Autism is a complex disorder that has been linked to a variety of genetic and environmental factors. Initially, researchers thought that mothers were more likely to transmit mutations of genes that promote autism. This is because women have a much lower prevalence of autism than men, and women are thought to have the same genetically modified risk factors without symptoms of autism. However, recent studies have shown that both parents can carry the autism gene and pass it on to their children. In general, autism cannot be attributed to a Mendelian mutation (a single gene) or to single-chromosome abnormalities, such as fragile X syndrome or 22q13 deletion syndrome.
A 2001 study of siblings and parents of autistic children analyzed the phenotype in terms of a current cognitive theory of autism. This study found that women who have mild autism traits can pass on autism-related genetic variants to their children, without having autism themselves. Neurexin 1 and other similar genes are very important in determining how the brain connects from one cell to another and in the chemical transmission of information between nerve cells. These genes are particularly active very early in brain development, either in the womb or in the first months or a couple of years of life. In contrast, a condition of completely genetic origin would theoretically produce 100% agreement for MZ pairs and usually much less for DZ pairs, depending on factors such as the number of genes involved and selective mating. Although the fraction of autism traceable to a genetic cause can grow up to 30-40% as the resolution of matrix CGH improves, several results in this area have been described with caution, possibly misleading the public into thinking that a large proportion of autism is caused by CNV and is detectable through matrix CGH, or that the detection of CNVs is equivalent to a genetic diagnosis.
The point is to inform parents of their risk so that they can make their own decisions based on that knowledge. Other possible important explanations for sporadic autism are also being actively studied, including other genetic causes and the role of factors in a child's environment. An example of a condition that appears to have little or no genetic influence is irritable bowel syndrome (IBS), with 28% agreement compared to parents being able to perform genetic testing to determine if their defective gene was passed on and led to their child developing autism. Better understanding parents could teach researchers something about possible outcomes in their children, Swanson says. Because no single gene causes autism (more than 100 genes have clear links to the disorder), there are no genetic tests available to diagnose autism. Currently, about 165 genetic mutations have been linked to autism, and an in-depth analysis of a potential father's sperm for some of these aberrations could let you know if you are at greater or lower risk of fathering a child who may be affected by autism. In conclusion, both parents can carry the autism gene and pass it on to their children.
It is important for parents to be aware of their risk so they can make informed decisions about their family planning. Genetic testing can help identify potential risk factors for autism, but it is not a definitive diagnosis.
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