First-trimester prenatal diagnosis of a familial subtelomeric translocation

A new fluorescent in situ hybridization (FISH) technique utilizes a complete set of telomeric probes to screen for deletions or rearrangements within the subtelomeric regions of all chromosomes on a single slide. Such cryptic chromosome rearrangements would otherwise remain undetected by standard cytogenetic analysis. In this case report, we describe the first-trimester prenatal diagnosis of an unbalanced rearrangement in a family where such a cryptic subtelomeric rearrangement is segregating. Interestingly the fetus was also noted to have an increased nuchal translucency at the time first-trimester chorionic villus sampling was performed and a FISH diagnosis made. The result was subsequently confirmed on fetal material obtained after elective termination of the pregnancy. We believe this to be the first report in the literature (as by Medline, December 1999) of a first-trimester prenatal diagnosis using such subtelomeric probes where confirmation by conventional cytogenetic analysis was not possible.