The clinical features of patients with Marfan syndrome are caused by unusually stretchable connective tissue. The most observed features in Marfan syndrome affect the eye, the skeleton, and the cardiovascular system. This is an example of:

Correct Answer: B

Rationale: Marfan syndrome’s multiple effects (eye, skeleton, heart) from FBN1 mutations exemplify pleiotropy (B). Rationale: One gene mutation (FBN1) affects connective tissue across systems, unlike allelic heterogeneity (different mutations, same phenotype) or anticipation (worsening generations).

Correct Answer: A

Rationale: Prepubertal vulvovaginitis features discharge (B), erythema (C), and pruritus (D), but exacerbation at puberty (A) is incorrect as it’s more common pre-puberty due to low estrogen. Rationale: Masturbation (E) may contribute but isn’t a defining feature; puberty increases estrogen, reducing incidence.

Correct Answer: B

Rationale: Bromocriptine (B), a dopamine agonist, is first-line for prolactinomas, shrinking tumors and normalizing prolactin. Rationale: Surgery (A) is for large/non-responsive tumors; Ondansetron (C) treats nausea, phenothiazine (D) increases prolactin, and antidepressants (E) are unrelated.

Correct Answer: D

Rationale: NF2 (A), Huntington (B), Marfan (C), are AD; Friedreich ataxia (D) is AR (GAA repeat on chromosome 9). Rationale: AD disorders need one allele; FRDA requires two.

Correct Answer: B

Rationale: Color blindness (B) is the most common XLR disorder (1 in 12 males). Rationale: Hemophilia (D) and fragile X (E) are less frequent; Rett (A) is XLD.