As previously stated, because the term dyslexia covers a wide variety of topics it is almost impossible to find a definition which adequately covers all relevant issues and is able

Jorm (1983), The psychology of reading and spelling disabilities, London: Routledge and Kegan Paul

There is greater agreement in the area of phonological awareness, i.e. the ability to perceive that words are made up of a combination of sounds (phonemes) to produce words and can be represented by written symbols (or graphemes) in English. McBride (1995) states three components of PA - verbal short term memory, speech perception and intelligence. The beginning of awareness is the ability firstly to divide the speech stream into words, and then segment the words into phonemes.

Ellis, H. & Miles, L.E. (1981) in Snowling (1987), Dyslexia - a cognitive developmental approach, Oxford: Blackwell

Galaburda, A.M., & Kemper (1981) in Hornsby (1992), Overcoming dyslexia, London: Optima

The question of genetics has long been linked to dyslexia, or "congenital word blindness" as Hinshelwood, Morgan and Kerr named it in 1900 after studying the incidences of intelligent people who could not read, and who were related, founding the idea that dyslexia is partly geneticall y determined (see Huston, 1987). This initial research into the relationship of genetics to dyslexia has been followed by a number of scientific research and personal observation reports through the past one hundred years. In 1976 Finucci found that in 45% of cases, immediate family members of the dyslexic person exhibited the same traits, confirming the belief that dyslexia runs in families. While in 1992, Dr B. Hornsby made the observation that 88% of the children treated by her had a family history of dyslexia. These studies and observations can be criticised for their lack of accounting for an environmental explanation (i.e. if one or both parents do not read well, then it could be argued that their children through a lack of parental modelling and guidance could "inherit" the same difficulties). Recent studies have attempted to overcome this flaw in genetic theory by using twin studies, which allow comparison between monozygotic twins (genes 100% the same) and dizygotic twins (50% the same), with the specification that these twins were brought up together to cancel any environmental discrepancies. Using this method Herman (1959) and Jorm (1983) found that a 100% concordance for monozygotic twins and a 33% concordance for dizygotic twins, suggesting a role for genetic factors. Cardon, Smith, Fulker, Kimberling, Pennington and De Fries (1994), and Grigorenko (1997) go even further in their research to suggest that dyslexia is controlled by chromosome six. However this does not explain how new instances of dyslexia occur in families without and past history or why not everyone in a family with dyslexic history has this condition. The only reliable conclusion that can be drawn, is that genetics appear to play a part in the causation of dyslexia, but they cannot fully explain it. A combination of factors, need to exist for dyslexia to manifest itself.

Miles, L.E. (1974) in Hornsby (1992), Overcoming dyslexia, London: Optima

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