A 5-year-old boy comes to the office with periorbital edema and rust-colored urine for 2 days.  His oral intake has been normal, but his parents are concerned that he is voiding less frequently than usual.  Three weeks ago, he had a pustule on his face that subsequently developed an overlying, adherent, honey-crusted layer and resolved with antibiotics.  The patient’s blood pressure is mildly elevated.  Urinalysis is positive for protein and red blood cell casts.  Which of the following characteristics best describes the bacteria involved in this patient’s condition?

A 34-year-old man comes to the urgent care center with urinary frequency, urgency, and dysuria, and is treated with antibiotics.  Three weeks later, he returns to the clinic due to worsening back pain, knee pain, and difficulty walking.  The pain is sharp and radiates to the left hip and buttock.  Past medical history is unremarkable, and the patient takes no long-term medications.  Temperature is 37.2 C (99.0 F), blood pressure is 119/70 mm Hg, pulse is 88/min, and respirations are 16/min.  Physical examination shows a swollen and tender right knee.  The patient also has redness and conjunctival edema of the left eye.  Which of the following is the most likely diagnosis?

A 3-year-old boy is evaluated in the genetics clinic.  His mother says that he has frequent temper tantrums, displays excessive food-seeking behavior, and does not like active play.  Physical examination shows marked obesity and small hands and feet.  Chromosomal analysis shows a 46,XY genotype.  No abnormalities are detected by fluorescence in-situ hybridization (FISH).  Which of the following chromosomal anomalies is most likely responsible for this patient’s condition?

A 43-year-old woman comes to the office for evaluation of diarrhea.  For the last 6 months, she has had watery diarrhea of variable severity associated with abdominal bloating and weight loss.  For the past 2 weeks, she has had a pruritic rash involving the elbows, as shown in the image below.  The patient initially attempted to manage her symptoms with changes in dietary fiber intake.  She has also tried a number of over-the-counter medications without relief.  After further discussion, she is scheduled for gastrointestinal endoscopy.

Intestinal biopsy in this patient is most likely to reveal which of the following pathological abnormalities?

Autopsy findings in a 42-year-old Caucasian female are shown on the image below.  She suffered from exertional dyspnea and experienced sudden death.

Which of the following best describes the changes in cardiac muscle cells responsible for the autopsy findings?

A 27-year-old woman comes to the clinic with a skin lesion on her right foot.  She started a job as a hotel concierge 1 month ago and has to wear uncomfortable dress shoes as part of her new uniform.  Physical examination reveals the findings seen in the exhibit.  This patient’s condition is most likely due to thickening of which of the following skin layers?

A 37-year-old mildly obese, nulliparous woman with a strong family history of breast cancer undergoes genetic testing that reveals a germline mutation in the BRCA1 gene.  After discussing the prognostic implications with her primary care physician, the patient elects to have prophylactic bilateral mastectomy and salpingo-oophorectomy.  Histopathologic analysis shows no evidence of malignancy.  Gross examination reveals scattered abnormalities throughout both ovaries, as shown in the image below.

Which of the following hormonal changes is most likely associated with this patient’s condition?

An 18-month-old boy is brought to the office for evaluation of developmental delay.  His parents describe an uneventful pregnancy and birth.  However, since infancy, the child has been very quiet and does not respond to many stimuli.  The patient’s developmental milestones were grossly delayed.  He smiled at age 6 months and began to hold his head up at age 9 months.  The patient also has a habit of aggressively biting his fingers, tongue, and lips.  Examination shows tongue and lip lacerations and several ulcerations on the fingers.  Laboratory studies reveal a high urinary uric acid level.  Which of the following enzymes is most likely deficient in this patient?

A novel antibiotic substance, drug X, is synthesized in the research and development laboratory of a pharmaceutical company.  Drug X is found to irreversibly bind to the 30s subunit of prokaryotic ribosomes; as a result, incoming aminoacyl-tRNA access to mRNA is blocked, leading to inhibition of protein synthesis and cell death.  On further testing of the antimicrobial spectrum of activity of drug X, several bacterial species are found to be resistant to the drug.  These bacterial species are most likely to also be resistant to which of the following antibiotics?

During a research study on factors affecting cell differentiation, investigators isolate mature fibroblasts from the skin of a healthy volunteer.  The fibroblasts are infected with a combination of retroviruses containing certain genes that encode human proteins.  These modified fibroblasts are subsequently cultured, and the colonies obtained from the cultures are found to contain cells resembling pluripotent embryonic stem cells.  The genes transferred by the retroviruses in this experiment most likely code for which of the following proteins?

