Author:Professor, Departments of Psychiatry and Pediatrics, and Director, Edwin H. Cook, Jr., MD - Associate Laboratory of Developmental Neuroscience, University of Chicago.
Summary: The first thing Dr. Cook wanted to clarify about genetics is that, finding genetic evidence of autism does not mean that that person's fate is sealed. This is a fallacy. Phenylketonuria is a purely genetic disease that can cause mental retardation. But we now know that if when this is discovered in babies at birth, if certain dietary substances are avoided, it is completely preventable - even though it is a genetic disease.
In studies of twins from 20 years ago, researchers found that identical twins much more commonly shared a tendency for autism than non-identical twins. These findings were replicated several times. The discrepancy between identical and non-identical twins is very high and suggests very high "inheritability" for autism. Thanks to a study published in Science a few years ago, several people recognized that autism should be getting more emphasis in genetics. This has brought more people from outside the field into it, and this is a positive development.
The most practical thing for families to know is that, if one child has autism, the risk of subsequent siblings having it is in the range of 5 to 9 percent, as opposed to the 1 in 1,000 prevalence of autism in the general population.
Autism is a complex genetic disorder, and the typical dominant/recessive gene numbers don't fit. There are several genes involved in autism risk, possibly located on three to five interacting loci (places or sites). There is also a sex influence, which means that the threshold of risk is different for males than females, yet this is not linked to the X chromosome, as it is in many genetic sex-linked disorders.
One reason for work on the genetic factors in autism is to gain experience with potent serotonin transport inhibitors in attempts to use SSRIs (selective serotonin reuptake inhibitors, a class of antidepressant drugs) to treat some behaviors. In some children we've found that, after four weeks (the time it takes for the drugs to have an effect), some rituals and repetitive behaviors may be reduced, especially if these were ones that seemed to be distressing to the autistic individual. The response to the drugs (such as Prozac, Anafranil, and Zoloft) isn't helpful for language, learning or social development, as we'd like it to be, but it can relieve some distressing, obsessive-compulsive type behaviors. A danger is that, in too high a dose, the drugs can cause the same behaviors or worse ones, such as hyperactivity and aggressiveness. This must be monitored carefully if drug therapy of this type is considered.
Back to the genetics research: The differences we've found in genes seems to be related not to the autism itself, but to the modulation of the severity of some symptoms of autism. Some of what we may learn from genetics has to do more with subtypes of autistic syndromes. If we learn to understand more about these differences, this can help us determine if some cases might respond to medicines like Prozac. In other words, the genetic research we're doing is more aimed at improving therapeutic measures to help autistic children and their families.
Collaborations Yield New Discoveries in Psychiatric Genetics - "Scientists at Rutgers, The State University of New Jersey, in collaboration with colleagues at the University of Medicine and Dentistry of New Jersey (UMDNJ) have unveiled new information regarding the genetic, cellular and neurological bases of susceptibility to these diseases. Using data drawn from the Rutgers Cell and DNA Repository on 518 families, each with multiple autistic children, James Millonig and Linda Brzustowicz, assisted by Emanuel DiCicco-Bloom, led a team that further substantiates the link between autism and Engrailed 2 (EN2), a gene important in central nervous system development. Their research is presented in the November issue of the American Journal of Human Genetics (AJHG).
Millonig and Brzustowicz had previously demonstrated an association with the gene in a sample of 167 families with autism. The new study adds another 351 families and now provides convincing statistical support for the existence of a mutated form of EN2 that increases the risk for autism. The statistics also showed EN2 may contribute to up to 40 percent of autism cases in the general population."
Exploring Autism: A Look At the Genetics of Autism - "This website is dedicated to helping families who are living with the challenges of autism stay informed about the exciting breakthroughs involving the genetics of autism." Also French and Spanish versions available.
Genetics and Autism: A Briefing - "Over the last decade, staggering and revolutionary advances in the methods of genetic investigation have made it possible to hunt for genetic abnormalities and susceptibility genes, searching through the entire human genome systematically. Several groups have now embarked on a hunt for the genes that create a susceptibility for autism, by undertaking genome searches. "
Autism Genetics Resource Exchange (AGRE) - "AGRE was created by parents of autistic children who want to see genetic research, medical treatment and maybe even a cure for autism happen sooner rather than later-in their own children's lifetime. AGRE exists to serve the needs of researchers in the field of autism and, as such, will be responsive and as flexible as possible to individual researchers, institutions and collaborative research groups."
Autism Speaks - The latest research on genetics and autism, current studies, and links to other research.
National Alliance for Autism Research (N.A.A.R.) - Looking for a Genetic Component of a Common Characteristic of Autism - The National Alliance for Autism Research and Autism Speaks presents a research article on the hunt for a genetic cause of autism.
The Hunt for Autism Genes: A Conversation With Researcher Ed Cook, M.D. , by Catherine Johnson - "finding the genes for autism may well mean finding treatments or cures for autism."
THE INTERNATIONAL MOLECULAR GENETIC STUDY OF AUTISM CONSORTIUM - "The International Molecular Genetic Study of Autism Consortium (IMGSAC) is a team of clinicians, laboratory researchers and statistical geneticists from several European countries and the U.S.A., established to investigate the genetic basis of autism and related disorders."
Errant Protein Could Solve the Riddle of Autism - A malfunctioning protein (metallothionein), located on chromosome 7, may be a cause of autism. "Metallothioneins (MTs) are ubiquitous low molecular weight proteins and polypeptides of extremely high metal and sulfur content. They are thought to play roles both in the intracellular fixation of the essential trace elements zinc and copper, in controlling the concentrations of the free ions of these elements, in regulating their flow to their cellular destinations, in neutralising the harmful influences of exposure to toxic elements such as cadmium and mercury and in the protection from of a variety of stress conditions." [Kagi, J.H. & Schaffer, A. Biochemistry of metallothionein. Biochemistry 1988 Nov 15;27(23):8509-15].
Scientists Discover New Gene Essential For The Development
Of Normal Brain Connections Resulting From Sensory Input - Biologists at the University of California, San Diego and the Johns Hopkins University have discovered a gene that plays a key role in initiating changes in the brain in response to sensory experience, a finding that may provide insight into certain types of learning disorders.
OMIM Article on Autistic Disorder and Gene Research - OMIM is the premier genetics web site. This article provides information on studies which have been done linking autism with specific genes and other findings.
PubMed (Medline) References To Autism AND Chromosomes - Medline journal articles from all years listed.
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