Public release date: 7-May-2012 [ | E-mail | Share ]

Contact: Glenna Picton picton@bcm.edu 713-798-4710 Baylor College of Medicine

HOUSTON -- (May 7, 2012) The deletion of part of a gene that plays a role in the synthesis of carnitine an amino acid derivative that helps the body use fat for energy may play a role in milder forms of autism, said a group of researchers led by those at Baylor College of Medicine (http://www.bcm.edu) and Texas Children's Hospital (http://www.texaschildrens.org).

"This is a novel inborn error of metabolism," said Dr. Arthur Beaudet (http://www.bcm.edu/genetics/index.cfm?pmid=10579), chair of molecular and human genetics at BCM and a physician at Texas Children's Hospital, and the senior author of the report that appears online in the Proceedings of the National Academy of Sciences (http://www.pnas.org). "How it is associated with the causes of autism is as yet unclear. However, it could point to a means of treatment or even prevention in some patients."

Beaudet and his international group of collaborators believe the gene deletion leads to an imbalance in carnitine in the body. Meat eaters receive about 75 percent of their carnitine from their diet. However, dietary carnitine levels are low in vegetarians and particularly in vegans. In most people, levels of carnitine are balanced by the body's ability to manufacture its own carnitine in the liver, kidney and brain, starting with a modified form of the amino acid lysine.

Carnitine deficiency has been identified when not enough is absorbed through the diet or because of medical treatments such as kidney dialysis. Genetic forms of carnitine deficiency also exist, which are caused when too much carnitine is excreted through the kidneys.

In this new inborn error, there is a deletion in the second exon the protein-coding portion of a gene of the TMLHE gene, which includes the genetic code for the first enzyme in the synthesis of carnitine (TMLHE stands for trimethyllysine epsilon which encodes the enzyme trimethyllysine dioxygenase).

Studies in the laboratory that identified the deletion were led by Dr. Patricia B.S. Celestino-Soper, as a graduate student in Beaudet's laboratory at BCM and by Dr. Sara Violante, a graduate student in the laboratory of Dr. Frdric M. Vaz of the Academic Medical Center in Amsterdam.

To determine the frequency of the gene deletion, Beaudet and his colleagues tested male autism patients who were the only people with the disorder in their families (simplex families) from the Simons Simplex Collection, the South Carolina Early Autism Project and Houston families. In collaboration with laboratories and researchers in Nashville, Los Angeles, Paris, New York, Toronto and Cambridge (United Kingdom), they tested affected male siblings in families with more than one male case of autism (multiplex families).

When they looked at the TMLHE genes in males affected by autism and compared them to normal controls, they found that the gene alteration is a fairly common one, occurring in as many as one in 366 males unaffected by autism. It was not significantly more common in males within families in which there is only one person with autism. However, it is nearly three times more common in families with two or more boys with autism.

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Defective carnitine metabolism may play role in autism