British Dyslexia Association Definition
Dyslexia is a developmental disorder which results in difficulties in learning to read, write and spell. Short-term memory, mathematics, concentration, personal organization and sequencing may also be affected. Dyslexia usually arises from a weakness in the processing of language-based information. Biological in origin, it tends to run in families, but environmental factors also contribute. Dyslexia can occur at any level of intellectual ability. It is not the result of poor motivation, emotional disturbance, sensory impairment or lack of opportunities, but may occur alongside any of these. The affects of dyslexia can be largely overcome by skilled specialist teaching and the use of compensatory strategies (emphasis added).
International Dyslexia Association Definition
Dyslexia is a neurologically-based, often familial, disorder that interferes with the acquisition and processing of language. Varying in degrees of severity, dyslexia causes difficulty in receptive and expressive language. Symptoms can include difficulty in phonological processing, reading, writing, spelling, handwriting, and sometimes arithmetic. Dyslexia is not the result of lack of motivation, sensory impairment (such as eyesight or hearing), inadequate instructional or environmental opportunity, or other limiting conditions. But dyslexia may occur together with those conditions. Although dyslexia is lifelong, individuals with dyslexia frequently respond successfully to timely and appropriate interventions.