Intellectual Disability Gene Discovered

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Definition

Intellectual Disability (ID)

Intellectual disability (ID) is a term used when a person has certain limitations in cognitive functioning and skills, including communication, social, and self-care skills. These limitations can cause a child to develop and learn more slowly or differently than a typically developing child. Intellectual disability can happen any time before a child turns 18, even before birth. According to the American Association of Intellectual and Developmental Disabilities, an individual has an intellectual disability if they meet three criteria:

• IQ is below 70-75.
• The condition manifests itself before the age of 18.
• There are significant limitations in two or more adaptive areas (skills needed to live, work, and play in the community, such as communication or self-care).

Intellectual disability affects about 2-3% of the general population. Seventy-five to ninety percent of the affected people have a mild intellectual disability. Non-syndromic or idiopathic cases account for 30 to 50% of these cases. A genetic disorder causes about a quarter of cases, and about 5% of cases are inherited from a person's parents. Cases of unknown cause affect about 95 million people as of 2013.

Main Digest

A new study involving Canada's Center for Addiction and Mental Health (CAMH) has found a gene connected with a type of intellectual disability called Joubert syndrome. CAMH Senior Scientist Dr. John Vincent has identified this gene that, when defective, leads to Joubert syndrome. This research is published in the May 13 issue of Cell.

This international study combined Dr. Vincent's gene mapping of a family with Joubert syndrome with the use of a protein network map established by researchers at Genentech Inc., Stanford University, and the University of California at San Francisco (UCSF). Together this approach identified two genes associated with a group of disorders called ciliopathies.

Joubert syndrome, a ciliopathy, affects brain functioning, resulting in intellectual deficits, movement and coordination problems, and other symptoms such as kidney and eye problems. This syndrome is reported to affect approximately 1 in 100,000 children, although this is likely to be a significant underestimate of the true prevalence.

Ciliopathies are caused by genetic defects to a part of the cell called the cilium. The cilium is crucial as it is involved with cell signaling pathways during cell development in different body parts. The other ciliopathy gene identified in this study leads to a condition called nephronophthisis, which is also associated with kidney and eye problems.

"A defect in any aspect of this molecular pathway may have very similar effects at the clinical level," says Dr. Vincent, who is also head of the Center for Addiction and Mental Health's Molecular Neuropsychiatry and Development Laboratory.

Dr. Vincent's team found defects in the TCTN2 gene occurring in a Pakistan-based family where four siblings had Joubert syndrome. The syndrome occurs when a child inherits a defective gene copy from each parent.

The researchers based in California led the mapping of a network of potential proteins related to ciliopathies that interact on common pathways as an approach to identifying the disease genes.

The study was a collaboration of researchers from six countries and more than a dozen centers. The lead authors were Peter Jackson and Liyun Sang at Genentech and Jeremy Reiter at UCSF, and other collaborators included Friedhelm Hildebrandt at the University of Michigan at Ann Arbor, Dan Doherty at the University of Washington in Seattle, and Muhammad Ansar of Quaid-e-Azam University in Islamabad, and Julie Miller at Stanford University.

Dr. Vincent previously discovered the CC2D2A gene, also associated with Joubert syndrome. Defects on this gene account for about nine percent of cases of Joubert syndrome. To date, ten genes have been connected with Joubert syndrome.

Center for Addiction and Mental Health (CAMH)

The Center for Addiction and Mental Health (CAMH) is Canada's largest mental health and addiction teaching hospital, as well as one of the world's leading research centers in the area of addiction and mental health. CAMH combines clinical care, research, education, policy development, and health promotion to help transform the lives of people affected by mental health and addiction issues. CAMH is fully affiliated with the University of Toronto and is a Pan American Health Organization/World Health Organization Collaborating Center.

Resources That Provide Relevant Information

• DNA that Causes Autism and Schizophrenia
• Link to Autism in Boys Found in Missing DNA
• Are Genetics to Blame for Intellectual Disability
• Mitochondrial DNA and Autism Link
• Gene Identified as Cause of Forms of Intellectual Disability
• Nab2/ZC3H14 Protein and Inherited Intellectual Disability

Attribution/Source(s):

This peer reviewed article relating to our Cognitive Disabilities section was selected for publishing by the editors of Disabled World due to its likely interest to our disability community readers. Though the content may have been edited for style, clarity, or length, the article "Intellectual Disability Gene Discovered" was originally written by Center for Addiction and Mental Health (CAMH), and published by Disabled-World.com on 2011/05/13 (Updated: 2022/08/12). Should you require further information or clarification, Center for Addiction and Mental Health (CAMH) can be contacted at camh.ca. Disabled World makes no warranties or representations in connection therewith.

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