Dyslexia by Margaret J. Snowling

Author:Margaret J. Snowling
Language: eng
Format: epub
ISBN: 9780192550422
Publisher: OUP Oxford
Published: 2019-04-02T16:00:00+00:00

Finding ‘dyslexia genes’

Estimating how much of the variability in reading in a population is due to genetic influences takes us some way towards understanding heritability, but it does not help us to identify the genes associated with dyslexia. From the outset it is important to understand that there is no single gene for dyslexia; rather, genetic influences on dyslexia are likely to be due to many genes with small effects operating together. In the past two decades there has been enormous interest in the molecular genetics of dyslexia. While progress has been rapid, and so-called candidate genes have been identified, we expect that there will be thousands of genes involved so there are still large gaps in understanding. It is often said that we are ‘a long way from accounting for the missing heritability’.

Before proceeding let us take a step back and rehearse what we know about how genes affect development. In each cell of the human body, there are twenty-three pairs of chromosomes (twenty-two pairs of autosomes and one pair of sex chromosomes). Chromosomes contain the hereditary material, or genes, from two parents and each person has two copies (or alleles) of each gene, one from their mother and one from their father. Genes are composed of sequences of DNA (deoxyribonucleic acid) and it is the sequences of DNA in the genes that carry what can be considered to be the ‘instructions’ for the development of the organism (see Figure 15). It is here, therefore, that the heritable differences between individuals originate.

15. The genetic make-up of an individual is contained in the chromosomes. This diagram illustrates how chromosomes comprise strings of genes. Some of the candidate genes associated with dyslexia risk include ROBO1 and KIAA0139 on chromosome 6.

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