I think that you may be confusing this diagnosis for dyslexia, which is a developmental reading disorder? Dyslexia results from the inability to process graphic symbols.

The first step to diagnosing dyslexia is to perform a complete medical, developmental, social, and school performance history. Physical and neurologic examinations are also necessary, followed by psychoeducational testing and psychological assessment. Other causes of learning disabilities will need to be ruled out before the diagnosis of DRD can be confirmed.