All people with dyslexia do not have the same underlying problem. The core problem of dyslexia is thought to be phonemic awareness, so understanding the correspondence of letters with their sounds, but there are also a number of other processes that are involved in reading, such as, working memory, linguistic retrieval and general language comprehension. For example, 2 people who have reading problems might have different underlying problems that lead to the same difficulty with reading. That's why it's really important when a child has a reading problem, to have a proper evaluation so that you know which components of the reading process are weak for that particular child.