WASHINGTON – Maternal asthma and allergic disorders may somehow be linked with autism spectrum disorders, according to preliminary research presented at a meeting of the Centers for Disease Control and Prevention's National Center for Birth Defects and Developmental Disabilities.
Mothers of autistic children were more likely to have asthma or allergic disorders than the mothers of healthy control children in a study of 2,500 children, said Lisa Croen, Ph.D., a researcher at Kaiser Permanente Northern California, Oakland.
Immune function abnormalities have been widely reported in association with autism, though the evidence has been largely anecdotal.
For the study, the researchers identified 407 children in an outpatient database (for Northern California) who were born between January 1995 and June 1999 and were diagnosed with an autism spectrum disorder. As controls, healthy children (2,095) were randomly sampled and frequency-matched on birth year, gender, and birth hospital.
Maternal disease status was determined based on diagnoses in the period 2 years prior to and 2 years after giving birth. The researchers specifically looked at diagnoses of 44 autoimmune diseases, such as psoriasis and type 1 diabetes; asthma; and allergic disorders, such as allergic rhinitis, conjunctivitis, atopic eczema, angioedema, anaphylaxis, and urticaria.
The group of autistic children was predominantly male (82%). Children in the autism group were more likely to be twins. Mothers of autistic children were slightly older than the mothers of control children. There was a strong association between increasing maternal education and autism.
The researchers found that 16% of the mothers of autistic children were diagnosed with asthma during the 5-year period surrounding their pregnancies, compared with 11% of the mothers of healthy children. Likewise, one-quarter of the mothers with autistic children had an allergic disease, compared with 18% of the control mothers. “Allergic rhinitis was the particular finding that drove the allergy finding,” Dr. Croen said.
Whether the mother was diagnosed with asthma or allergy made no difference in terms of the child's risk of autism. Mothers diagnosed with asthma at any time prior to, during, and after pregnancy, always had a greater risk of having a child with autism than healthy mothers. Although the same was true for mothers with allergic disorders, the associations were not as strong.
The researchers also looked for associations between medications that mothers were taking and the frequency of autism in the children, to see if this could account in part for the association between maternal asthma/allergy and autism. They found no correlation between asthma or allergy medication use and an increased frequency of autism. The researchers also noted that the association between maternal asthma or allergy and autism was greater for autistic children who had one or more autistic siblings than for those with healthy siblings.
Maternal autoimmune diseases did not appear to be associated with a greater risk of autism. Mothers of children in the control group were just about as likely as mothers of autistic children to have any of the 44 autoimmune diseases–10% vs. 8%, respectively.
The researchers have postulated several biologic mechanisms for the association. First, it could be because of maternal immune response during pregnancy. In particular, they hypothesize that maternal antibodies may cross the placenta and disrupt fetal neurodevelopment by crossreacting with fetal brain antigens, through a process called molecular mimicry. The second hypothesis is that asthma and allergy share environmental risk factors with autism spectrum disorders. Another possibility is that asthma and allergy share genetic susceptibility with autism spectrum disorders–in other words, the diseases share common genes.