Which of the following is the most common known genetic cause of intellectual disability?

• A Fragile X syndrome
• B Phenylketonuria
• C Trisomy 21 (Down syndrome) ✓
• D Tuberous sclerosis

Explanation

Trisomy 21 affects roughly 1 in 700 live births and accounts for the largest single group of children with intellectual disability, making it the most common chromosomal and overall genetic cause. Fragile X syndrome is the commonest inherited cause and the leading single-gene cause, but its total burden is lower than trisomy 21. Phenylketonuria and tuberous sclerosis are important but far less frequent.

Reference: Kaplan and Sadock's Synopsis of Psychiatry, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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