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Exam Section 1: Item 2 of 50
National, Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
- Free purine and pyrimidine bases are reutilized in normal metabolism. In children with Lesch-Nyhan syndrome who have intellectual disability, poor muscle coordination, and self-mutilation tendencies, there is a defect in the salvage of which of the following
pairs of bases?
A) Adenine and thymine
B) Guanine and hypoxanthine
C) Guanine and uric acid
D) Uracil and cytosine
E) Xanthine and hypoxanthine - ✔✔✔B.
Lesch-Nyhan syndrome presents with intellectual disability, aggressive behavior, self-mutilation, gout, and dystonia. The disorder is due to inactivating mutations of hypoxanthine-guanine phosphoribosyltransferase (HGPRT), a key enzyme in the purine salvage
pathway, and is inherited in an X-linked recessive fashion. HGPRT catalyzes the conversion of guanine to guanosine monophosphate and hypoxanthine to inosine monophosphate. Patients with deficient activity of HGPRT are unable to salvage guanine and
hypoxanthine and develop resultant increased levels of xanthine and uric acid. Hyperuricemia in Lesch- Nyhan syndrome is treated with xanthine oxidase inhibitors, such as allopurinol or febuxostat, in order to reduce the synthesis of uric acid.
Incorrect Answers: A, C, D and E.
Adenine and thymine (Choice A) are purine and pyrimidine bases, respectively. Purine and pyrimidine salvage are handled through two distinct pathways that are not commonly involved in a single disease process.
Guanine and uric acid (Choice C) accumulation may occur as part of Lesch-Nyhan syndrome, however, the accumulation of uric acid is also secondary to accumulation of hypoxanthine. Choice B more accurately describes defective salvage of guanine and
hypoxanthine as the fundamental effect of HGPRT dysfunction. The accumulation of uric acid is secondary.
Uracil and cytosine (Choice D) are pyrimidine nucleotides. Pyrimidine salvage is not affected by mutations of HGPRT.
Defects of xanthine and hypoxanthine (Choice E) metabolism may result from defects in HGPRT. However, HGPRT dysfunction results in impaired hypoxanthine salvage with resultant excessive production of xanthine, rather than impaired xanthine salvage.
Educational Objective: Lesch-Nyhan syndrome presents with intellectual disability, aggressive behavior, self-mutilation, gout, and dyst
Exam Section 1: Item 11 of 50
National, Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
- An 8-year-old boy is brought to the physician by his parents because of disruptive behavior. They say, "He is easily distracted, constantly interrupts us while we are talking, and seems to be always moving. His teacher says he is always talking with his
neighbors, has trouble completing tasks, and refuses to wait his turn when playing games." Physical examination shows no abnormalities. If drug therapy is indicated, administration of a drug with which of the following mechanisms of action is most
appropriate?
A) Antagonism at B-adrenergic receptors
B) Blockade of voltage-gated Na+ channels
C) Enhanced action of y-aminobutyric acid (GABA) at GABAA receptors
D) Increased release of dopamine and norepinephrine
E) Selective inhibition of uptake of serotonin at nerve terminals - ✔✔✔D.
The first-line treatment for attention-deficit/hyperactivity disorder (ADHD) is stimulant medication such as amphetamine salts, which increase presynaptic release of dopamine and norepinephrine. ADHD presents with chronic symptoms of hyperactivity/impulsivity
and/or inattention that occur in more than one setting and impair academic, social, or emotional function. Children with predominant hyperactivity symptoms are unable to sit still and may have difficulty taking turns (postulated to result from a dysregulated reward
pathway), whereas children with predominant inattentive symptoms tend to daydream, process information slowly, and demonstrate difficulty in completing tasks (likely related to norepinephrine dysregulation). This patient is experiencing symptoms of both
This patient has a moderate to large patent ductus arteriosus (PDA) as evidenced by a continuous murmur and respiratory distress. In utero, oxygenated blood is obtained from the placenta, not from the lungs, and the ductus arteriosus (DA) allows the shunting of
oxygenated blood from the pulmonary
called a PDA, and if large enough, can lead to a profound left-to-right shunt, with consequent heart failure, respiratory distress, and pulmonary hypertension. PDAS that are small often go undetected until adulthood because the left-to-right shunt is not significant
enough to cause symptoms. The DA arises from the sixth aortic arch, which also gives rise to the proximal right pulmonary artery.
