Autism and mental retardation – genetic overlap

30 May

Post taken from Medical News Today

Researchers working with Professor Gudrun Rappold, Director of the Department of Molecular Human Genetics at Heidelberg University Hospital, have discovered previously unknown mutations in autistic and mentally impaired patients in what is known as the SHANK2 gene, a gene that is partially responsible for linking nerve cells. However, a single gene mutation is not always enough to trigger the illness. In some cases, a certain threshold of mutation must be exceeded. The researchers conclude from their results that a correct inner structure of the nerve cell synapses is necessary to enable the normal development of language, social competence, and cognitive capacity. Essential for the success of the project were the studies by the Heidelberg research team with the doctoral student Simone Berkel and collaboration with a Canadian research team headed by Steve Scherer. The study has already been published online in the leading scientific journal Nature Genetics.

Autism is a congenital perception and information-processing disorder of the brain that is often associated with low intelligence, but also with above-average intelligence. The disease is characterized by limited social communication and stereotypical or ritualized behavior. Men are affected much more frequently than women. Autism and mental retardation can occur together but also independently of one another and are determined to a great extent by hereditary factors. Some of the responsible genes have already been identified but the precise genetic mechanisms have not yet been explained.

Genetic makeup of hundreds of patients analyzed

Professor Rappold and her team focused their studies on the SHANK2 gene, which encodes a structural protein at the nerve cell synapses. It is responsible for the mesh structure of the basic substance in the postsynapse. Only when the postsynapse is properly structured can nerve impulses be correctly transmitted. The researchers analyzed the genetic material of a total of 396 patients with autism and 184 patients with mental retardation. They found different mutations in their SHANK2 genes in the area of individual base pairs, but also variants in the number of gene copies. The mutations led to varying degrees of symptoms. None of the observed gene variants occurred in healthy control persons. “Apparently an intact postsynaptic structure is especially important for the development of cognitive functions, language, and social competence,” explained Professor Rappold.

Identical mutations as the cause of different diseases

Some of the genetic mutations identified were new occurrences of mutations that were not inherited from the parents, but some of the mutations were also found in one parent. Since there are also healthy carriers of gene variants, we must assume that a certain threshold of gene mutations must be exceeded for the disease to appear. “Moreover, the same mutation can be present in an autistic patient with normal intelligence and in a mentally impaired patient,” said Professor Rappold. There is some overlap in the clinical symptoms of mental retardation and autism, which can now be explained by a common genetic cause.

7 Responses to “Autism and mental retardation – genetic overlap”

  1. Niksmom May 30, 2010 at 15:16 #

    I worry about the way this study is being portrayed in the media thus far; the headline of the article you linked to says the gene variants “lead to autism…” yet the study (from what I understand) doesn’t make that broad jump. It seems that there’s a good deal of necessary information omitted from the news article…

    Was there a control group of “normal/typical” subjects used to compare the inner structures of the SHANK2 genes? Did they account for any variations found in subjects who wer non-verbal but able to communicate in writing/typing or using other AAC? What was the threshold for “mental retardation”—IQ (questionable at best), clinical observation? How did they choose the subjects?

    I know you don’t have the answers and I’m not assuming you should. Merely commenting on the spotty coverage in the media thus far, I suppose. :-/

  2. Kev May 30, 2010 at 22:31 #

    You’re right, its far from perfect, but its interesting – particularly the relationship between the two.

  3. Laurentius Rex May 30, 2010 at 23:03 #

    Bollox me old pal me old beauty

    No science logic research, statistics and much less verity in it at all.

    I expect over time that improved brain scanning computational and indeed revised statistical techniques (believe me the maths does need an overhaul) will show something else.

    You don’t have to believe me of course, but if you have the advantage of having at least twenty years under me in age, all you will have to do is wait, I will just have to go to my grave knowing that 🙂

  4. Tsu Dho Nimh May 31, 2010 at 16:17 #

    Niksmom … yes there was a control group. “None of the observed gene variants occurred in healthy control persons.”

  5. Laurentius Rex June 1, 2010 at 18:53 #

    Well that says it all “health control persons” if that does not portray the delusions and the illusions, that is to say the prejudices of the observers, how can I trust much beyond that when they make such an ill omened mistake.

    It is a case I suspect of deciding that autism and mental retardation are the same, and only looking at four legged chairs as something to sit on, as if stools with three legs don’t exist. A classic putting the cart before the horse, circular argument, self definition.

    I’m still not buying. WTF is a “healthy control”

  6. Niksmom June 4, 2010 at 02:15 #

    TDN, I must’ve missed that in my wonderings about all the other stuff. LOL. Thanks.

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