All are causes of intellectual disability except

A. Fetal alcohol syndrome (FAS) is a leading preventable cause of intellectual disability. Prenatal alcohol exposure disrupts brain development, leading to cognitive impairment, behavioral problems, and facial abnormalities. B. Down syndrome (trisomy 21) is a genetic disorder that causes intellectual disability, developmental delays, and characteristic physical features. It results from an extra copy of chromosome 21, affecting brain development and cognitive function. C. Serotonin syndrome is an acute, life-threatening condition caused by excessive serotonin activity due to medication overdose or drug interactions (e.g., SSRIs, MAOIs, MDMA). Symptoms include hyperreflexia, autonomic instability, and altered mental status, but it does not cause intellectual disability. D. Fragile X syndrome is a genetic disorder caused by a mutation in the FMR1 gene on the X chromosome. It is the most common inherited cause of intellectual disability, leading to cognitive impairments, social anxiety, and hyperactivity, often resembling autism spectrum disorder (ASD).