CYP17A1基因新突变致17α-羟化酶/17,20-裂解酶部分性缺陷症

目的研究1例17α-羟化酶/17,20-裂解酶部分性联合缺陷症患者CYP17A1基因突变特点,并结合患者的临床表现与基因突变类型初步探讨P450C17酶蛋白的结构与功能的关系。方法收集1例17α-羟化酶/17,20-裂解酶部分性联合缺陷症患者的临床资料及其亲属血标本,提取基因组DNA,设计7对引物扩增CYP17A1基因的8个外显子及外显子与内含子的连接区域,琼脂糖凝胶电泳鉴定PCR产物,产物胶回收后直接做为DNA双链模板测序。DNA双链模板不一致的PCR产物经克隆后测序。测序结果在核苷酸序列数据库进行比较分析。结果患者CYP17A1基因突变检测结果为5994-5995delAT/7541C>T复合杂合子。这两种突变均未见报道。推测5994-5995delAT导致I259H,274X,突变形成的截短蛋白质缺少血红素结合区域,因此是没有功能的;而通过人类P450C17酶计算机模型分析显示7541C>T导致的A398V远离酶的活性中心,推测突变可能使酶的活性减弱,而不是完全地丧失。患者临床表现为有自发不规则月经及轻度高血压、低血钾,结合激素测定结果提示肾上腺和性腺保留部分功能。因而患者的基因型与其临床表型是一致的。结论应进行突变P450C17酶的功能学研究来进一步明确结构改变对功能的影响。

New compound heterozygous mutation causes partial combined 17α-hydroxylase/17,20-lyase deficiency

OBJECTIVE: To investigate the CYP17A1 gene mutations in a Chinese 46,XX patient with partial combined 17 alpha-hydroxylase/17,20-lyase deficiency. METHODS: Clinical data were retrospectively analyzed. The genomic DNA of the patient and her parents was isolated from whole blood. Seven pairs of primers were used to amplify eight exons and exon-intron boundaries of the CYP17A1 gene. The amplified PCR products were purified by agarose gel and then directly sequenced. In order to confirm the DNA sequences of different alleles, some fragments were inserted into pMD 18-T vector and then subclone sequenced. Sequencing results were compared to the established human CYP17A1 sequence. RESULTS: The patient was new compound heterozygous of 5994-5995 delAT/7541 C>T. The mutation 5994-5995 del AT, causing amino acid I259H, 274X, was proposed to result early truncated protein which was lack of the activity center site of P450C17, whereas missense mutation 7541 C>T causing A398V did not lie in the active site of the enzyme according to the computer model of human P450C17. The 46, XX case had irregular menstruation and slightly hypertension and hypokalemia. The ACTH stimulating test as well as the result of the sex hormones suggested that there was partial 17 alpha-hydroxylase/17, 20-lyase enzyme activities in the adrenal and sexual gland. We speculate that A398V might conserve partial of the enzyme's activities. The genotype was coincident with phenotype. CONCLUSION: More study should be done to have better understanding of the function of the mutated P450C17 enzymes.