Prenatally detected marker chromosome identified as an i(22)(p10) using (micro)FISH

MicroFISH was used to elucidate the chromosomal origin of a prenatally dete cted marker chromosome. Five copies of the marker chromosome were collected from GTG-banded metaphases and amplified by means of DOP-PCR. The PCR prod uct was labeled with biotine-14-dATP and used as a FISH probe for hybridiza tion to metaphase chromosomes of the fetus (reverse painting). The marker a ppeared to be derived from the short arm of (an) acrocentric chromosome(s). After FISH with centromere-specific and band-specific probes complete char acterization was possible and the marker chromosome appeared to consist of two short arms of chromosome 22. The pregnancy was continued and one year a fter birth the patient is developing normal.