Researchers at the Centre for Addiction and Mental Health (CAMH) led a study discovering a gene for a new form of intellectual disability, as well as how it likely affects cognitive development by disrupting neuron functioning.
CAMH Senior Scientist Dr. John Vincent and his team made the discovery after mapping genes in a Pakistani family, in which three of seven siblings had intellectual disability as well as muscle weakness and walking difficulties. The findings were published in the May issue of the American Journal of Human Genetics.
Intellectual disability is a condition in which individuals have limitations in their mental abilities and in functioning in daily life. It affects one to three per cent of the population, and is often caused by genetic mutations.
Another study in the same journal, submitted together with the CAMH-led research, also identified NSUN2 gene mutations in Iranian and Kurdish families with intellectual disability. As with the Pakistani family, first cousin marriages in these families carrying the mutations increased the likelihood of intellectual disability among their children, and enabled researchers to focus on areas to map genes.
“The combined results from these two studies mean that NSUN2 is among the most common causes of intellectual disability resulting from recessive genes,” says Dr. Vincent.
As a recessive disorder, a child must inherit one defective NSUN2 gene from each parent to develop intellectual disability. This gene, located on chromosome 5p, encodes a type of protein called an RNA methyltransferase.
At the cellular level, the researchers found that the mutated protein was prevented from reaching its target area within the nucleus of a cell. As a result, it was unable to perform its normal role in cell division and/or RNA methylation.
To date, Dr. Vincent’s lab has identified five genes causing different forms of recessive intellectual disability. This research was supported by grants from Pakistan’s Higher Education Commission and the Canadian Institutes of Health Research.