Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Dyslexia

What Is It?

Dyslexia is the most common learning disability. Someone with dyslexia has trouble reading even though he or she has the intelligence and motivation needed to learn to read. Although people with dyslexia have trouble understanding words they read, they usually can understand the same words when they are read aloud by another person.

Researchers don't know exactly what causes dyslexia, but they think a problem during development may affect the way the brain processes information. They also believe that genetics (inheritance) plays a part. Although a gene for dyslexia has not been found, dyslexia does tend to run in families. Dyslexia is not caused by a physical disability, such as vision or hearing problems. Many people with dyslexia have average or above average intelligence. Basically, the brains of people with dyslexia have a hard time receiving, organizing, remembering or using information.

In the United States, approximately 5% to 10% of the population probably has some sort of dyslexia.