Cognitive Decline Not Evident in Black Americans with Sickle Cell Trait, Study Finds

African-Americans with sickle cell trait, carriers for sickle cell but without the disease, have no greater risk of cognitive decline than other adults of similar age, an analysis of a large population study shows.

The study “Sickle cell trait and risk of cognitive impairment in African-Americans: The REGARDS cohort” was published in the journal EClinicalMedicine.

In sickle cell anemia (SCA), patients inherit two mutated copies of the hemoglobin (HBB) gene, deforming red blood cells into a sickle shape that tend to obstruct small blood vessels. People with African ancestry are at a higher risk for this disease compared to other populations.

Vascular complications, like small strokes, are thought to contribute to cognitive decline and can be fairly common among people with SCA. In fact, evidence shows that both children and adults with sickle cell score lower on cognition tests than those without this disease. Adults with sickle cell may even have changes in their brain linked to poorer cognitive performance.

A team of researchers hypothesized that carriers of  sickle cell trait (SCT) — those with only one mutated copy of the HBB gene — could also be at risk for cognitive impairments, especially older adults.

The researchers analyzed data from the REGARDS study that followed 30,239 white and black Americans for a median of 7.1 years, investigating racial and geographic influences on stroke and cognitive impairment in the U.S.

Among those enrolled in REGARDS between 2003 and 2007, the team identified 7,743 African-Americans 45 years or older, among whom 583 had SCT but no signs of cognitive impairment at the study’s start.

Cognition was evaluated annually using a six-item screener test that assesses a person’s orientation regarding the current year, month, and day of the week, and the ability to recall three items within five minutes of the test starting.

With a scale that runs from zero to six, a score of four or below is considered evidence of cognitive impairment.

Every two years, participants also completed three additional verbal tests of learning, memory, and executive function: the word list learning (WLL) test, the delayed recall by word list recall (WLR) test, and tests of semantic fluency (the ability to categorize words) and phonemic fluency (fluency in coming up with words starting with a given letter).

Results showed that during the seven years black participants were followed, 14.5% of those with SCT (85 out of the 583) experienced cognitive decline, as did 12.6% (902 out of 7,160) of those without this trait. These findings, in other words, were not evidence of “clinically significant cognitive dysfunction in adults aged 45 and older” with sickle cell trait.

“In this large contemporary cohort of black Americans, there were no associations of SCT with incidence of cognitive impairment or with changes over time in test scores included in a 3-test battery assessing learning, memory, and semantic and phonemic fluency,” the researchers added.

“The findings we present are clinically relevant, as they might be reassuring to patients with SCT who are worried about cognitive function. The results suggest there is not cause for concern about cognitive dysfunction for SCT patients in this age group and their primary care providers,” their study concluded.