ectly to the aorta while bypassing the fetal lungs, which are filled with amniotic fluid. At birth, closure of the DA occurs by the release of prostaglandins and increased arterial oxygen tension. A DA that fails to close is
Incorrect Answers: A, B, C, and D.
First (Choice A) and second (Choice B) aortic arch structures include the maxillary artery, a part of the external carotid artery, the ascending pharyngeal artery, and the stapedial artery.
Fourth (Choice C) aortic arch structures include the right subclavian artery and the aortic arch from the origin of the left carotid artery to the beginning of the DA.
Fifth (Choice D) aortic arch structures regress and do not contribute to adult cardiovascular structures.
Educational Objective: The sixth aortic arch gives rise to the ductus arteriosus, a structure that allows shunting of placental oxygenated blood from the pulmonary artery to the systemic circulation during development in utero but closes shortly after birth. Persistence of
this structure is called a patent ductus arteriosus (PDA). Symptoms are dependent upon the size of the PDA and the degree of left-to-right shunting, with
Exam Section 3: Item 1 of 50
Natjonal, Board of Medical Examinersent
- The higher incidence of birth defects in children born to women more than 35 years old may be the result of environmental influences on chromosomes in developmentally arrested oocytes at which of the following stages of cell division?
O A) Prophase, meiosis I
O B) Prophase, meiosis II
C) Metaphase, meiosis I
O D) Metaphase, meiosis II
E) Telophase, meiosis I - ✔✔✔A.
In the normal development of the oocyte, women are born with a complement of follicles that develop in utero and arrest in prophase of meiosis I. Upon reaching menarche, some of the follicles mature during the menstrual cycle prior to being released during
ovulation. In response to the hormonal stimulation from pituitary follicle-stimulating hormone (FSH), the oocytes that may be ovulated advance from prophase of meiosis I to metaphase of meiosis II. If fertilization occurs, the oocyte advances through the remainder of
metaphase Il to completion. In prophase of meiosis I, the chromosomes remain dormant in a paired tetrad (four total chromosomes: duplicated maternal and paternal chromosomes). As meiosis I advances through metaphase, anaphase, and telophase, the
recombined, crossed-over tetrads normally divide into two separate cells, where they subsequently arrest in metaphase II. Normal progression through meiosis Il then leads to a single haploid chromosome in each of the four daughter cells. Nondisjunction during
prophase I results in the daughter cells receiving an uneven complement of chromosomes. A nondisjunction event in meiosis I followed by a normal meiosis Il results in four gametes, two of which lack a maternal or paternal chromosome, and two of which contain
both a maternal and paternal chromosome. In the instance of normal separation in meiosis I followed by a nondisjunction event of meiosis |l there are two chromosomes (both from the same parent) within one gamete, with the other gamete lacking the chromosome.
In the case of a 35-year-old woman, oocytes maturing and ovulated at that time would have remained arrested in prophase I for the lifetime of the patient until that point.
Incorrect Answers: B, C, D, and E.
Prophase, meiosis II (Choice B); metaphase, meiosis I (Choice C); and telophase, meiosis I
Exam Section 3: Item 2 of 50
Natjonal, Board of Medical Examinersment
- A 50-year-old man collapses and dies while running to catch an airplane. A photograph of his aortic valve is shown. Which of the following best describes the lesion?
O A) Calcified congenital bicuspid valve
O B) Infective endocarditis
O C) Myxomatous degeneration
B) Herpes simplex virus
O C) HIV
O D) Human papillomavirus
E) Varicella-zoster virus - ✔✔✔D.
