Of the following, the study that is MOST useful in diagnosis of an aneuploidy is

Correct Answer: A

Rationale: Karyotyping (A) directly visualizes aneuploidy (e.g., trisomy 21). Rationale: FISH (B) confirms specific regions; microarray (C) detects microdeletions, not whole chromosome changes.

Correct Answer: D

Rationale: Williams syndrome (7q11.23 deletion) includes hypercalcemia (A), elfin face (B), blue irides (C), and friendly personality (E); IQ is typically low (D is false). Rationale: Mild intellectual disability is common.

Correct Answer: D

Rationale: Fluorescence In Situ Hybridization (FISH) uses fluorescent probes to locate specific DNA sequences on chromosomes, identifying gene locations or chromosomal abnormalities. It doesn’t involve RNA prep, enzyme assays, buccal scraping, or fibroblast inhibition.

Correct Answer: D

Rationale: Hypomelanosis of Ito features hypopigmented skin patterns, ocular/CNS issues, and mosaic chromosomal anomalies (autosomal or sex chromosomes). Skin fibroblast studies often show mosaicism, not normal chromosomes.

Correct Answer: B

Rationale: Advanced paternal age increases de novo mutations (e.g., in sperm), linked to conditions like hearing loss or autism. Trisomies (e.g., Edwards) and recessive disorders (e.g., CF, Tay-Sachs) are more tied to maternal age or inheritance, not paternal age.