Dyslexia is believed to be caused by the interaction of genetic and environmental factors. Some cases run in families. Dyslexia that develops due to a traumatic brain injury, stroke, or dementia is called "acquired dyslexia". The underlying mechanisms of dyslexia are problems within the brain's language processing. Dyslexia is diagnosed through a series of tests of memory, vision, spelling, and reading skills. Dyslexia is separate from reading difficulties caused by hearing or vision problems or by insufficient teaching or opportunity to learn.