Clinical Findings and Genetic Analysis of Isolated Hypermethioninemia Patients in Korea

단독성 고메티오닌혈증 환아들의 임상적 특성과 유전자 분석

Purpose: MAT-I/III deficiency by MAT1A gene mutation causes isolated hypermethioninemia, which is considered to be a clinically benign disease. But in some patients, mental retardation, developmental delay, myelination disorder may be shown. This study was performed to find out the clinical manifestations and genetic characteristics of patients with isolated hypermethioninemia. Methods: Clinical, biochemical and genetic analysis were done to 10 patients with isolated hypermethioninemia who were referred to department of pediatrics, Soonchunhyang University Hospital from March 1999 to March 2012. Results: At first visit, all patients' mean plasma methionine level was 5.5 mg/dL (2.1-14.6) and there were no increase of amino acid levels including homocystine in all patients. Serum homocysteine level was evaluated in seven patients who visited after year 2003, and ranged from 4.96 to $11.15{\mu}mol/L$ (normal < $25{\mu}mol/L$). Methionine restricted diet was started to all patients. Nine patients who managed regularly showed normal development, but one patient whose initial plasma methionine level was 14.6 mg/dL showed language delay at 1 year of age and was diagnosed as mild mental retardation (IQ=66) at 6 years of age. Genetic analysis was done to eight patients, R264H mutation was identified in seven patients. Also, both R299C and R356Q mutation were identified in one patient. Conclusion: Clinical findings in patients with isolated hypermethioninemia were generally good, but one patient showed mental retardation and language difficulty. R264H mutation which usually inherits as an autosomal dominant trait was most frequently found in our patients, and R299C/R356Q mutation were also identified.