Sally Shaywitz, in Overcoming Dyslexia (page 40) reviews research findings and states:

• Understanding that dyslexia reflected a language problem and not a general weakness in intelligence or a primary visual impairment represented a major step forward. Further advances have clarified the nature of the language impairment.
• Dyslexia does not reflect an overall defect and language, rather, a localized weakness within a specific component of the language system: the phonologic module.
• The phonologic module is the language factory, the functional part of the brain were the sounds of language are put together to form words and where words are broken down into the elemental sounds
• We and other dyslexia researchers have found that the phonologic module provides a cogent explanation as to why some very smart people have trouble learning to read --- hence, the paradox