Sometimes, vitamin B12 deficiency is caused by an inherited genetic disorder. Vitamin B12, which can only be obtained by dietary consumption, is required for red blood cell formation, neurological functions and DNA synthesis. A B12 deficiency can cause a myriad of symptoms, some quite serious. Proper diagnosis and possibly genetic testing can determine B12 deficiencies caused by inherited disorders. Currently, disorders of B12 absorption or metabolism have been linked to several different gene mutations of which a person needs only one mutation to experience vitamin B12 deficiency.
Vitamin B12, also known as cobalamin, is required by two important enzymes in your body. These enzymes, methionine synthase and L-methylamalonyl-CoA mutase, assist with nearly 100 different biochemical reactions. Most dietary vitamin B12 is absorbed through your intestinal cells after it combines with a compound called gastric intrinsic factor. An inherited genetic mutation that doesn't allow intrinsic factor binding will prevent B12 absorption, causing biological B12 deficiency. Having one of several types of genetic mutations that prevent B12 metabolism inside your cells can cause a deficiency as well.
Intrinsic Factor Mutations
Pernicious anemia can be an inherited autoimmune disorder in which your own body destroys gastric intrinsic factor-producing cells. Without the intrinsic factor, your body cannot absorb vitamin B12 and a deficiency develops; it is most often seen among those with northern European heritage. Cases of pernicious anemia may cluster within certain families. Bypassing intestinal absorption with vitamin B12 injections or intranasal sprays can treat this condition. Large amounts of oral B12 may promote some intestinal diffusion. Also, any other genetic mutations that prevent intrinsic factor protein formation will cause a vitamin B12 deficiency. Undetected pernicious anemia can be fatal.
Transcobalamin is a protein present in your blood that binds to vitamin B12. It helps transport the vitamin to all the cells in your body. If you have a genetic mutation that doesn't allow transcobalamin construction, cells will not be able to receive any vitamin B12 and a deficiency will result. Additionally, genetic defects may be present that provide transcobalamin but do not allow its uptake by the cells, causing B12 deficiency. This is a rare condition that is fatal soon after birth.
Cellular Uptake Mutations
Defects in certain genes can cause abnormal cellular metabolism of vitamin B12. A genetic disorder of B12 metabolism allows normal intestinal absorption of vitamin B12 and normal blood levels, but the cells cannot metabolize the vitamin after uptake. Since a slew of different enzymes within the cell require vitamin B12 to function properly, too much or too little of any affected enzymes will cause a cellular metabolism imbalance. Injection therapy depends on which B12 metabolism protein is missing within the cell.
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