Lena M. Thorn

New susceptibility loci associated with kidney disease in Type 1 diabetes

Diabetic kidney disease, or diabetic nephropathy (DN), is a major complication of diabetes and the leading cause of end-stage renal disease (ESRD) that requires dialysis treatment or kidney transplantation. In addition to the decrease in the quality of life, DN accounts for a large proportion of the excess mortality associated with type 1 diabetes (T1D). Whereas the degree of glycemia plays a pivotal role in DN, a subset of individuals with poorly controlled T1D do not develop DN. Furthermore, strong familial aggregation supports genetic susceptibility to DN. However, the genes and the molecular mechanisms behind the disease remain poorly understood, and current therapeutic strategies rarely result in reversal of DN. In the GEnetics of Nephropathy: an International Effort (GENIE) consortium, we have undertaken a meta-analysis of genome-wide association studies (GWAS) of T1D DN comprising ∼2.4 million single nucleotide polymorphisms (SNPs) imputed in 6,691 individuals. After additional genotyping of 41 top ranked SNPs representing 24 independent signals in 5,873 individuals, combined meta-analysis revealed association of two SNPs with ESRD: rs7583877 in the AFF3 gene (Pu200a=u200a1.2×10−8) and an intergenic SNP on chromosome 15q26 between the genes RGMA and MCTP2, rs12437854 (Pu200a=u200a2.0×10−9). Functional data suggest that AFF3 influences renal tubule fibrosis via the transforming growth factor-beta (TGF-β1) pathway. The strongest association with DN as a primary phenotype was seen for an intronic SNP in the ERBB4 gene (rs7588550, Pu200a=u200a2.1×10−7), a gene with type 2 diabetes DN differential expression and in the same intron as a variant with cis-eQTL expression of ERBB4. All these detected associations represent new signals in the pathogenesis of DN.

Association Testing of Previously Reported Variants in a Large Case–Control Meta-Analysis of Diabetic Nephropathy

We formed the GEnetics of Nephropathy–an International Effort (GENIE) consortium to examine previously reported genetic associations with diabetic nephropathy (DN) in type 1 diabetes. GENIE consists of 6,366 similarly ascertained participants of European ancestry with type 1 diabetes, with and without DN, from the All Ireland-Warren 3-Genetics of Kidneys in Diabetes U.K. and Republic of Ireland (U.K.-R.O.I.) collection and the Finnish Diabetic Nephropathy Study (FinnDiane), combined with reanalyzed data from the Genetics of Kidneys in Diabetes U.S. Study (U.S. GoKinD). We found little evidence for the association of the EPO promoter polymorphism, rs161740, with the combined phenotype of proliferative retinopathy and end-stage renal disease in U.K.-R.O.I. (odds ratio [OR] 1.14, P = 0.19) or FinnDiane (OR 1.06, P = 0.60). However, a fixed-effects meta-analysis that included the previously reported cohorts retained a genome-wide significant association with that phenotype (OR 1.31, P = 2 × 10−9). An expanded investigation of the ELMO1 locus and genetic regions reported to be associated with DN in the U.S. GoKinD yielded only nominal statistical significance for these loci. Finally, top candidates identified in a recent meta-analysis failed to reach genome-wide significance. In conclusion, we were unable to replicate most of the previously reported genetic associations for DN, and significance for the EPO promoter association was attenuated.

Serum adiponectin concentration is a positive predictor of all‐cause and cardiovascular mortality in type 1 diabetes

Abstract.u2002 Forsblom C, Thomas MC, Moran J, Saraheimo M, Thorn L, Wadén J, Gordin D, Frystyk J, Flyvbjerg A, Groop P‐H, on behalf of the FinnDiane Study Group (Folkhälsan Institute of Genetics, Helsinki; Department of Medicine Helsinki University Central Hospital, Helsinki, Finland; The Baker IDI Heart and Diabetes Institute, Melbourne, Vic.; The Queen Elizabeth Hospital, Woodville, SA, Australia; and Aarhus University Hospital, Aarhus C., Denmark). Serum adiponectin concentration is a positive predictor of all‐cause and cardiovascular mortality in type 1 diabetes. J Intern Med 2011; 270: 346–355.

