Submicroscopic rearrangements at the end of the chromosomes have been shown to be responsible for a small but significant percentage of otherwise unexplained mental retardations. Approximately 5% individuals with mental retardation of unknown etiology have an abnormality of the ends of the chromosomes, called sub-telomeres that can be detected by FISH sub-telomere analysis. A family history of mental retardation, growth retardation, dysmorphic features and congenial anomalies increase the likelihood of detecting a subtelomeric abnormality.
Sub-Telomere FISH probes cover unique sequences at the subtelomeric end of the short or long arm of a specific human chromosome. This enables identification of deletions or rearrangements at the telomeric end of chromosomes.