Using phenotype-genotype analysis, we found that although patient S3 and her mother had the same mutation (heterozygous EDA p.Arg156Cys mutation and heterozygous WNT10A p.Gly213Ser mutation), patient S3 showed typical phenotypic expression of HED while her mother only had microdontia. The gene discussed is EDA; the disease is hypohidrotic ectodermal dysplasia.