Genetic study of diabetic retinopathy: recruitment methodology and analysis of baseline characteristics

Background Diabetic retinopathy ( DR ) is a blinding disease of increasing prevalence that is caused by a complex interplay of genetic and environmental factors. Here we describe the patient recruitment methodology, case and control definitions, and clinical characteristics of a study sample to be used for genome‐wide association analysis to detect genetic risk variants of DR . Methods One thousand six hundred sixty‐nine participants with either type 1 ( T 1) or type 2 ( T 2) diabetes mellitus ( DM ) aged 18 to 95 years were recruited in Australian hospital clinics. Individuals with T 2 DM had disease duration of at least 5 years and were taking oral hypoglycaemic medication, and/or insulin therapy. Participants underwent ophthalmic examination. Medical history and biochemistry results were collected. Venous blood was obtained for genetic analysis. Results Six hundred eighty‐three diabetic cases (178 T 1 DM and 505 T 2 DM participants) with sight‐threatening DR , defined as severe non‐proliferative DR , proliferative DR or diabetic macular oedema were included in this analysis. Eight hundred twelve individuals with DM but no DR or minimal non‐proliferative DR were recruited as controls (191 with T 1 DM and 621 with T 2 DM ). The presence of sight‐threatening DR was significantly correlated with DM duration, hypertension, nephropathy, neuropathy, HbA 1 C and body mass index. Diabetic macular oedema was associated with T 2 DM ( P  < 0.001), whereas proliferative DR was associated with T 1 DM ( P  < 0.001). Conclusions Adoption of a case‐control study design involving extremes of the DR phenotype makes this a suitable cohort, for a well‐powered genome‐wide association study to detect genetic risk variants for DR .