USMLE STEP 1 Exam with Complete Solutions 2023

USMLE STEP 1 Exam with Complete Solutions 2023 2-year-old boy. Blood in wet diaper. abdominal mass in the right flank. CT revelers a large tumor in the right kidney. deletion in chromosome 11. - CORRECT ANSWER Wilms tumor: Deficiency of Phobilinogen deaminsde aka (Uroporphyrinogen) causing acute intermittent prophyria (AIP) 6-year old boy. worsening ataxic gait and a cardiac dysrhythmia. Uncle also has this condition. what is causing this? unstable protein folding unstable protein splicing unstable amino acid substitution unstable protein translation unstable truncated protein - CORRECT ANSWER Unstable Protein Translation: uncle and child appear to have Friedreich ataxia (a trinucleotide repeat disease) this happens bc of unstable microsatellite regions on certain chromosomes has 3x codons that expand: typically worsening from generation (often makes onset earlier from each generation) 3-moth year old. has a social smile but doesn’t hold his head up on his own. He has, pale skin, eczema, odd odor, and hyperreflexia. how do we treat this patient? - CORRECT ANSWER a diet in low Phenylalanine F Phe (non-polar molecule with a Phenyl group) Vignette suggest Phenylketonuria (PKU), a deficiency of phenylalanine hydroxylase (enzyme that break down phenylalanine) infants with PKU have high levels of phenylalanine in their blood, which is neurotoxic- can cause retardation. 63-year old man. alcoholic. poor memory, creates elaborate yet untrue stories. Examination reveals: ataxia and bilateral horizontal nystagmus. Wernicke-Korsakoff syndrome, caused via water-soluble vitamin deficiency, is suspected. what else is a result of water-soluble vitamin deficiency? - CORRECT ANSWER Pellagra: Vitamin B3 (niacin) deficiency. Patients will represent: diarrhea, dermatitis, and dementia other e.g. of water-soluble Vitamin are B2 (Riboflavin), biotin, folate, and B12 (cobalamin) Child is delivered w/out any complications. Upon check-up, he has, bilateral hip dislocation, restricted movement in shoulder, elbow joints, and coarse facial features. Lab results: beta- hexosaminidase, iduronate sulfatase, and arylsulfatase A , are deficient filbroblast, but 20X the normal in patients serum. Which organ is involved with the primary abnormalities? HINT: think the grinche - CORRECT ANSWER This patient has: I-cell disease. Caused by failure of adding mannose-6-phosphate by GlcNAc on the Golgi apparatus. W/out Mannose-6-phosphate it cannot be directed to a lysosome and will instead be excreted from the cell. Thus, beta- hexosaminidase, iduronate sulfatase, and arylsulfatase A will be found extracellularly, but not intracellular. Patients with albinism have (white-pink) skin, have white hair, nonpigmented or blue irises. They have melanocytes but lack melanin in their skin. what is deficient with albinism? - CORRECT ANSWER Tyrosine (Y) Tyr (Polar)