Autism is a brain disorder that affects approximately 1 in 150 children. Signs and symptoms of this disorder include difficulties with social interactions and communication as well as a restricted pattern of activities and interests. The cause is unknown. Males are diagnosed as having autism more often than females for unknown reasons. The number of people known to have autism has increased dramatically since the 1980s, partly due to changes in diagnostic practice and also increased awareness; the question of whether prevalence has increased is unresolved. It has been suggested that the cause of autism may be genetic, due to immune system problems, environmental factors such as infections, or some combination of these. Scientific studies in other neurodevelopmental disorders (e.g., schizophrenia) have suggested the role of high levels of maternal antibodies in causality. In this project, we will test the theory that certain antibodies in pregnant women and infants may cause alterations in the development of the fetal brain that lead to the autism spectrum disorders. These antibodies are formed by the immune system as part of the normal host defense activity that is essential for life. They protect us against common bacteria and other microbes that may cause infections. These antibodies help maintain our health, and they do not ordinarily enter the brain because of the blood-brain barrier. However, in pregnant women, these antibodies may cross the placenta and enter the fetal blood brain barrier. Because the blood-brain barrier of the fetus develops slowly over time, its brain can be exposed to these maternal antibodies. If the level of these antibodies is sufficiently high and the fetal blood-brain barrier is not yet fully formed, the concentration of cross-reactive antibodies reaching the fetal brain could have effects on the developing nervous system.
The types of antibodies we will investigate are those that react both with microbial antigens and with nerve or endocrine tissue antigens, which is why they are called "cross-reactive." One of the common building blocks of certain bacteria (such as those that can cause meningitis) is a chemical called sialic acid. It is a major component of their outer capsule, and it is also a major component in human brain tissue. Sialic acid is critically important for regulation of neuronal growth. Antibodies that react with sialic acid on bacteria could also react with sialic acid in brain tissue. Other cross-reactive antibodies may be formed to polysaccharide components of bacteria and to certain viruses such as herpes simplex and cytomegalovirus. Our project will identify these antibodies by using very sensitive assays that can detect both antibodies that react with bacteria and viruses, and antibodies that react with brain tissue antigens.
Heel stick blood samples are collected from every baby born in the United States and are tested for many treatable disorders (newborn screening). Some of these spots have been archived and, with consent, will be used for retrospective research studies. In order to determine whether the developing fetus has been exposed to cross-reactive antibodies, we will test archived spots (DBS) of newborn children who later developed autism, and others who developed normally and did not develop autism. If the blood spot contains cross-reactive antibodies, we will know that the fetus was exposed to them. In samples containing cross-reactive antibodies, we will determine more about the type of antibody and how strongly it reacts with brain tissue antigens. If the theory is correct, newborn blood spot samples from children who develop autism will have higher levels of antibody that bind strongly to brain tissue antigens. We will also look for antibodies that bind to other tissues, particularly the thyroid, because these could also disrupt normal brain development in the fetus.
We have already developed a very sensitive method to detect multiple analytes from very small volumes of samples (a single drop collected from heel stick when the baby is born) such as those obtained from a dried blood spot punch. The assays we have developed have already been validated and a few others need to be further refined. Our preliminary studies show that these antibodies are found in normal individuals and newborn DBS. If the hypothesis proves to be true, the findings of our study will aid in early diagnosis, which in turn would allow for development of possible intervention significantly impacting the research, and contributing to a better understanding of the cause, and eventual treatment or prevention, of this often devastating brain disorder.