遗传性蛋白C缺陷症家系的一个基因突变

目的 研究一个遗传性蛋白C（PC）缺陷症家系的遗传表型及基因特征。方法 PC活性用凝固法测定，PC抗原用ELISA方法测定。用PCR扩增2代家系12个成员中4个PC活性及抗原减低的PCⅡ-Ⅸ号外显子片段，用单链构象多态性（SSCP）分析cDNA变性后的差异，用测序法检测突变点。用限制性酶切验证突变点，同时分析家系的基因型。结果 该家系2代4名成员PC抗原水平在34．3％－67．8％（参考值80％－120％）。PC活性在22％－49％（参考值70％－130％），较正常参考范围明显减低。限制性酶切分析该家系12名成员时发现9名成员存在基因的突变。基因突变位点在Ⅶ号外显子第6219位核苷酸G→A突变，使正常编码的CGG精氨酸突变为CAG谷氨酰胺。结论 该家系为I型PC缺陷症，基因分析证明先证为杂合子型。在PCⅦ号外显子上第6219位核苷酸G→A突变，在蛋白质合成过程中第169位精氨酸被谷氨酰胺替代（R→Q），为目前国内献中尚未报道的一个基因突变点。

A point mutation of protein C gene in a congenital protein C deficiency pedigree

OBJECTIVE: To study the phenotypes and genotypes of a protein C (PC) deficiency pedigree. METHODS: Immunoassay (ELISA) was used for PC antigen and activated PC (APC) detection, PCR for amplification of the fragment of protein C gene exon II to exon IX, single-strand conformation polymorphism (SSCP) for difference of denatured cDNA and DNA sequencing for gene mutation. RESULTS: Four members in the pedigree were found to be PC antigen levels between 34.3% - 67.8% and PC activity between 22% - 49% which are lower in comparison with normal references (80% - 120% and 70% - 130%, respectively). A G-to-A mutation in exon VII of the protein C gene at 6 219 position was identified in 9 members. This mutation resulted in the substitution of Arg for Gln at 169 amino acid. CONCLUSION: The proband is of heterozygosity. The G6219 A mutation in exon VII of the protein C gene leads to the substitution of Arg 169 Gln. This mutation is reported for the first time in China.