INTRODUCTION

Vitamin B12 deficiency is a rare and treatable cause of failure to thrive and delayed development in infants. These infants can exhibit a prominent disorder of movement, a presentation that might be unfamiliar to many physicians. Treatment with vitamin B12 can reverse all of the adverse effects but permanent sequelae may result.¹ In developed countries the deficiency usually occurs in infants who are exclusively breastfed, whose mothers have unrecognized pernicious anemia or are vegetarians, causing low stores of vitamin B12 in the infant at birth and inadequate amounts of the vitamin in the breast milk.²

Symptoms and signs of vitamin B12 deficiency appear between the ages of 2 to 12 months and include vomiting, lethargy, failure to thrive, hypotonia, and arrest or regression of developmental skills. Approximately one half of the infants exhibit abnormal movements, variously described as tremors, twitches, chorea, or myoclonus. These movements can be present before the start of treatment or can appear several days after the start of treatment when the infant is improving. The duration of the movements has ranged from 10 to 30 days.^3-5

Urinary concentrations of methylmalonic acid and homocystine are characteristically elevated in vitamin B12 deficiency. Hyperglycinuria is sometimes present. Two prior reports described infants with vitamin B12 deficiency who exhibited abnormal movements after the start of therapy.^6,7 Methylmalonic aciduria and . . . [Full Text of this Article]