Dyslexia is a common neurologically-based, often familial, disorder which interferes with the acquisition and processing of language. It is estimated that up to one in five people may have varying degrees of this condition. It is characterised by difficulties in receptive and expressive language, including phonological processing, in reading, writing, spelling, handwriting, and sometimes in arithmetic. People with dyslexia are no less intelligent than their peers but may encounter more challenges to achieve the same success or reach the same milestones due to their disorder. Dyslexia makes it difficult for the brain to learn sounds and process written words on the page. Research has debunked the theory that people with dyslexia see letters and words backward, although they may have problems attaching the appropriate labels to written content. Although dyslexia is lifelong, individuals with dyslexia frequently respond successfully to timely and appropriate intervention.