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mental retardations

Monday 23 January 2006

Nonsyndromic mental retardation is one of the most important unresolved problems in genetic health care. Autosomal forms are far more common than X-linked forms, but, in contrast to the latter, they are still largely unexplored.

Mental retardation (MR), defined as an intelligence quotient (IQ) below 70, is the most frequent serious handicap in children and young adults. Moderate to severe MR (IQ@<@50) affects 1% of the population and this prevalence increases to 2-3% if mild MR is included (50@<@IQ@<@70).

MR can result from multiple causes including environmental factors, chromosomal anomalies, and monogenic disorders. Despite recent advances in cytogenetics and molecular genetics, the cause of the mental handicap remains unexplained in about 40% of cases.


Taken together, chromosomal anomalies are believed to account for 4-28% of cases of MR.


- autosomal
- X-linked
- CNV-associated mental retardation


- Schoumans J, Ruivenkamp C, Holmberg E, Kyllerman M, Anderlid BM, Nordenskjold M. Detection of chromosomal imbalances in children with idiopathic mental retardation by array based comparative genomic hybridisation (array-CGH). J Med Genet. 2005 Sep;42(9):699-705. PMID: 16141005

- Rosenberg C, Knijnenburg J, Bakker E, Vianna-Morgante AM, Sloos W, Otto PA, Kriek M, Hansson K, Krepischi-Santos AC, Fiegler H, Carter NP, Bijlsma EK, van Haeringen A, Szuhai K, Tanke HJ. Array-CGH detection of micro rearrangements in mentally retarded individuals: clinical significance of imbalances present both in affected children and normal parents. J Med Genet. 2006 Feb;43(2):180-6. PMID: 15980116