Dr. Jeff Hersh: Explaining sickle cell disease

Dr. Jeff Hersh

Q: My cousin went to the ER in pain from sickle cell disease and had to be admitted. What is sickle cell and how does it cause pain?

A: We all have two copies of each gene, one inherited from our mother and one from our father. Each gene is a strand of DNA, broken up into three nucleotides making up a codon. The codons define in detail the specific amino acids that are used to build the proteins that make up our cells, hormones, enzymes, etc.

Some people have an incorrect nucleotide in a codon of their hemoglobin gene. For example, HbS (sickle hemoglobin) has a codon that specifies valine instead of glutamine in the sixth position on the hemoglobin's beta globin chain.

In sickle cell disease, both hemoglobin genes are HbS (one from each parent). People with one HbS gene and one normal gene have sickle cell trait; although this is usually a benign condition it means there is a 50 percent chance of passing the HbS gene to their child.

HbS is very common in African Americans; one of every 12 carries the gene and one in 400 has sickle cell disease. Overall, about 100,000 Americans have sickle cell disease and two million have sickle trait.

Sickle cell disease may cause red blood cells to become rigid and change into a sickle shape -- hence the name of the disease -- after they deliver the oxygen they carry. This can destroy some of the red blood cells, so anemia and problems from the high turnover of red blood cells -- such as gallbladder disease -- are common.

Furthermore, a rigid, sickle-shaped red blood cells can clog small blood vessels, blocking blood flow. This causes an oxygen-deprived state in the tissues or organs these vessels nourish (ischemia), possibly leading to temporary or even permanent damage.

Symptoms and complications of sickle cell disease depend on where the vessel blockage occurs. Ischemia to muscle or bone can cause pain, the most common symptom in sickle cell disease. Stroke, kidney failure, infections (from the spleen becoming non-functional), as well as lung, eye, heart and bone complications can also occur. Many other conditions and complications are possible as well.

With the high prevalence of sickle cell disease and its many possible complications, it is not surprising that it accounts for more than 200,000 visits to emergency rooms every year. Two-thirds of these are for painful crises: about 10 percent for chest pain, 5 percent for fever or infections and 5 percent for breathing problems. Between a quarter and a third of these patients require hospital admission for further care.

Newborns in all 50 states are now screened for sickle cell disease, so it is most often diagnosed at birth. Sickle cell disease patients should be followed by a health care provider with expertise in monitoring and treating it since early interventions can minimize -- or at least delay -- some of the complications.

In addition to regular checkups (including close monitoring of blood pressure and eye exams), periodic testing of sickle cell disease patients is needed to help indentify developing problems. Blood tests (for example, to check kidney function), heart echocardiograms and other tests may be indicated.

Routine vaccinations and immunizations against certain infections (such as pneumococcal disease) should be given to all sickle cell disease patients. Certain vitamins - such as folate - are also indicated. Chronic antibiotic therapy is recommended for all sickle cell disease children until at least age 5 to minimize infections; some patients may continue this treatment longer, even their whole lives.

Many treatment decisions need to be made on a case-by-case basis. For example, the 10 percent of sickle cell disease patients who have a stroke by age 20 and the 25 percent who have a stroke by age 40 may have their risk of subsequent strokes decreased by receiving periodic blood transfusions. Certain medications -- such as hydrea -- can decrease the frequency of painful crises in some patients. Kidney failure may require dialysis, and other conditions may require other treatments.

The necessary evaluation for acute flare-ups of sickle cell disease patients depends on their specific symptoms. Blood tests, X-rays and many other tests may be required.

Despite appropriate care, life expectancy for sickle cell disease patients is reduced. However, there is hope for the future. Active research on gene therapy approaches, bone marrow transfusions and new medications may develop improved treatments for the many people who suffer from this common disease.

Massachusetts-based Jeff Hersh, Ph.D., M.D., F.A.A.P., F.A.C.P., F.A.A.E.P., can be reached at