Intellectual Disability: Genetics


The extent to which genetics plays a role in intelligence has long been a matter for debate. However, it is now well established that genetic effects can contribute to intellectual disability (ID), in particular, moderate to severe ID. The discovery of chromosomal rearrangements and the cloning of causal genes have both clinical and scientific value. Clinically, they help the families of those affected by providing molecular diagnoses, alleviating feelings of guilt and allowing more accurate genetic counselling. Scientifically, they provide important clues regarding the underlying biology of cognition.

Key concepts

  • Both intellectual ability and disability are strongly influenced by genetics.

  • ID is usually divided into syndromic and nonsyndromic categories.

  • Most recognized forms of ID are X‚Äźchromosome linked.

  • Single gene mutations can cause syndromic and nonsyndromic ID.

  • Causative gene products can be biochemically linked, signposting functionally important processes.

  • Genome imbalance (aneusomy and segmental aneusomy) is a significant cause of syndromic ID.

  • Array comparative genomic hybridization is a powerful new technique for identifying submicroscopic genome imbalances.

  • Genome architecture can predispose to recurrent genomic disorders.

  • Clinically, the provision of a molecular diagnosis is important to families with affected members.

Keywords: mental retardation; learning disability; intelligence quotient; aneusomy; copy number variant; genomic disorder

Figure 1.

Two‐group hypothesis of intellectual disability. The explanation for the excess of low intelligence quotient (IQ) is shown as an additional curve superimposed to the left of a normal distribution that has its mean at 100.

Figure 2.

Processes implicated in intellectual disability. Part (b) adapted from image available at and reproduced with permission of Jena Bioscience GmBH.



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Knight, Samantha JL(Dec 2008) Intellectual Disability: Genetics. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0005515.pub2]