A male infant with failure to thrive was found to have a previously unreported combination of chromosomal structural abnormalities. Evidence is presented which characterizes the abnormal chromosomes as a late-replicating G ring and a pericentric inversion in an early replicating B group chromosome. The mechanisms of pericentric inversion and ring formation are discussed, and possible genetic consequences are noted. The patient's phenotype differed significantly from that of previously reported subjects with G rings, G deletions, and structural abnormalities of the B group. This phenotypic difference could be attributed to the apparent fact that the proband's G ring was a late replicator (G1) and earlier cases were not, on to the seeming variability in ring size which suggested partial trisomy/partial monosomy, or perhaps to the probability that the abnormal B chromosome was pericentrically inverted rather than deleted.
The question of the etiologic significance of broken parental chromosomes must be raised, although more study is needed in the area of chromosome breakage, its relationship to abnormal progeny, and the possible role of environmental agents, e.g., drugs and irradiation.
Partial monosomy 5p and partial trisomy 5q due to paternal pericentric inversion of chromosome 5
