目的　探讨甲硫氨酸腺苷转移酶Ⅰ/Ⅲ缺陷症的临床和基因变异特点。方法　回顾分析串联质谱新生儿筛查 发现的5例甲硫氨酸腺苷转移酶Ⅰ/Ⅲ缺陷患儿的临床资料及基因检测。结果　22万例新生儿筛查中发现甲硫氨酸腺苷 转移酶Ⅰ/Ⅲ缺陷5例，发病率为1/44000。 5例患儿中， 3例血甲硫氨酸在70~150 μmol/L之间。基因检测2例符合常染色 体显性遗传、 1例符合常染色体隐性遗传。 3例随访至今预后良好，另2例血甲硫氨酸持续>500 μmol/L；予以特殊饮食治疗， 1例头颅磁共振成像和肝功能异常， 1例伴有微缺失综合征，发育落后。结论　甲硫氨酸腺苷转移酶Ⅰ/Ⅲ缺陷可通过串联 质谱新生儿筛查结合基因检测而早期诊断，需要长期随访。

Objective　To explore the clinical and gene variation characteristics of methionine adenosyltransferase Ⅰ/Ⅲ deficiency. Methods　The clinical data and gene detection of methionine adenosyltransferase Ⅰ/Ⅲ deficiency in 5 newborns found by tandem mass spectrometry in neonatal screening were retrospectively analyzed. Results　In the 220000 newborns screened, 5 cases of methionine adenosyltransferase Ⅰ/Ⅲ deficiency were found and an incidence rate was 1/44000. In the 5 newborns, the concentrations of methionine were 70~150 μmol/L in 3 newborns, among whom 2 were autosomal dominant inheritance and one was autosomal recessive inheritance and all of them had a good prognosis. The blood methionine concentrations of the other 2 newborns were continuously greater than 500 μmol/L and they were autosomal recessive inheritance. These 2 newborns were treated with special diet. During follow-up, 1 patient had abnormal cranial magnetic resonance and abnormal liver function, and 1 patient had microdeletion syndrome and developmental retardation. Conclusion　Methionine adenosyltransferase Ⅰ/Ⅲ deficiency can be diagnosed early by tandem mass spectrometry combined with gene detection and the disease requires long-term follow-up.