Dyscalculia is a learning disability affecting a person's ability to understand and manipulate numbers. Like dyslexia, it can be caused by visual perception. Some even perceieve it to be a variation of dyslexia. Dyscalculia affects people across the whole IQ range, but means they have problems with mathematics, time, measurement, etc. The disability is not rare and many of those who have Dyslexia or Dyspraxia also have the disability. There is some evidence to indicate it may be hereditary.