21号染色体STR多态与Down's综合征基因诊断的研究

The STR polymorphism on chromosome 21 and the diagnosis of Down' syndrome

目的:探讨应用短串联重复序列(Short tandem repeat,STR)进行Down's综合征诊断的可行性,同时对Down's综合征患儿双亲进行分析,找寻该病的遗传规律。方法:选择21号染色体上D21S1l和D21S1414 2个STR基因座,应用聚合酶链式反应(Polymerase chain reaction,PCR)、变性聚丙烯酰胺凝胶电泳(8%)、硝酸银染色技术分别对100例Down's综合征患儿及20例患儿父母的基因组进行分析。结果:(1)正常人在1个STR基因座上的基因型有2种情况:①2个不同等位基因构成的杂合子,凝胶电泳上表现为粗细一样的2条带。②2个相同等位基因构成的纯合子,凝胶上是2条相同等位基因条带的重叠,其宽度和浓度约为单个等位基因条带的2倍。(2)Down's综合征患儿的等位基因数目和(或)条带浓度有3种特征性改变:①3个不同的等位基因,电泳图上为浓度相同的3条带。②3个等位基因中的2个相同,电泳图上为2条带,其中1条的浓度足另外1条的2倍。③3个相同的等位基因,电泳图上为1条带,这条带的浓度和宽度约为正常对照条带的3倍。(3)20例Down's综合征双亲分析显示,Down's综合征患儿电泳条带包含了母亲的全部电泳条带,而与父亲的电泳条带只有部分相同。结论:(1)利用21号染色体STR位点作为遗传标记,采用PCR扩增技术结合变性聚丙烯酰胺凝胶电泳及硝酸银染色技术,可用于诊断和筛查Down's综合征。(2)Down's综合征患儿与双亲比对电泳结果表明,Down's综合征发病与父母的核型无关,多余的1条21号染色体一般来自于母亲。

Objective：To probe the possibility of using STR polymorphism on chromosome 21 to diagnose Down＇s syndrome. At the same time,some parents of Down＇s syndrome were analysed using the same mothed. To develop a rapid and accurate method for Down＇s syndrome diagnosis and review its pattern. Methods：The small tandem repeats （STR） of D21Sll and D21S1414 on chromosome 21 were analysized by polymerase chain reaction （PCR）.100 Down＇s syndrome samples （blood） and 20 parents＇ samples（blood ） were analyzed with.denaturing polyacrylamide gel（8% ） and Silver Nitrate staining. Results： （1） The normal person and two kinds of status in the genotype of a STR gene： （1）Two bands of same size on the gel electrophoresis were displayed to the heterozygote of two different alleles. （2）A band on gel electrophoresis was shown to the homozygote of two same allele But the width and thickness of the band were about two times of a single one. （2）There were three kinds of characteristic changes of the number and/or the bands thickness of allele for the Down＇s Syndrome： （1）Three different alleles,with three bands of same thickness on gel electrophoresis. （2）Only two of the three alleles are the same,two bands on gel electrophoresis, and one of the two bands was two times thicker than the other. （3）Three alleles were the same, only one band on gel electrophoresis. The width and thickness of the band are about three times than single band of normal. （3） The analysis about parents of 20 cases Down＇s syndrome shows that the two bands were usually derived from mother,and another derived from father in bands of the Down＇s syndrome on gel electrophoresis. Conclusions：（1）As genetic marker with STR sites （D21Sll and D21S1414） of chromosome 21,Down＇s syndrome can be diagnosed by PCR,denaturing polyacrylamide gel and Silver nitrate staining analysis. （2）Genetic analysis of the parents of Down＇s syndrome show that onset of Down＇s syndrome does not have relationship with the karyotype of the parents.Besides,the extra chromosome 21 is derived from mother usually.