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Professional boxers are at higher risk of developing Parkinson disease from repeated blows to the head. Muhammed Ali has Parkinson disease from many years of head injuries.

heavyweight champ Mohammed Ali, who suffers from the disorder (fig. 11D). The chemical exposures and injury may increase the rate of oxygen free-radical formation, which damages brain tissue.

Clues to the cause of Parkinson disease may come from genetics. Researchers have identified a mutant gene that accounts for the disease in several well-studied, large families. The gene encodes a protein called alpha-synuclein, which is found in the basal nuclei. When abnormal, the protein folds improperly, which may cause deposits to form in the brain. The next step in the research will be to determine whether the brain deposits characteristic of Parkinson disease, called Lewy bodies (fig. 11E), are comprised of mis-folded alpha-synuclein.

Only a small percentage of cases of Parkinson disease are inherited. However, understanding how the symptoms arise in these individuals will provide clues that may eventually help the many others with the disease too. The human genome project will eventually reveal genes that cause or increase the risk of developing Parkinson disease. ■

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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