遗传性蛋白C缺陷症家系的一个基因突变

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

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%～ 6 7.8% (参考值 80 %～ 12 0 % )。PC活性在 2 2 %～ 4 9% (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 6 2 19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 ,基因分析证明先证者为杂合子型。在PCⅦ号外显子上第 6 2 19位核苷酸G→A突变 ,在蛋白质合成过程中第 16 9位精氨酸被谷氨酰胺替代 (R→Q) ,为目前国内文献中尚未报道的一个基因突变点。

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.