Genetic disorders are caused by a defect in a gene, which is a specific piece of DNA (the building block of the genetic code) in a specific location on a chromosome. Recessive genetic disorders are diseases that require two defective genes, meaning that each parent has one recessive gene (called a carrier), and there is a 25 percent chance of their child receiving both recessives resulting in the disorder. The majority of the recessive disorders are autosomal recessive, meaning that the defective gene lies in one of the 22 non-sex-linked chromosomes.
Cystic Fibrosis
Cystic fibrosis (CF), a chronic disease that is inherited, affects more than 30,000 people in the United States, as reported by the Cystic Fibrosis Foundation. CF is an autosomal recessive disease that occurs most frequently in people of Northern European decent. The defective gene, called the CFTR, produces a protein that does not correctly regulate the movement of salts and water in and out of cells. Therefore, those with CF have thick, sticky mucus that can lead to chronic lung infections and shortness of breath.
Although at one time CF was considered a fatal disease, advancements in diagnosis and treatment have helped to increase life expectancy.
Sickle Cell Anemia
Sickle cell anemia, also an autosomal recessive disorder, is more prevalent in those of African American decent because one in 12 are carriers of the disease, according to the National Heart Lung and Blood Institute. The defective gene causes the normal round, doughnut-shaped red blood cells to instead be shaped like a "C" because the hemoglobin (the protein that carries the oxygen) is abnormal. The red blood cells then become sticky, causing poor blood flow that can result in pain, infections or organ damage.
In addition, the sickle red blood cells only live for 10 to 20 days, while normal red blood cells live for up to 120 days. Because the sickle cells die so rapidly, the body cannot keep up with replenishing them, which results in anemia (low red blood cell count).
Tay-Sachs Disease
Tay-Sachs disease is an autosomal recessive disease caused by a defect in the HEXA gene, which is the gene responsible for instructing the body to produce beta-hexosaminidase A. This enzyme is responsible for breaking down fatty substances in the brain. People with Tay-Sachs disease therefore have a build-up of this fatty substance, which then becomes toxic and kills nerve cells. This leads to a deterioration in both mental and physical abilities and may result in vision loss, hearing loss and the inability to swallow. The outlook for patients with Tay-Sachs disease is grim because most die in early childhood.
