Isochromosome-formation in chromosome 9.

A new case of de novo isochromosome-formation in chromosome 9 associated with the translocation of long arm material of chromosome 9 onto chromosome 1 is described. The female patient is mentally retarded and shows only minor dysmorphisms. The cytogenetic investigation revealed a two-cell-line mosaicism with different isochromosomes of chromosome 9. In both cell lines, a translocation of 9qter-9q13 onto the short arm of chromosome 1 is observed.