Abstract:

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, 21q11.2q21.3(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.

Key words: Translocation, genetic, Karyotyping, Microarray analysis, In situ hybridization, fluorescence, Tandem repeat sequences, Adjacent-2 segregation