Associated enzyme deficiencies, abnormally shaped hemoglobin and immune system activities will also lead to excessive destruction of red blood cells. Generally, the disease manifests in two forms, a rare congenital form and an adult onset acquired form. Prevalence The disease is more prevalent in people of Scandinavian, English and Irish ancestry. It is less common in Caucasians of Italian or Greek decent and rare in Blacks and Asians. In addition, it seems to be more predominant in females.
Age is a major factor in the acquired cases.
Since the body can store up to a three-year supply of Vitamin B12, clinical onset is gradual and delayed. Contributing factors to the disease include a vegetarian diet, thyroid disease, stomach surgery or disease, eating disorder, diabetes mellitus, family history and genetic factors. It functions as a coenzyme for only two reactions in the human body, methionine synthase and L-methylmalonyl CoA mutase. Methionine synthase is involved in the synthesis of the amino acid methionine from homocysteine. Therefore methionine can not be regenerated and levels decrease.