An investigator is studying the effects of various drugs on the denervated eye.  The experimental findings are shown on the graph below.

Drug X is most likely to be which of the following?

A 56-year-old woman comes to the office due to a 3-month history of excessive fatigue, along with progressive numbness in both feet.  Her sleep is adequate, and she eats a normal diet.  The patient has a history of hypothyroidism that was diagnosed following pregnancy 20 years ago.  Her only current medication is levothyroxine, and she does not use alcohol.  Physical examination shows mucosal pallor with a flat, shiny tongue.  Neurologic examination finds diminished vibratory sensation in both feet.  TSH level is normal.  Peripheral blood smear is shown in the image below.

Which of the following is most likely increased in this patient?

A 26-year-old man comes to the office due to a scrotal mass.  He first noticed a painless mass in the scrotum 4 weeks ago while in the shower and thinks it may be getting larger.  The patient has no history of abdominal or genital trauma.  On examination, he has a left-sided scrotal mass that is palpable when he stands but disappears when he lies down.  Light does not shine through the mass when a penlight is held behind it.  Which of the following is the most likely diagnosis?

A 57-year-old man comes to the clinic due to poor appetite and weight loss.  His symptoms have been present for 6 weeks and are progressively worsening.  The patient has smoked 2 packs of cigarettes daily for 30 years and drinks 3-5 alcoholic beverages daily.  Vital signs are normal.  On physical examination, the patient is thin and has pale conjunctivae and a shiny tongue.  Velvety, hyperpigmented plaques on the skin are noted in the axillae and neck.  The abdomen is nontender.  Laboratory studies show a moderate, hypochromic microcytic anemia.  Which of the following is the most likely diagnosis?

A 42-year-old woman is evaluated for several months of dyspnea.  The patient reports being diagnosed with a cardiac murmur in her early adolescence, which was attributed to mild valvular insufficiency.  She has been asymptomatic until recently, when she started having progressive dyspnea on exertion, fatigue, and occasional paroxysmal nocturnal dyspnea.  The patient has no other medical problems.  Examination reveals a grade III/VI holosystolic murmur at the apex that radiates to the axilla.  Echocardiogram shows thickened, redundant mitral valve leaflets with posterior leaflet prolapse and severe mitral regurgitation.  Mitral valve replacement is performed with a mechanical valve, and the postoperative course is uncomplicated.  Which of the following is indicated for long-term management of this patient?

A 64-year-old man comes to the office with a 6-week history of back pain.  The pain is severe at times, is not related to activity, and often wakes him from sleep.  The patient has no history of spinal trauma.  On further questioning, he reports mild weight loss and occasional pinkish hematuria.  Examination reveals an enlarged prostate with a hard nodule.  Laboratory studies are notable for mild anemia and a markedly elevated prostate-specific antigen level.  Biopsy and subsequent imaging confirm adenocarcinoma of the prostate with evidence of bony metastases in the lumbar spine.  The patient declines orchiectomy but is willing to consider leuprolide therapy.  Long-term treatment with this medication would result in which of the following?

In embryonic development, both melanocytes and germ cells undergo which of the following?

A pediatric cardiologist is consulted about a 2-week-old boy with a suspected congenital heart defect.  The patient struggles while feeding, developing tachypnea, tachycardia, and transient cyanosis.  The boy’s postnatal course was complicated by a seizure during the first week.  Physical examination shows low-set ears and increased distance between the eyes.  Karyotype analysis reveals a partial deletion on chromosome 22.  Disturbed development of which of the following cardiac structures most likely occurred in utero?

A 2-year-old boy is brought to the office due to recurrent otitis media and pneumonia.  His most recent pneumonia episode required intubation and mechanical ventilation.  During that admission, Pneumocystis jiroveci was identified on bronchoscopy.  Neither the patient’s parents nor his two older siblings have evidence of an immunodeficiency disorder.  The patient’s HIV test is negative.  Flow cytometry demonstrates a lack of CD40 ligand expression on CD4 lymphocytes.  Which of the following serum concentrations are most likely low in this patient?

Chromosomal DNA is isolated from a malignant cell and subjected to restriction endonucleases, yielding a large number of DNA fragments.  These DNA fragments are then separated by gel electrophoresis and their nucleotides are sequenced.  One of the DNA fragments is found to have a region rich in cytosine-phosphate-guanine (CpG) dinucleotide repeat sequences.  Further analysis reveals that most of the cytosine residues have been methylated to 5-methylcytosine.  Which of the following statements regarding this DNA fragment is most accurate?

