Evidence for preferential involvement of chromosome bands 6p21 and 13q14 in amniotic fluid cell balanced translocation pseudomosaicism.

Chromosome rearrangement is a relatively common finding in cultured amniotic fluid cells. When cytogenetic abnormalities are confined to one cell or cells from a single culture, they are generally assumed to have arisen in culture (pseudomosaicism). To determine whether or not there might be some specificity in chromosome break-points in balanced translocation multiple cell pseudomosaicism, data has been pooled for 18 cases studied at PDL and 30 cases from the U.S. survey on mosaicism and pseudomosaicism (Hsu & Perlis 1984). Out of a total of 97 break-points, 87 were assigned to Giemsa-staining light bands and 12 to Giemsa-staining dark bands. An excess of break points (29%) were assigned to terminal bands. Two loci appeared to be preferentially involved in rearrangement: six break-points (4 PDL cases and 2 others) were assigned to band 6p21; the region to which the major histocompatibility complex (HLA) has been assigned; Four break-points (all PDL cases) were assigned to 13q14, the region associated with the retinoblastoma locus. This preliminary evidence for specific break-points needs confirmation and long-term follow-up information is needed to determine whether or not there is any clinical significance to these observations.