Human papillomavirus (HPV) is a common human pathogen that infects epithelial cells. There are multiple strains which may be low- or high-risk for the development of squamous cell carcinoma, which result in the development of a variety of lesions. Anogenital
manifestations are common (eg, cervical intraepithelial neoplasia, condylomata acuminata). Non- anogenital manifestations include verruca vulgaris, plantar warts, and mucosal lesions of the oropharynx, respiratory epithelium, and larynx. Laryngeal papillomatosis
frequently affects the vocal cords and presents as a vocal cord nodule. Symptoms include dysphonia (hoarseness) and may progress to dyspnea, chronic cough, dysphagia, globus sensation, and airway obstruction if the lesion becomes large enough. Risk factors for
clinically significant HPV infection include immunodeficiency and injury to the epithelium from another cause (eg, trauma, coinfection). HPV is primarily transmitted through genital contact. In children, the most common vector for HPV infection is transmission from an
affected mother during labor and transit through the birth canal, though the presence of these lesions may also raise concern for sexual assault in the correct clinical context. Treatment focuses on maintaining a patent airway, surgical removal of symptomatic lesions,
and preserving voice quality.
Incorrect Answers: A, B, C, and E.
Cytomegalovirus (Choice A), also known as human herpesvirus-5 (HHV-5), can be transmitted through multiple modes, including sexual contact, urine, respiratory droplets, and across the placenta. It can cause a variety of presentations, including mononucleosis in
immunocompetent patients, along with retinitis, infectious esophagitis, and pneumonia in immunocompromised patients. It is not associated with laryngeal papillomatosis.
Herpes simplex virus (Choice B)
Exam Section 3: Item 4 of 50
National, Board pf Medical Examiners
ancive Basic Science
ment
- A 16-year-old boy has a 6-month history of type 1 diabetes mellitus and requires daily insulin injections. His blood glucose control has been poor recently, which the physician suspects may be related to the patient's reluctance to self-administer insulin. Which of
the following questions is most appropriate to broach this issue with the patient?
A) "Giving yourself insulin injections can be difficult. Whať's it like for you?"
O B) "I get the feeling you have not been taking your insulin regularly. Would you like me to arrange some training for you by our nurses?"
O C) "It's been my experience that most poorly controlled diabetics have trouble giving themselves insulin. Do you have this problem?"
O D) "You are clearly having difficulty with insulin injections. Would you like to arrange for a family
member - ✔✔✔A.
A physician who suspects that a patient is not adhering to treatment should take a nonjudgmental and curious stance and ask open-ended questions to elicit the patient's reasons for not adhering. This physician is nonjudgmental in acknowledging that taking insulin
can be hard and assuming that the patient is experiencing an external barrier to adherence rather than inferring or implying that the patient is at fault. Using nonjudgmental, open-ended questioning can improve therapeutic alliance, help the physician and patient
problem-solve around the nonadherence, and increase the patient's motivation to adhere. Motivational interviewing similarly uses open-ended questions to encourage patients to explore their reasons to change or maintain behavior and increases a patient's readiness
to make or maintain a behavioral change such as adhering to insulin.
Incorrect Answers: B, C, D, and E.
Immediately proposing solutions to the problem such as arranging training (Choice B) or help from family members (Choice D) presumes knowledge of the underlying barrier to adherence. Alternatively, open-ended questions serve to identify the specific barriers.
Choices B and D also assume that the patient has not been self-administering insulin and subtly infer that the patient is at fault, which may injure therapeutic alliance.
Calling this patient a "poorly controlled diabetic" (Choice C) may be interpreted by the patient as judgmental. In this statement, the physician is placing the patient as a whole person into a category or stereotype rather than maintaining a narrow focus on the specific
behavior of taking insulin. This type of statement may damage the therapeutic alliance and promote defensiveness rather than an open discussion about the factors contributing to this patient's inability to adhere.
Asking how frequently the patient h
Incorrect Answers: A, B, D, and E.
Calcification of the mitral valve (Choice A) can result in mitral stenosis, classically heard as an opening snap, followed by a diastolic rumble that is loudest over the cardiac apex and radiates to the axilla. Mitral stenosis is commonly seen as a manifestation of
rheumatic heart disease.
