Question

In a child with Klinefelter syndrome, which of the following is NOT a characteristic feature?

• A. Increased height
• B. Macrotestis
• C. Gynaecomastia
• D. Decreased fertility

Hint:

Testicular Size in Genetic Disorders:
- Klinefelter syndrome (47,XXY): Microtestis (small, firm testes) + Tall stature + Gynecomastia.
- Fragile X syndrome: Macroorchidism (large testes post-puberty) + Large ears + Long face + Intellectual disability.

Answer 1

The Correct Option is B

Concept:
Klinefelter syndrome is the most common sex-chromosome aneuploidy in males, occurring in approximately 1 in 600 live male births, with the classic karyotype 47,XXY.
It results in primary testicular failure (hypergonadotropic hypogonadism) beginning during pubertal maturation.
Explanation:
• The classical clinical and phenotypic features of Klinefelter syndrome include:
1. Tall stature with disproportionately long lower limbs (eunuchoid proportions) due to the presence of three copies of the $SHOX$ gene.
2. Small, firm testes (microorchidism microtestis), measuring typically $< 4\text{ mL}$ or $< 2\text{ cm}$ in length, caused by progressive hyalinization and fibrosis of seminiferous tubules.
3. Primary infertility azoospermia due to complete loss of germ cells.
4. Gynecomastia (seen in approximately 40--50% of patients) caused by an increased estrogen-to-androgen ratio, which carries a 20-fold increased risk of male breast cancer.
5. Hypergonadotropic hypogonadism: Elevated serum LH and FSH with low to low-normal serum testosterone levels.

• Macrotestis (abnormally enlarged testes) is NOT seen in Klinefelter syndrome; it is the classic hallmark feature of Fragile X syndrome.
Final Answer:
Macrotestis is characteristic of Fragile X syndrome, whereas Klinefelter syndrome is characterized by small, firm testes (microtestis).