It is clear that dyslexia is very frequently found in families, and is often accompanied by left-handedness somewhere in the family. This does not mean to say that a dyslexic parent will automatically have a dyslexic child, or that a left-handed child will necessarily be dyslexic. But where dyslexia is identified, between a third and a half of children have a history of learning difficulties in their family, and more than half have a family member who is left-handed.
With the technical advances that have come about in brain-scanning in recent years, a lot of research has been carried out examining the brains of dyslexic people. Bunches of cells beneath the surface of the brain have been detected which lie on the surface in the brain of a non-dyslexic person.
These groups of cells ought to have moved to the brain's surface at the time when the brain was developing in the foetus, but failed to make the journey. They are known as 'ectopic' cells (like an ectopic pregnancy, where the egg fails to reach the womb and is fertilized in the Fallopian tube).
These ectopic clusters of cells are mainly found in the left and the front of the brain - the areas which are important for reading and writing. Another area of the brain - the magno-cellular system, which deals with our ability to see moving images - is smaller in the brains of dyslexic people. This makes reading harder, where the brain has to quickly interpret the different letters and words which the eyes see as they scan words and sentences.
With the use of EEG (electroencephalogram), where small electrodes with wires are temporarily attached to the outside of a person's head, it has been possible to see increased brain activity on the right side of the brain when a child is beginning to learn to read. Increased activity is noticeable on the left side in an advanced reader.