Suspected gonadal mosaicism for isochromosomes 18p and 18q unsubstantiatedby fluorescence in situ hybridization analysis of sperm

Purpose: A father had two children, one with isochromosome 18p, and another with isochromosome 18q. The father was counseled that he might have gonada l mosaicism for isochromosomes 18p and 18q, which could confer a high recur rence risk. Methods: A sperm sample from the father was analyzed with fluor escence in situ hybridization probes for 18p and 18q. Results: More than 1, 000 sperm were scored and none were found with two 18p or 18q signals. Ther e were no differences in the father's specimen compared to a control. Concl usions: There was no evidence for gonadal mosaicism. It is important to con firm clinical hypotheses whenever possible.