Molecular cytogenetic analysis using FISH and HD-oligo micro array identified an unusual novel Down syndrome caseMolecular cytogenetic analysis using FISH and HD-oligo micro array identified an unusual novel Down syndrome case

Background: Down syndrome, caused due to trisomy of chromosome 21.
Methods: 131 suspected cases of DS from university hospital after obtaining written informed consent clinical history and photographs were also recorded. Diagnosis carried out by tacking peripheral blood from the children, setting up whole blood culture as well as DNA extraction from leukocytes for molecular analysis. G-banding by Saline-Trypsin-Giemsa (STG) method and Karyotyping.
Results: They were into four categories using automated Karyotyper. Category 1, out of 131 96(73.28%) cases of these had trisomy 21 while Category 2, showed 3(2.29%) cases with translocation or isochromosome involving chromosome 21. Category 3, was 0 mosaics cases. Category 4, was 0, will be karyotypically 46,/XY but show partial duplications case. An unusual Down syndrome is Category 5, had remaining 32(24.42%) cases, though referred for DS were karyotypically 46,XX or 46,XY. Of these only one cases were judiciously selected and tested for partial duplication of Down syndrome critical region (DSCR) with the help of FISH by using LSI 21 chromosome 21 specific probe but as such no duplication was observed. One of the above two case was further investigated through oligo-based cytogenetic array for micro-duplication or deletion of region on chromosome 21 other than the DSCR and it revealed no duplication or deletion of any part of chromosome 21 or whole genome.
Conclusion: This study suggested besides trisomy 21 and chromosomal rearrangements there might be genetic imbalances leading to perturbations of pathway/s could result unusual Down syndrome.