What Causes Sickle Cell Anemia?
Sickle cell anemia is an inherited disease. People who have the disease inherit two copies of the sickle cell gene—one from each parent.
The sickle cell gene causes the body to make abnormal hemoglobin. Hemoglobin is an iron-rich protein in red blood cells. It carries oxygen from the lungs to the rest of the body.
In sickle cell anemia, the hemoglobin sticks together after it delivers oxygen to the body's tissues. These clumps of hemoglobin are like liquid fibers. They cause the red blood cells to become stiff and have a sickle, or crescent, shape.
Sickle cells tend to stick together or to blood vessel walls, causing them to get caught in the blood vessels. (Other cells also may play a role in this process.)
Two copies of the sickle cell gene are needed for the body to make the abnormal hemoglobin found in sickle cell anemia.
Sickle Cell Trait
If you inherit one copy of the sickle cell gene (from one parent), you won't have sickle cell anemia. Instead, you'll have sickle cell trait.
People who have sickle cell trait usually have no symptoms and lead normal lives. However, some people may have medical complications.
People who have sickle cell trait also can pass the sickle cell gene to their children. The following image shows how two parents who have sickle cell trait can pass the sickle cell gene to their children.
When both parents have a normal gene and an abnormal gene, each child has a 25 percent chance of inheriting two normal genes; a 50 percent chance of inheriting one normal gene and one abnormal gene; and a 25 percent chance of inheriting two abnormal genes.
Signs and Symptoms of Sickle Cell Anemia
The signs and symptoms of sickle cell anemia vary. Some people have mild symptoms. Others have very severe symptoms and often are hospitalized for treatment.
Sickle cell anemia is present at birth, but many infants don't show any signs until after 4 months of age.
The most common signs and symptoms are linked to anemia and pain. Other signs and symptoms are linked to the disease's complications.
Signs and Symptoms Related to Anemia
The most common symptom of anemia is fatigue (feeling tired or weak). Other signs and symptoms of anemia may include:
- Shortness of breath
- Coldness in the hands and feet
- Paler than normal skin or mucous membranes (the tissue that lines your nose, mouth, and other organs and body cavities)
Signs and Symptoms Related to Pain
Sudden pain throughout the body is a common symptom of sickle cell anemia. This pain is called a sickle cell crisis. Sickle cell crises often affect the bones, lungs, abdomen, and joints.
These crises occur when sickled red blood cells form clumps in the bloodstream. (Other cells also may play a role in this clumping process.) These clumps of cells stick to small blood vessels and block blood flow to the limbs and organs. This can cause pain and organ damage.
The pain from sickle cell anemia can be acute or chronic, but acute pain is more common. Acute pain is sudden and can range from mild to very severe. The pain usually lasts from hours to as long as a week or more.
Chronic pain often lasts for weeks or months. Chronic pain can be hard to bear and mentally draining. This pain may limit your daily activities.
Almost all people who have sickle cell anemia have painful crises at some point in their lives. Some have these crises less than once a year. Others may have crises once a month or more.
Many factors can play a role in sickle cell crises. Often, more than one factor is involved and the exact cause isn't known.
You can control some factors. For example, the risk of a sickle cell crisis increases if you're dehydrated (your body doesn't have enough fluids). Drinking plenty of fluids can lower the risk of a painful crisis.
You can't control other factors, such as infections.
Painful crises are the leading cause of emergency room visits and hospital stays for people who have sickle cell anemia.
Complications of Sickle Cell Anemia
Sickle cell crises can affect many parts of the body and cause many complications.
Sickle cells can block the small blood vessels in the hands and feet in children (usually those younger than 4 years of age). This condition is called hand-foot syndrome. It can lead to pain, swelling, and fever.
Swelling often occurs on the back of the hands and feet and moves into the fingers and toes. One or both hands and/or feet may be affected at the same time.
The spleen is an organ in the abdomen. Normally, it filters out abnormal red blood cells and helps fight infections. In some cases, the spleen may trap red blood cells that should be in the bloodstream. This causes the spleen to grow large and leads to anemia.
If the spleen traps too many red blood cells, you may need blood transfusions until your body can make more cells and recover.
Both children and adults who have sickle cell anemia may have a hard time fighting infections. This is because sickle cell anemia can damage the spleen, an organ that helps fight infections.
Infants and young children who have damaged spleens are more likely to get serious infections that can kill them within hours or days. Bloodstream infections are the most common cause of death in young children who have sickle cell anemia.
Medicines and vaccines can help prevent severe illness and death. For example, vaccines are available for infections such as meningitis, influenza, and hepatitis.
Getting treatment right away for high fevers (which can be a sign of a severe infection) also helps prevent death in infants and children who have sickle cell anemia.
Acute Chest Syndrome
Acute chest syndrome is a life-threatening condition linked to sickle cell anemia. This syndrome is similar to pneumonia. An infection or sickle cells trapped in the lungs cause acute chest syndrome.
People who have this condition often have chest pain, shortness of breath, and fever. They also often have low oxygen levels and abnormal chest x ray results.
Damage to the small blood vessels in the lungs makes it hard for the heart to pump blood through the lungs. This causes blood pressure in the lungs to rise.
Increased blood pressure in the lungs is called pulmonary hypertension (PH). Shortness of breath and fatigue are the main symptoms of PH.
Delayed Growth and Puberty in Children
Children who have sickle cell anemia often grow more slowly than other children. They may reach puberty later. A shortage of red blood cells causes the slow growth rate. Adults who have sickle cell anemia often are slender or smaller in size than other adults.
Two forms of stroke can occur in people who have sickle cell anemia. One form occurs if a blood vessel in the brain is damaged and blocked. This type of stroke occurs more often in children than adults. The other form of stroke occurs if a blood vessel in the brain bursts.
Either type of stroke can cause learning problems and/or lasting brain damage, long-term disability, paralysis (an inability to move), or death.
Sickle cells also can affect the small blood vessels that deliver oxygen-rich blood to the eyes. Sickle cells can block these vessels or cause them to break open and bleed. This can damage the retinas—thin layers of tissue at the back of the eyes. The retinas take the images you see and send them to your brain.
This damage can cause serious problems, including blindness.
Males who have sickle cell anemia may have painful, unwanted erections. This condition is called priapism (PRI-a-pizm). It happens because the sickle cells block blood flow out of an erect penis. Over time, priapism can damage the penis and lead to impotence.
When red blood cells die, they release their hemoglobin. The body breaks down this protein into a compound called bilirubin. Too much bilirubin in the body can cause stones to form in the gallbladder, called gallstones.
Gallstones may cause steady pain that lasts for 30 minutes or more in the upper right side of the belly, under the right shoulder, or between the shoulder blades. The pain may happen after eating fatty meals.
People who have gallstones may have nausea (feeling sick to the stomach), vomiting, fever, sweating, chills, clay-colored stools, or jaundice (a yellowish color of the skin or whites of the eyes).
Ulcers on the Legs
Sickle cell ulcers (sores) usually begin as small, raised, crusted sores on the lower third of the leg. Leg sores may occur more often in males than in females. These sores usually develop in people who are aged 10 years or older.
The cause of sickle cell ulcers isn't clear. The number of ulcers can vary from one to many. Some heal quickly, but others persist for years or come back after healing.
Multiple Organ Failure
Multiple organ failure is rare, but serious. It happens if you have a sickle cell crisis that causes two out of three major organs (lungs, liver, or kidneys) to fail. Often, multiple organ failure occurs during an unusually severe pain crisis.
Symptoms of this complication are fever, rapid heartbeat, problems breathing, and changes in mental status (such as sudden tiredness or confusion).