Heteromorphic variants of chromosome 9

Background

Heterochromatic variants of pericentromere of chromosome 9 are reported and discussed since decades concerning their detailed structure and clinical meaning. However, detailed studies are scarce. Thus, here we provide the largest ever done molecular cytogenetic research based on >300 chromosome 9 heteromorphism carriers.

Results

In this study, 334 carriers of heterochromatic variants of chromosome 9 were included, being 192 patients from Western Europe and the remainder from Easter-European origin. A 3-color-fluorescence in situ hybridization (FISH) probe-set directed against for 9p12 to 9q13~21.1 (9het-mix) and 8 different locus-specific probes were applied for their characterization. The 9het-mix enables the characterization of 21 of the yet known 24 chromosome 9 heteromorphic patterns. In this study, 17 different variants were detected including five yet unreported; the most frequent were pericentric inversions (49.4%) followed by 9qh-variants (23.9%), variants of 9ph (11.4%), cenh (8.2%), and dicentric- (3.8%) and duplication-variants (3.3%). For reasons of simplicity, a new short nomenclature for the yet reported 24 heteromorphic patterns of chromosome 9 is suggested. Six breakpoints involved in four of the 24 variants could be narrowed down using locus-specific probes.

Conclusions

Based on this largest study ever done in carriers of chromosome 9 heteromorphisms, three of the 24 detailed variants were more frequently observed in Western than in Eastern Europe. Besides, there is no clear evidence that infertility is linked to any of the 24 chromosome 9 heteromorphic variants.

Thirty-two new cases with small supernumerary marker chromosomes detected in connection with fertility problems: detailed molecular cytogenetic characterization and review of the literature

Thirty-two patients with fertility problems were identified as carriers of small supernumerary marker chromosomes (sSMC). Molecular cytogenetic techniques were used to characterize their chromosomal origin. Together with the other cases available in the literature 111 sSMC cases have now been detected in connection with fertility problems in otherwise clinically healthy persons and characterized for their genetic content. According to this study, in 60% of the cases the sSMC originated from chromosomes 14 or 15. Euchromatic imbalances were caused by the sSMC presence in 30% of the cases. Notably, in 53% of infertile sSMC carriers, the sSMC was parentally transmitted. As we found indications of an as yet unknown mechanism for the elimination of sSMC from the human gene pool, sSMC could also play a role in elucidating the process of chromosome gain and loss during evolution. Nonetheless, further detailed molecular analysis will be necessary in the future to characterize the mechanisms and genetic basis for this phenomenon.