This report is the first to identify MYH9
SNP associations with presumed diabetic ESRD in European Americans. We evaluated the presence of APOL1
risk variants (0.28% of chromosomes in T2DM–ESRD cases and 0.32% of the chromosomes in controls) confirming the relative rarity of APOL1
nephropathy risk variants in European Americans. APOL1
G1 and G2 variants and MYH9
SNPs rs4821480, rs2032487, rs4821481 and rs3752462 are known to be strongly associated with a spectrum of related, predominantly non-diabetic kidney diseases in African Americans as well as idiopathic FSGS and non-diabetic kidney disease in European Americans and non-diabetic ESRD in Hispanic Americans [8
]. Additionally, there is evidence that MYH9
accounts for residual risk beyond that attributable to these APOL1
variants in African Americans [C. Langefeld (personal communication)]. Although a recessive model has been emphasized in the literature for these MYH9
], in the current analyses we detected an association between MYH9
SNPs and T2DM–ESRD in European Americans in a recessive as well as an additive model. Due to the low frequency of MYH9
risk alleles in European Americans, few individuals homozygous for risk alleles will be detected. Only 10.26% (55/536) of T2DM–ESRD cases had at least one copy of the MYH9
risk alleles at the four E1 haplotype SNPs and 1.31% (7/536) had two copies of risk alleles. Of all 1963 European Americans in the analyses, 8.66% (170) had at least one copy of the MYH9
risk alleles at the four SNPs and 0.61% (12) had two copies of risk alleles at the four SNPs. It was apparent that individuals homozygous for risk alleles were over-represented in T2DM–ESRD cases, consistent with prior reports. Additional analyses limited to individuals not homozygous for the risk allele revealed a lack of statistical evidence for association (rs4821480 P = 0.941, OR = 0.89; rs2032487 P = 0.612, OR = 2.65; rs4821481 P = 0.614, OR = 2.64; rs3752462 P = 0.113, OR = 1.31), indicating that the recessive model drove the association observed in the additive model.
To account for the possibility that some T2DM non-nephropathy controls will develop future kidney disease, only those with serum creatinine concentrations <1.5 mg/dL and urine albumin:creatinine ratio <30 mg/g were evaluated. Since a small percentage of these controls will likely develop progressive nephropathy, a subsequent analysis excluded those with <5 year diabetes duration; results were similar to those in the initial analysis. Furthermore, comparing T2DM–ESRD to T2DM non-nephropathy controls, the recessive model P-value for the strongest signal (rs4821480) did not change when excluding individuals with diabetes duration <5 years. Combined non-diabetic non-nephropathy controls and T2DM non-nephropathy controls with diabetes duration ≥5 years were compared to T2DM–ESRD cases, the P-value for the strongest signal (rs2032487) increased only slightly, from 0.017 to 0.020. We attribute this slight increase to the decreased sample size associated with removing 48 individuals with <5 years diabetes duration.
Although previous studies indicated that MYH9
polymorphisms were not associated with diabetic nephropathy [10
], our findings indicate that these variants contribute to risk for ‘clinically diagnosed’ type 2 diabetes-associated ESRD in European Americans, although clearly with smaller effect size as compared to that in non-diabetic kidney disease in African Americans. Our samples were recruited in the southern USA and likely represent a homogeneous sample consistent with Northern European heritage [21
]. Genome-wide ancestry analyses would be required to comprehensively rule out the unlikely possibility that the observed signal is actually marking cryptic population substructure. In our report evaluating MYH9
in African Americans with T2DM–ESRD, we proposed that association could have resulted from inclusion of MYH9
-associated FSGS in the sample of cases with coincident T2DM and ESRD [8
]; an observation that was subsequently proven [22
]. Concurrent FSGS and diabetic nephropathy would appear less likely in European Americans, as the prevalence of both T2DM and FSGS are markedly lower than in African Americans (as is the frequency of MYH9
E1 risk haplotypes); nonetheless, it remains possible that some of these European Americans with clinically diagnosed T2DM–ESRD had MYH9
-related FSGS. Renal biopsies are required—to determine the true cause of nephropathy in these clinically diagnosed cases, a procedure that is infrequently performed.
Prior reports have detected associations of these SNPs and haplotypes primarily with non-diabetes-associated kidney diseases [9
]. A genetic predisposition to T2DM–ESRD is clearly established in African Americans and European Americans. Polymorphisms in the non-muscle myosin heavy chain IIA gene, expressed in glomerular podocytes and mesangial cells [6
], may lead to alterations in the cytoskeleton, impair the glomerular filtration barrier and result in proteinuria with progressive renal failure in subjects with T2DM [7
]. Genetic variants which have the potential to alter risk for diabetic nephropathy, such as TCF7L2
, in addition to others [23
], have previously been described [23
]. It would not be unreasonable to postulate that these and other variants may be interacting with one another and/or with MYH9
risk variants to modify risk for diabetic and non-diabetic ESRD. The existence of ‘second hits’ genes that may be interacting with MYH9
to mediate either genetic predisposition to, or protection from kidney disease of various causes needs to be explored in African- and European-derived populations.
This manuscript reports the results of a focused a priori
hypothesis that E1 haplotype SNPs were associated with diabetic nephropathy in European Americans. Although the statistical power of the tests in this paper are low for a recessive model for the E1 haplotype (~10%), significant association was observed for the individual SNPs comprising the E1 haplotype. The strength of the association between MYH9
polymorphisms and T2DM-associated ESRD in this European American cohort is weaker than that detected in African Americans with diabetic and non-diabetic forms of kidney disease [8
]. In conclusion, this is the first report investigating and identifying MYH9
SNP association with presumed diabetic nephropathy in European Americans. Variation at the MYH9–APOL1
gene region on Chromosome 22q is associated with nephropathy susceptibility, including in European American populations.