GAINESVILLE---Findings from two novel animal studies indicate autism and schizophrenia may be linked to an individual's inability to properly break down a protein found in milk, University of Florida researchers report in this month's issue of the journal Autism.
The digestive problem might actually lead to the disorders' symptoms, whose basis has long been debated, said UF physiologist Dr. J. Robert Cade, cautioning that further research must take place before scientists have a definitive answer. When not broken down, the milk protein produces exorphins, morphine-like compounds that are then taken up by areas of the brain known to be involved in autism and schizophrenia, where they cause cells to dysfunction.
The animal findings suggest an intestinal flaw, such as a malfunctioning enzyme, is to blame, says Cade, whose team also is putting the theory to the test in humans. Preliminary findings from that study -- which showed 95 percent of 81 autistic and schizophrenic children studied had 100 times the normal levels of the milk protein in their blood and urine -- have been presented at two international meetings in the past year but have not yet been published.
When these children were put on a milk-free diet, at least eight out of 10 no longer had symptoms of autism or schizophrenia, says Cade, a professor of medicine and physiology at UF's College of Medicine and inventor of the Gatorade sports drink. His research team includes research scientist Dr. Zhongjie Sun and research associate R. Malcolm Privette.
"We now have proof positive that these proteins are getting into the blood and proof positive they're getting into areas of the brain involved with the symptoms of autism and schizophrenia," Cade said.
More than 500,000 Americans have some form of autism, according to the Autism Society of America. The developmental disability typically appears during the first three years of life and is characterized by problems interacting and communicating with others. Many individuals exhibit repeated body movements such as hand-flapping or rocking and may resist changes in routine. In some cases, they may display aggressive or self-injurious behavior.
Schizophrenia is noted for disturbances in thinking, emotional reaction and behavior and is the most common form of psychotic illness. More than 2 million Americans suffer from it, according to the National Institute of Mental Health. People with schizophrenia often hear internal voices not heard by others, or believe others are reading their minds, controlling their thoughts or plotting to harm them. In addition, their speech and behavior can be so disorganized that they may be incomprehensible or frightening to others.
In the UF studies, researchers injected rats with the protein beta-casomorphin-7, one of the key constituents of milk and the part that coagulates to make cheese. They then observed their behavior and later examined brain tissue to see whether the substances accumulated there.
Beta-casomorphin-7 was taken up by 32 different areas of the brain, Cade said, including sections responsible for vision, hearing and communication.
"This could explain several of the things one sees in autism and schizophrenia, such as hallucinations," he said. "If part of the brain] puts out a false signal because of casomorphin, it could result in the person seeing something that's not really there; either a visual or auditory hallucination could occur.
"There are a whole number of behaviors that the rat has after beta-casomorphin-7 that are basically the same as one sees in the human with autism or schizophrenia," he added. "If we ring a bell beside a rat's cage, it normally looks up to see where the noise is coming from. But the rats after beta-casomorphin-7 didn't do that -- they were completely oblivious to the bell-ringing above them. This struck us as interesting because many mothers of autistic children comment that they seem at times to be totally deaf -- they talk to their children and they just don't seem to hear them."
Researchers suspect the process begins in the intestine, where the body absorbs the protein when a person eats foods containing it.
"We think this process is linked to the production of antibodies in the gut when you eat something you're sensitive to," Cade said. "Both schizophrenics and autistics have a high incidence of [certain] antibodies, and a high incidence of diarrhea, which points to an intestinal disorder. So we think that with autism and schizophrenia, the basic disorder is in the intestine, and these individuals are absorbing beta-casomorphin-7 that they normally should break down in the body as amino acids, rather than peptide chains up to 12 amino acids long."
Dr. Bennett L. Leventhal, professor of psychiatry and pediatrics and director of child adolescent psychiatry at the University of Chicago School of Medicine, said other studies exploring a dietary link to autism or schizophrenia have been less than convincing, and the notion has not generally been accepted in the field.
"Autism and schizophrenia certainly are distinctly different disorders," Leventhal said. "I think the best hypothesis sitting out there today is that some genetic abnormality is causing these disorders. It is certainly possible that these genetic abnormalities could lead to the metabolic effects Dr. Cade mentions, though there is not substantial support for that at this time.
"With autism in particular, there are three or four genes that have sparked interest," he added. "The assumption is that it is not a single gene disorder but rather a polygenic disorder. Given that, it means not only does one have to figure out what the genes are but also what they do and their relative contribution to the symptoms of the disorder. This is not unusual -- the vast majority of medical conditions for which there is genetic substantiation are complex disorders. Single gene disorders are relatively rare."
Journal
Autism