Genetic Association of Diabetic Retinopathy-1 (DMR-1)

• The differences in the distribution of candidate genotypes and alleles between the study groups [ Time Frame: 12 months ] [ Designated as safety issue: No ]
  Patients with diabetes who have received ophthalmic fundus examination within 6 months before the study. The eligible participants will be grouped by the results of prior fundus examination: those with known history of diabetic retinopathy; those without known history of diabetic retinopathy.
  
  

• the frequencies of haplotypes of different single nucleotide polymorphisms [ Time Frame: 12 months ] [ Designated as safety issue: No ]
  We will estimate the frequencies of haplotypes of different single nucleotide polymorphisms, calculate linkage disequilibrium between single nucleotide polymorphisms, and conduct haplotype analysis.
  
  

Diabetic retinopathy (DR) is one of the most frequent microvascular complications of diabetes (DM). Current guidelines recommend that patients with DM should receive ophthalmic fundus examination annually. DR poses a serious threat to the health of millions patients who have DM. Nowadays, DR has become the leading cause of new cases of visual impairment and blindness among adults.

Genetic factors are likely to account for the susceptibility to DR for the differences in DR incidence between individuals with diabetes. Familial aggregation studies showed that increased risk of severe DR was noted among family members with diabetes with moderate heritability of DR risk. Racial and ethnic differences in the prevalence of DR may also explain some parts of influence of genetic or environmental/cultural risk factors. There were over 30 candidate genes involved in metabolic mechanisms and functional pathways associated with DR. However, consistent associations between candidate genes and DR have yet been identified. The current study is designed to build up a working platform for future large-scale genetic studies of diabetic retinopathy. The investigators also hope to set up priority of candidate loci for future researches.

In the present study, the investigators plan to recruit 200 Chinese patients with DM who have received ophthalmic fundus examination (either by an ophthalmoscope or fundus camera) within 6 months before the study. Each subject will receive anthropometric and blood pressure measurements. Then, fasting blood samples will be taken for the measurements of glucose, HbA1c, lipid profile, and biochemistry. An additional 10 ml blood sample will be taken for DNA extraction from buffy coat. Single nucleotide polymorphisms (SNPs) in candidate genes and in targeted chromosome regions will be genotyped by using the ABI TaqMan assays. The differences in the distribution of genotypes and alleles between the study groups will be analyzed using appropriate statistical methods.