Gene found for mental retardation

Scientists looked at gene mutations

Scientists say they may have found a specific gene responsible for developmental problems in children.

They believe the discovery could lead to new therapies for mental retardation and better understanding of how the brain develops.

The researchers from J. C. Self Research Institute of Human Genetics in South Carolina said it appeared that abnormalities on a single gene on the X chromosome, could lead to mental retardation.

Genes tell the body how to make one or more proteins which then perform specific activities within the body's cells.

This is an important advance in our understanding of the biology of mental retardation

Dr Jonathan Flint, Wellcome Trust Centre for Human Genetics

But mutated genes produce altered proteins, or no proteins at all.

Sometimes this will not affect the body, but other mutations can cause disease or disrupt development.

Broken chromosome

Scientists studied a female patient with unexplained retardation.

It was known that during her development, two of her chromosomes had broken and switched places.

It was suspected this could have led to her learning disabilities.

Scientists looked at two genes near to the broken chromosome to see if any of them were damaged or altered.

It was found the AGTR2 (Angiotensin II receptor 2) gene was affected and did not express, or transmit its messages to the body.

A related gene plays an important role in ensuring blood vessels function properly and in regulating blood pressure and hormone secretion.

The researchers suspect that AGTR2 is also involved in blood vessel function or development which could play a part in how the brain develops and functions.

The team then looked at the gene 590 other patients who had unexplained developmental problems.

Eight of them had a mutation of the gene.

The researchers said that even though that was a small percentage of the patients examined, it was still a significant finding.

Further research is planned.

Mutation test

Dr James Hanson, head of the US National Institute for Child Health and Development's Mental Retardation and Developmental Disabilities Branch, said: "With a total of 30,000-35,000 genes in the human body, the discovery of even a single gene that may play a pivotal role in brain development could be an extremely important discovery.

"This study also shows that the technique of identifying candidate genes in a single individual with mental retardation and testing them for mutations is useful for identifying genes related to mental retardation."

Dr Jonathan Flint, consultant psychiatrist at the Wellcome Centre for Human Genetics, Oxford, told BBC News Online: "This is an important advance in our understanding of the biology of mental retardation.

"Just like the authors of this paper, European researchers have been identifying unusual patients with chromosomal rearrangements, identifying the genes that are disrupted and then looking for mutations in other patients."

The research is published in the journal Science.