Diagnostic Exome Sequencing in Persons with Severe Intellectual Disability

Severe intellectual disability, which is also referred to as cognitive impairment or mental retardation, affects approximately 0.5% of the population in Western countries1,2 and represents an important health burden. A clinical diagnosis of severe intellectual disability is generally based on an IQ of less than 50 and substantial limitations in activities of daily living. In early childhood, the diagnosis is based on substantial developmental delays, including motor, cognitive, and speech delays. Children with different nonsyndromic forms of intellectual disability are clinically indistinguishable. Intellectual disability can be caused by nongenetic factors, such as infections and perinatal asphyxia. In developed countries, . . .