Paracentric Inversions of Human Chromosomes and their Risks

Overview

The incidence of paracentric inversions in the general population has not been clearly established, it ranges from0.09 to 0.49/1,000. Homologue pairing during meiosis in a paracentric-inversion heterozygote is maximized by theformation of an inversion loop. If a crossing-over occurs within this loop, dicentric and acentric chromosomes areformed. Resulting gametes can have variety of duplications and deficiencies and give a non-viable progeny. One ofthe exceptions to the rule is a mutation event „U loop recombination“. FromU-loop event a monocentric recombinantchromosome can arise by an abnormal process, which involves chromatid breakage and reunion. Most of theparacentric inversions inman are harmless and the risk of heterozygotes having a child with an unbalanced karyotypeis relatively low. In carriers of an accidentally discovered paracentric inversion, amniocentesis is optional. However,in some cases, it is difficult to distinguish between a paracentric inversion and paracentric insertion - the risk of theinsertion is about 15 %. When a de novo inversion is detected in amniotic fluid, the overall risk for two-breakrearrangements is 6.7 %.

Key words:
chromosomes, paracentric inversion, recombination, prenatal diagnosis.