Enlargement of the mitral valve annulus (Choice B) causes mitral regurgitation, whi
Exam Section 3: Item 6 of 50
National, Board pf Medical Examiners
mont
- A 65-year-old man with diabetes mellitus develops a neuropathy of the cranial nerve indicated by the arrow in the normal brain stem. Which of the following is the most likely associated functional deficit?
O A) Complete ptosis of the ipsilateral eye
O B) Inability to abduct the ipsilateral eye
O C) Ipsilateral sensorineural deafness
D) Lack of tear formation in the ipsilateral eye
O E) Paralysis of ipsilateral jaw muscles - ✔✔✔B.
The abducens nerve (cranial nerve VI) arises from the mid-pons and exits the brainstem ventrally at the pontomedullary junction. It ascends steeply through the subarachnoid space across the clivus before proceeding through Dorello's canal to the cavernous sinus.
It exits the cavernous sinus through the superior orbital fissure before reaching its target, the lateral rectus muscle, in the lateral orbit. The most common etiologies of acute abducens nerve palsy in adults include microvascular ischemia (secondary to diabetes,
hypertension, and atherosclerotic cardiovascular disease), idiopathic etiologies, and trauma. The abducens nerve is fragile and vulnerable to injury as it crosses the clivus by any mechanism causing downward traction, such as brain herniation. Abducens nerve
palsy presents with binocular horizontal diplopia and an inability to abduct the ipsilateral eye. Treatment includes systemic workup for vasculopathic risk factors and patching to reduce diplopia. Abducens nerve palsy secondary to microvascular disease may resolve
spontaneously over several months.
Incorrect Answers: A, C, D, and E.
Complete ptosis of the ipsilateral eye (Choice A) can occur as a component of oculomotor nerve (cranial nerve III) palsy, or in association with Horner syndrome, myasthenia gravis, trauma, or age-related dehiscence of the aponeurosis of the levator palpebrae
superioris muscle. The abducens nerve is not responsible for innervation of the muscles of the upper eyelid.
Ipsilateral sensorineural deafness (Choice C) suggests pathology of the vestibulocochlear nerve (cranial nerve VIII), which may be caused by microvascular ischemia, multiple sclerosis, compression secondary to acoustic neuroma, trauma, or infection.
Lack of tear formation in the ipsilateral eye (Choice D) may be a feature of facial nerve palsy, otherwise
Exam Section 3: Item 7 of 50
National, Board pf Medical Examiners
ment
- A 2-year-old boy has had recurrent bacterial infections with markedly increased absolute neutrophil counts in the blood (30,000-150,000/mm3). Studies of neutrophils show:
Patient (%
Control)
Test Substance
Bacterial killing
opsonized patient
Normal
80±
serum
opsonized normal
Patient
70±
serum
Phagocytosis
opsonized patient
to LAD type 1. The actions of leukocyte phagocytosis and bacterial killing are not impaired. Laboratory studies in patients with LAD will show increased absolute neutrophil counts in the blood due to failure to marginate. Neutrophils from the patient's serum will perform
similarly to controls with respect to phagocytosis and bacterial killing. In this case, the neutrophil response to C5a is diminished relative to the control, which suggests an impaired chemotactic and adhesive response and a diagnosis of LAD.
Incorrect Answers: A, C, D, and E.
Chronic granulomatous disease (Choice A) results from a defect or deficiency in the NADPH oxidase complex (Choice D). This impairs the production of reactive oxygen species and the respiratory burst in neutrophils, increasing a patient's susceptibility to catalase
positive pathogens. Diagnosis is made by an abnormal dihydrorhodamine test, or a nitroblue tetrazolium reduction test. Decreased bacterial killing compared to control would be expected with opsonized patient serum.
