目的 探讨罕见的甲基丙二酸尿症合并先天性肾上腺皮质增生症患儿的诊疗方法。方法 分析1例甲基丙二酸尿症变位酶缺乏合并21 羟化酶缺乏症患儿的临床及实验室资料。结果 患儿，男，生后3 个月起病，接种疫苗及高蛋白饮食后出现喂养困难、腹泻、代谢紊乱及智力运动发育倒退，1 岁8 个月时确诊为甲基丙二酸尿症，治疗后好转。5 岁后出现性早熟表现，确诊为21 羟化酶缺乏症男性化型。基因证实MUT基因存在c.866G > C和c.2179C > T两个突变，CYP21A2基因存在c.188A > T和c.518T > A 两个已知突变。结论 遗传代谢病及内分泌病临床表现复杂，鲜有病例共患多种疾病，该患儿共患甲基丙二酸尿症及21 羟化酶缺乏症两种罕见疾病。

Objective To explore the diagnosis and treatment of a rare case of methylmalonic aciduria combined with congenital adrenal hyperplasia. Methods The clinical and laboratory data of the first case of methylmalonyl CoA mutase deficient methylmalonic aciduria combined with 21-hydroxylase deficiency in China were analyzed. Results The male patient with age of onset at 3 months presented with feeding difficulty, diarrhea, metabolic acidosis, and psychomotor retardation after polio vaccination or high protein diet. At one year and 8 months of age, methylmalonic aciduria was diagnosed, and the patient was clinically improved after treatment. At 5 years of age, precocious puberty was noticed, and virilizing form of 21-Hydroxylase deficiency was diagnosed. Genetic testing confirmed 2 known mutations in MUT gene (c.866G > C, c.2179C > T) and 2 known mutations in CYP21A2 gene (c.188A > T, c.518T > A). Conclusions The clinical manifestations of inherited metabolic disorders and endocrine diseases are complex and it is rare that multiple disorders occurred simultaneously in one patient. This male patient has two rare diseases, methylmalonic aciduria and 21-hydroxylase deficiency.