B12 opname probleem
Scientists at the MUHC and McGill
University explain genetic disease first discovered in Quebec 24 years ago
Scientists at the MUHC and McGill
University have identified a gene essential for the uptake of vitamin B12 in human cells.
The discovery of this gene finally completes a 24 year-old hunt for the cause of an
incredibly rare genetic disorder called, cblF combined homocystinuria and methylmalonic
aciduria (cblF-Hcy-MMA), first documented in a Quebec infant in 1985. The work, which was
funded in part by the CIHR and involved collaboration among researchers in Canada,
Germany, Switzerland and France, was published online in Nature Genetics this week. Two
contrasting approaches combined to crack the genetic puzzle at the heart of cblF. In
Germany, Dr. Frank Rutsch and his colleagues used DNA from patients to conduct a genome
scan for shared regions of DNA sequence. Simultaneously in Montreal, Isabelle R. Miousse,
a graduate student of Dr. David Rosenblatt – Chairman of Human Genetics and Director
of the Division of Medical Genetics in Medicine at McGill – conducted research that
confirmed a gene on chromosome 6 could correct the cellular defect in cells from these
patients. Strikingly, the vast majority of patients with this rare disease share a common
mutation despite the fact that they come from different countries and different ethnic
groups. “This discovery offers the prospect of earlier diagnosis and treatment
options for this disease,” says Dr. Rosenblatt, who was the first to describe this
rare genetic condition in 1985. “Vitamin B12 plays an important role in our
lives,” says Dr. Rosenblatt. “Studying rare genetic diseases like cblF-Hcy-MMA
offers a window into its basic properties and how it behaves in healthy cells.” The
cblF idisease is a rare genetic disorder characterized by an inability to metabolize
vitamin B12. Patients afflicted with this condition build up toxic levels of homocysteine
and methylmalonic acid in their bodies. Vitamin B12, which is found in all animal
products-including dairy, eggs, meat, poultry, and fish, is vital for the synthesis of red
blood cells and the maintenance of the nervous system. It also helps control homocysteine
levels in the human body, an excess of which is associated with an increased risk of heart
disease, stroke and dementia.
Lees verder
Is it time for vitamin B-12
fortification? What are the questions?
Since the introduction of folic acid
fortification of flour 10 y ago, an initiative to consider fortifying flour with vitamin
B-12 has gained momentum in the United States. The impetus for this move stems from
several considerations, including some evidence that a proportion of neural tube defect
pregnancies may be the result of vitamin B-12 rather than folate deficiency. However, no
interventional trials have taken place to show the efficacy of vitamin B-12
supplementation or fortification in the primary prevention or recurrence of neural tube
defect pregnancies, as was the case with folic acid. Other reasons put forward for the
institution of vitamin B-12 fortification include the high prevalence of vitamin B-12
deficiency in certain demographic groups, including the elderly and the young in some
countries. Much of this deficiency, however, is subclinical and not associated with
manifest morbidity.
Moreover, individuals affected by the most
severe cases of vitamin B-12 deficiency that are associated with morbidity would not
benefit from the concentrations of vitamin B-12 fortification that are practical or that
are being considered, because such individuals suffer from malabsorption of vitamin B-12
rather than from an inadequacy of intake of the vitamin. In addition to the
well-recognized complications of vitamin B-12 deficiency, such as macrocytic anemia and
neurological complications affecting sensory and motor function, more subtle effects have
also been described, including osteopenia, neurocognitive impairment, and increased
vascular disease risk associated with elevated homocysteine. This analysis focuses on the
research questions that are pertinent to the consideration of whether or not to introduce
mandatory vitamin B-12 fortification in the United States.
Address correspondence to R Green, UC Davis
Medical Center, Department of Medical Pathology and Laboratory Medicine, PATH, 4400 V
Street, Sacramento, CA 95817. E-mail: ralph.green@ucdmc.ucdavis.edu.
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