Sickle cell is a disease where a simple mutation in the hemoglobin gene creates a mutant hemoglobin that deforms blood cells into sickle shaped ones when the oxygen levels are low (like when they’re unloading oxygen in tissues). They can then clog up the blood vessels leading to pain and tissue damage.
Sickle cell usually shrinks the spleen away to nothing early in life. Thus, sickle patients are more vulnerable to infections, particularly encapsulated organisms like strep pneumonia, H. Influenzae, and N. meningitidis. This can occur with overwhelming sepsis. Salmonella can be more dangerous for sickle patients, who can classically get osteomyelitis from it (bone infection) which is otherwise very rare. Prevention consists of vaccinations, early treatment, and may also include long term preventive antibiotics.
Sickle cell can also cause stroke. It damages many organs (impairing the kidney’s ability to concentrate urine; infarcting (death from low oxygen/blood flow) areas of bone marrow, etc–it’s how the spleen is lost too). When this happens in the brain you get permanent neurologic damage (mild to severe). A quarter of sickle patients get a stroke by mid life. Perhaps related, epilepsy is more common. Treatment after stroke consists of transfusion regimens to replace the sickle hemoglobin.
When bone is infarcted, it’s very painful, but another complication that can occur is fat embolism. The fat that’s naturally in marrow can loosen and travel through the veins into the heart and get pumped into the lungs, where it can trigger respiratory failure and severe lung injury.
Lung injury can be acute or chronic–acute injury happens is called “acute chest syndrome,” and is treated with oxygen, antibiotics (because we usually can’t tell whether it’s pneumonia or not, or both, or something else like infarction or fat embolism), and supportive care, and often exchange transfusions (replacement of sickle blood with donated blood, instead of just adding donated blood to the patient). Chronic lung injury from sickle cells can cause fibrotic lungs, or high pressure on the lung side of the circulation (pulmonary hypertension), which can cause the right side of the heart to give out from having to pump against the higher pressure (cor pulmonale).
From pumping harder to compensate for anemia, hearts enlarge and can malfunction–congestive heart failure. Also, heart attacks are more common.
Liver injury can occur, and be very serious. This can be from infarction of liver, stones that form from pigment related to high blood turnover, which can block bile ducts and cause liver failure or infections.
Kidneys can be partially infarcted, or parts can die near the collection system (papillary necrosis). They can gradually give out leading to renal failure which is fatal unless treated with dialysis or transplantation (and there can be fatal complications of either of those treatments). Sickle predisposes to a type of cancer called renal medullary carcinoma, which happens almost only in sickle patients; most kidney cancers are renal carcinomas.
Lastly, sickle requires treatment, so patients can be injured by treatments. Transfusions can cause infection like hepatitis C, or bacterial or parasitic infections. They can cause iron overload, allergic reactions, blood breakdown (hemolysis) which can be dangerous or fatal, or cause immunologic lung injury (transfusion related acute lung injury or TRALI). They can simply cause volume overload especially if the heart is weak (transfusion related circulatory overload, TACO). Sickle patients also require lots of opiates (morphine, dilaudid, etc) for painful crisis or chronic pain, and they can cause abuse or overdose problems, even accidental ones.
It’s a difficult life, and it’s all due to bad luck–bad luck inheriting genes we think got spread around in African populations because having one hit is partially protective against the blood infection malaria. But sickle disease (two hits, or one hit and something else like S-C disease) causes a lot of suffering in places where there is no malaria, of course.