Question 91: 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?
- A. 47,XYY
- B. 47,XXY (Correct Answer)
- C. 45,X
- D. 46,XX
Explanation: ***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