There are risk factors that have been established (trauma, family history, obesity,and older age), but we don't know what actually causes it.
Zikhona izinto ezibubungozi baso ezifunyanisiweyo (ukwenzakala, imbali yosapho, ukutyeba ngokugqithisileyo kunye nokwaluphala), kodwa eyona nto ibangela esi sifo asiyazi.