Circulating ACE2 activity is increased in patients with type 1 diabetes and vascular complications.

Objective: Angiotensin-converting enzyme 2 (ACE2) is a homolog of ACE that counterbalances the actions of angiotensin (AT)II and promotes vasodilatation. Circulating ACE2 activity is increased in diabetes in experimental models. The role of ACE2 in human pathophysiology is unknown. We examined whether ACE2 activity is altered in patients with type 1 diabetes (T1D), with and without diabetic nephropathy. Methods: Quantitative ACE2 activity in serum was measured by a fluorometric assay in 859 patients with T1D in the Finnish Diabetic Nephropathy (FinnDiane) study and in 204 healthy controls. Pulse-wave analysis with augmentation index (AIx) measurement was performed in 319 patients with T1D and 114 controls. Results: ACE2 activity was increased in men with T1D and microalbuminuria (30.2u200a±u200a1.5u200angE/ml) when compared to patients without albuminuria (27.0u200a±u200a0.5u200angE/ml, Pu200a<u200a0.05) or controls (25.6u200a±u200a0.8u200angE/ml, Pu200a<u200a0.05). ACE2 activity was increased in male and female patients who were on ACE inhibitor (ACEi) treatment, also independently of albuminuria. Male and female patients with coronary heart disease (CHD) had significantly increased ACE2 activity (35.5u200a±u200a2.5 vs. 27.0u200a±u200a0.5u200angE/ml, Pu200a<u200a0.001 among male T1D patients vs. male controls). ACE2 activity correlated positively with systolic blood pressure (rsu200a=u200a0.175, Pu200a<u200a0.001), AIx (rsu200a=u200a0.191, Pu200a=u200a0.010) and diabetes duration (rsu200a=u200a0.198, Pu200a<u200a0.001), and negatively with estimated glomerular filtration rate (rsu200a=u200a−0.109, Pu200a=u200a0.016) among male T1D patients. Conclusions: ACE2 activity increases with increasing vascular tone and when the patient with T1D has microvascular or macrovascular disease, indicating that ACE2 may participate as a compensatory mechanism in the regulation of vascular and renal function in patients with T1D.

Urinary Liver-Type Fatty Acid-Binding Protein and Progression of Diabetic Nephropathy in Type 1 Diabetes

OBJECTIVE Diabetic nephropathy (DN) has mainly been considered a glomerular disease, although tubular dysfunction may also play a role. This study assessed the predictive value for progression of a tubular marker, urinary liver-type fatty acid–binding protein (L-FABP), at all stages of DN. RESEARCH DESIGN AND METHODS At baseline, 1,549 patients with type 1 diabetes had an albumin excretion rate (AER) within normal reference ranges, 334 had microalbuminuria, and 363 had macroalbuminuria. Patients were monitored for a median of 5.8 years (95% CI 5.7–5.9). In addition, 208 nondiabetic subjects were studied. L-FABP was measured by ELISA and normalized with urinary creatinine. Different Cox proportional hazard models for the progression at every stage of DN were used to evaluate the predictive value of L-FABP. The potential benefit of using L-FABP alone or together with AER was assessed by receiver operating characteristic curve analyses. RESULTS L-FABP was an independent predictor of progression at all stages of DN. As would be expected, receiver operating characteristic curves for the prediction of progression were significantly larger for AER than for L-FABP, except for patients with baseline macroalbuminuria, in whom the areas were similar. Adding L-FABP to AER in the models did not significantly improve risk prediction of progression in favor of the combination of L-FABP plus AER compared with AER alone. CONCLUSIONS L-FABP is an independent predictor of progression of DN irrespective of disease stage. L-FABP used alone or together with AER may not improve the risk prediction of DN progression in patients with type 1 diabetes, but further studies are needed in this regard.

Sex-related differences in the long-term risk of microvascular complications by age at onset of type 1 diabetes.

