(l) The cause of the disease is unknown.
(2) It has a hereditary nature, and appears in
both sexes. It can be transmitted by both
male and female.
(3) There is a tendency to increase in severity
with advancing years.
(4) Recovery is rare.
(5) It is rarely a primary cause of death.
(6) There is no satisfactory treatment. Treatment
at present is purely symptomatic