title: Bloom's syndrome. XIX. Cytogenetic and population evidence for genetic heterogeneity.
abstract: Cells with abnormally high rates of sister-chromatid exchange (SCE) are uniquely characteristic of Bloom's syndrome (BS). However, in one in five persons a minor population of cells with a low-SCE phenotype circulates in the blood. The origin and significance of the low-SCE cells in BS have never been understood, although they are assumed to arise by somatic mutation. In the present investigation, the enigmatic high-SCE/low-SCE mosaicism was investigated by comparing the incidence in several subpopulations of persons in the Bloom's Syndrome Registry who exhibit the two types of cells, and a striking negative correlation emerged: in persons with BS whose parents share a common ancestor, the case in approximately half of registered persons, low-SCE cells are found only rarely; conversely, the mosaicism occurs almost exclusively in persons with BS whose parents are not known to share a common ancestor. Because those who share a common ancestor are predominantly homozygous-by-descent at the mutated BS locus, the negative correlation is interpreted to mean that the emergence of low-SCE cells in BS in some way depends on the pre-existence of compound heterozygosity. A corollary to this is that BS is genetically heterogeneous.
authors.affiliation: Laboratory of Human Genetics, New York Blood Center, New York 10021, USA.
authors.forename: J
authors.initials: J
authors.lastname: German
authors.forename: N A
authors.initials: NA
authors.lastname: Ellis
authors.forename: M
authors.initials: M
authors.lastname: Proytcheva
mesh_terms: D001816:Bloom Syndrome / Q000235:genetics*; D018740:Genetic Heterogeneity; D006801:Humans; D012042:Registries; D012854:Sister Chromatid Exchange