Cobalamin D deficiency (cblD) is one of the least common cobalamin metabolism disorders. It may result in isolated homocystinuria, isolated methylmalonic aciduria, or combined methylmalonic aciduria and homocystinuria (cblD-combined). Only seven cases of the combined cblD form have been reported to date. Due to the rarity of this disorder, the presentation and symptoms are not well described. We present an eighth case of the cblD-combined subtype, who had a positive newborn screen (NBS) on day of life 3. She was symptomatic and developed lethargy and poor oral intake at 8 days of life. She was treated with 10% dextrose, folinic acid, intramuscular hydroxocobalamin, and betaine. Despite the early initiation of treatment, she developed complications of the disease and was found to have abnormal brain imaging findings at 17 days of age and macular atrophy at 3 months of age and has global developmental delay. We provide detailed description of her presentation, her treatment, and her complications to aid in the understanding of this rare disorder, which is very similar to the more common cobalamin C disorder (cblC).
Keywords: Cobalamin D; Homocystinuria; Methylmalonic aciduria; cblD combined.