 The cause of dyslexia is believed to involve both genetic and environmental factors . Some cases run in families . It often occurs in people with attention deficit hyperactivity disorder ( ADHD ) and is associated with similar difficulties with numbers . It may begin in adulthood as the result of a traumatic brain injury , stroke , or dementia . The underlying mechanisms are problems within the brain 's language processing . Dyslexia is diagnosed through a series of tests of memory , spelling , vision , and reading skills . Dyslexia is separate from reading difficulties caused by insufficient teaching ; or either hearing or vision problems . 
