Trisomy 18 syndrome with an unusual karyotype: possible double isochromosome.

Abstract

Chromosome analysis of an infant with characteristic features of trisomy 18 is presented. The chromosome complement contained a modal count of 47 but there was only one No. 18. In addition, there were two metacentric chromosomes of different sizes. The two metacentric chromosomes were identified by G- and C-banding to be possible isochromosomes of the long and short arms of a No. 18 chromosome.