Genetic etiology of adult intellectual disability (ID) of unknown cause in Qatar: a retrospective study

Background: Intellectual disability (ID) is a common condition that consists of a heterogeneous group of clinical conditions with different etiologies, including genetic conditions. Identifying those with a genetic cause results in better clinical management. Aim: To identify the genetic etiology of ID in adult patients with unknown etiology presenting to a specialist learning disability service in Qatar. Methods: Retrospective review of chart notes of patients referred for ID service from January 1, 2015 to January 1, 2020. Results: Of the 228 patients, 82 had a known cause of ID and did not require genetic testing, 22 had an unknown cause and underwent genetic testing, and 124 had an unknown cause and did not undergo genetic testing. Of the 82 patients with a known cause of ID, about one-half had an autistic spectrum disorder (ASD) and 18 patients had a genetic disorder. Of the 22 patients who underwent genetic testing, 2 were positive for the Fragile-X mental retardation 1 gene, 3 underwent chromosomal microarray, and 7 underwent whole-exome sequencing. Seven abnormal genes were identified. Conclusions: Identifying the underlying genetic etiology of patients with ID has major implications for diagnostic and therapeutic approaches. Additionally, it guides a prediction of the natural history of the disease and makes it possible to test at-risk family members.