The finding, reported in the August issue of Diabetes, comes from the Finnish Diabetic Nephropathy Study, a nationwide study aimed at identifying genetic and environmental risk factors for complications of type 1 diabetes.
To date, the study has characterized 20% of adults with type 1 diabetes in Finland, a total of 4800 patients.
According to Dr. Per-Henrik Groop from Helsinki University Central Hospital, Helsinki, and colleagues, in 188 families, there were at least two siblings with type 1 diabetes. These 188 sibships yielded 369 study patients, of whom 115 (31%) had proliferative retinopathy.
The researchers estimated the familial risk of proliferative retinopathy in 168 of the 188 sibships, adjusted for hemoglobin A1C, duration, and mean blood pressure.
Results showed a greater than twofold increased risk (odds ratio, 2.76) of proliferative retinopathy in siblings of probands with proliferative retinopathy in type 1 diabetes. “The observation cannot be accounted for by conventional risk factors,” the investigators note.
The degree of familial clustering, they also point out, is similar to the previously reported clustering for diabetic nephropathy in type 1 diabetic patients and “suggests that genes may play a major role also for the development of severe retinopathy.”