Said to be a neurological disorder with biochemical and genetic markers. Dyslexia was originally defined as a difficulty with reading and writing that could not be explained by general intelligence. One diagnostic approach is to compare their ability in areas such as reading and writing to that which would be predicted by his or her general level of intelligence, but some would say that it is not certain that intelligence should be a predictor of reading or writing ability; and also that the causes, effects and treatments of reading disabilities may be similar for all levels of intelligence.