Myeloperoxidase deficie
Exam Section 3: Item 8 of 50
Natjonal, Board pf Medical Examiners
S ent
- A 36-year-old man comes to the physician's office without an appointment and demands to be seen immediately. He has had a sore throat for 24 hours and explains his problem is more important than the other patients' because he is a vocalist. He is extremely
upset when the receptionist explains he will need to wait for 1 hour to see the physician. He talks with her constantly while he waits. He says, "My wife and I split like 3 months ago. We have a 6-month-old boy, but she was just so into her pregnancy, she had no
time for me. And she doesn't really appreciate my music. I need full support from my lady. Especially when my band's just about to make it big." Which of the following is the most likely personality disorder?
%3D
O A) Antisocial
O B) Borderline
O C) Compulsive
O D) Dependent
O E) Histrionic
F) Narcissistic
O G) Paranoi - ✔✔✔F.
Narcissistic personality disorder, a cluster B disorder (the dramatic or emotional cluster), is characterized by fragile self-esteem and compensatory arrogant, self-aggrandizing behavior to gain admiration, sometimes at others' expense. For example, a patient with
narcissistic personality disorder may berate their physician for making a small mistake, which unconsciously inflates the patient's ego. This patient also demonstrates this entitled attitude, expecting special treatment from both his wife and doctor's office. He expects
the receptionist to be interested in learning about his life, and he likely hopes she will verbalize approval of his grandiose perspective. First-line treatment for narcissistic personality disorder is psychotherapy.
Incorrect Answers: A, B, C, D, E, G, and H.
Antisocial personality disorder (Choice A) is a cluster B personality disorder that arises from a deficit in empathy, resulting in pervasive violations of others' rights, aggression, and a hostile and manipulative attitude toward others. These patients may also be
chronically bored and hence sensation-seeking, leading to a high rate of substance abuse and gambling. Though this patient self-promotes at the expense of others, he does not demonstrate the aggression or violations of basic human rights that would be expected in
antisocial personality disorder.
Borderline personality disorder (Choice B) is a cluster B personality disorder that features an unstable sense of self and tumultuous relationships. Likely due to a combination of genetics and emotional invalidation during childhood and maturation, patients with
borderline personality disorder unconsciously learn to make impulsive and dramatic gestures, including self-harm, to obtain emotional fulfilment from others. This patient fulfils his emotional needs through gaining others' ad
Exam Section 3: Item 9 of 50
National, Board pf Medical Examiners
ment
- In biosynthesis of thyroid hormones, iodide is concentrated by the thyroid gland and oxidized by thyroidal peroxidase to iodine. lodine iodinates amino acid residues within the thyroglobulin molecule. Which of the following amino acids undergoes iodination?
National, Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
- A previously healthy 35-year-old woman develops hypoxemia 35 minutes after ingesting a near- lethal dose of barbiturates. She has not aspirated. Which of the following sets of arterial blood gas values (in mm Hg) is most likely in this patient?
Po
Pco
(A-a)
A)
40
50
35
B)
40
60
40
C)
50
25
10
D)
50
80
10
E)
60
35
25 - ✔✔✔D.
