Congenital chromosome breakage clusters within Giemsa-light bands and identifies sites of chromatin instability.

Analysis of the distribution of published chromosome breaks in cells with constitutional chromosome aberrations showed a nonrandom distribution of breaks among chromosomes and chromosome regions. A significant amount of breakage occurred at Giemsa-negative bands. In addition, chromosome sites associated with a number of fragile sites and cellular oncogene sites were affected nonrandomly. The data are consistent with the hypothesis that chromosome breakage occurs in somatic or germ cells as a result of recombinational errors involving actively transcribing chromatin regions or regions of unstable DNA sequence structure placed in proximity during interphase.