The nature and the origin of de novo small marker chromosome found at prenatal diagnosis were determined by fluorescence in situ hybridization (FISH) using chromosome centromere-specific probes and by chromosome in situ suppression (CISS) using chromosome specific libraries. The small marker was characterized as being derived from chromosome 22. The fetus which exhibited a minichromosome had kidney malformations and after birth showed clinical features consistent with the Duane anomaly. One previous case with Duane anomaly and abnormalities of urogenital tract associated to a bisatellitated marker derived from chromosome 22 was reported. These findings indicate that a gene or genes located in the region of chromosome 22pter-->q11 may be associated with the Duane anomaly and the development of the urogenital tract.