Cryptic Translocations

The analysis of telomeric regions has been a significant challenge using conventional clinical cytogenetics methods (G-banding analysis at the 450-550 band level), since most terminal bands stain G-band negative making cryptic rearrangements difficult, if not impossible, to detect (National Institutes of Health et al., 1996).  Many patients considered to be cytogenetically normal by conventional cytogenetics methods have actually had cryptic telomeric rearrangements which contributed to their phenotypes. 

One of the first examples of such a cryptic translocation was reported by Lamb et al. (1989), in which a young boy presented with (-thalessemia, dysmorphic features and a mental handicap.  Although his high-resolution karyotype was normal, this boy was later found to be an unbalanced telomeric translocation carrier through a combination of DNA analysis and in situ hybridization, which was prompted due to his clinical diagnosis.