Aims/hypothesisThis study examined sex-related differences in the cumulative risk of proliferative retinopathy (PR) and end-stage renal disease (ESRD) over 40xa0years of duration of type 1 diabetes according to age at diabetes onset.MethodsWe assessed 4,416 patients from the Finnish Diabetic Nephropathy Study population. Kaplan–Meier analysis was used to provide cumulative incidence rates and Cox regression analyses for HRs.ResultsThere were no sex-related differences in the cumulative incidence of ESRD in patients diagnosed with type 1 diabetes between 0 to 4 and 5 to 9xa0years. Thereafter the risk started to diverge. The cumulative incidence of ESRD in patients diagnosed between 10 to 14 and ≥15xa0years was 17.4% (95% CI 13.4–21.2) and 13.0% (9.6–16.2) respectively in women, while in men it was 32.2% (28.0–36.1) and 24.6% (20.8–28.1) respectively. The respective HRs were (onset at 10 to 14xa0years) 1.9 (pu2009<u20090.0001) and (onset at ≥15xa0years) 1.8 (pu2009<u20090.001), respectively. There was no difference in the risk of PR between men and women diagnosed between 0 and 4xa0years of age, but progressive sex-related differences in the cumulative incidence of PR were observed with increasing age at onset. The HRs for men in the age-at-onset groups 5 to 9, 10 to 14 and ≥15xa0years of age were 1.3 (95% CI 1.0–1.6), 1.3 (1.1–1.6) and 2.1 (1.6–2.6) compared with women in these groups, respectively.Conclusions/interpretationThe difference between the sexes with regard to risk of diabetic microvascular complications is highly dependent on the age at onset of diabetes. The risk of ESRD and PR risk doubled in men compared with women when age at onset was ≥15xa0years.

Serum Concentration of Cystatin C and Risk of End-Stage Renal Disease in Diabetes

OBJECTIVE Patients with diabetes have a high risk of end-stage renal disease (ESRD). We examined whether prediction of this outcome, according to chronic kidney disease (CKD) staging by creatinine-based estimates of the glomerular filtration rate (eGFRcreat), is improved by further staging with serum cystatin C–based estimates (eGFRcyst). RESEARCH DESIGN AND METHODS Patients with diabetes in CKD stages 1–3 were selected from three cohorts: two from Joslin Diabetes Center, one with type 1 diabetes (N = 364) and one with type 2 diabetes (N = 402), and the third from the Finnish Diabetic Nephropathy (FinnDiane) Study of type 1 (N = 399). Baseline serum concentrations of creatinine and cystatin C were measured in all patients. Follow-up averaged 8–10 years and onsets of ESRD (n = 246) and death unrelated to ESRD (n = 159) were ascertained. RESULTS Although CKD staging by eGFRcyst was concordant with that by eGFRcreat for 62% of Joslin patients and 73% of FinnDiane patients, those given a higher stage by eGFRcyst than eGFRcreat had a significantly higher risk of ESRD than those with concordant staging in all three cohorts (hazard ratio 2.3 [95% CI 1.8–3.1]). Similarly, patients at a lower stage by eGFRcyst than by eGFRcreat had a lower risk than those with concordant staging (0.30 [0.13–0.68]). Deaths unrelated to ESRD followed the same pattern, but differences were not as large. CONCLUSIONS In patients with diabetes, CKD staging based on eGFRcyst significantly improves ESRD risk stratification based on eGFRcreat. This conclusion can be generalized to patients with type 1 and type 2 diabetes and to diabetic patients in the U.S. and Finland.

Metabolic diversity of progressive kidney disease in 325 patients with type 1 diabetes (the FinnDiane Study).

