Your genetic material controls every detail of your physical being. Within your cells are microscopic structures called chromosomes; people normally have 46 chromosomes. Each chromosome contains thousands of genes, which control everything from your eye color to your immune responses. The Human Genome Project estimates there are 20,000 to 25,000 human genes. An inherited abnormality in just one of your genes may cause a genetic disorder.
Down Syndrome
You have two copies of each of the 23 chromosomes of the human genome. Down syndrome occurs when a child has an extra copy of chromosome 21. Down syndrome causes distinctive physical characteristics such as small stature, short neck, flat face, upward slanting eyes and decreased muscle tone. People with Down syndrome have cognitive impairment, which typically varies from mild to moderate. Down syndrome increases the risk of certain medical conditions, including hearing problems, heart defects, thyroid disorders, cataracts and celiac disease. The National Institute of Child Health and Human Development reports approximately 1 out of every 800 babies born in the United States has Down syndrome.
Hemophilia
Hemophilia is an inherited bleeding disorder. Different gene abnormalities cause different types of hemophilia. The most common form is classic hemophilia, or hemophilia A. A less common form of the disorder is hemophilia B, also known as Christmas disease. Because of the pattern of inheritance, hemophilia occurs almost exclusively in males. The Centers for Disease Control and Prevention states 1 out of every 5,000 male babies born in the United States has hemophilia. People with hemophilia are prone to easy bruising, spontaneous bleeding, and bleeding into the joints. Injuries that might cause uncontrollable bleeding are a serious concern for hemophiliacs. A head injury with bleeding into the brain can be life threatening.
Cystic Fibrosis
Cystic fibrosis (CF) is a genetic disorder of the secretory glands. The secretory glands make sweat, tears, digestive fluids and mucus. CF is caused by an abnormality in the CFTR gene located on chromosome 7. Both copies of the CFTR gene are abnormal in a person with CF. The gene abnormality causes unusually thick secretions. Thick mucus in the lungs causes a buildup of phlegm, coughing and frequent bacterial infections. Thick digestive juices do not flow well, causing decreased digestion and absorption of nutrients from the intestine. Children with CF often have delayed growth and low body weight because of their digestive problems. The National Heart, Lung and Blood Institute (NHLBI) estimates that 30,000 Americans have CF. CF is most commonly seen in people of Northern European descent.
Sickle Cell Disease
An inherited abnormality of the hemoglobin gene (HBB) on chromosome 11 causes sickle cell disease. Both copies of the HBB gene are abnormal in sickle cell disease. The gene abnormality causes structurally defective hemoglobin--the substance in red blood cells that carries oxygen to the body. The defective hemoglobin distorts the red blood cells into a sickle shape. The sickled cells have a shorten lifespan in the circulation, leading to chronic anemia. Additionally, sickled cells often clog small blood vessels causing episodes of severe pain called sickle cell crises. NHLBI estimates 70,000 to 100,000 Americans have sickle cell disease. African Americans are most frequently affected.
References
- National Institute of Child Health and Human Development: Facts about Down Syndrome
- National Down Syndrome Society: Down Syndrome Fact Sheet
- Centers for Disease Control and Prevention: Hemophilia Facts
- National Heart, Lung and Blood Institute: Hemophilia
- Cystic Fibrosis Foundation: About Cystic Fibrosis
