Researchers describe a “familial clustering” in retinopathy secondary to type 2 diabetes mellitus. They observed a more than three-fold higher prevalence of retinopathy among siblings of patients with diabetic retinopathy. The occurrence of diabetic retinopathy in some patients with good glycemic control "points to the possible role of genetic factors in conferring susceptibility to retinopathy," Dr. M. Rema and colleagues from the Madras Diabetes Research Foundation report.
To investigate a possible genetic basis for retinopathy in type 2 diabetes mellitus, Dr Rema’s team evaluated 322 families having at least two siblings. In each family, the sibling with longest standing diabetes was identified as the proband. A detailed clinical, biochemical and retinoscopic examination estimated the prevalence of retinopathy in the probands and in 355 other siblings with type 2 diabetes.
Diabetic retinopathy was present in 136 probands and in 53 (35.3%) of their siblings, Dr. Rema and colleagues report in the November issue of Diabetic Medicine. In contrast, the prevalence of retinopathy among siblings of probands without retinopathy was only 11.2%, they note.
Siblings of patients with diabetic retinopathy had a 3.37 higher odds ratio of developing retinopathy compared with siblings of diabetics without retinopathy, the researchers report. The higher risk of retinopathy was not influenced by duration of diabetes, glycemic control, or the presence of hypertension, they add.
The "familial clustering of retinopathy" could have a genetic or environmental basis, Dr Rema and colleagues write. A previous report of familial clustering of microalbuminuria "suggests a similar pattern of inheritance of microangiopathy among diabetic subjects," the investigators postulate.
The genetic basis for retinopathy in type 2 diabetes can be explained by the presence of strong "familial aggregation," even after correcting for glycemic status and duration of diabetes, Said, Dr Rema.
"There seems to be a separate genetic basis to diabetic retinopathy apart from type 2 diabetes," Dr Rema concludes. Diabet Med 2002;19:910-916.