Vitamin B12 deficiency: tracking the genetic causes

 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 genetic disorder 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 McGill University Health Centre (RI MUHC) and Dodd Q. Chu and Family Chair in Medical Genetics and the Chair of the Department of Human Genetics at McGill University. “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 Switzerland, Germany 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 Zurich’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

Funding

This work was funded by the Canadian Institutes of Health Research (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.

The Research Institute of the McGill University Health Centre (The RI MUHC) is a world-renowned biomedical and health-care hospital research centre. Research is organized by eleven research axes. Located in Montreal, Quebec, Canada, the Institute is the research arm of the McGill University Health Centre (MUHC) affiliated with the Faculty of Medicine at McGill University. The Institute supports over 600 researchers, over 1,200 graduate students and post-docs and fellows devoted to a broad spectrum of fundamental and clinical research. Over 1,800 clinical research studies are conducted within our hospitals each year. The Research Institute of the MUHC is supported in part by the Fonds de recherche du Québec - Santé (FRQS). www.muhc.ca/research/

About McGill University

Founded in Montreal, Que., in 1821, McGill is Canada’s leading post-secondary institution. It has two campuses, 11 faculties, 11 professional schools, 300 programs of study and more than 37,000 students, including 8,300 graduate students. McGill attracts students from over 150 countries around the world, with more than 7,200 international students making up 20 per cent of the student body. Almost half of McGill students claim a first language other than English, including more than 6,200 francophones. www.mcgill.ca

The Canadian Institutes of Health Research (CIHR) is the Government of Canada’s health research investment agency. CIHR’s mission is to create new scientific knowledge and to enable its translation into improved health, more effective health services and products, and a strengthened Canadian health care system. Composed of 13 Institutes, CIHR provides leadership and support to more than 14,100 health researchers and trainees across Canada. www.cihr-irsc.gc.ca