Sickle-cell anemia tied to cognitive impairment

People with sickle-cell anemia harbor cognitive deficits that show up as lower-than-average scores on IQ tests, a new study suggests. The poor performance comes even when MRI scans show no brain damage and the patients have no other complications from the disease apart from anemia and pain, researchers report in the May 12 Journal of the American Medical Association.

“These neurocognitive effects are an invisible complication of the central nervous system in sickle-cell disease,” says Samir Ballas, a hematologist at Thomas Jefferson University in Philadelphia who was not involved in the research.

Sickle-cell anemia results from an inherited genetic mutation that causes red blood cells to take on a curved, or sickle, shape that impairs blood flow, thwarts oxygen delivery and leads to a host of other health problems.

In the new study, hematologist Elliott Vichinsky of Children’s Hospital & Research Center Oakland, in California, and his colleagues identified 149 adults, average age 32, who had sickle-cell anemia but were otherwise free of severe complications. The scientists also recruited 47 people similar in age to serve as a control group. All participants were black.

The participants completed standardized tests designed to gauge a wide array of mental capabilities. Overall, 33 percent of the sickle-cell anemia group fell below the normal range of performance IQ, a broad measure of cognitive abilities. In the general population, about 16 percent of people fall below this benchmark, and 15 percent of the controls did in this study. The sickle-cell group scored lower in tasks specifically involving memory, attention, information retrieval, number sequencing and executive function — the ability to think through tasks, make plans and execute them.

MRI scans looking for tissue damage in the brain showed no substantial differences between the groups. The researchers accounted for differences in age, gender and education level.

The results are somewhat surprising, says W. Keith Hoots, a hematologist at the National Heart, Lung, and Blood Institute in Bethesda, Md. None of the study participants had been diagnosed with serious cognitive disabilities beforehand. “If anyone would have normal neurocognitive function [among sickle-cell patients] this would have been the group,” he says.

Sickle-cell disease causes pain and tissue damage when red blood cells become bent, rigid and sticky. Neurological problems could arise, says Ballas, if the rigid red blood cells irritate cells lining blood vessels in the brain, causing those cells to proliferate and narrow the vessel. When that happens, inadequate blood gets to the brain.

Vichinsky agrees that a chronic lack of oxygen may underpin the subtle cognitive declines seen in the people in his study. If so, he says, “this is possibly reversible.”

He and his colleagues are now giving blood transfusions to people with sickle-cell anemia whose test scores indicate mild cognitive deficits to see if those scores change. These data are not yet available.