A 7-year-old boy is brought to the pediatrician by his parents due to concerns about developmental delay, hyperactivity, and poor eye contact. The parents report that he has difficulty with speech and social interactions, often avoiding eye contact and displaying repetitive behaviors such as hand-flapping. On physical examination, the child has a long face, large protruding ears, and macroorchidism (enlarged testicles). His family history is notable for a maternal uncle with intellectual disability and similar physical features. Given these findings, which genetic mutation is most likely responsible for his condition?
