Unmasking of heterozygosity by inherited balanced translocations. Implications for prenatal diagnosis and gene mapping.

Phenotypic abnormalities in individuals with balanced chromosome rearrangements can be caused by loss of function at the break points and consequent functional homozygosity for recessive genes. This has obvious implications in prenatal diagnosis. Relevant cases are presented and discussed. Mendelian disorders and possibly also disorders which are under polygenic control may be assigned to certain chromosome regions or bands by means of such translocations. Several assignments have been accomplished lately, the approach being much the same as with deletion mapping.