目的　探讨线粒体3-羟基-3甲基戊二酰辅酶A合成酶缺乏症（HMCSD）的临床及遗传学特征。方法　回顾 分析1例HMCSD患儿的临床资料，并复习相关文献。结果　女性患儿， 9个月余，先后因呕吐、抽搐及发热、咳嗽就诊。血 生化检查示低血糖、代谢性酸中毒、肝功能异常、凝血功能异常，尿筛查示双羧酸尿。基因检测发现HMGCS2基因存在6 号外显子c.1187+1G>C和3号外显子c.648G>T 复合杂合突变，确诊为HMCSD。此突变未见报道。患儿经积极抗感染、 纠正代谢性酸中毒、维持血糖稳定及补充左卡尼汀等治疗后好转。随访半年智力运动发育正常。结论　HMCSD临床表现 多样，基因检测可明确诊断，早期识别、早期诊治有助于改善预后。

　Objective　To explore the clinical features and genetic characteristics of mitochondrial 3-hydroxy-3methylglutaryl CoA synthase deficiency（HMGSD） . Method　The clinical data of mitochondrial HMGSD in a child was retrospectively analyzed, and related literature was reviewed. Result　A 9-month-old infant was admitted to the hospital with vomiting and convulsion for the first time and fever and cough for the second time. Laboratory tests showed hypoglycemia, acidosis, abnormal liver function and coagulation dysfunction. Urine organic acid analysis indicated dicarboxylic aciduria. Genetic testing showed that there were compound heterozygous mutations in HMGCS2 gene: c.1187+1G>C in exon 6 and c.648G>T in exon 3, which had not been reported before. Progressive clinical and biochemical improvement were observed after acidosis and hypoglycemia being corrected, anti-infectious and L-carnitine treatment. The child developed normally after a follow-up of half a year. Conclusion　Clinical manifestations of mitochondrial HMGSD in children are complex and varied. Definitive diagnosis can be achieved by gene analysis. Prompt diagnosis and early treatment are essential.