目的 总结单亲二倍体致3 -甲基巴豆酰辅酶A羧化酶缺乏症（MCCD）基因型的临床特征。方法 回顾分 析1例MCCD患儿的临床资料并复习相关文献。结果 男性患儿，9月龄；运动发育不良，右下肢外旋，双下肢肌力稍低， 0~6岁儿童心理行为发育评估66分。血串联质谱示3 -羟基异戊酰肉碱增高，尿气相色谱-质谱示3 -羟基异戊酸、3 -甲基 巴豆酰甘氨酸及甲基巴豆酰甘氨酸增高。全基因组测序发现 患儿MCCC1基因存在c.1853_1856delTTTA纯合变异，来自 母亲，尚未见报道；染色体微阵列证实染色体3 p 24 - 3 q 29为单亲二倍体，该片段包含MCCC1基因，来自母亲。结论 发 现单亲二倍体所致MCCD及导致MCCD的新的MCCC 1基因c. 1853 _ 1856 del TTTA纯合变异。

Objective To improve the understanding of the genotype of 3 - methylcrotonyl-CoA carboxylase deficiency (MCCD) caused by uniparental disomy. Methods Clinical data of a patient diagnosed with MCCD was retrospectively analyzed and relevant literature was reviewed. Results A 9 -month-old boy presented with external rotation of his right leg for one week. Physical examination showed dysplasia, right lower extremity external rotation and slightly low muscle strength of lower extremity. His score after psychological and behavioral development assessment of children aged 0 - 6 was 66 points. Blood tandem mass spectrometry and urine gas chromatography-mass spectrometry indicated MCCD. Whole genome sequencing found a c. 1853 _ 1856 delTTTA homozygous variation of MCCC1 gene not reported in the literture, inherited from his mother. Chromosomal microarray confirmed that the proband was maternal uniparental disomy on chromosome 3p24- 3 q 29 , which contained MCCC 1 gene. Conclusion It is firstly found that MCCD was of caused by uniparental disomy. and a novel homozygous variation c. 1853 _ 1856 delTTTA in MCCC 1 gene was found.