"This is the only report of this type in African-Americans," said Friedman, adding that the genes causing diabetic kidney disease may be the same as those found in some other ethic groups.
Freedman and a team that included eight other Wake Forest investigators studied 171 black families in which at least two siblings had developed kidney disease from type 2 diabetes; 312 individuals already had end-stage kidney disease. On average, diabetes began at age 39.
Using genome scans, the team's first set of analyses identified only weak evidence for the presence of kidney failure genes. But Freedman said that Carl D. Langefeld,. Ph.D., assistant professor of public health sciences (biostatistics) and Stephen S. Rich, Ph.D., professor of public health sciences and neurology, came up with a new way of analyzing the genetic data. "Using their novel analytic techniques allowed us to detect these regions containing kidney failure genes," he said.
The technique involved ranking 216 families by age when diabetes began and looking for linkages. Chromosome 18 emerged in the genomic study in people whose diabetes began at a younger age, while there was virtually no relationship to chromosome 18 in the older people. This indicated, they reported, that susceptibility in the younger group likely was related to the unidentified gene. Finding the region on a chromosome that is linked to a genetic defect is a major step toward identifying the gene, since it dramatically narrows the possibilities.
Freedman pointed out that other investigators already had linked the same region on chromosome 18 as harboring a susceptibility to kidney damage from type 2 diabetes in the Pima tribe of Native Americans and in Turkish families. The Pimas have long been identified as having an extraordinarily high rate of diabetes.
"This is the biggest African-American group ever studied," said Freedman. "Wake Forest has the largest existing collection of DNA from African-Americans with multiple members on dialysis or with diabetes."
Wake Forest University Baptist Medical Center is an academic health center including Wake Forest University School of Medicine and N.C. Baptist Hospital.