Dyslexia is regarded as a neurobiological condition that is genetic in origin. This means that individuals can inherit this condition from a parent and it affects the performance of the neurological system (specifically, the parts of the brain responsible for learning to read). It's not uncommon for a child with dyslexia to have an immediate family member who also has this condition. Also, it's not unusual for two or more children in a family to have this type of learning disability. It may be hard to know if an older relative has dyslexia if he left school before the condition was diagnosed. If you have relatives who "hated school," who were "drop-outs," or who left school early to join the armed forces or get a job, these folks may have been dyslexic. Without the proper help, school could have become a very frustrating and unrewarding place for them.
Unfortunately, unless children get the right kind of services early in life, very young poor readers often grow up to be poor readers as adults. The good news is that if children with dyslexia are given proper instruction, particularly in the very early grades, the more likely it is that they will have fewer or milder difficulties later in life. In order to be successful readers, young children with dyslexia need to be exposed to a systematic, relentless program of early instruction designed to help them make the associations between letters and the sounds they make.
For more information about dyslexia, read " When Reading is Rough" or visit the website of the International Dyslexia Association at http://www.interdys.org.