Simultaneous occurrence of two supernumerary autosomal ring chromosomes r(1) and r(16) in twins

Ring chromosomes are estimated to occur in 3/10 000 newborns and the simult aneous occurrence of two autosomal rings must be a very rare event. Recentl y, the characterisation of these markers using fluorescence in situ hybridi sation (FISH) has greatly enhanced cytogenetic-phenotypic correlations in p atients with these marker chromosomes. This kind of analysis enabled us to clarify a unique karyotype containing a r(1) and a r(16) in identical twins born after a 26 week gestation with minimal somatic abnormalities. The ori gin of the rings was identified using a satellite and whole chromosome pain ting probes. FISH analysis showed the same abnormal female karyotype in bot h twins, 48,XX,+r(1)(p13s21),+r(16)(p11q11).ish r(1) (D1Z5+,wcp1+), r(16) ( D16Z2+,wcp16+) in about two thirds of the cells. Each also had minor clones with a normal female karyotype or with one or the other supernumerary ring . Half of the r(1) contained CBG band negative material and the r(16) appea red to be totally CBG band positive. These twins represent the second repor t of the simultaneous occurrence of multiple autosomal rings. Their descrip tion may help to delineate a new chromosome disorder and shows the usefulne ss of FISH analysis.