GENETICS AND AUTISM
The past decade has been scientists make significant breakthroughs in understanding the genetics of autism. Researchers are focusing on specific chromosomal regions that may contain autism related genes.This involves the study of chromosomal abnormalities in individuals with autism and screening chromosomes for evidence of genes associated with autism. Currently there are several major studies looking into the genetics of autism.These studies are linked to the International Molecular Genetics study of Autism Consortium (IMGSAC),an international research project initiated in 1996 to identify the specific genes that may influence autism. One of the studies from Oxford University,suggests that the search for the genetic link to autism can be narrowed to the regions of two specific chromosomes.if Confirmed ,these genes may make some people more susceptible ton autism (IMGSAC,Centre for Human Genetics,Oxford University).The picture that is emerging from genetic studies is,however,very complex and autism seems to be linked to many different locations on the genome.It is likely that several genes may be operating together to make certain people more susceptible to autism. Some scientists believe that what is inherited is an irregular segment of genetic code or a small cluster of unstable genes.In most people,the faulty code may cause only minor problems.But under certain conditions,the unstable genes may interact and seriously interfere with the brain development of the unborn child. While there may be a genetic component to autism,it remains unclear what genes are involved estimates run from as few as three to as many as twenty genes acting together.Among the most popularly indicated genes are those that regulate the action of three powerful neurotransmitters: glutamate (involved in both learning and memory),seratonin and gammaaminobutiric acid (GABA)both of which have been implicated in obsessive -compulsive behavior , anxiety and depression).Many other genes are also under consideration for the possible impact they have on a person`s susceptibility to autism,including the genes that control brain development and immune system function. In a small number of cases,various single gene disorders and chromosomal abnormalities such as untreated phenylketonuria ,tuberous sclerosis and fragile X syndrome, have been reported in individuals with autism spectrum disorders indicating that the phenotype may be derived from a number of different genetic components.’It is entirely plausible that the autism phenotype may be derived from a number of different genetic components`(MRC Review of Autism Research,Dec 2001,p 3). Researchers have found that the traits of autism,far more than autism itself,tend to run in families. Although few severely autistic individuals form relationships and have children,scientists have found that in many instances,some aspect of the disorder affects a close relative.For example,a sister may have difficulties academically at school,a cousin may have some very rigid behaviors and limited interests or an adult uncle may still live at home with parents,be very shy and anti-social with few,or no,friends. There is increasing evidence of a genetic link to autism in some families,with several studies of twins suggesting that autism or at least a higher likelihood of some brain dysfunction can be inherited. One of the most effective ways of determining whether a particular syndrome or disorder is genetic is to examine the incidence in identical(monozygotic) and fraternal(dizygotic)twins. In research at the MRC Child Psychiatry Unit at the institute of Psychiatry in London ,it was found that in studies of identical twins using a strict definition of autism,if one identical twin had autism, there was a 60% chance that the second twin would also,and a greater than 75% chance that the twin without autism would still exhibit some autistic traits. On the other hand,if a fraternal twin is affected by autism the other twin in unlikely to have autism or any related disorder.Using a broader definition of autism (autism spectrum disorder ),research has shown that when one twin has autism,approximately 92% of monozygotic(identical) and 10% of dizygotic (fraternal) twins will also have autism.These findings support the hypothesis that there is a strong genetic basis to autism. It also appears that parents who have one child with autism are at slightly increased risk of having another child with the disorder. however,with researchers from around the world finding possible links to such things as genetics,vaccines mercury poisoning and other potential causes,it is becoming more and more likely that autism is the result of a combination of factors that come into play in approximately 1-500 children.It is for this reason that no area of research can be ignored.