Microvascular and macrovascular complications of type 2 diabetes mellitus: Exome wide association analyses.

Background: Type 2 diabetes mellitus (T2DM) is a chronic, metabolic disorder in which concomitant insulin resistance and β-cell impairment lead to hyperglycemia, influenced by genetic and environmental factors. T2DM is associated with long-term complications that have contributed to the burden of morbidity and mortality worldwide. The objective of this manuscript is to conduct an Exome-Wide Association Study (EWAS) on T2DM Emirati individuals to improve our understanding on diabetes-related complications to improve early diagnostic methods and treatment strategies.

Methods: This cross-sectional study recruited 310 Emirati participants that were stratified according to their medically diagnosed diabetes-related complications: diabetic retinopathy, diabetic neuropathy, diabetic nephropathy, and cardiovascular complications. The Illumina's Infinium Exome-24 array was used and 39,840 SNPs remained for analysis after quality control.

Findings: The analysis revealed the associations of various genes with each complication category: 1) diabetic retinopathy was associated to gene in locus 22q13.33 (SNP rs9616915; p=5.18 x10), gene in locus 19q13.43 (SNP rs7252603; p=7.55 x10), and gene in locus 12p13.33 (SNPs rs715146, rs1044950, rs113147414, rs34730825; p=7.62 x10); 2) diabetic neuropathy was associated to gene in locus 4q23 (SNP rs4148883; p=1.23 x10), gene in locus 2q35 (SNP rs17235409; p=1.85 x10), and gene in locus 20q13.12 (SNP rs2072788; p=2.68 x10); 3) diabetic nephropathy was associated to gene in locus 7q31.1 (SNP rs1799999; p=1.91 x10), gene in locus 19p13.2 (SNP rs140861589; p=2.80 x10), and gene in locus 20p13 (SNP rs6076550; p=2.86 x10); and 4) cardiovascular complications was associated to gene in locus 21q22.3 (SNPs rs7279204, rs6518289, rs2839227, rs2839223; p=2.18 x10,3.04 x10,4.51 x10,5.22 x10 respectively), gene in locus 7p11.2 (SNP rs146350220; p=2.77 x10), and gene in locus 15q25.2 (SNP rs72750868; p=4.47 x10).

Interpretation: We have identified susceptibility loci associated with each category of T2DM-related complications in the Emirati population. Given that only 16% of the markers from the Illumina's Infinium Exome chip passed quality control assessment, this demonstrates that multiple variants were, either, monomorphic in the Arab population or were not genotyped due to the use of a Euro-centric EWAS array that limits the possibility of including targeted ethnic-specific SNPs. Our results suggest the alarming possibility that lack of representation in reference panels could inhibit discovery of functionally important loci associated to T2DM complications. Further effort must be conducted to improve the representation of diverse populations in genotyping and sequencing studies.