Pericentric inversion of chromosome 1: frequency and possible association with cancer

Abstract

Pericentric inversions involving the heterochromatic regions of the no. 1 chromosomes are relatively common, at least among individuals who develop cancer. A minimum of 12 of the 76 patients with cancer (15%) had the inversion, as compared with 3 of 68 controls (4%), i.e., a total incidence of 15 of 144 (10%). In 2 previous population surveys the incidence of an inversion (regarded as present when at least 1/3 of the C-band extended onto the short arm) was estimated to be of the order of 1-2%. Although this estimate is subject to some uncertainty owing to the number of cases that were not assessed, the data suggest an incidence of at least 4% and possible 10% or more. As association with cancer seems possible from (but has not been proven by) the present results. Heterochromatin polymorphism, pericentric inversion and the risk of cancer are interrelated. There may be a direct relationship between the presence of an inversion, unequal amounts of heterochromatin or both, on the no. 1 chromosomes and risk of cancer. This might be a consequence of somatic pairing and crossing-over between these homologs, perhaps resulting in daughter chromosomes which have undergone deletions or duplications. Evidence for the occurrence of mitotic crossing-over in man came from various sources, especially the observation of chiasmata. Since mosaicism for C-band polymorphisms was observed in man, the mosaicism is the consequence of the production of C-band variants through unequal crossovers following homologous pairing in somatic cells, and this may occur more frequently in some families than in others.