Abstract
Ring chromosomes are estimated to occur in 3/10 000 newborns and the simultaneous occurrence of two autosomal rings must be a very rare event. Recently, the characterisation of these markers using fluorescence in situ hybridisation (FISH) has greatly enhanced cytogenetic-phenotypic correlations in patients 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 origin of the rings was identified using α satellite and whole chromosome painting probes. FISH analysis showed the same abnormal female karyotype in both twins, 48,XX,+r(1)(p13q21),+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) appeared to be totally CBG band positive. These twins represent the second report of the simultaneous occurrence of multiple autosomal rings. Their description may help to delineate a new chromosome disorder and shows the usefulness of FISH analysis. Keywords: ring chromosome 1; ring chromosome 16; marker chromosomes; whole chromosome painting probes
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