2 22Q TELOMERE DELETIONS SERENDIPITOUSLY DETECTED BY FISH

Cryptic telomere deletions have been proposed to be a significant caus e of idiopathic mental retardation. We present two unrelated subjects, with normal G banding analysis, in whom 22q telomere deletions were s erendipitously detected at two different institutions using fluorescen ce in situ hybridisation (FISH). Both probands presented with several of the previously described features associated with 22q deletions, in cluding hypotonia, developmental delay, and absence of speech. Our two cases increase the total number of reported 22q telomere deletions to 19, the majority of which were identified by cytogenetic banding anal ysis. With the limited sensitivity of routine cytogenetic studies (sim ilar to 2-5 Mb), these two new cases suggest that the actual prevalenc e of 22q telomere deletions may be higher than currently documented. O f additional interest is the phenotypic overlap with Angelman syndrome (AS) as it raises the possibility of a 22q deletion in patients in wh om AS has been ruled out. The use of telomeric probes as diagnostic re agents would be useful in determining an accurate prevalence of chromo some 22q deletions and could result in a significantly higher detectio n rate of subtelomeric rearrangements.