相邻分离-2(adjacent-2 segregation)在平衡易位携带者的配子形成中属于较为少见的分离方式。报告1例严重胎儿生长受限并伴染色体异常胎儿，联合G显带染色体核型分析、染色体微阵列分析(chromosomal microarray analysis，CMA)、荧光原位杂交(fluorescence in situ hybridization，FISH)、定量荧光聚合酶链反应(quantitive fluorescent polymerase chain reaction，QF-PCR)等多项技术进行产前诊断。羊水CMA结果为 arr[hg19]18p11。32q1 1。2(141，354-21，994，637)×3，21q11。2q21。3(15，502，777-29，700，071)×1，参考 CMA 结果，胎儿核型分析结果描述为46，XX，+der(18)t(18;21)(q11。2;q22。1)，-21。为验证胎儿核型异常来源，检测父母外周血染色体，胎儿父亲核型为46，XY，t(18;21)(q11。2;q22。1)，孕妇核型正常;FISH结果显示羊水细胞有2条正常18号染色体、1条正常21号染色体和1条衍生18号染色体，父亲为18号染色体长臂与21号染色体长臂相互易位携带者。为了排除胎儿2条正常18号染色体是单亲二体的可能，利用母血污染鉴定的结果，通过短串联重复序列(short tandem repeat，STR)位点验证出胎儿的2条正常18号染色体仅1条来自母亲。所以，应用多项检测技术联合诊断相邻分离-2等少见分离方式，能帮助临床医生为平衡易位携带者提供准确的产前遗传学咨询，明确其胎儿染色体异常的类型。
Genetic Analysis of A Fetus with Chromosomal Abnormalities Caused by Sperm Generated by Adjacent-2 Segregation
The adjacent-2 segregation is a rare separation mode in the gametic formation of balanced translocation carriers.A fetus with severe fetal growth restriction(FGR)and chromosomal abnormalities is reported,and the prenatal diagnosis was performed by G-banding karyotype analysis,chromosomal microarray analysis(CMA),fluorescence in situ hybridization(FISH),quantitive fluorescent polymerase chain reaction(QF-PCR).The CMA result of amniotic fluid was arr[hg19]18p11.32q11.2(141,354-21,994,637)×3,21q1 1.2q21.3(15,502,777-29,700,071)×1;Refer to the CMA results,the fetal karyotype was described as 46,XX,+der(18)t(18;21)(q11.2;q22.1),-21.In order to verify the source of abnormal karyotype,the chromosomes of parents'peripheral blood were detected.The father's karyotype was 46,XY,t(18;21)(q11.2;q22.1),and the pregnant woman had normal karyotype.FISH results showed that the amniotic fluid cells had two normal 18 chromosomes,one normal 21 chromosome and one derived 18 chromosome,and that the father was a cross-translocation carrier of the 18p and 21p.To rule out the possibility that the fetus's two normal chromosomes 18 were uniparental disomy,this study used the results of identification of maternal blood contamination,and the results of short tandem repeat(STR)test confirmed that only one of the two normal chromosome 18 came from the mother.Therefore,the application of multiple detection techniques in the diagnosis of rare separation methods such as adjacent-2 segregation can help doctors to provide accurate prenatal genetic counseling for those balanced translocation carriers,and to identify the types of chromosomal abnormalities in their fetuses.
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