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Dyslexia is increasingly believed to be a disorder that has a genetic and biological origin ; a deficit in phonological ( language sound ) processing is thought to be the causal link between brain abnormality and reading difficulties . It is a disorder of older patients , more often affecting men than women ages 50-60 . " The 1998 classification system requires that a problem cause personal distress to be defined as a disorder , but Tiefer and others note that the JAMA study only asked about women 's experiences , not whether women were distressed . Sarcoidosis is a disorder that affects many body systems . Twenty-five to 30 percent of people with PRS have Stickler 's Syndrome , a disorder that can affect the joints , eyes , palate , heart , and hearing .