Children with sickle cell disease, an inherited red blood-cell disorder, are living longer, dying less often from their disease and contracting fewer fatal infections than ever before, researchers at UT Southwestern Medical Center at Dallas report.
Their study, which will appear in the June edition of the scientific journal Blood, is the first to evaluate survival rates of children receiving the most modern treatments for sickle cell disease. It's also one of the largest published sickle cell studies to date. Researchers followed more than 700 Dallas-area children with the disease over two decades.
Thirty years ago, only half of children with sickle cell disease were expected to reach adulthood. This new study showed that patients with sickle cell anemia, the severest and most common form of the disease, had a survival rate of 85.6 percent at 18 years old, and patients with milder forms of sickle cell disease had a survival rate of 97.4 percent at 18. Also, 11.5 percent of patients with sickle cell anemia had a stroke by 18 years old. Although this rate remains constant, fewer children are dying as a result of the stroke, researchers said.
"There weren't any modern or contemporary survival data for children with sickle cell until now," said Dr. Charles Quinn, assistant professor of pediatrics and the study's lead author. "Previous survival studies began in the 1970s, and there have been significant advancements made in the medical care of these children since then."
People with sickle cell disease have a genetic error in their hemoglobin, a component of red blood cells. Instead of being soft and round, the red blood cells of a sickle cell patient are inflexible and sickle-shaped, causing blockages in the blood vessels and preventing body tissues from receiving oxygen.
It is estimated that between 60,000 and 70,000 Americans suffer from the disease. The disease is most common among people of African descent. In the United States, it is estimated that 9 percent of African-Americans have the sickle cell trait, and 1 in 600 has sickle cell anemia.
UT Southwestern researchers attribute the improved prognosis to widespread newborn screening that allows physicians to identify the disease early and begin treatment sooner; prophylactic penicillin used to prevent fatal infections; effective, conjugated vaccines for the pneumococcus bacteria, which is responsible for blood infections, pneumonia, meningitis and Hemophilus influenzae type b; and the increased use of disease-modifying therapies such as bone marrow transplants, long-term blood transfusions and the medicine hydroxyurea.
"Research developments during the past several decades have improved the lives of many persons with sickle cell disease," said Dr. George Buchanan, the study's senior author and director of the National Institutes of Health-funded Southwestern Comprehensive Sickle Cell Center. "Yet, the true impact of these investigations on survival of children and adolescents with sickle cell disease has not been clear until now."
"This work gives us contemporary and accurate data confirming the success of our research. It was only a half-century ago that very few persons with sickle cell anemia and related conditions survived beyond 21 years of age," continued Dr. Buchanan.
Experts still have no way of knowing who will have severe, moderate or mild forms of the disease until complications occur, Dr. Quinn said. Discovering risk factors can help a physician develop the best treatment and match the risk of treatments to the risk of the disease.
"The next step is trying to capture and measure long-term survival as these children transition into adulthood," Dr. Quinn said. "We also hope to one day identify risk factors that can help doctors and patients know what to expect from the disease."
All study participants were diagnosed through newborn screening and were all born in Texas on or after Nov. 1, 1983, when the state's screening program went into effect. The patients were observed through Aug. 1, 2002.
Of the 711 patients, 15 deaths were attributed at least partly to sickle cell disease. The average age of death was 5.6 years old, and all those who died from sickle cell disease had sickle cell anemia, the most severe form. The overall incidence of death among patients with sickle cell anemia was 0.59 per 100 patient-years, compared with 1.1 per 100 patient years in a 1994 study sponsored by the National Institutes of Health.
The proportion of deaths from infection was 20 percent compared with 50 percent in the NIH-sponsored study. The most common age of death was 4 to 6 years compared with 1 to 3 years in the NIH-sponsored study.
Dr. Zora Rogers, associate professor of pediatrics, also worked on the study.