A 6-year-old boy has a long face, large ears, macroorchidism, and intellectual disability. His maternal grandfather also had cognitive issues. Cytogenetic analysis reveals an expanded CGG trinucleotide repeat in the FMR1 gene. This is consistent with:

• A Angelman syndrome
• B Prader-Willi syndrome
• C Williams syndrome
• D Fragile X syndrome ✓

Explanation

Fragile X syndrome is caused by expansion of CGG trinucleotide repeats (>200 repeats = full mutation) in the FMR1 gene on the X chromosome, leading to silencing of the FMR1 protein (FMRP). Classic features include intellectual disability, long face, large protruding ears, macroorchidism (post-pubertal), and autism-like behavior. It shows X-linked inheritance with anticipation and is the most common inherited cause of intellectual disability.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.