Vitamin B12 deficiency in infancy as a cause of developmental regression.

Vitamin B12 deficiency can cause serious developmental regression, hypotonia and cerebral atrophy in infants. We report a 6-month-old infant, with insidious developmental regression and brain atrophy showed by CT scan, secondarily to vitamin B12 deficiency. His mother was a strict vegetarian and the patient was exclusively breastfed. The clinical symptoms and the brain CT were normalized after vitamin B12 administration.