Molecular Diagnosis of Genic Abnormalities using Human Tissue Materials

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1) A fluorescent in situ hybridization (FISH) study was carried out on paraffin sections of human embryonic and fetal tissues with two DNA probes, DXZ1 and DYZ1 (Oncor), for X and Y chromosome-specific DNA sequences, respectively. The paraffin blocks of the human embryonic and fetal tissues examined in the present study had been stored at room temperature for up to 5 years after fixation in 4% paraformaldehyde. All the 7 embryos and 5 fetuses examined were successfully sexed by FISH.The cells from 3 embryos and 4 fetuses were positive for a hybridization signal with each of the DXZ1 and DYZ1 probes and they were classified as male. The cells from the remaining 4 embryos and 1 fetus were positive for two identical hybridization signals with DXZ1 probe in a nucleus instead of the absence of the signal hybridized with DYZ1, indicating that their cells have two X chromosomes but no Y chromosomes. The FISH results for the 5 fetuses examined were consistent with their genital sex and/or gonadal histology. Thus, the FISH technique has been shown to visualize specific DNAs in situ on paraffin sections and to be useful to determine the sex of fixed embryos and fetuses retrospectively.2) A FISH study was carried out on paraffin sections of tissues from fetuses with 45, X karyotype which had been fixed in neutralized formalin. The results of the FISH with their tissues showed that the nucleus of each cell had one hybridization signal with the DXZ1 probe but was entirely negative for signals with the DYZ1 probe, indicating that the constitution of sex chromosomes of the fetuses was XO.The present results showed it feasible to retrospectively identify chromosome aneuploidies by FISH with chromosome-specific DNA probes if fixed tissues or paraffin blocks are available.