目的　探讨同胞共患先天性肾上腺皮质增生症（17α羟化酶缺乏）的临床特点及基因突变。方法　回顾分 析确诊的2例17α羟化酶缺乏症姐妹患儿临床资料，以及CYP17A1基因Sanger测序及MLPA检测结果。结果　2例患儿 分别于4岁及10岁确诊，均有感染后低血钾，高促性腺激素性性腺功能减退表现。 1例血压偏高。血钾1.9~4.0 mmol/L， 17羟孕酮及脱氢表雄酮降低，增强CT提示肾上腺有不同程度的增粗。姐姐染色体为46，（ XY）。2例患儿基因结果显示 CYP17A1基因复合杂合突变，即来自父源的 c.985_987delTACinsAA 突变及母源的CYP17A1 基因外显子 1-7 区域杂合缺 失。结论　先天性肾上腺皮质增生症（17α羟化酶缺乏）可在青春期前被发现，当临床出现不明原因低血钾及高血压，需 要考虑本病可能。基因检查可以帮助诊断。

Objective　To report clinical characteristics and genetic results of two sisters suffered from congenital adrenal cortex hyperplasia (17-α-hydroxylase deficiency), and relevant literatures were reviewed. Methods　Clinical manifestation and laboratory examination data of two sister cases of 17-α-hydroxylase deficiency enrolled in Capital Institute of Pediatrics in March 2016 were analyzed. Sanger sequencing and MLPA for CYP17A1 genes were performed and the parents' genes were also verified. Results　The two  patients were four years and 10 years old, both suffered from hypokalemia after infections, and hypergonadotrophin gonad hypofunction. One case was with slightly high blood pressure. Laboratory test results showed potassium fluctuation tendency in 1.9~4.0 mmol/L, 17-OHP and DHEA was decreased. Enhanced CT showed different degree of adrenal gland enlargement. Chromosome examination of the older sister is 46, XY. Both sisters demonstrated heterozygous mutation of CYP17A1 gene.  The molecular genetic analysis suggested a c.985_987delTACinsAA from father and a deletion spanning exons 1-7 of the CYP17A1 gene from mother. Conclusion　17-α-hydroxylase enzyme deficiency can be diagnosed before adolescence. Clinical hypokalemia with unknown reason and high blood pressure may indicate the disease. The diagnosis  can be confirmed with gene sequencing of CYP17A1.