Finding the genes behind intellectual disability

Intellectual disability (ID) involves impaired cognition and limited mental function beginning in early childhood and persisting into adulthood. A variety of factors are at play but the exact contribution of genetics to the condition is unclear. 

Researchers in Saudi Arabia together with colleagues in other Arab countries and the United States genetically assessed 337 individuals with ID. They found a genetic cause behind 74% of the cases, 81% of which were due to a recessive gene, consistent with the high number of cases resultant from consanguineous marriages¹.  

The study identified 68 new ID-causing mutations and discovered 35 new genes not previously linked to human disease. 

They also found a potentially treatable form of ID caused by a gene mutation involved in manganese transport.

“There are so many syndromes that present with intellectual disability that any clinical geneticist will tell you it’s an absolute nightmare to make a clinical diagnosis based only on clinical assessment. That’s where the power of genomics comes in,” says geneticist Fowzan Alkuraya from Saudi Arabia’s King Faisal Specialist Hospital and Research Center. 

The study found that genetic testing revealed a likely diagnosis for up to three quarters of the cases studied. Traditional methods led to possible diagnoses in only 16% of the cases. Subsequent genetic testing found only 70% of those to be correct.

Clinicians “should stop blaming birth asphyxia on every case of intellectual and developmental disability and employ due diligence to rule out a genetic cause,” says Alkuraya. 

Genomic sequencing, which is a cost-effective tool, should be considered early on in diagnosing individuals with ID, he adds.

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