Diagnostic FISH probes for del(17)(p11.2p11.2) associated with Smith–Magenis syndrome should contain the RAI1gene

Smith–Magenis syndrome (SMS) is a mental retardation syndrome with distinctive behavioral characteristics, dysmorphic features, and congenital anomalies usually associated with an interstitial deletion of chromosome 17p11.2. While high quality G‐banding will identify most SMS patients, fluorescent in situ hybridization (FISH) is the recommended test for confirmation of an SMS diagnosis. Recently, haploinsufficiency of the RAI1gene due to deletion or mutation was determined to be the likely cause of SMS. All diagnostic FISH probes available commercially contain the FLIIgene and are approximately 580 kb centromeric to RAI1. We present two patients with SMS who have interstitial deletions at 17p11.2 but are not deleted for currently available commercial FISH probes that include FLII; both patients have deletions that are demonstrated with probes containing the RAI1gene. We recommend that for diagnostic accuracy, all future FISH tests for SMS be performed with probes containing the RAI1gene, as some atypical deletions in the region critical to the SMS phenotype will otherwise be missed. © 2004 Wiley‐Liss, Inc.