OBJECTIVETo explore whether chromosomal microdeletions have a role in the pathogenesis of unexplained mental retardation (MR) and the value of fluorescence in situ hybridization (FISH) in the detection of microdeletions in MR.

METHODSSelection of patients was based on the following criteria: (1) MR with two or more of the following: dysmorphic features, prenatal growth retardation, postnatal growth abnormalities, a suggestive family history; (2) Chromosome karyotype at the level >450 bands was normal; (3) Exclusion of other identified genetic or environmental diagnosis. FISH was carried out with specific DNA probe to 47 undiagnosed MR to identify interstitial microdeletions and further screen the integrity chromosome subtelomere.

RESULTSSix cases were analyzed by FISH for special interstitial microdeletions and anomaly was found in one case with 7q11.23 deletion. Subtelomeric FISH analyses were performed in 46 patients, and two cases with a deletion of subtelomeric region of chromosome 6q and 2q respectively were identified.

CONCLUSIONChromosome microdeletions are supposed to be a significant cause of idiopathic MR, once recognizable syndromes have been excluded, FISH analyses for interstitial microdeletions and subtelomeric rearrangements are warranted in children with unexplained MR.