Type 1 diabetic patients with varying severity of kidney disease were investigated to create multimetabolite models of the disease process. Urinary albumin excretion rate was measured for 3358 patients with type 1 diabetes. Prospective records were available for 1051 patients, of whom 163 showed progression of albuminuria (8.3-year follow-up), and 162 were selected as stable controls. At baseline, serum lipids, lipoprotein subclasses, and low-molecular weight metabolites were quantified by NMR spectroscopy (325 samples). The data were analyzed by the self-organizing map. In cross-sectional analyses, patients with no complications had low serum lipids, less inflammation, and better glycemic control, whereas patients with advanced kidney disease had high serum cystatin-C and sphingomyelin. These phenotype extremes shared low unsaturated fatty acids (UFAs) and phospholipids. Prospectively, progressive albuminuria was associated with high UFAs, phospholipids, and IDL and LDL lipids. Progression at longer duration was associated with high HDL lipids, whereas earlier progression was associated with poor glycemic control, increased saturated fatty acids (SFAs), and inflammation. Diabetic kidney disease consists of diverse metabolic phenotypes: UFAs, phospholipids, IDL, and LDL may be important in the subclinical phase, high SFAs and low HDL suggest accelerated progression, and the sphingolipid pathway in advanced kidney injury deserves further research.

Hyperfiltration in type 1 diabetes: does it exist and does it matter for nephropathy?

Aims/hypothesisHyperfiltration is widely regarded as a contributing factor to the development of microalbuminuria and progressive nephropathy in type 1 diabetes. However, recent studies have questioned this conclusion.MethodsTo address this conflicting evidence, we examined the association between hyperfiltration and progression to microalbuminuria in 2,318 adults with type 1 diabetes. We also compared the estimated GFR in our diabetic patients with rates observed in 6,247 adults from the Finnish general population, using age- and sex-specific z scores.ResultsThe distribution of estimated GFR in adults with type 1 diabetes and normoalbuminuria was not significantly different from that expected in the general population (pu2009=u20090.51, Mann–Whitney test). Type 1 diabetic patients with a higher estimated GFR were also no more likely to develop microalbuminuria over a median of 5.2xa0years of follow-up than those with normal estimated GFR. This was the case regardless of whether hyperfiltration was defined by an absolute threshold, deciles of estimated GFR or a z score, using creatinine- or cystatin-based clearance formulas in men or in women.Conclusions/interpretationTogether with other studies, these data suggest that creatinine- or cystatin-based estimates of GFR do not predict the development of microalbuminuria in patients with type 1 diabetes. Moreover, in the absence of incipient or overt nephropathy, conventionally determined renal function in patients with type 1 diabetes appears no different from that in the general population. This is hardly surprising, given that these individuals, by all definitions, do not have kidney disease.

Incidence of Stroke According to Presence of Diabetic Nephropathy and Severe Diabetic Retinopathy in Patients With Type 1 Diabetes

OBJECTIVE Type 1 diabetes is associated with a markedly increased risk of stroke, but only a few studies on the incidence of stroke in type 1 diabetes exist. Therefore, we assessed the incidence of stroke in patients with type 1 diabetes and studied the impact of diabetic nephropathy (DN) and severe diabetic retinopathy (SDR) on this risk. RESEARCH DESIGN AND METHODS We studied 4,083 patients with type 1 diabetes from the Finnish Diabetic Nephropathy Study. Mean age was 37.4 ± 11.8 years, duration of diabetes was 21.6 ± 12.1 years, and 52% were men. Strokes were identified from medical records, death certificates, and the National Hospital Discharge Register and classified based on medical files and brain images. RESULTS During 36,680 person-years of follow-up, 149 (4%) patients suffered an incident stroke (105 infarctions and 44 hemorrhages). Of the infarctions, 58 (55%) were lacunar. The incidence of stroke, cerebral infarction, and cerebral hemorrhage was 406 (95% CI 344–477), 286 (234–347), and 120 (87–161) per 100,000 person-years, respectively. In an adjusted analysis, microalbuminuria increased the risk of stroke with a hazard ratio (HR) of 3.2 (1.9–5.6), macroalbuminuria 4.9 (2.9–8.2), and end-stage renal disease 7.5 (4.2–13.3), and SDR increased the risk with an HR of 3.0 (1.9–4.5). The risk of cerebral infarction, cerebral hemorrhage, and lacunar infarction increased in a similar manner. The proportion of lacunar versus nonlacunar infarction did not change across DN groups. CONCLUSIONS The presence of SDR and DN, independently, increases the risk of stroke, cerebral infarction, and cerebral hemorrhage in patients with type 1 diabetes.