Suspected gonadal mosaicism for isochromosomes 18p and 18q unsubstantiated by 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 gonadal mosaicism for isochromosomes 18p and 18q, which could confer a high recurrence risk. Methods: A sperm sample from the father was analyzed with fluorescence 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. There were no differences in the father's specimen compared to a control. Conclusions: There was no evidence for gonadal mosaicism. It is important to confirm clinical hypotheses whenever possible.