Dyslexia

Researchers generally agree that genetics play a role in dyslexia. Studies of twins show that if one twin is dyslexic, the other is far more likely to have the disorder. Other studies show that dyslexia, which affects about 8% of the population, tends to run in families. It's common for a child with dyslexia to have a parent or other close relative with the disorder.

A student with dyslexia has difficulty copying words. © Will & Deni McIntyre/Science Source, National Audubon Society Collection/Photo Researchers, Inc. Reproduced with permission.

Because dyslexia affects males far more often than females (the rate is about three to one), investigators are exploring the relationship of male hormones to dyslexia. Several studies indicate that an excess of the male hormone testosterone prior to birth may slow the development of the left side of the fetus's brain. Other researchers argue, however, that those with dyslexia rarely have problems with spoken language, which is also controlled by the left side of the brain and depends on some of the same areas that control reading and writing.