RECOMBINANT CHROMOSOME-9 POSSIBLY DERIVED FROM BREAKAGE AND REUNION OF SISTER CHROMATIDS WITHIN A PARACENTRIC INVERSION LOOP

Chromosomally unbalanced offspring resulting from the recombination of parental paracentric inversions are uncommon. We report on a 20-month -old boy with a partial duplication of 9p due to the recombination of a paternal paracentric inversion. The patient's recombinant chromosome was designated rec(9)(p13-->p24::p12-->p24::p12-->qter). The patient' s father and paternal aunt have a paracentric inversion of chromosome 9: inv(9)(p13p24). Although several mechanisms have been proposed to e xplain the chromosome imbalance generated from paracentric inversions, none of the previously described mechanisms can account for the struc ture of the recombinant chromosome observed in the propositus. We prop ose an unusual mechanism of formation involving breakage and unequal r eunion of sister chromatids within the inversion loop to explain the s tructure of the patient's recombinant chromosome.