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 2 metacentric chromosomes of different sizes. The 2 metacentric chromosomes were identified by G[Giemsa]- and C[constitutive heterochromatin]-banding to be possible isochromosomes of the long and short arms of a No. 18 chromosome.