Washington: In what could be called a major finding, scientists claim to have discovered a gene linked to intellectual disability.
Intellectual disability is a broad term describing individuals with limitations in mental abilities and in functioning in daily life. It affects one to three per cent of the population and is often caused by genetic defects.
A team at the Centre for Addiction and Mental Health, led by Dr John Vincent, has identified defects on the gene, MAN1B1, among five families in which 12 children had intellectual disability.
The subjects affected had similar physical features, and all had delays in walking and speaking. Some learned to care for themselves, while others needed help bathing and dressing. In addition, some had epilepsy.
All were found to have two copies of a defective MAN1B1 gene, one inherited from each parent. These were different types of mutations on the same gene -- yet the outcome, intellectual disability, was the same in different families, confirming this gene was the cause of the disorder.
"This mutation was seen in five families, which is one of the most seen so far for genes causing this form of recessive intellectual disability," Vincent said.
MAN1B1 codes an enzyme that has a quality control function in cells. This enzyme is believed to have a role in "proofreading" specific proteins after they are created in cells, and then recycling faulty ones, rather than allowing them to be released from the cell into the body. With the defective gene, this does not occur.
"This is a process that occurs throughout a person`s lifetime, and is probably involved in most tissues in the body, so it is surprising that the children affected didn`t have more symptoms," Vincent said.