The study is the first to look at brain function in adults with sickle cell disease, and it may mean new drugs are needed to protect the brains of patients the inherited disorder.
The differences in intelligence were striking enough that researchers worry some patients might have trouble staying employed, managing their money and keeping track of their medications.
"What this shows is that people who have even fairly clinically mild sickle cell disease seem to be having some effects from the disease in terms of their neurocognitive function," said Dr. Susan Shurin, acting director of the National Heart Lung and Blood Institute, whose agency funded the study published in the Journal of the American Medical Association.
In sickle cell disease, the body makes abnormally shaped forms of hemoglobin, the protein in red blood cells that carries oxygen to the body's tissues.
It affects 70,000 Americans and 3 to 5 million people globally. At one time, most people with the disease died in childhood, but new treatments allow people to live into middle age, Shurin said.
Dr. Elliott Vichinsky of Children's Hospital & Research Center in Oakland, California tested 149 adult sickle cell patients and 47 healthy people of similar age and education levels from the same communities.
Patients were considered low risk for complications because they had no history of frequent pain, hospitalization, stroke, high blood pressure or other problems that could affect brain function.
The researchers found people with sickle cell disease scored lower on tests of intellect, working memory, processing speed and attention span than the healthy study participants.
The oldest and the sickest sickle cell patients scored the worst, suggesting the longer a person lived with the disease or the worse it was, the bigger the effect on brain function.
Shurin said the findings suggest the need for more study of potential new treatments that could help protect brain function in people with sickle cell disease.
"It also raises the question of should we be more aggressive earlier in life," Shurin said in a telephone interview.
A cancer pill called hydroxyurea, which is available generically, can stop the severe pain and prevent the need for blood transfusions.
Shurin said the study may mean more patients should start taking the drug at an earlier age.
