(0.25), or 0.0025.
    Choice A, 0.25, could be obtained if the parents are carriers, so the probability of a Tay-Sachs child is equal to the probability that two heterozygotes will produce a child with the disease, or 0.25.
    Choice B, 0.11, could be obtained if both of the parents had a sibling with Tay-Sachs. This would mean that the grandparents must have carried the disease, and that their normal children had a 0.67 chance of carrying the allele. This gives the probability that the parent's child would have Tay-Sachs as (0.67)(0.67)(0.25), or 0.11.
    Choice C, 0.0625, is also incorrect. It is the product of (0.25)(0.25).
    Choice E incorrectly assumes that because q2, the frequency of the disease, cannot be calculated, and hence the allele frequencies cannot be calculated, that an estimate of the frequency of heterozygotes cannot be made. The problem can be done, however, because the heterozygote frequency (0.1) was given in the question stem.
    19The correct answer is D. This man's presentation can be explained either by alcohol withdrawal or by cocaine intoxication. Nausea, vomiting, sympathetic nervous system activation, and weakness could be produced in either case. Visual hallucinations (seeing monsters) can also be accompanied by tactile and auditory hallucinations. In severe cases, either alcohol withdrawal or cocaine intoxication can cause convulsions.
    Alcohol intoxication (choice A and B) is characterized by disinhibition, aggression, impaired attention and judgment, unsteady gait and imbalance, slurred speech, nystagmus, and a decreased level of consciousness.
    Other symptoms associated with alcohol withdrawal (choices C and D) include insomnia, headache, and tremors of the tongue, eyelids, and outstretched hands.
    Withdrawal from cocaine (choices B and F) is characterized by dysphoria, lethargy, psychomotor retardation or agitation, increased appetite, sleep disturbances, and bizarre or unpleasant dreams.
    Other symptoms associated with cocaine intoxication (choices D and E) include grandiosity, paranoid ideation, and pupillary dilatation. Orientation usually remains intact.
    20The correct answer is C. Men have higher reference intervals than women in tests related to iron and hemoglobin (Hb) concentration in blood. The normal reference interval for Hb concentration in women is lower (12.0-16.0 gm/dL) than that for men (13.5-17.5 gm/dL) due to lower serum testosterone levels (testosterone is higher in men and stimulates erythropoiesis) and blood loss during menses. Furthermore, women normally have about 400 mg of iron (as ferritin) in their bone marrow iron stores versus an average of 1000 mg of iron for men. In the absence of inflammation, the small circulating fraction of ferritin (choice C) correlates well with ferritin stores in the bone marrow. Hence, men have different reference intervals for serum ferritin than do women (15-200 ng/mL in men versus 12-150 ng/mL in women).
    The mean corpuscular volume (choice A), serum alkaline phosphatase (choice B), serum glucose (choice D), and serum sodium (choice E) are similar in both sexes.
    21The correct answer is A. The most important chemotactic factors for neutrophils are the complement factor C5a and the interleukin IL-8.
    The cytokines IL-1 and tumor necrosis factor (choice B) have complex, similar actions, including stimulation of production of many acute-phase reactions, stimulation of fibroblasts, and stimulation of endothelium.
    Leukotrienes LTC4 and LTD4 (choice C) cause increased vascular permeability.
    Prostaglandins PGI2 and PGD2 (choice D) mediate vasodilation and pain.
    Thromboxane and platelet activating factor (choice E) induce platelet changes
    22The correct answer is D. The presence of sickle cell disease in a question stem is usually a significant clue. This question tests if you know that patients with sickle cell anemia are more susceptible to osteomyelitis caused by Salmonella. (The patient's fever, bone pain, and x-ray results indicate osteomyelitis). But note that Staphylococcus aureus (gram-positive coccus) is the most common cause of osteomyelitis in both sicklers and nonsicklers. If it had not been ruled out on bone culture, you should have looked for it in the answer choices. Notice that you were required to know more than just the organism's name; you needed to know its distinguishing features. Choice D describes Salmonella (a gram-negative rod) accurately. Salmonella exists in over 1800 serotypes and is known to contaminate poultry.
    A facultative intracellular parasite (choice A) is Legionella, a catalase-positive gram-negative rod. It contaminates air-conditioning cooling towers and causes Legionnaire's disease (a type of pneumonia).
    A nonmotile, facultative anaerobe (choice B) is Shigella, a gram-negative rod that does not produce H2S. All Shigella contain an endotoxic lipopolysaccharide. The organism causes bacillary dysentery, with abdominal cramps, fever, and mucoid, bloody diarrhea.
    A comma-shaped organism that is sensitive to acidic pH (choice C) is Vibrio cholerae, a gram-negative rod that causes severe enterotoxin-induced diarrhea, with "rice-water" stools and dehydration. The toxin acts by stimulating adenylyl cyclase to overproduce cAMP in the brush border of the small intestine.
    A motile and oxidase positive organism (choice E) is Pseudomonas, a gram-negative rod with pili that sometimes produces a polysaccharide slime layer. P. aeruginosa is the prototype and commonly colonizes the lungs of patients with cystic fibrosis. It is associated with blue-green pus.
    23The correct answer is E. Sublimation is the diversion of unacceptable impulses into more acceptable ones. In this case, the girl would like to continue to talk to her best friend, but since that is not possible, she substitutes writing in her diary. An example of sublimation seen fairly frequently in medical settings is the mother whose child died of a disease who becomes active in a state or national organization designed to help families with the disease.
    Identification (choice A) is the adoption of characteristics or activities of another person.
    Projection (choice B) occurs when someone attributes their own thoughts to a different person.
    Rationalization (choice C) is the offering of a false, but acceptable, explanation for behavior.
