Homodicentric chromosomes: a distinctive type of dicentric chromosome.

Abstract

Two patients with a distinctive type of dicentric autosomal chromosome formed by breakage and union between homologous chromosomes are described. These stable chromosomes possess 2 C bands, implying the presence of 2 centromeric regions. The 1st child, evaluated for dysmorphic features, had an abnormal chromosome 16, designated as 46,XX,-16,+dic(16)(pter .fwdarw. cen .fwdarw. q22::p11 .fwdarw. qter). The 2nd case is a child with the typical features of trisomy 18 whose karyotype is designated as 46,XX,-18,+dic(18)(qter .fwdarw. p11.cntdot.1::p11.cntdot.3 .fwdarw. cen .fwdarw. qter). The stability of these chromosomes is presumably the result of centromere suppression and associated premature centromere division of the suppressed centromere. The possible mechanism of formation of these homodicentric chromosomes is presented and a comparison is made between them and 3 patients with dicentric X chromosomes.