FMGE 2025 — Internal Medicine

Q: A teenage boy, who was previously raised as a girl, presents with primary amenorrhea and lack of secondary sexual characteristics. On examination, he has tall stature, small testes, and gynecomastia. Which of the following is the most likely genotype?

47,XXY. ***Correct: 47,XXY (Klinefelter Syndrome)*** - This patient presents with **classic features of Klinefelter syndrome**: tall stature, small firm testes, gynecomastia, and hypogonadism [1]. - The **47,XXY karyotype** results from meiotic nondisjunction leading to an extra X chromosome. - **Hypogonadism** causes decreased testosterone, leading to lack of secondary sexual characteristics and increased FSH/LH [1]. - Patients typically have **eunuchoid body proportions** (tall stature with long limbs) due to delayed epiphyseal closure [1]. - The presence of **gynecomastia** is due to relative estrogen excess compared to testosterone [1]. - Primary amenorrhea mentioned here likely refers to the lack of pubertal development (developmental delay). *Incorrect: 47,XYY (Supermale Syndrome)* - These individuals are **tall males with normal virilization** and normal-sized testes - No gynecomastia or hypogonadism - Often associated with learning difficulties but normal sexual development *Incorrect: 45,X (Turner Syndrome)* - Presents in **phenotypic females** with **short stature** (not tall) [2]. - Features include webbed neck, shield chest, coarctation of aorta - Primary amenorrhea present but patient would be raised as female throughout - Does not explain male phenotype or gynecomastia in this case *Incorrect: 46,XX (Normal Female Karyotype)* - Normal female karyotype would not explain **male phenotype** with testes - Does not account for gynecomastia or the clinical presentation described

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A teenage boy, who was previously raised as a girl, presents with primary amenorrhea and lack of secondary sexual characteristics. On examination, he has tall stature, small testes, and gynecomastia. Which of the following is the most likely genotype?