    Regression (choice D) is the adoption of behavior more appropriate to a younger age.
    24The correct answer is A. The syndrome described is Edwards' syndrome (trisomy 18), which is typically characterized by the features noted and additionally causes severe mental retardation, which would not be recognizable in the neonatal period. This disease is relatively common, with an incidence of about 1 in 5000 births (Down syndrome has an incidence of 1 in 2000 births). The average life span is only 2-3 months.
    25The correct answer is C. Ki-67 is a nuclear factor (of uncertain function) whose expression correlates with neoplastic replicative activity. Its expression can be visualized by immunostaining of formalin-fixed, paraffin-embedded sections. Ki-67 labeling correlates with a neoplasm's rate of growth and, therefore, with prognosis.
    The bcl-2 gene (choice A) suppresses apoptosis by different mechanisms. Its abnormal activation is involved in the pathogenesis of low-grade lymphomas but not astrocytomas.
    GFAP (choice B) is an intermediate cytoskeletal filament (analogue of keratin and vimentin) expressed exclusively by certain types of glial cells, e.g., astrocytes and ependymal cells. Immunohistochemistry for GFAP is used diagnostically to confirm an astrocytic origin of a neoplasm, but gives no information about mitotic or proliferative rate.
    The gene p53 (choice D) encodes a protein that blocks the cell cycle when damage to DNA occurs. If the damage is successfully repaired, p53 allows the cell cycle to resume; if not, p53 induces apoptosis, thus eliminating dangerous DNA mutations. Mutations of p53 have been found in the great majority of human neoplasms, including gliomas. However, its expression gives no information concerning neoplastic replicative activity.
    Ubiquitin (choice E) is a low-molecular-weight heat-shock protein. Its function is to tag aberrant proteins for degradation. It is present in many abnormal intraneuronal inclusions associated with neurodegenerative disorders, such as Lewy bodies, Pick bodies, and neurofibrillary tangles. It has no relationship with mitotic activity or growth rate.
    26The correct answer is E. First, it is necessary to know that it is the uncharged, lipid-soluble form that can be rapidly absorbed. For an acid: HA <-------> H+ + A-. Therefore, the protonated form is uncharged. The Henderson-Hasselbalch equation is:
    pH = pKa - log[protonated form/unprotonated form]
    In this case,
    2.0 = 3.0 - log [HA/A-]
    1.0 = log [HA/A-]
    10 = HA/A- = 10/1
    HA/(HA + A-) = 10/(10 + 1) = 91%, or approximately 90%
    27The correct answer is B. Lyme disease should be suspected in a patient who is bitten by a tick in the northeastern U.S. Lyme disease was named after a township in eastern Connecticut where the disease was endemic. The disease is spread via a tick vector of the genus Ixodes, which transmits a spirochete that causes a systemic illness. Erythema chronicum migrans is usually the first sign of the illness. This is a large red patch on the buttocks or chest that slowly expands as the center blanches. Generally, patients also have constitutional symptoms, such as fever and chills, during this phase. Stiff neck may develop, along with other signs of meningeal irritation, because of an aseptic meningitis. Other neurologic complications of Lyme disease include Bell's palsy due to involvement of branches of the facial nerve. Arthritis is a prominent feature in about half the patients with Lyme disease. It tends to appear several months after the infection but may persist for several years. The course of the chronic arthritis shows exacerbations and remissions; the most commonly affected joints are the knees and hips. Cardiac abnormalities in Lyme disease include pericarditis and heart block.
    Skin manifestations do not include aphthous ulcers (choice A).
    Flaccid or spastic paralysis of limbs (choices C and E) does not accompany Lyme disease; neurologic involvement is generally limited to cranial nerves and meningitis.
    Purpura (choice D) is associated with vasculitis and does not occur in Lyme disease.
    28The correct answer is A. Arteriovenous malformations are composed of complex tangles of congenitally malformed vessels that typically involve the superficial or deep cerebral hemispheres. There is a slight male predominance, and bleeding typically occurs in adolescence or young adulthood. Symptoms may be those of subarachnoid hemorrhage (headache, increased intracranial pressure) and/or seizures. Surgical resection is usually required for therapy.
    Berry aneurysms (choice B) can produce both subarachnoid and parenchymal hemorrhage, but are usually centered near the base of the brain.
    Bleeding from bridging veins (choice C) causes subdural hematoma.
    Charcot-Bouchard aneurysms (choice D) are small, intraparenchymal aneurysms that are related to hypertension.
    Rupture of the middle meningeal artery (choice E) causes epidural hematoma.
    29The correct answer is A. This is Patau syndrome, or trisomy 13. This disorder is also associated with severe mental retardation, abnormal forebrain structures, and death within one year of birth. Patau syndrome has an incidence of 1:6000 births, making it the second most common form of autosomal trisomy.
    Trisomy 18 (choice B) is Edwards syndrome, characterized by severe mental retardation, rocker bottom feet (also sometimes seen in Patau syndrome, so be careful!), low-set ears, micrognathia, clenched hands, prominent occiput, and death within one year. Edwards syndrome has an incidence of 1:8000, making it the third most common autosomal trisomy.
    Trisomy 21 (choice C) is Down syndrome, and is characterized by mental retardation, flat facial profile, prominent epicanthal folds, simian crease, duodenal atresia, and congenital heart disease. Down syndrome is the most common autosomal trisomy, with an incidence of 1:700.
    XXY (choice D) is Klinefelter syndrome and is associated with male hypogonadism and infertility, eunuchoid body habitus, gynecomastia, and lack of male secondary sexual characteristics.
    XYY (choice E) is double Y syndrome.
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