Sickle cell disease (SCD) is a genetic blood disorder that affects millions of people globally, primarily those of African, Mediterranean, and South Asian descent. It involves atypical hemoglobin, a protein within red blood cells responsible for carrying oxygen throughout the body. This condition causes red blood cells to become misshapen and rigid, which can lead to various health problems affecting nearly every organ system. The disease is a lifelong illness, but treatments are available to manage symptoms and improve longevity.
Red Blood Cell Alterations
Sickle cell disease originates from a genetic mutation that leads to the production of an abnormal form of hemoglobin, known as hemoglobin S (HbS). Unlike normal, round, and flexible red blood cells, those containing HbS become stiff, sticky, and crescent- or “sickle”-shaped, especially under low oxygen conditions. This change in shape and flexibility hinders their ability to move easily through blood vessels.
The sickled red blood cells also have a significantly shorter lifespan compared to healthy red blood cells. While normal red blood cells typically circulate for about 120 days, sickled cells often die within 10 to 20 days. This premature destruction of red blood cells results in a constant shortage of healthy cells, a condition known as chronic hemolytic anemia. This anemia contributes to overall fatigue and reduces the body’s capacity to transport oxygen effectively.
Impaired Blood Flow and Oxygen Transport
The altered shape and rigidity of sickle red blood cells directly impact the circulatory system. These misshapen cells do not flow smoothly and can aggregate, blocking small blood vessels, a process termed vaso-occlusion. This blockage impedes the delivery of blood to tissues and organs throughout the body.
When blood flow is obstructed, tissues are deprived of oxygen, leading to a condition called ischemia. Prolonged or severe ischemia can cause tissue damage and even tissue death, known as infarction. Chronic hemolytic anemia also diminishes the body’s oxygen-carrying capacity. These combined mechanisms of vaso-occlusion and chronic anemia contribute to the widespread effects of sickle cell disease, including pain and organ damage.
Impact on Body Systems
Chronic issues from impaired blood flow and oxygen deprivation can lead to long-term damage across multiple body systems. The spleen, an organ that filters blood and fights infections, is particularly susceptible. Sickled cells can get trapped in the spleen, causing it to enlarge initially, but repeated damage often leads to functional autosplenectomy, where the spleen becomes scarred and non-functional early in life.
Kidneys can also suffer chronic damage. Reduced blood flow and oxygen can impair kidney function, leading to kidney disease and kidney failure. The lungs may develop complications such as pulmonary hypertension (high blood pressure in the lung arteries) and chronic lung disease due to persistent microvascular obstruction.
The brain is vulnerable to stroke, both overt and silent, when sickled cells block blood flow to brain tissue. This can result in cognitive impairments and neurological deficits. Bones and joints are affected by avascular necrosis, which is the death of bone tissue due to a lack of blood supply, frequently occurring in the hips and shoulders, and can also contribute to chronic bone pain.
Retinopathy and vision loss can occur as blood vessels supplying the eyes become blocked by sickled cells. The heart may experience enlargement and potential heart failure due to the increased workload from chronic anemia. Liver complications, including blood congestion and iron overload (often from repeated blood transfusions), are also observed.
Frequent Health Complications
A range of acute and recurring health complications are often experienced. Pain crises, or vaso-occlusive crises, are common and debilitating. These episodes involve severe pain in various body parts due to blocked blood vessels and tissue ischemia. The intensity and duration of these crises can vary.
Acute Chest Syndrome (ACS) is a serious lung complication, characterized by chest pain, fever, and difficulty breathing, resembling pneumonia. It is a medical emergency caused by vaso-occlusion within the pulmonary vasculature and is a leading cause of hospitalization and mortality in SCD. Increased susceptibility to bacterial infections is a concern, particularly in early childhood, largely due to the compromised function of the spleen. This heightened risk includes infections such as pneumonia, meningitis, and bloodstream infections.
Leg ulcers, painful open sores on the lower legs, frequently develop, typically appearing between 10 and 50 years of age. These ulcers are linked to poor blood circulation and inflammation. Gallstones are also common due to the rapid breakdown of red blood cells, which releases excess bilirubin that can form stones in the gallbladder.
Priapism, a painful and prolonged erection, can occur from sickled cells blocking blood flow in the penis. Delays in growth and development are common, with children and adolescents experiencing slower growth and delayed puberty. This is mainly attributed to chronic anemia and increased energy demands.