Allergy in autistic children
Autism is a developmental disorder characterized by a spectrum of symptoms ranging from decreased verbal skills and social withdrawal, to restrictive repetitive behavior and uncontrolled outbursts. The genetic analysis of this disorder has yielded about ten linked genes consistent with a polygenic mode of inheritance. Environmental factors, such as over-exposure to antibiotics, toxic effect of mercury and lead, reactions to immunizations, may also participate in a yet undetermined manner in the development of this disorder. In recent years there has been much discussion of the link between food hypersensitivities and such other behavioral conditions including Attention Deficit Disorder, Autism and Hyperactivity. Both true allergies (IgE-mediated) and non-allergic hypersensitivity (non-immune mediated reactions) may be present in children with these disorders.

Just like in normal children about 30 % of autistic children also develop true IgE-mediated allergies. In some children the IgE-mediated allergic reaction may be severe but in others it may be mild. Our observation show that some autistic children may react to a wide variety of foods including egg white, cows milk, fish, wheat, peanut, soya bean, rice, chicken meat, potato, barley, oats, maize, sesame seed, pea, lentil, coconut, garlic, onion, cheese, cucumber, egg plant, chillipepper, red kidney bean, goat milk, crab, shrimp, pacific squid, tuna, sardine, abalone, scallop, oyster, tomato, orange, melon, mango fruit, banana, apple, lemon, papaya and jack fruit. These children also react to house dust mites. Planning to avoid such a large list of common foods may interfere with the nutrition of the growing child. Thus it is important to involve a nutritionist to advice on the diet plan.

Non-allergic hypersensitivity was in the past referred to as ‘pseudoallergy’ or ‘food intolerance’ to describe clinical symptoms that develop without the intervention of the immune system. In the majority of autistic children, usually due to enzyme deficiency, the body cannot adequately process a portion of the offending food. Researchers have found that a large proportion of autistic children, particularly those with late onset autism, respond well when wheat, milk and some types of meat is eliminated from their diet. Interestingly many parents have long seen the link between autism and diet specifically gluten and casein. Gluten is a protein that is found in many cereals such as wheat, barley, rye and oats. Casein is a major protein found in milk and it is present in all foods containing milk products such as yogurt, cheese, ice cream.

In normal digestion in the gut, the food proteins are broken down initially into peptides, then amino acids that are readily absorbed. In some genetically predisposed children it is believed that gluten and casein are enzymatically broken into peptides but further digestion cannot take place due to lack of a certain peptidase enzymes (Dipeptidyl peptidase IV) in the gut tissues. The movement of larger peptide molecules across the intestine is possible because the intestinal defense barrier is inadequate, sometimes called the ‘leaky gut’ syndrome often associated with high levels of IgA and IgG antibodies to food proteins in such children. Recent research studies show that peptides derived from the partial digestion of gluten and casein, possess opiate-like activity. Opioids may also be formed from hemoglobin (hemoceptins) and therefore, such children should also avoid bloody meat products.

One molecule of gluten contains 15 opioid sequences. Thus, even 2.5 nanomoles of protein per ml blood could therefore cause large number of peptides to be formed. The amount of opioid-peptides that must accumulate before symptoms appear varies. Thus, some children react fast and some only slowly after weeks and months on re-exposure. This probably depends on firstly, protein uptake from the gut and the level of peptide in circulation, and secondly, on the nature of the enzyme defects.

There is a suggestion that autistic children may be more prone to the production of such opiate-like peptides due to selective enzyme deficiency. The absorbed peptides derived from the partial digestion of gluten are converted into opiate-like metabolites in blood called gluteomorphine and the peptides from casein undergo a similar conversion to casomorphine. These opiate-like peptides are found in large quantities in the urine of about 80% of autistic children. Most of the food derived opiate-like peptides are removed in the urine (although the kidney is remarkably efficient in conserving peptides). In addition, a small portion of these opiate-like peptides crosses the blood-brain barrier to reach the brain tissue. There is evidence of elevated levels of "endorphin-like substances" in the cerebro-spinal fluid of some individuals with autism. These opiate-like peptides can bind to receptors in the brain and can cause harmful effects just like regular opiates. Opiates can either cause or magnify autistic symptoms.

In our brain, natural opiate-like peptide called ‘enkephalins’ function as neurotransmitters and participate as a natural painkillers. Thus, when gluteomorphins and casomorphines diffuse into the synaptic space between neurons in the brain, it triggers the same response as the enkephalins and mitigates anxiety, pleasure and pain. Usually the body breaks down enkephalins by specific proteolytic enzymes after their use as neurotransmitters. Since specific proteolytic enzymes for gluteomorphins and casomorphines are absent in the brain it cannot break them down easily. Thus, the effects of these food peptides persist for many months. Some observations suggest it is possible for these peptides to accumulate over months and cause an adverse reaction. A marked improvement in the clinical symptoms of these autistic children was noted after a period of 8 weeks on an elimination diet of gluten and milk.

Currently there is no test for non-allergic hypersensitivity. The immune system is not involved in this type of hypersensitivity reactions. Some private laboratories market IgG antibodies for detection of non-allergic hypersensitivity. There is NO scientific evidence to suggest that IgG-antibody test can identify non-allergic hypersensitivity (see under unproven allergy tests).