Assessment of diabetic retinopathy by measuring retina-specific mRNA in blood

Diabetic retinopathy (DR) is the leading cause of blindness in adults. Early detection and treatment of DR has been shown to reduce the risk of visual loss by as much as 90%. At present, there are no blood tests to detect DR. Previous studies have demonstrated the presence of nucleic acids in blood and raised levels of these markers have been reported in many conditions. The aim of this study was to evaluate the circulating levels of retina-specific mRNA in the assessment of DR.Blood samples were taken into PAXgene Blood RNA tubes from 89 diabetic patients and 19 healthy individuals. A reverse-transcription quantitative real-time PCR assay was used to measure circulating levels of mRNA for rhodopsin (Rho), retinal amine oxidase (RAO) and phosphodiesterase 6C (PDE6C). The results were normalized against mRNA for β-actin and total RNA. While mRNA for Rho, RAO and β-actin were detected in 100% of the subjects, PDE6C mRNA was only found in 60% of the individuals and melanopsin mRNA was not detected. When diabetic subjects were divided according to their DR status, significant differences were observed for Rho and RAO-Rho increased while RAO tended to decrease. The area under the curve ROC for Rho and Rho/RAO ratio to differentiate mild or no DR from significant DR (pre-proliferative and proliferative stages) were 0.756 and 0.823, respectively.These findings suggest that circulating mRNA may be useful in assessing DR.