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

BACKGROUND: Classical homocystinuria is an autosomal recessive disorder caused by profound cystathionine β‐synthase deficiency. Its biochemical hallmarks are high concentrations of plasma homocyst(e)ine and methionine. Clinical manifestations include lens dislocation, developmental delay, skeletal anomalies, or thromboembolism. Limited literature exists outlining the risk of encephalopathy associated with hypermethioninemia presenting in children with classical homocystinuria. AIM: To assess the quality of metabolic control and plasma methionine concentrations in infancy in a cohort of 36 patients with classical homocystinuria in the Republic of Ireland. METHODS: Review of biochemical and clinical data including neuroradiological results that are available for the first year of life in our patients diagnosed on newborn screening was performed with appropriate consent and ethical approval. RESULTS AND DISCUSSION: 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.