Barbiturates are central nervous system depressants which act on the chloride pore of the GABA receptor, increasing the time the receptor is opened. Symptoms of overdose include encephalopathy and respiratory depression. Respiratory depression leads to
hypoventilation as a decreased volume of air is moved to the alveolar-capillary interface for gas exchange. Hypoventilation can be identified by decreased PO2, increased CO-2, and a normal alveolar- arterial (A-a) gradient on arterial blood gas analysis. The
alveolar-arterial (A-a) gradient, also written as (A-a)O2, is the difference between the partial pressure of oxygen in the alveoli (PAO 2) and the arterial blood (PaO2). The PaO2 is measured directly on the blood gas analysis. The PAO2 must be estimated using the
alveolar gas equation, which is a function of the fraction of inspired oxygen (FiO2), the partial pressure of carbon dioxide (PaCO2), and the respiratory quotient (RQ), which relates the volume of CO2 produced by tissue to the volume of O2 consumed. If there is
no disruption of the alveolar-capillary interface or impaired perfusion to ventilated lung, the PAO2 and PaO2 will equalize as oxygen diffuses readily across the membrane. A normal A-a gradient of~10 mm Hg exists based on physiologic shunt, which is a volume
of blood that does not interact with ventilated lung. This occurs due to a normal ventilation-perfusion mismatch that exists due to gravity (increased ventilation in the apices of the lung, increased perfusion in the bases) as well as circulation that bypasses the
alveolar-capillary interface entirely (eg, bronchial arteries to pulmonary veins, smallest cardiac veins that drain directly into the left ventricle). This deoxygenated blood mixes with freshly oxygenated blood returning from the lungs, leading to a decreased PaO
relative to the PAO¬
Exam Section 3: Item 10 of 50
Natjonal, Board pf Medical Examinersment
V 10. A 56-year-old man comes to the physician for a routine examination. His stool is positive for occult blood. Colonoscopy shows a pedunculated growth that is coarsely lobulated and 1.4 cm in diameter. The excised lesion is covered by colonic epithelium and
composed of branching glands lined by tall hyperchromatic cells. Some areas appear mildly dysplastic, but there is no evidence of invasion of the stalk. Which of the following oncogenes is most likely to be activated in this lesion?
O A) erb
O B) fos
- A 27-year-old man has hepatomegaly and mild jaundice. Serum alkaline phosphatase and y- glutamyltransferase activities are increased. Which of the following properties of these enzymes allows them to be used to detect defects in bile flow?
O A) Present in bile ductules
O B) Present on the basal surface of hepatocytes
O G)Released from the gallbladder
O D) Required for bile salt synthesis
O E}Required for-bilirubin-conjugation
O F) Required for heme catabolism - ✔✔✔A.
Alkaline phosphatase and y-glutamyltransferase are enzymes present in bile ductules. Serum levels are increased in disorders of the biliary tract due to defects in bile flow. An increase in serum alkaline phosphatase, total bilirubin (especially with a conjugated or
direct bilirubin predominance), and y-glutamyltransferase is termed a cholestatic liver injury pattern. Alkaline phosphatases are isoenzymes that catalyze the hydrolysis of organic phosphate esters. They are found on the outer membrane of numerous cell types. The
majority of serum alkaline phosphatase is produced by the liver and bone. The small intestine may produce a small detectable amount. In the liver, alkaline phosphatase is found on the canalicular membrane of hepatocytes. Increased serum alkaline phosphatase is
associated with cholestasis, infiltrative disease, and bone disease. Increased y-glutamyltransferase levels are associated with disorders of the liver, biliary tract, and pancreas, as well as alcohol ingestion.
Incorrect Answers: B, C, D, E, and F.
Present on the basal surface of hepatocytes (Choice B) is incorrect as alkaline phosphatase and y- glutamyltransferase are located on the canalicular membrane (apical surface) of hepatocytes. The basal surface interfaces with the sinusoids.
Bile is the principle substance released from the gallbladder (Choice C). Bile aids in digestion, neutralizes gastric acid, promotes fat absorption, and is the primary means of excreting cholesterol and bilirubin. Alkaline phosphatase and y-glutamyltransferase are
membrane-bound enzymes, which are not excreted into bile.
Required for bile salt synthesis (Choice D) describes the enzyme cholesterol 7a-hydroxylase, which catalyzes the initial step in synthesizing bile salts from cholesterol. Deficiencies in this enzyme increase the risk of cholesterol gallstone f
Exam Section 3: Item 12 of 50
Natjonal, Board of Medical Examinersment
- A 62-year-old man has had petechiae and easy bruising for the past month. He has a 2-year history of alcoholic cirrhosis with portal hypertension. Laboratory studies show:
10 g/dL
Hemoglobin
Hematocrit
30%
4000/mm
65%
Leukocyte count
Neutrophils
Lymphocytes
Monocytes
Eosinophils
Basophils
Reticulocyte count
Mean corpuscular volume
Platelet count
30%
4%
1%
0%
8% of red cells
102 um
68,000/mm
Prothrombin time
16 sec
Partial thromboplastin time
