Dyslexia: A disorder involving difficulties with reading and spelling. The prevalence rate of childhood stuttering in dyslexia is around 30-40%, while in adults the prevalence of dyslexia in adults who stutter is around 30-50%. Causes No single, exclusive cause of developmental stuttering is known. A variety of hypotheses and theories suggest multiple factors contributing to stuttering. Among these is the strong evidence that stuttering has a genetic basis. Children who have first-degree relatives who stutter are three times as likely to develop a stutter. However, twin and adoption studies suggest that genetic factors interact with environmental factors for stuttering to occur, and many stutterers have no family history of the disorder. There is evidence that stuttering is more common in children who also have concurrent speech, language, learning or motor difficulties. Robert West, a pioneer of genetic studies in stuttering, has suggested that the presence of stuttering is connected to the fact that articulated speech is the last major acquisition in human evolution. Another view is that a stutter or stammer is a complex tic. This view is held for the following reasons. It always arises from repetition of sounds or words. Young children like repetition and the more tense they are feeling, the more they like this outlet for their tension – an understandable and quite normal reaction. They are capable of repeating all types of behaviour. The more tension that is felt, the less one likes change. The more change, the greater can be the repetition. So, when a three-year-old finds he has a new baby brother or sister he may start repeating sounds. The repetitions can become conditioned and automatic and ensuing struggles against the repetitions result in prolongations and blocks in his speech. More boys stammer than girls, in the ratio of 3–4 boys : 1 girl. This is because the male hypothalamic-pituitary-adrenal (HPA) axis is more active. As males produce more cortisol than females under the same provocation, they can be tense or anxious and become repetitive. In a 2010 article, three genes were found by Dennis Drayna and team to correlate with stuttering: GNPTAB, GNPTG, and NAGPA. Researchers estimated that alterations in these three genes were present in 9% of those who have a family history of stuttering. For some people who stutter, congenital factors may play a role. These may include physical trauma at or around birth, learning disabilities, and cerebral palsy. In