目的　探讨先天性黑色素细胞痣（CMN）的临床及遗传学特点。方法　回顾分析1例CMN患儿的临床资料。 结果　男性患儿， 5岁，受损皮肤组织HE染色病理切片显示真皮组织广泛分布大量黑色素细胞，确诊先天性黑色素细胞痣。 患儿受损皮肤组织染色体核型分析未见明显异常；基因检测显示受损皮肤组织存在NRAS基因c.182A>G（Q61R）杂合突 变，家系分析表明患儿及其父母的外周血对应位点为野生型。结论　本例患儿NRAS基因体细胞突变而引起CMN，受损皮 肤组织遗传学检测有助于CMN确诊以及预后判断。

　Objective　To explore the clinical and genetic characteristics of congenital melanocytic naevi (CMN). Method　The clinical data of CMN in a child was retrospectively analyzed. Results　HE staining of damaged skin tissue in a 5-year-old boy showed a large number of melanocytes were widely distributed in the dermis and he was diagnosed of CMN. The chromosome karyotype analysis of the damaged skin tissue showed no significant abnormalities. The results of gene detection showed a heterozygous mutation of NRAS gene, C. 182A > G (Q61R), in the damaged skin tissues. Pedigree analysis showed that the correspondent loci in the peripheral blood of the child and his parents were wild-type. Conclusions　CMN was caused by somatic mutation of NRAS gene in this case, and genetic test of damaged skin tissue was helpful for diagnosis and prognosis of CMN