The risk of proliferative retinopathy in siblings with Type 1 diabetes

Diabet. Med. 29, 15671573 (2012) Abstract Aims The siblings first affected by Type 1 diabetes (probands) within a sibship have been shown to have a lower age at onset of Type 1 diabetes compared with their later-affected siblings. The aim of the present study was to investigate whether this difference affects the long-term risk of proliferative diabetic retinopathy. Methods A cohort of 396 siblings with Type 1 diabetes in 188 sibships was drawn from a larger Finnish Diabetic Nephropathy Study population (4800 patients). Ophthalmic records were obtained for 369/396 (93%) patients. Retinopathy was graded based on fundus photographs and/or repeated ophthalmoscopies. Results The median age at onset of Type 1 diabetes was 8.4 (interquartile range 4.213.3) years in probands and 16.9 (interquartile range 10.227.8) years in later-affected siblings (P < 0.001). Proliferative retinopathy was diagnosed in 115/369 (31%) patients. The cumulative incidence estimates for proliferative retinopathy, accounting for the competing risk of death, were 21% (95% CI 1527) in probands and 26% (95% CI 1935) in later-affected siblings at 20 years of diabetes duration, and the respective 30 years incidences were 37% (95% CI 2945) and 53% (95% CI 4064), (P = 0.05, Grays test). The risk of proliferative retinopathy, adjusted for conventional risk factors, age at onset and sibship size, was higher in later-affected siblings [hazard ratio 1.75 (95% CI 1.132.75), P = 0.01] compared with their probands. Conclusion The siblings first affected by Type 1 diabetes had a better long-term prognosis with regards to development of proliferative retinopathy compared with their later-affected siblings.