Certain disorders have some of the same effects as aging. Scientists study what happens in these disorders to try to learn what causes aging. For example, they identify the genes that are defective in these disorders and compare them with the same genes in older people.
(See also Overview of Aging.)
In progeroid syndromes, the aging process is greatly accelerated. Affected children develop all of the external signs of old age, including baldness, hunched posture, and dry, inelastic, and wrinkled skin. However, in contrast to normal aging, the ovaries or testes are inactive, resulting in sterility. Females have no menstrual periods. Affected children are unusually short. Thus, progeroid syndromes are not an exact model of accelerated aging.
There are several progeroid syndromes. In Hutchinson-Gilford syndrome and Werner syndrome, the central nervous system and therefore the ability to do many daily activities are largely unaffected unless a stroke occurs.
Hutchinson-Gilford syndrome begins in early childhood. It is caused by a genetic abnormality but is usually not inherited. That is, the genetic abnormality (mutation) occurs on its own. It causes inelastic and wrinkled skin, baldness, and other problems usually associated with aging (such as disorders of the heart, kidneys, and lungs and osteoporosis). The body does not grow normally and thus appears too small for the head. Most children with Hutchinson-Gilford syndrome die in their teens. The cause is usually a heart attack or stroke. The mutation that causes this disorder has been identified, and a clinical trial of an inhibitor of the faulty gene has had encouraging results.
Werner syndrome, a hereditary syndrome, begins in adolescence or early adult life. It causes inelastic and wrinkled skin, baldness, and problems associated with aging, including
In contrast to progeroid syndromes, Down syndrome greatly impairs the central nervous system. It usually causes intellectual disability and, later in life, symptoms of Alzheimer disease. Also, brain tissue, obtained during an autopsy and examined under a microscope, has the same type of degeneration that is seen in people with Alzheimer disease.