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What Causes Autism?
June 18, 2007 5:42 PM
Our medical unit’s Dr. Monya De blogs about the debate:
Autism’s sinister attack on children that start out appearing healthy, even precocious, is one of the most devastating trials a parent can endure. Fluent speech degenerates to monosyllables. Creative play becomes hand-flapping and repeated purposeless motion. Children react with the same indifference to strangers and loving parents. It is no wonder that immense resources have been poured into finding a definitive explanation. Research studies have investigated many different causes, leading to controversy over which is the "right" one.
Evidence certainly exists that genes and environment both play a role in autism. For example, autism is more common in boys, and autistic children frequently have mutations in chromosome number 15. Identical twins, who share one hundred percent of their DNA, offer a strong evidence that autism's cause is genetic; when one twin is affected by autism, chances are very high, as much as eighty to ninety percent, that the other twin will also have autism.
Because childhood vaccine use and autism have increased in the same era, thimerosal—a basic vaccine ingredient—is often blamed for the condition. Vaccine abstainers point out that mercury is a neurotoxin, and thimerosal, an ingredient in many vaccines, contains levels of ethylmercury that may exceed threshold levels established by the EPA when several vaccines are given. But the time that many children present with autism--age two-- occurs soon after many of them receive a series of vaccines, and that the apparent link may just be a coincidence of timing. Also, autism rates continue to climb even though thimerosal has been removed from both vaccines, and symptoms of a person with mercury poisoning are utterly different from those of an autistic person.
Researchers are looking for other environmental triggers of autism. For instance, children who have had certain infections at an early age also develop autism at higher rates. The Institute of Medicine has also just recently conducted a special workshop to look at potential environmental toxins that might be involved in the development of autism. Their report is due out this fall.
The best evidence the medical community has is that autism develops from "multifactorial" causes. That means that, like heart disease, a variety of genetic and environmental factors likely play a role in whether the disease develops or not. The "two-hit" hypothesis is often mentioned in the context of autism; one defective gene might be inherited from a parent, but the other one mutates as a result of unknown external factors.
Unraveling this painful mystery, for this reason, will continue to be a challenge.
June 18, 2007 | Permalink | Share | User Comments (4)
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There is scientific evidence linking the little-known thermal effects of prenatal ultrasound to autism. Although pregnant women cannot hear or feel ultrasound, when sound waves hit tissue, they are transformed into heat. Heat can interrupt key enzyme reactions, potentially damaging heat-shock proteins, which protect cells when temperatures rise. In the case of regressive autism, most likely heat shock proteins were damaged in utero, but it was not until the first high fever -- sometimes following vaccinations -- that the damage was done. This explains why genetically identical twins only have similar outcomes, not identical outcomes: if prenatal ultrasound is the culprit, one twin could have taken the brunt of the sound waves during a routine ultrasound exam, sparing the other. It also explains why twins are more likely to develop autism; multiple gestations are exposed to more ultrasound scans. Many mothers and even doctors will be surprised to learn that prenatal ultrasound does not improve pregnancy outcomes, even when it uncovers major birth defects. Expectant mothers should be advised of this information before submitting to ultrasound.
Posted by: Caroline Rodgers | Jun 19, 2007 5:57:25 AM
In several areas of medicine, we know more than we used to, and yet autism seems to be on the rise and to be a condition which baffles even the experts. It may take a Sherlock Holmes of medicine to unravel the mystery. The rare expert is known by his accurate diagnosis of the unusual, after which a cure may follow.
Posted by: Candadai Tirumalai | Jun 19, 2007 11:31:54 AM
It doesn't take Sherlock Holmes to figure out what is causing autism when so much evidence points to prenatal ultrasound. Research published in 2004 showed that pregnant mice exposed to prenatal ultrasound produced mice with disturbed neuronal migration -- the process that correctly wires the brain. Autopsies of people with autism showed the same kind of disturbed neuronal migration. What is needed is not a legendary detective, but scientists to use their training to read the data already available and regard an evolving technology in a new light.
Posted by: Caroline Rodgers | Jun 19, 2007 3:48:25 PM
It is inappropriate to label a condition as genetic when the cause(s) of the condition is not known or proven. Sadly, this is the case with genetic theories of causation in autism based on classic twin studies, multiple incidence families, high male to female ratios and findings of genetic mutations of small or unknown effect (chromosome 15).
The cause of leprosy is exposure to myobacterium Laprae. Leprosy genetic data published over many decades is strikingly similar to the genetic data published in autism over many decades.
In leprosy there is a strong genetic component with Indian twin studies reporting a high concordance rate ( 60 - 85% ) found in identical twins and a rapid falloff in concordance in fraternal twins ( 5 - 20% ). Multiplex leprosy families have been recruited to search the genome for leprosy susceptibility genes. Mutations in chromosome 10P13 have been found. The sibling risk ratio of 2.4 is the same as has been reported in some autism studies.
Data extracted from Leper Registries in China including over 400,000 cases recorded over a fifty year period report a high male female ratio of 3:1
No one considers leprosy to a 'genetic condition' since the cause is envirnmental and has been known for over 100 years.
Autism researchers may have misinterpreted the genetic data reported in autism or at least overstated the genetic component in autism.
Posted by: RA Jensen | Jul 14, 2007 10:27:21 AM
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