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A major challenge for human genetics is to identify new causes of mental retardation, which, although present in about 3% of individuals, is unexplained in more than half of all cases. We have developed a strategy to screen for the abnormal inheritance of subtelomeric DNA polymorphisms in individuals with mental retardation and have detected three abnormalities in 99 patients with normal routine karyotypes. Pulsed-field gel electrophoresis and reverse chromosome painting showed that one case arose from an interstitial or terminal deletion and two from the de novo inheritance of derivative translocation chromosomes. At least 6% of unexplained mental retardation is accounted for by these relatively small chromosomal abnormalities, which will be an important resource in the characterization of the genetic basis of neurodevelopment.

Original publication




Journal article


Nat Genet

Publication Date





132 - 140


Adult, Child, Child, Preschool, Chromosome Aberrations, Chromosome Disorders, Chromosomes, Human, Pair 13, Chromosomes, Human, Pair 22, Female, Gene Deletion, Gene Rearrangement, Humans, Intellectual Disability, Karyotyping, Male, Prevalence, Telomere