An 18-year-old man comes to the emergency department with severe right groin pain and difficulty bearing weight on the right lower extremity.  He has had no fever or trauma.  The patient was hospitalized 6 months ago for a similar pain in his proximal humerus but was discharged without a definitive diagnosis.  On physical examination, he appears to be in pain but there is no visible abnormality of his lower extremities or hips.  He also has nontender hepatosplenomegaly.  A radiograph of the proximal right femur reveals marked osteopenia with cortical collapse.  Following an extensive workup, an enzyme deficiency is found to be the cause of his presentation.  Which of the following enzymes is most likely deficient in this patient?

A 34-year-old man is brought to the emergency department after several episodes of coffee ground emesis.  The patient says his mouth feels dry and that he becomes dizzy on standing.  He has recently taken ibuprofen for a back injury sustained several weeks ago.  Blood pressure is 90/60 mm Hg and pulse is 120/min.  His skin is cool and clammy, and there is mild epigastric tenderness.  Increased levels of which of the following molecules are most likely to be seen within the vascular smooth muscle of this patient?

A researcher develops a particular mouse lineage that carries a human tumor necrosis factor-alpha transgene with a modified 3′ region from a human globin gene.  As a result, the mice develop symmetric polyarthritis and intestinal inflammation.  Which of the following medications would most directly counteract these inflammatory changes?

A 63-year-old man comes to the physician with occasional squeezing chest pain while jogging or walking uphill.  The pain occurs shortly after beginning physical activity and subsides spontaneously within 1–2 minutes after he stops.  He also complains of shortness of breath during these episodes.  Cardiac enzyme markers are within normal range.  The use of low-dose aspirin is most likely to reduce this patient’s risk of cardiovascular events by inhibiting which of the following enzymes?

A newborn boy is in the neonatal intensive care unit for management of prematurity.  He was delivered vaginally at 26 weeks gestation due to premature labor and preterm rupture of membranes.  The patient is intubated and has an umbilical arterial catheter in place.  The medical team is preparing to place another catheter through the umbilical vein.  To reach the inferior vena cava and right atrial junction, the umbilical venous catheter most likely passes through which of the following structures?

A 53-year-old man who recently emigrated from Russia comes to the office due to several months of productive cough with occasional hemoptysis.  Medical history is significant for tuberculosis and chronic bronchitis.  The patient has smoked a pack of cigarettes per day for the past 20 years.  Tuberculin skin testing yields 15 mm of indurated erythema.  Bronchoalveolar lavage fluid is cultured, and microscopic examination of the cultured organism is shown in the image below:

Which of the following is the most likely cause of this patient’s current symptoms?

A colony of bacteria resistant to gentamicin and a colony resistant to ampicillin are mixed on an agar plate containing both antibiotics.  Bacterial growth is noted after incubation for 24 hours.  The same experiment is then repeated with the addition of deoxyribonuclease (DNAse) to the agar plate.  The enzyme is functional in the culture medium but is not able to penetrate the bacterial cell membrane.  During this second experiment, no bacterial growth is observed.  Which of the following is the most likely mechanism of bacterial survival in the first experiment?

A 39-year-old male complains of facial puffiness in the morning. He is HIV positive.  Laboratory evaluation reveals proteinuria (3.5 g/day).  Renal biopsy shows glomerular epithelial cell enlargement and vacuolization, as well as varying degrees of glomerular capillary wall collapse.  Many renal tubules show cystic dilation and are filled with proteinaceous material.  This patient most likely suffers from which of the following?

A 23-year-old woman comes to the emergency department with sudden-onset dyspnea.  She has a history of mild intermittent asthma and takes an inhaled beta-2 adrenergic agonist as needed to manage her symptoms.  Her chest x-ray is shown below.

Which of the following treatment options is most likely to relieve this patient’s symptoms?

A 17-year-old girl, gravida 1, para 0, is brought to the office by her mother for follow-up after a miscarriage.  Physical examination shows a longitudinal vaginal septum and a duplication of the cervix.  The patient also has hypoplastic great toes and thumbs.  MRI of the pelvis reveals a uterus didelphys.  On further evaluation, the patient’s mother is found to have similarly shortened first digits and a history of several miscarriages.  Mutation of which of the following genes is most likely responsible for this patient’s findings?

