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Gene for debilitating vitamin B12 disease identified


Researchers at the MUHC and McGill University have identified a gene responsible for a disease that impairs the body's ability to handle vitamin B12 and that may contribute to heart disease, stroke and dementia.

The study is published in the Nature Genetics.

The research, which began more than 20 years ago, will allow doctors to perform earlier diagnosis, assess 'carriers' of the disease -- combined methylmalonic aciduria and homocystinuria -- and open the door to new and improved treatments for this debilitating disease.

" Although this disease sometimes starts in adolescence or adulthood, we usually diagnose this rare inability to process vitamin B12 in the first few months of life," says David Rosenblatt, at McGill and MUHC, at the Jewish General Hospital and lead researcher of the new study. " Babies may have breathing, feeding, visual and developmental difficulties, older patients may develop sudden neurological disease."

Vitamin B12, which is found in all animal products -- including dairy, eggs, meat, poultry, and fish--but not in plants, is vital for synthesis of red blood cells and maintenance of the nervous system.
Vitamin B12 also helps control homocysteine levels in the human body. Homocysteine control is important because in excess this compound can increase the risk of heart disease, stroke, and dementia.

17 year-old Michael -- a typical methylmalonic aciduria and homocystinuria patient -- was diagnosed at 6-months of age, and has battled numerous medical challenges as a result of his condition.
Michael is developmentally delayed, visually impaired and does not talk; he has suffered seizures since he was three years old, had a stroke by the age of seven and has since developed rheumatoid arthritis and scoliosis. Michael's diagnosis, which led the way to treatment involving injections of vitamin B12, was conducted at Rosenblatt's laboratory at the MUHC.

After more than 20-years of data collection, Rosenblatt and his team have now unlocked some of the secrets of this rare but debilitating condition.

" Using over 200 patient samples, representing the majority of the world's 350 known cases, we have identified the responsible gene, called MMACHC," says Rosenblatt. " In collaboration with the laboratory of James Coulton, at McGill, we used computer modelling to demonstrate the similarity between the protein encoded by the MMACHC gene and a protein involved in bacterial vitamin B12 metabolism."

This new link between bacterial and mammalian species may help us better understand how humans use vitamin B12. Ultimately these discoveries have enabled us to develop early diagnosis and carrier assessment tests for the disease -- something that was not previously possible.

Source: McGill University, 2005


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