Hereditary-Genetic cause of autism

Everyone knows genetics play a large part in our lives: what color hair you will have, how tall you will be, the color of your skin, basically your overall appearance. Scientists say the same goes for autism; there is not just one kind of autism. Some people have very mild autism, where you won’t even notice they have it. During the past decades, scientists have made breakthroughs in finally beginning to understand the genetic bases of autism.

International research into the causes of Autism Spectrum Disorders (including the genetic aspects) is being fueled by recent developments. Evidence points to genetic factors playing a prominent role in the causes for ASD.

The consensus nowadays is that heritability contributes a very great deal to the risk of a child developing autism, but the genetics of autism are complex and typically it is unclear which genes are responsible.

Twin and family studies have suggested an underlying genetic vulnerability to ASD. To further research in this field, the Autism Genetic Resource Exchange is recruiting genetic samples from several hundred families.

Each family with more than one member diagnosed with ASD is given a two-hour, in-home screening. With a large number of DNA samples, it is hoped that the most important genes will be found. This will enable scientists to learn what the culprit genes do and how they can go wrong.

So it seems that congenital (existing at birth) factors play an important part. Some scientists believe that a cluster of unstable genes that adversely affects the development of the brain may cause autism. The first research results indicate that various chromosome spots are found where genomes could not possibly be. The most obvious spots are found on chromosomes 2, 7 and 16.Especially chromosome 7 stands out. However, the room on chromosome 7 is rather large and comprises a couple of hundred genomes. The next problem to be investigated carefully is which genome(s) on chromosome 7 in fact is/are connected to autism.

Recent neuroimaging studies have shown that a contributing cause for autism may be abnormal brain development beginning in the infant’s first months. This “growth dysregulation hypothesis” holds that the anatomical abnormalities seen in autism are caused by genetic defects in brain growth factors. It is possible that sudden, rapid head growth in an infant may be an early warning signal that will lead to early diagnosis and effective biological intervention or possible prevention of autism.

For detailed information on Autism Spectrum Disorders research, see the NIMH website, Autism Spectrum Disorders Research.

Some scientists believe in a genetic theory called “complex inheritance.” What scientists mean by“complex theory” is that many different factors are probably included in this inheritance. While an autistic person must have the right genes to have autism, environmental factors may add to the development of autism. Here is an example: let’s say you have a specific type of gene which makes a special type of chemical and which causes a chain reaction with another type of chemical. By studying autistic people, scientists may be able to find out the exact environmental issue, like chemicals in paint, that could contribute to causing autism.

Prof. dr. R.B. Minderaa points out that in Autism, as a rough estimate, between 80 to 90% of hereditary factors play a part. Autism can be hereditary in three ways.
•In most people with an ASD hereditary factors play a part. This is a combination of(hereditary) risk factors and coincidence.
•In a very small percentage (1 to 1,5%) autism shows up as a part of a syndrome existing at birth (i.e. Tuberous sclerosis, Williams-Beuren Syndrome, Landau Kleffner Syndrome, Lennox Gasteau Syndrome, Lujan Frijns Syndrome).
•In a very small percentage (1 to 1,5%) autism is the result of a specific chromosome deviation (i.e. fragile X-syndrome, Klinefelter, Turner). In these syndromes it can, from a medical point of view, be clearly indicated where the cause originates. In these cases heredity research can be conducted.

The hereditary factor
It appears that autism may run in families, since families with multiple children often have more than one child exhibiting signs on the autistic spectrum. In addition, parents may show signs of autism.

The chance that in a family with an ASD child another child with ASD is born lies between 2 and 5%. Therefore, parents with an ASD child have a chance up to 100 times greater to have another child with ASD than parents who have ‘normal’ children.
Studies of twins also indicate a hereditary factor in the occurrence of autism.
Family researches have proven that in families where autism is found, disorders are more often met than in families without autism. It then involves disorders such as reading, spelling, language and/or motor disorders or other development disorders such Attention Deficit and Hyper Activity Disorder (ADHAD) or a tic disorder and also milder forms of autism.

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