What is the most frequent genetic cause of mild to moderate intellectual and developmental disabilities?

Down Syndrome is recognized as the most frequent genetic cause of mild to moderate intellectual and developmental disabilities. This condition is caused by the presence of an extra copy of chromosome 21, leading to a range of cognitive, physical, and health challenges. Individuals with Down Syndrome often exhibit developmental delays and may require various support services to enhance their learning and inclusion.

In terms of frequency, Down Syndrome occurs in approximately 1 in 700 live births, making it the most common genetic anomaly associated with intellectual disabilities. The other conditions listed, while associated with intellectual and developmental disabilities, do not occur with the same prevalence as Down Syndrome. For example, Autism Spectrum Disorder encompasses a broad range of behaviors and has varying levels of intellectual involvement; similarly, Rett Syndrome primarily affects girls and is much less common overall. Asperger Syndrome, which is now considered to be part of the Autism Spectrum, typically does not result in intellectual disabilities but rather can sometimes manifest alongside average or above-average intelligence. Thus, Down Syndrome stands out as the most frequently identified genetic condition linked to these disabilities.