OBJECTIVETo assess subtelomeric chromosome anomalies in patients with idiopathic mental retardation (MR).

METHODSSubtelomeric screening was performed in 46 patients with undiagnosed mental retardation. The patients were selected based on the following criteria: (1) MR with two or more of the following conditions: dysmorphic features, prenatal growth retardation, postnatal growth abnormalities, a suggestive family history; (2) chromosome karyotype at the level >450 bands being normal; (3) exclusion of other identified genetic or environmental diagnosis. Fluorescence in situ hybridization (FISH) was performed using ToTelVysion DNA probes. Abnormal findings were confirmed by FISH with a specific subtelomeric probes and family studies were carried out to determine its inheritance.

RESULTClinically significant aberrations were detected in two cases with 6q and 2q terminal microdeletion. The deletion in one case was inherited from a similarly affected father. Subtle chromosomal subtelomeric abnormalities occurred with a frequency of 7.6% in children with moderate to severe mental retardation and of 3.0% in the children with mild retardation.

CONCLUSIONThe results suggest that cryptic abnormalities of the ends of chromosomes might represent a significant cause of mental retardation, and screening for subtelomeric rearrangements might be warranted in children with unexplained mental retardation.

Adolescent ; Child ; Child, Preschool ; Chromosome Aberrations ; Chromosome Deletion ; Humans ; In Situ Hybridization, Fluorescence ; Infant ; Intellectual Disability ; genetics ; Telomere

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.

Chromosome Deletion ; Chromosomes, Human, Pair 2 ; genetics ; Chromosomes, Human, Pair 6 ; genetics ; Genetic Predisposition to Disease ; Humans ; In Situ Hybridization, Fluorescence ; Intellectual Disability ; genetics