Progeria is premature old age. There are two distinct forms of the condition, both of which are extremely rare. In Hutchinson-Gilford syndrome, aging starts around the age 4, and by 10 or 12, the affected child has all the external features of old age, including gray hair, baldness, and loss of fat, resulting in thin limbs and sagging skin on the trunk and face. There are also internal degenerative changes, such as atherosclerosis (fatty deposits lining the artery walls). Death usually occurs at puberty. Werner’s syndrome, or adult progeria, starts in early adult life and follows the same rapid progression as the juvenile form with individuals developing disorders usually associated with aging as early as in their twenties and thirties. Most individuals with Werner’s syndrome live until their late forties or early fifties. The cause of progeria is unknown.