More than 200 million people around the world are affected by an intellectual disability. Yet not much is known about the genetics or molecular pathways behind intellectual disability. Researchers recently discovered a new form of intellectual disability that is especially prevalent in countries where marriages between genetically related individuals are common. The hope is that this research will provide a better understanding of the underlying genetics involved in intellectual disability.
The study uncovered five individuals from two unrelated families in Saudi Arabia and Pakistan who suffer from the syndrome. All five individuals had the same symptoms, which included intellectual disability, developmental delays, speech loss, small stature, low muscle tone, and in some cases, aggression and seizures. Analysis of the patients' DNA showed that they shared mutations in gene IQSEC1.
This was the first study to reveal that an IQSEC1 mutation could result in intellectual disability. Mutations in IQSEC2 and IQSEC3 have been previously implicated in intellectual disabilities. The researchers looked at fruit flies to determine whether the mutation was the cause of the intellectual disability and other symptoms. They eliminated the schizo gene in the fruit flies and replaced it with a functioning IQSEC1 gene and found that the flies behaved normally. When mutated IQSEC1 genes were placed in the flies, they found dead fruit fly embryos with severe neural defects. They found that variants in the gene produced nonfunctional IQSEC1 proteins. In addition, studies on mice showed that a deletion of the IQSEC1 protein resulted in defects in certain neural projections.
All of the individuals with the disability came from families where marriages between relatives were common. The individuals inherited two defective copies of IQSEC1, one from each parent. The defective copies of IQSEC1 produced altered proteins in the patients. Further research must be done to uncover how prevalent this syndrome may be.
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