Dyslexia

Dyslexia is a mental learning disability that manifests primarily as a difficulty understanding written language, particularly with reading decoding, reading comprehension, spelling, and reading fluency.

Description
Those who suffer from dyslexia are often unable to view letters in their proper order and some have described seeing "words fly off the page." In mortals, dyslexia is often caused by a dominant right brain, which makes it hard for the brain itself to interpret words.

However, through the Percy Jackson and the Olympians series and beyond, Percy Jackson, along with other demigods, suffer from dyslexia. This is explained to Percy by Annabeth, who informs him that their dyslexia is a result of demigods' brains being "hard-wired" to interpret Ancient Greek, not English. It is usually coupled with ADHD. Like all demigods an English word like "arithmetic" is read as "tahricietm" or similar.

While in actual terms, Dyslexia covers both reading and writing in technical /medical terms, it is limited to reading. The related written learning disorder is Dysgraphia.

Trivia

 * Unlike most demigods, Frank Zhang is not dyslexic since he competed in his school's spelling competitions.