Review Question - QID 215034

A 31-year-old man presents to clinic for evaluation of a 3-year history of infertility. He has no significant medical history and takes no medications. He exercises twice a day, often with heavy weightlifting, and eats a high-protein diet. He reports occasional alcohol use and remote marijuana use. His temperature is 99.5°F (37.5°C), blood pressure is 148/90 mmHg, pulse is 84/min, and respirations are 15/min. He is sexually active with his wife and has no history of sexually transmitted infections. Physical exam reveals small testes and a receding hairline. He also has palpable tissue underneath his nipples bilaterally. His muscle tone is normal in his upper and lower extremities bilaterally. His laboratory values are below:

Serum:
Creatinine: 1.3 mg/dL
Glucose: 110 mg/dL
Total bilirubin: 0.8 mg/dL
Aspartate aminotransferase (AST, GOT): 410 U/L
Alanine aminotransferase (ALT, GPT): 275 U/L

Hemoglobin: 12 g/dL
Leukocyte count: 5,300/mm^3
Platelet count: 250,000/mm^3

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