Clinical, biochemical, molecular characteristics and clinical outcome of hyperhomocysteinemia in Malaysian children

Abstract

Background: Hyperhomocysteinemia can be due to various abnormalities of the complex interaction of methionine, folate and vitamin B12. It has been known to be a cardiovascular risk factor. This study aims to review the clinical presentation, underlying causes and clinical outcome in paediatric patients diagnosed with significant hyperhomocysteinemia in Malaysia.

Design and methods: Data were obtained from the medical records and the laboratory information system. Paediatric patients with significant hyperhomocysteinemia were identified from a selective high-risk screening of 96,721 patients, performed between 2010 and 2022. Inclusion criteria for the study were paediatric patients with significant hyperhomocysteinemia (>40 µmol/L).

Results: Sixteen patients were identified. The average total homocysteine (tHcy) and methionine were 269 µmol/L and 499 µmol/L in cystathionine β-synthase deficiency (CBS), 127 µmol/L and 29 µmol/L in patients with remethylation defects and 390 µmol/L and 4 µmol/L in congenital B12 deficiency. We found c.609G>A as the most prevalent mutation in MMACHC gene and possible novel mutations for CBS (c.402del, c.1333C>T and c.1031T>G) and MTHFR genes (c.266T>A and c.1249del). Further subclassification revealed CBS was 5/16 patients (31 %), remethylation defects was 9/16 (56 %) and congenital B12 deficiency was 2/16 (13 %). All patients received standard treatment and regular monitoring of the main biomarkers. The average age at the time of diagnosis were 9.2 years (CBS) and 1.2 years (remethylation defects). Congenital B12 deficiency had slight delay in milestones, remethylation defects had mild to moderate learning disabilities, CBS had variable degree of intellectual disability, delayed milestones, ophthalmological abnormalities, and thrombosis at an early adolescent/adulthood.

Conclusions: The majority of significant hyperhomocysteinemia in Malaysian children was due to remethylation defects. Screening for hyperhomocysteinemia in Malaysian children is recommended for earlier treatment and improved clinical outcome.

Keywords: Cobalamin; Cystathionine β-synthase; Homocysteine; Inborn errors of metabolism; MTHFR; Remethylation.