Practice Test 9 - USMLE Step 1

20 questions. Answer them in any order, then submit to see your score and every explanation.

Start practice test

1. This pattern of serum markers is most suggestive of a fetus with which of the following chromosomal abnormalities?
2. Which of the following sets of hemodynamic changes is most characteristic of a normal pregnancy?
3. Which of the following is the most accurate conclusion based on these results?
4. A 26-year-old woman has recurrent epistaxis and visible telangiectasias on the lips and tongue. She reports exertional dyspnea; CT angiography shows pulmonary arteriovenous malformations. Her mother had similar nosebleeds. Karyotype is 46,XX. Genetic testing reveals a heterozygous pathogenic variant in ENG (endoglin), consistent with hereditary hemorrhagic telangiectasia. The physician explains that endoglin is part of the TGF-$\beta$/BMP signaling complex in endothelial cells, influencing SMAD-dependent transcription required for normal vessel development. Which of the following is most likely disrupted in this patient?
5. A 3-year-old girl has normal early development followed by loss of speech and purposeful hand use, with repetitive hand-wringing movements. She develops seizures and gait instability. Family history is negative. Karyotype is 46,XX. Sequencing shows a pathogenic variant in MECP2. The clinician explains that MeCP2 normally represses transcription by binding methylated CpG sites and recruiting histone deacetylases; mutation causes inappropriate gene expression in neurons. How does the identified mutation affect protein function?
6. The pathogenic mechanism in this patient's disorder involves silencing of the affected gene primarily through which of the following molecular events?
7. Which of the following best explains why increasing heart rate above 180 beats/min can lead to a fall in cardiac output in a normal adult?
8. Which of the following molecules is essential for transporting the resulting peptide fragments into the endoplasmic reticulum for loading onto MHC class I molecules?
9. A deficiency of which of the following enzymes best explains this patient's clinical and laboratory findings?
10. A 35-year-old man is evaluated for recurrent spontaneous pneumothoraces and multiple lung cysts on CT. He has numerous small, dome-shaped papules on his nose and cheeks. His mother had bilateral renal tumors at age 50. The patient's brother has similar skin lesions. Physical exam is otherwise normal. Karyotype is 46,XY. Targeted molecular analysis reveals a heterozygous pathogenic variant in FLCN consistent with Birt-Hogg-Dubé syndrome. The genetic counselor explains that folliculin acts as a tumor suppressor and influences transcriptional programs by modulating nutrient-sensing pathways, including AMPK–mTOR balance. Which of the following is most likely disrupted in this patient?
11. The massive proteinuria in this patient is most directly caused by which of the following ultrastructural changes in the kidney?
12. A 62-year-old woman has early satiety and vomiting; CT shows gastric outlet obstruction. Which physiological process is likely disrupted in this condition?
13. Which of the following correctly describes the vessels within a normal umbilical cord and the type of blood they carry?
14. A newborn with mitochondrial DNA mutation has hypotonia and cardiomyopathy with lactate 9.0 mmol/L (0.5–2.2). The clinician explains that oxidative phosphorylation occurs across the inner mitochondrial membrane and depends on a proton gradient. Which of the following mechanisms best explains decreased ATP production in this disorder?
15. This over-representation of less aggressive tumors is characteristic of which type of bias?
16. This phenomenon is a classic example of which of the following regulatory mechanisms?
17. The existence of many different disease-causing mutations at a single genetic locus is an example of which of the following?
18. An 11-year-old boy develops cola-colored urine and periorbital edema 2 weeks after healing from impetigo caused by group A streptococcus. Laboratory studies reveal red blood cell casts, low C3, and elevated anti-DNase B titers. Which of the following immunopathologic mechanisms best accounts for his renal findings?
19. This drug exerts its primary effect by inhibiting which of the following transport processes in the thick ascending limb of the loop of Henle?
20. This patient has an increased lifetime risk of developing breast and ovarian cancer due to an impaired ability to repair DNA damage via which of the following pathways?

Practice tests