Duchenne muscular dystrophy is a very common (1 out of 3,500 male births) disorder that results from the presence of an abnormal muscle protein. Muscles of young boys gradually deteriorate until even the muscles required for normal respiration become ineffective. These boys usually die of pulmonary infections before the age of 20.
Hemophilia A is seen in 1 out of 10,000 male births. The defective protein (coagulation factor VIII) is required for normal blood clotting. Affected individuals require injections of the protein or transfusion of blood products to prevent internal bleeding. Until recently, when the genetically engineered protein became available, many of these individuals contracted viral hepatitis or AIDS as a result of their many transfusions.
Familial hypercholesterolemia (FHC) is a fairly common disorder (1 out of 500 individuals are heterozygous). The affected gene codes for a protein which is found on the external surface of most of the body's cells. This so-called receptor protein mediates the uptake of cholesterol into the cells. This cholesterol is transported in the blood by a lipoprotein called LDL. When LDL can't get into cells, it increases to high levels in the blood. High levels of LDL (with its associated cholesterol) increases the risk of developing arteriosclerosis and coronary artery disease. Homozygous individuals (about 1 out of 1,000,000 births) have extremely high levels of LDL and develop coronary heart disease in childhood.
Huntington's disease is a neurodegenerative disease which doesn't appear until approximately age 30. It has recently become possible to test for the presence of the abnormal gene at any age. This information may be of great interest to individuals who know they will develop the disease later in life since they may wish to modify their plans in regards to marriage and childbearing. Other individuals prefer not to know as the prognosis is grim and there is no effective treatment.
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