Plasma methionine concentrations and incidence of hypermethioninemic encephalopathy during infancy in a large cohort of 36 patients with classical homocystinuria in the Republic of Ireland.

Median total homocyst(e)ine and methionine plasma concentrations were 78 and 55 μmol/L, respectively. Methionine concentrations were significantly higher in neonates as opposed to older children. The highest methionine level identified was 1329 μmol/L in a child who presented clinically with encephalopathy. Elevated homocyst(e)ine and methionine levels are associated with significant morbidities. Therefore, prevention of complications requires prompt recognition and treatment. Chronic and acute complications may be encountered in patients with classical homocystinuria and plasma methionine concentrations pose an additional risk factor.