The various known accelerated aging conditions can teach us about the mechanisms of normal aging. Here, USA Today looks at Down syndrome in this context: "People with Down syndrome tend to age prematurely as they develop conditions such as menopause, brittle bones, arthritis, hearing loss, wrinkles and sagging skin about two decades earlier than usual ... Yet researchers suspect that this unique genetic profile also protects people with Down syndrome from many common ailments. ... most adults with Down syndrome are overweight with high cholesterol. Despite these risks, however, people with Down syndrome virtually never develop high blood pressure, heart attacks or hardening of the arteries ... with the exception of a rare pediatric leukemia, even elderly adults with Down syndrome rarely develop solid tumors, such as those of the breast or lung. ... Although people with Down syndrome are at higher risk for cataracts, they rarely develop a form of blindness called macular degeneration, caused by an overgrowth of blood vessels in the retina ... Doctors suspect that the same genes [duplicated in Down syndrome] that restrict blood vessel growth in tumors may also prevent abnormal blood vessel growth in the eye. ... Adults with Down syndrome appear to develop the brain plaques and tangles characteristic of Alzheimer's disease very early in life ... By age 40 to 45, virtually everyone with Down syndrome has these plaques and tangles, [and by] age 65, up to 75% of people with Down syndrome have dementia."