PRENATAL EXCLUSION OF SEGMENTAL TRISOMY IN FAMILIAL CHROMOSOME-21 PERICENTRIC-INVERSION BY FLUORESCENCE IN-SITU HYBRIDIZATION

We report the prenatal exclusion of partial trisomy in a family with m aternal pericentric inversion of chromosome 21 by fluorescence in situ hybridization (FISH). After determining the structural rearrangement in the mother and her affected son with 46,XY,rec(21)dup(21q)inv(21)(p lq22) resulting in Down syndrome (DS), a chorionic villus sample from the current pregnancy was analysed for the copy number of the DS criti cal region with a cosmid contig. The signal distribution was normal an d the cytogenetic analysis revealed that the fetus had inherited the i nverted chromosome 21 in a balanced form. FISH probes specific for the DS region are of great value in supporting cytogenetic results, regar dless of the structural status of chromosome 21. (C) 1997 by John Wile y & Sons, Ltd.