African-Americans' increased risk of chronic kidney disease has been attributed to gene variants that can be traced back tens of thousands of years to sub-Saharan Africa. A new study, however, reveals blacks have a higher risk of kidney failure regardless of genetics, leaving scientists clueless about why disparities exist between blacks and whites when it comes to kidney disease.

Chronic kidney disease is marked by a gradual loss in kidney function over time, which can lead to kidney failure. Blacks are more than three times as likely to suffer from kidney failure than whites. And while they represent just 13.2 percent of the U.S. population, they make up 35 percent of all patients receiving dialysis for kidney failure, according to the National Kidney Foundation.

Past research has shown that black people face higher risk of developing kidney disease because most have mutatations of the gene apolipoprotein L1 (APOL1), a component of high-density lipoprotein, or "good cholesterol." These gene variants have been shown to cause about a 40 percent decline in kidney function in African-Americans. These variants can be traced back tens of thousands of years to sub-Saharan Africa, and are present in approximately five million African-Americans, but not everyone with this gene develops kidney disease. Unsure why, researchers from Johns Hopkins University set out to investigate the role this variant plays in the development of kidney disease and how it affects health over time.

For the study, researchers collected and analyzed 25 years of data from more than 15,000 people who participated in the Atherosclerosis Risk in Communities (ARIC) study. Among the cohort, 75 percent of the participants were white; 22 percent were black, with either a low-risk of APOL1 or a variant unassociated with an increased risk of kidney disease; and 3 percent were black with a high-risk genotype for APOL1. The researchers associated high risk with adverse health events, including acute kidney injury, kidney failure, hypertension, diabetes, cardiovascular disease, hospitalization, and death.

At one point during the study, researchers examined the risk of kidney failure between black people with high-risk APOL1 variants and black people with low-risk variants. Although APOL1 high-risk variants were linked to a higher risk of kidney disease, there was a high variability in kidney failure among those with low- and high-risk variants, meaning the risks were virtually indistinguishable.

"We found great variability in kidney function trajectory, such that most African-Americans with the high-risk genotype experienced similar decline as African Americans with the low-risk genotype," said Dr. Morgan Grams, lead author of the study, in a statement.

Furthermore, after adjusting for differences in demographics, researchers found that black people had a higher risk for all the assessed adverse health events. However, when researchers also adjusted for socioeconomic status and whether or not participants had one or more additional diseases co-occuring with the primary disease, they found that black people only had a higher risk for hypertension, diabetes, and kidney failure.

"We did find pervasive racial disparities in adverse health outcomes not explained by the APOL1 risk variants, which suggests that interventions to improve health and health outcomes in African-Americans are needed," Grams concluded.

Based on these findings, researchers believe that widespread screening for these variants in the black general population to gauge their risk of kidney failure is "not yet justified."

Currently, people can take a blood or urine test to see if they have kidney disease. Doctors then examine the blood or urine samples for waste products and proteins that should have been filtered through the kidneys — this indicates that the bean-shaped organs are damaged and not doing their job properly, according to the National Kidney Foundation. People can reduce their risk of kidney disease by keeping their blood pressure and blood sugar at normal levels, and maintaining a healthy body weight.

Source: Grams M, Rebholz C, Chen Y, et al. Race, APOL1 Risk, and eGFR Decline in the General Population. Journal of The American Society of Nephrology. 2016.