The cause is unknown. For some reason the body's immune system acts as if it needs to fight an invader, in a way. You can't get it from or give it to others according to known research. Through the media we know that some prominent Dutchmen have Sarcoidosis, like our Dutch crownprince Willem-Alexander. Nobody can be cured from this disease, sometimes nature itself takes care of a relapse for some time.
Sarcoidosis sometimes mimics other diseases and vice versa, so it is hard to trace.
Genetics seem to be playing a role, in some families it can occur more often. A piece from Dutch NRC paper from 28 June 1997. Holland, they found a gene in APC's responsible for triggering our T-cells. What this means for Sarcoidosis is not known until proper research has been done on this gene. This discovery is also important for research in all immune disorders.