An 18-year-old woman comes to the office due to a long history of polyuria and polydipsia.  She is carrying a large bottle of water from which she has to drink constantly throughout the day to stay hydrated.  Her sister has similar symptoms and was found to have a mutation in the aquaporin-2 gene.  Blood pressure is 110/70 mm Hg and pulse is 89/min.  Physical examination shows no abnormal findings.  The 24-hour urine output is 4 L.  After several hours of water deprivation, her urine output remains unchanged.  Which of the following is likely to be seen in this patient?

A researcher conducts experiments on isolated skeletal muscles.  Decreasing which of the following would increase contraction velocity?

A 34-year-old woman comes to the office due to intermittent abdominal bloating and diarrhea for the past several years that has been progressively worsening.  She also has weight loss, fatigue, and bone pain over her lower spine and pelvis.  The patient does not use tobacco, alcohol, or illicit drugs.  Laboratory testing is positive for antitissue transglutaminase antibodies; biopsy specimens taken during upper gastrointestinal endoscopy reveal villous atrophy in the proximal small intestine.  Additional studies show decreased serum calcium and 25-hydroxyvitamin D levels.  The patient is advised to follow a strict gluten-free diet.  Which of the following changes are most likely to occur in this patient after the recommended treatment is begun?

A 56-year-old man is brought to the emergency department with recent-onset lethargy, confusion, and vomiting.  The patient has been seeing a psychiatrist for the last several months for depression following the death of his wife.  Laboratory findings are as follows:

Several hours later, he develops back pain, gross hematuria, and oliguria.  An overdose involving which of the following substances is most likely responsible for this patient’s symptoms?

Polymerase chain reaction is used to amplify Chlamydia trachomatis DNA fragments present in tissue samples.  DNA polymerase obtained from Thermus aquaticus is used in the reaction.  The procedure involves initial heating of the solution to 95°C (203°F) followed by cooling the solution to 55°C (131°F). Immediately upon cooling, which of the following happens?

A 21-year-old man comes to the office for evaluation of an acute illness.  His symptoms began 2 weeks ago with rhinorrhea, sore throat, and sneezing.  After an initial period of improvement, the patient developed nasal congestion, facial pain, and persistent low-grade fever.  Medical history is unremarkable and vaccinations are up to date.  The patient is single and works as a gas station attendant.  He does not smoke tobacco but occasionally uses an electronic cigarette.  Temperature is 37.7 C (100 F).  A coronal CT scan of the sinuses is shown in the image below.

The structure involved by this patient’s disease process communicates directly with which of the following spaces?

A 65-year-old man is brought to the emergency department after his daughter found him on the floor of his apartment.  His daughter reports that he had an episode of slurred speech a week ago, which resolved spontaneously after several hours.  The patient has a history of hypertension, hyperlipidemia, and type 2 diabetes mellitus.  He had smoked a pack of cigarettes daily for 30 years but quit 2 years ago.  Blood pressure is 170/95 mm Hg and pulse is 78/min and regular.  Further evaluation with cerebral CT angiogram reveals involvement of the artery indicated by the white arrow in the image below.

Which of the following visual abnormalities is most likely to be seen in this patient?

A 64-year-old man comes to the office due to 6 months of progressive epigastric pain that is worsened by food ingestion.  The patient also reports a 10-kg (22-lb) weight loss within this period and several episodes of vomiting in the last 2 weeks.  He has been taking over-the-counter omeprazole without any relief.  Physical examination shows epigastric fullness with succussion splash.  Fecal occult blood test is positive.  Gastric outlet obstruction due to malignancy is suspected.  Biopsy of which of the following lymph node structures is most likely to show deposits of malignant cells?

In an experiment, the circulating blood volume of an anesthetized animal is increased by intravenous saline infusion.  It is found that this increase in preload raises left ventricular myocardial inotropy and stroke volume.  Further evaluation with myocardial biopsy reveals an increase in sarcomere length.  Electron microscopy of the cardiac muscle is shown in the image below.

Which of the following labeled regions was most likely lengthened in this experiment?

A 16-year-old student is brought to the office due to difficulty falling asleep at night and excessive daytime sleepiness.  He has had these symptoms for several years, but they have worsened during the past year.  The patient typically does not fall asleep until 4:00 AM but sleeps comfortably once he does.  The patient often plays on his computer, watches TV, or reads in bed until after 3:00 AM.  His parents have to wake him up repeatedly for school in the morning.  The patient has been falling asleep in his morning classes, and his grades have declined.  On weekends, he sleeps until the afternoon.  His father had a similar behavior pattern at the patient’s age.  Which of the following is the most likely diagnosis?