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

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Abstract
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 and 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: (1) 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; (2) 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.