14 DAY TRIAL // A team of researchers at the Ben-Gurion University of the Negev and Soroka University Medical Center in Beer-Sheva, Israel, have found a genetic defect which caused progressive mental retardation and epilepsy, starting at infancy.
This progressive brain atrophy is caused by the production of the 21st amino acid, called selenocysteine (SEC), found the team led by BGU Professor Ohad Birk of the National Institute for Biotechnology in the Negev.
Normally the human genetic code includes 20 amino acids that build blocks of all proteins in the human body, as researchers discovered some 50 years ago.
Lately, scientists have discovered that a 21st amino acid exists too, formed by the selenium which enters the body through food, and is incorporated in human tissues to form the selenocysteine.
This new amino acid is rather unique because it is encoded by a stop codon, which is a DNA sequence that normally determines the protein building system to stop the amino acids chain.
Unlike most genes, there is a group of 25 genes that contain a unique component which alters the functioning of the stop codon, so that instead of ending the evolving protein chain, it adds a SEC building block.
Professor Birk says that “one out of every 40 Jews of both Moroccan and Iraqi ancestry may be carriers of this mutation.
“As the disease is both severe and common, testing for these mutations is expected to become a routine prenatal genetic screening test in these two populations, enabling prevention of future cases.”
More research should help identify other mutations in the same gene, that cause epilepsy along with mental retardation in other communities too.
Because this disease is progressive, understanding its molecular mechanisms could lead to new treatments.
The research was recently published in the American Journal of Human Genetics.