Texas Education Code (TEC) §38.003 Defines dyslexia and related disorders in the following way:
Dyslexia is a disorder of constitutional origin manifested by difficulty in learning to read, write, or spell, despite conventional instruction, adequate intelligence, and sociocultural opportunity. “Related disorders” include disorders similar to or related to dyslexia, such as developmental auditory imperceptions, dysphasia, specific developmental dyslexia, developmental dysgraphia, and developmental spelling disability.
Taken from: The Texas Dyslexia Handbook