Stuart Gallacher, Helen Prunty, Alison Jones, Robin H Lachmann and Paul Gissen
Inherited methylmalonic acidurias are a group of autosomal recessive disorders caused by mutations in the genes encoding methylmalonyl CoA mutase and proteins involved in cobalamin (Vitamin B12) metabolism. Methylmalonic aciduria can also arise as a result of severe cobalamin deficiency. We report the case of a male infant presenting at 5 months of age with a cobalamin sensitive methylmalonic aciduria, pancytopaenia, developmental delay, failure to thrive, hepatosplenomegaly and hypotonia. MRI brain imaging showed reduced white matter quantity and maturity. The cause was investigated and discovered to be a maternal subclinical pernicious anaemia. A rapid clinical improvement was made upon initiation of B12 supplementation. At follow up aged 18 months weight was above the 91st centile and height between the 75th and 90th. Although no delay in fine motor or social skills was noted at 18 month assessment, gross motor and language delay persisted and may reflect central nervous system damage due to the initial B12 deficiency.
Methylmalonic aciduria is relatively frequently detected in patients with lack of dietary B12. If careful assessment of the diet does not provide the answer, it is important to perform laboratory investigations even if no clinical signs or symptoms of pernicious anaemia can be detected. Cobalamin deficiency is common due to dietary restriction or malabsorption. As severe maternal cobalamin deficiency during pregnancy and breastfeeding can lead to devastating effects on the child, universal screening of cobalamin level in pregnancy should be considered.
