Some children with a common mental disorder may have newly identified genetic mutations that affect learning and memory.

In Thursday's issue of the New England Journal of Medicine, Dr. Jacques Michaud, a geneticist at the Sainte-Justine University Hospital Research Centre in Montreal, and an international team of colleagues said they've identified mutations for non-syndromic mental deficiency or NSMD. 

'For a lot of parents, especially for mothers, knowing the cause has really allowed them to close the loop or to relieve a lot of anxiety.'— Dr. Jacques Michaud

Children with the mutations look normal physically but may have delays in language and mental development and, in some cases, a mild form of epilepsy.

The cases occur independently of a known condition and with no apparent genetic explanation.

The researchers discovered that three per cent of the 94 subjects with NSMD they studied had harmful mutations in the SYNGAP1 gene.

"Several observations indicate that new mutations are a frequent cause of neurodevelopmental disorders, but their identification has been difficult because it requires the study of a large fraction of genes, which represents a challenging task," said Dr. Fadi Hamdan, an author of the study.

Looking to diagnostic tests, therapies

To identify the mutations, the researchers used a new technology to study hundreds of genes in people with NSMD, and 142 subjects with autism spectrum disorders, 143 subjects with schizophrenia, and 190 control subjects. The mutations were only found in people with NSMD.

Now that the mutations have been identified, diagnostic tests could be offered to children with NSMD.

"It's a bit like a black hole when you're telling a family or a parent that their kid has a mental deficiency," said Michaud, who noted many press for answers medical science cannot always provide.

"Not for everybody, but for a lot of parents, especially for mothers, knowing the cause has really allowed them to close the loop or to relieve a lot of anxiety."

It may also be possible to apply knowledge about how the gene works to design drugs aimed at improving cognition and complications such as epilepsy, the researchers said.

Parents often want to know if subsequent children would be at risk of having the same condition. Based on these findings, the chances would be low, Michaud said.

And current therapies aimed at allowing normal production of the protein coded for by the gene could help at least two of the subjects in the study, the study's authors noted.

The gene codes for a protein involved in the development and function of the connections between brain cells known as synapses. When the gene is disrupted in mice, learning and memory is impaired.

Mental retardation, as it is still called in scientific journals, is the most prevalent severe handicap of children, affecting one to three per cent of the population, according to the researchers. Most have the nonsyndromic form of the disorder.

The research was supported by grants from the Canadian Institute of Health Research, Fonds de la Recherche en Santé, Genome Canada and Genome Quebec and the Université de Montréal.

With files from the Canadian Press