Intellectual disability (ID), sometimes also referred to as ‘mental retardation’ and ‘cognitive disability’, is a lifelong disability that presents in infancy or the early childhood years and is typically measured in three domains: intelligence (IQ), adaptive behavior and systems of support. The term ‘global developmental delay’ is typically reserved for younger children (less than 5 years of age), whereas the term ID is typically applied to older children when IQ testing is valid and reliable. Non-syndromic ID refers to the presence of ID without accompanying additional physical, neurological, and/or metabolic abnormalities.
The prevalence of ID (syndromic and non-syndromic) is estimated to be between 1% - 3%. In general, there is wide variation in the causes of ID: 18 – 44% of cases have exogenous causes (like teratogen exposure or infection) and 17 – 47% have genetic causes. X-linked mental retardation (XLMR) affects between 1/600-1/1000 males and a substantial number of females (3). The etiology remains unknown in up to 80% of cases with mild intellectual disability. Depending on the underlying etiology, the recurrence risk can vary between the background and 50%. The best approach to the genetic evaluation of a child with ID is to do a careful history, 3-generation family history, and dysmorphologic and neurologic examination. Based on this alone, a geneticist will suspect or establish a diagnosis in as many as two thirds of cases. Being able to provide a genetic etiology allows for the opportunity of prenatal diagnosis, guidance with disease management, acceptance of the disability, and connection with other parents and support groups.
The distinction between syndromic and non-syndromic ID is not precise. Conditions previously regarded as non-syndromic forms of ID may have additional clinical findings that were not intially recognized or emphasized, thus a range of mutations in a single gene can sometimes confer both syndromic and non-syndromic phenotypes. Our ‘non-specific’ ID panels include mainly non-syndromic forms of ID, but also include many syndromic forms of ID to account for the above.
Our X-linked ID panel includes sequencing of 77 genes (see information sheet for more details).
Any gene in the X-linked ID panel can also be ordered separately. Please contact us directly for cost and CPT code information.