According to Sally Shaywitz in Overcoming Dyslexia, dyslexia is a problem that intelligent people have with reading.
Dyslexia is very common. It is the reason why many are not able to read at grade level, despite regular reading instruction.
It has nothing to do with how smart a person is.
Words have sounds the come apart. People with dyslexia have trouble pulling the sounds apart. Instead of hearing three sounds in a word, a dyslexic may hear only one or two.
For people who have dyslexia, the regular route to reading is blocked. They have to take alternative routes: bumpier and slower. It will take longer and it is more work.
Dyslexia is highly treatable and can be helped with the right teaching. Orton-Gillingham based programs are the best.
After a dyslexic student learns to read with an Orton-Gillingham based program, their brain scan (as seen by an MRI during a reading task) will be very similar to that of a non-dyslexic’s brain scan.