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Tracking The Genetic Causes Of Inherited Vitamin B12 Deficiency

Vitamin B12 is essential to human health. However, some people have inherited conditions that leave them unable to process vitamin B12. As a result they are prone to serious health problems, including developmental delay, psychosis, stroke and dementia. An international research team recently discovered a new genetic disease related to vitamin B12 deficiency by identifying a gene that is vital to the transport of vitamin into the cells of the body. This discovery will help doctors better diagnose this rare and open the door to new treatments. The findings are published in the journal Nature Genetics.

“We found that a second transport protein was involved in the uptake of the vitamin into the cells, thus providing evidence of another cause of hereditary vitamin B12 deficiency”, said Dr. David Rosenblatt, one of the study’s co-authors, scientist in medical genetics and genomics at the Research Institute of the Health Centre (RI MUHC) and Dodd Q. Chu and Family Chair in Medical Genetics and the Chair of the Department of Human Genetics at . “It is also the first description of a new genetic disease associated with how vitamin B12 is handled by the body”.

These results build on previous research by the same team from the RI MUHC and McGill University, with their colleagues in , and the United States. In previous work, the researchers discovered that vitamin B12 enters our cells with help from of a specific transport protein. In this study, they were working independently with two patients showing symptoms of the cblF gene defect of vitamin B12 metabolism but without an actual defect in this gene. Their work led to the discovery of a new gene, ABCD4, associated with the transport of B12 and responsible for a new disease called cblJ combined homocystinuria and methylmalonic aciduria (cblJ-Hcy-MMA).

Using next generation sequencing of the patients’ genetic information, the scientists identified two mutations in the same ABCD4 gene, in both patients. “We were also able to compensate for the genetic mutation by adding an intact ABCD4 protein to the patients’ cells, thus allowing the vitamin to be properly integrated into the cells,” explained Dr. Matthias Baumgartner, senior author of the study and a Professor of metabolic diseases at ’s University Children’s Hospital.

Vitamin B12, or cobalamin, is essential for healthy functioning of the human nervous system and red blood cell synthesis. Unable to produce the vitamin itself, the human body has to obtain it from animal-based foods such as milk products, eggs, red meat, chicken, fish, and shellfish – or vitamin supplements. Vitamin B12 is not found in vegetables.

“This discovery will lead to the early diagnosis of this serious genetic disorder and has given us new paths to explore treatment options. It also helps explain how vitamin B12 functions in the body, even for those without the disorder,” said Dr. Rosenblatt who is the director of one of only two referral laboratories in the world for patients suspected of having this genetic inability to absorb vitamin B12. Dr. Rosenblatt points out that the study of patients with rare diseases is essential to the advancement of our knowledge of human biology.

Source

Funding
This work was funded by the (CIHR) and by the Swiss National Science Foundation and by the Deutsche Forschungsgemeinschaft.
Research partners
The study was co-authored by David Coelho (first co-author), Terttu Suormala and Brian Fowler of the University Children’s Hospitals in Basel and Zürich, Switzerland; David Rosenblatt of McGill and the RI MUHC and his graduate student Jaeseung C Kim (first co-author) of McGill, Isabelle R Miousse, Stephen Fung, David Watkins, Eric A Shoubridge of McGill University and Jacek Majewski of the McGill University and Genome Quebec Innovation Centre; Patricie Burda, Michele Frapolli of University Children’s Hospital, Zürich, Switzerland; Martin Stucki and Matthias R Baumgartner of University Children’s Hospital and University of Zürich; Marcel du Moulin, Insa Buers, Frank Rutsch of University Children’s Hospital, Münster, Germany; Peter Nürnberg and Holger Thiele of University of Cologne, Germany; Nicola Longo of University of Utah, Salt Lake City, USA and ARUP Laboratories, Salt Lake; Marzia Pasquali1 of ARUP Laboratories and University of Utah, Salt Lake City, Utah, USA; Horst Robenek of Leibniz Institute for Arteriosclerosis Research, Münster University, Germany; Wolfgang Höhne of Charité University Medicine, Berlin, Germany; Eugen Mengel of University Children’s Hospital, Mainz, Germany.
McGill University Health Centre