Inborn errors of
cobalamin (Cbl,
vitamin B(12)) absorption include hereditary
intrinsic factor deficiency (HIFD) and Imerslund-Gräsbeck disease (
IGD). HIFD is secondary to mutations in the HIF gene while
IGD is due to mutations in one of the 2 subunits of the
intrinsic factor receptor that is
cubilin (CUBN) or amnionless (AMN). These disorders lead to intracellular Cbl depletion which in turn causes megaloblastic
bone marrow failure, accumulation of
homocysteine and
methylmalonic acid (MMA), and
methionine depletion. The clinical presentation reflects Cbl deficiency, with gastrointestinal symptoms,
pancytopenia, and
megaloblastic anemia. Mixed
proteinuria, when it is present is strongly suggestive of
IGD. Accurate diagnosis is always an emergency because early detection and treatment with life-long parenteral pharmacological doses of
hydroxocobalamin are life saving and prevent further deterioration. However, the optimal frequency for
cobalamin injections as a maintenance
therapy is poorly reported. In order to evaluate the optimal maintenance schedule of
cobalamin injections, we retrospectively collected clinical,
biological, molecular and treatment data on 7 patients affected with congenital Cbl malabsorption. Unlike previous recommendations, we showed that a maintenance dosage of 1 mg
cobalamin twice a year was enough to ensure a normal clinical status and keep the hematological and metabolic parameters in the normal range. These data suggest that patients affected with inborn errors of
cobalamin absorption may be safely long-term treated with
cobalamin injections every 6 months with careful follow-up of hematological and metabolic parameters. This maintenance regime is beneficial because the patients' quality of life improves.