Autism and Potential Environmental Causes - Maternal Antibody IgG
Posted Aug 25 2008 6:24pm
Maternal IgG (an antibody) may be a factor in causing autism according to a study conducted by researchers from the UC-Davis MIND Institute. The study report, Stereotypies and hyperactivity in rhesus monkeys exposed to IgG from mothers of children with autism , by researchers Loren A. Martin, Paul Ashwood, Daniel Braunschweig, Maricel Cabanlit, Judy Van de Water, and David G. Amarala , is currently an article in press in Brain, Behavior, and Immunity and the abstract is available on line from Science Direct . The report notes an emerging consensus that Autism Spectrum Disorders have multiple etiologies (causes or origins) and indicates that the study tested the proposition that one cause of ASD may be exposure of the fetal brain to maternal autoantibodies during pregnancy. The study essentially involved comparing a group of rhesus monkeys exposed to human IgG collected from mothers of multiple children with ASDs to rhesus monkeys exposed to IgG from mothers of multiple typically developing children and to a further control group of untreated rhesus monkeys.
"four rhesus monkeys were exposed prenatally to human IgG collected from mothers of multiple children diagnosed with ASD. Four control rhesus monkeys were exposed to human IgG collected from mothers of multiple typically developing children. Five additional monkeys were untreated controls. Monkeys were observed in a variety of behavioral paradigms involving unique social situations. Behaviors were scored by trained observers and overall activity was monitored with actimeters. Rhesus monkeys gestationally exposed to IgG class antibodies from mothers of children with ASD consistently demonstrated increased whole-body stereotypies across multiple testing paradigms. These monkeys were also hyperactive compared to controls. Treatment with IgG purified from mothers of typically developing children did not induce stereotypical or hyperactive behaviors. These findings support the potential for an autoimmune etiology in a subgroup of patients with neurodevelopmental disorders. This research raises the prospect of prenatal evaluation for neurodevelopmental risk factors and the potential for preventative therapeutics. "
A helpful definition of IgG can be found at the Dalhousie University Faculty of Medicine Immunology Bookcase web site. The definition points out that IgG is the most abundant form of antibody in the blood, that it is able to leave the blood stream and enter tissues and that it is the only form of antibody to pass the placental barrier:
IgG is the most abundant form (class) of antibody in the blood (serum concentration is 13 mg/ml !). There are four subclasses of IgG which are all monomeric and they usually have a very high affinity for antigen. Unlike IgM, IgG is able to leave the blood stream and enter tissues.
IgG is also the only class of antibody to pass the placental barrier. Therefore IgG provides the only antibody protection for newborns until their own immune system is able to contribute to antibody production.