Severe vitamin B12 deficiency in a 7-month-old boy.

Introduction Vitamin B12 defi ciency in infants can result in profound and permanent health consequences. Prevention, early diagnosis and early treatment are crucial to ensure a better outcome for those affected.1 However, the symptoms of vitamin B12 defi ciency in infants can be non-specifi c, leading to delayed or missed diagnosis. Vitamin B12 (cobalamin) is a water-soluble vitamin found naturally only in animal products. It is a cofactor for the reaction that converts methylmalonyl-CoA to succinylCoA. It is also a cofactor for the enzyme methionine synthase which catalyses the methylation of homocysteine to methionine, an essential amino acid. Additionally, cobalamin is involved in the reaction that demethylates methyl-tetrahydrofolate (CH3-THF) to THF, a substrate essential in DNA synthesis. In infants, vitamin B12 defi ciency is associated with a wide spectrum of clinical manifestations. These include macrocytic anaemia, failure to thrive, irritability, lethargy, hypotonia, developmental delay, psychomotor delay, regression, tremor, convulsions and coma.1 Less specifi c manifestations include pallor, vomiting, diarrhoea, oedema and apathy.1,2 Cerebral atrophy is usually also seen on magnetic resonance imaging (MRI).1 Biochemically, vitamin B12 deficiency is associated with elevated methylmalonate acid (MMA) blood and urine levels, elevated blood folate (due to the folate trap) and elevated plasma homocysteine level. Unfortunately, the vast array of non-specifi c signs and symptoms pose a challenge for diagnosis of vitamin B12 defi ciency.