An idiopathic disease is any disease with an unknown cause or mechanism of apparent spontaneous origin. From Greek ἴδιος idios "one's own" and πάθος pathos "suffering", idiopathy means approximately "a disease of its own kind". For some medical conditions, one or more causes are somewhat understood, but in a certain percentage of people with the condition, the cause may not be readily apparent or characterized. In these cases, the origin of the condition is said to be idiopathic. With some other medical conditions, the root cause for a large percentage of all cases has not been established—for example, focal segmental glomerulosclerosis or ankylosing spondylitis; the majority of these cases are deemed idiopathic. Certain medical conditions, when idiopathic, notably some forms of epilepsy and stroke, are preferentially described by the synonymous term of cryptogenic.