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Genetics behind developmental brain disorders may play a wider role with congenital diseases

July 07, 2006

Findings of a recent genetic study on developmental brain disorders may be the "tip of an iceberg" revealing factors involved with a number of congenital diseases, according to UC Irvine researchers.

The study is the first to find that mutations in the structural proteins in brain cells — beta-actin — are linked to disorders such as deafness and dystonia, a debilitating neural disease, and further suggests that genetic variants of these proteins may play a wider role with inherited human diseases. Study results appeared in the June issue of the American Journal of Human Genetics.

The findings give vital clues to the basis of some developmental disorders and make early diagnosis possible for diseases such as dystonia, allowing for greater treatment opportunities, said Dr. Vincent Procaccio of UCI's Center for Molecular and Mitochondrial Medicine and Genetics and lead author, though the study does not point to potential therapies.

"These types of actin proteins are prevalent throughout the body and play a key role in processes that are an essential part of development," said Procaccio, who is also an assistant professor of pediatrics. "To find that these mutations are involved with brain disorders seems to be the tip of an iceberg. Since beta-actin is involved with many developmental cell functions, it would appear that its genetic variants can be involved with a number of other congenital disorders."

Procaccio and his colleagues studied brain tissue samples from deceased twins who had a number of developmental disabilities including dystonia, a neurological disorder that causes twisting or jerking movements in parts of the body. Genetic analysis revealed mutations in the beta-actin gene. These mutations affected protein conformation, which would not allow beta-actin to bind with ATP — the chemical fuel synthesized by mitochondria that give a cell its energy.

Beta-actin is a structural protein that helps form the cytoskeleton — a cell's skeleton that gives it structure and strength. Unable to receive fuel, the mutated beta-actin proteins break down, ultimately damaging and destroying the cell. In the brain, this leads to the neural tissue damage related to congenital neurological disorders like dystonia.

Taking this information, Procaccio and his fellow researchers are working to demonstrate that beta-actin mutations are a common cause of neurological disorders. They are currently analyzing several DNA samples from patients to identify additional abnormalities. In addition, they are investigating the cellular and biophysical abnormalities resulting from beta-actin mutations, which will serve as a basis to identify other mutations and disease phenotypes arising from genetic abnormalities of beta-actin proteins.

"Ultimately, we hope to prove that the identification of genetic abnormalities of the beta-actin are likely to explain the causes of a spectrum of disease phenotypes, including congenital malformation syndromes and other inherited degenerative diseases, that are presently poorly understood," he said.

Study co-authors are Antonio Davila and Richard Jimenez of UCI; Gloria Salazar, Shoichiro Ono, Melanie Styers, Victor Faundez, Marla Gearing, Jorge Juncos, Claire-Anne Gutekunst and Bruce Wainer of Emory University in Atlanta; Estelle Sontag and Jean Marie Sontag of University of Texas Southwest Medical Center in Dallas; and Germana Meroni and Bianca Fontanella of the Telethon Institute of Genetics and Medicine in Naples, Italy. The National Institutes of Health supported the study.

About mitochondria: Mitochondria are the power plants of cells that are responsible for burning the calories in our diet with the oxygen that we breathe to generate carbon dioxide, water and the energy for our cells. The cellular energy is used for two purposes, to generate heat to maintain our body temperature and to synthesize ATP (adenosine triphosphate), a chemical form of energy which permits us to do work such as exercise, think, write, and make and repair cells and tissues. At least 50 percent of energy provided by brain mitochondria is used to maintain beta-actin cytoskeleton in neuronal cells.

About the Center for Molecular and Mitochondrial Medicine and Genetics: The Center for Molecular and Mitochondrial Medicine and Genetics, under the direction of Douglas C. Wallace, brings together basic scientists, clinical investigators and patients at UCI to determine the causes of the common degenerative diseases, cancer and aging with special emphasis on the role of mitochondria in these diseases' processes. This includes the development of more effective diagnostics and therapeutics. To achieve this goal, MAMMAG takes a novel approach to understanding these problems with special emphasis on the evolutionary, molecular and mitochondrial medicine perspectives. The result is a uniquely integrated, multidisciplinary research and clinical program that intends to expand the human horizons of medical understanding.

University of California, Irvine