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目的 研究一个遗传性蛋白S(PS)缺陷家系的遗传表型及基因型特征。方法 PS活性用凝固法测定 ,PS抗原用ELISA方法测定。用聚合酶链反应扩增 5代家系 34个成员中 9个PS活性及抗原减低的PS 1～ 15号外显子片段 ,用单链构象多态性 (SSCP)分析cDNA变性后的差异 ,用测序方法检测突变点。结果 该家系 5代 9名成员游离PS抗原在 10 %～ 45 % (正常值为 5 5 %～ 12 8% )。PS活性在 13%～ 37% (正常值为 70 %～ 130 % ) ,较正常参考范围明显降低 ,二者呈平行下降 ,但总PS抗原均在正常范围。在这些成员中均检测到 10号外显子上第 16 3位核苷酸G→T突变 ,使AGT→ATT ,在mRNA转录时 ,转录为终止密码子 ,阻断蛋白质的合成。结论 本家系的Ⅲ型PS缺陷症基因分析证明 ,先证者为杂合子型。在PS 10号外显子上第 16 3位核苷酸发生G→T突变 ,在蛋白质合成过程中丝氨酸被终止密码子替代 ,为目前文献中尚未报道的一个新的基因突变点。
Objective To study the genetic phenotype and genotypic characteristics of a hereditary protein S (PS) -deficient pedigree. Methods PS activity was determined by coagulation method and PS antigen by ELISA method. Nine PS-active and antigen-reduced exons 1 to 15 of 34 members of 5 generations of pedigree were amplified by polymerase chain reaction (PCR). The differences of cDNA denaturation were analyzed by single strand conformation polymorphism (SSCP) Methods Detection of mutation points. Results The 9 generations of 5 generations of this family had 10% -45% free PS antigen (normal range: 5 5% -12 8%). PS activity in 13% to 37% (normal 70% to 130%), significantly lower than the normal reference range, the two decreased in parallel, but the total PS antigen in the normal range. In these members, the 16th nucleotide G → T mutation on exon 10 was detected, allowing AGT → ATT to be transcribed as a stop codon upon mRNA transcription, blocking the protein synthesis. Conclusion The genotypes of type Ⅲ PS deficiency in this pedigree prove that the probands are heterozygous. G → T mutation occurs at nucleotide 16 3 of PS 10 exon, and the substitution of stop codon for serine during protein synthesis is a new gene mutation point not yet reported in the literature.