Anna Möllsten

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 (P = 1.2×10−8) and an intergenic SNP on chromosome 15q26 between the genes RGMA and MCTP2, rs12437854 (P = 2.0×10−9). 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, P = 2.1×10−7), 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.

Thirty Years of Prospective Nationwide Incidence of Childhood Type 1 Diabetes: The Accelerating Increase by Time Tends to Level Off in Sweden

OBJECTIVE During the past few decades, a rapidly increasing incidence of childhood type 1 diabetes (T1D) has been reported from many parts of the world. The change over time has been partly explained by changes in lifestyle causing rapid early growth and weight development. The current study models and analyzes the time trend by age, sex, and birth cohort in an exceptionally large study group. RESEARCH DESIGN AND METHODS The present analysis involved 14,721 incident cases of T1D with an onset of 0–14.9 years that were recorded in the nationwide Swedish Childhood Diabetes Registry from 1978 to 2007. Data were analyzed using generalized additive models. RESULTS Age- and sex-specific incidence rates varied from 21.6 (95% CI 19.4–23.9) during 1978–1980 to 43.9 (95% CI 40.7–47.3) during 2005–2007. Cumulative incidence by birth cohort shifted to a younger age at onset during the first 22 years, but from the birth year 2000 a statistically significant reversed trend (P < 0.01) was seen. CONCLUSIONS Childhood T1D increased dramatically and shifted to a younger age at onset the first 22 years of the study period. We report a reversed trend, starting in 2000, indicating a change in nongenetic risk factors affecting specifically young children.

A functional polymorphism in the manganese superoxide dismutase gene and diabetic nephropathy.

Oxidative stress has been suggested to contribute to the development of diabetic nephropathy. Manganese superoxide dismutase (MnSOD) protects the cells from oxidative damage by scavenging free radicals. The demand for antioxidants is increased by smoking, which could disturb the balance between antioxidants and radicals. The present study aimed to determine whether a valine/alanine polymorphism in MnSOD (V16A, rs4880), alone or in combination with smoking, can contribute to development of diabetic nephropathy in 1,510 Finnish and Swedish patients with type 1 diabetes. Overt diabetic nephropathy (n = 619) was defined as having an albumin excretion rate (AER) >200 μg/min or renal replacement therapy; incipient diabetic nephropathy was defined as having an AER of 20–200 μg/min (n = 336). The control subjects had diabetes duration of ≥20 years, without albuminuria (AER <20 μg/min) and without antihypertensive treatment (n = 555). In addition to male sex and elevated A1C, smoking was significantly associated with diabetic nephropathy (overt plus incipient), odds ratio (OR) 2.00 (95% CI 1.60–2.50). When controlling for age at onset, diabetes duration, A1C, smoking, and sex, the Val/Val genotype was associated with an increase in risk of diabetic nephropathy (1.32 [1.00–1.74], P = 0.049). When evaluating the combined effect of genotype and smoking, we used logistic regression with stratification according to smoking status and genotype. The high-risk group (ever smoking plus Val/Val genotype) had 2.52 times increased risk of diabetic nephropathy (95% CI 1.73–3.69) compared with the low-risk group, but no departure from additivity was found. Our results indicate that smoking and homozygosity for the MnSOD Val allele is associated with an increased risk of diabetic nephropathy, which supports the hypothesis that oxidative stress contributes to the development of diabetic nephropathy.

Higher Intakes of Fish Protein Are Related to a Lower Risk of Microalbuminuria in Young Swedish Type 1 Diabetic Patients

OBJECTIVE To examine the influence of dietary intake from various protein and fat sources on the occurrence of microalbuminuria in type 1 diabetic patients. RESEARCH DESIGN AND METHODS In this nested case control study, 1,150 patients with diabetes duration >5 years reported dietary habits for the previous 12 months and submitted urinary samples for the analysis of albumin excretion rate (AER). A total of 75 cases of albuminuria (overnight AER > or = 15 microg/min) were identified and compared with 225 duration-matched control subjects. RESULTS Neither mean protein, fat intake, average fish protein intake (control subjects 4.56 +/- 3.83 g/day and cases 3.82 +/- 2.87 g/day; P = 0.12), nor intake of meat and vegetable protein differed between the cases of albuminuria and the control subjects. High consumers of fish protein (greater than the 75th percentile) (12 cases and 63 control subjects, mean intake 9.35 g fish protein/day, i.e., approximately 53 g fish/day) had lower odds ratios (ORs) for microalbuminuria than individuals consuming less fish protein (mean 2.72 g/day) (crude OR 0.49 and 95% CI 0.25-0.97). When adjusted for known confounding factors, such as HbA1c, mean arterial pressure, diabetes duration, age, sex, smoking, BMI, country region, and total energy, individuals with a high intake of fish protein and fish fat showed a reduction in the risk for microalbuminuria (OR 0.22 and 0.31, respectively; 95% CI 0.09-0.56 and 0.13-0.76, respectively). When fish protein and fat were adjusted for each other, a high intake of fish protein but not of fish fat was still significantly associated with a decrease in the risk for microalbuminuria. CONCLUSIONS Total protein and fat intake were not associated with the presence of microalbuminuria, but a diet including a high amount of fish protein seemed to lessen the risk.

Genetic influences of the intercellular adhesion molecule 1 (ICAM-1) gene polymorphisms in development of Type 1 diabetes and diabetic nephropathy.

Aim  The intercellular adhesion molecule‐1 (ICAM‐1) gene is located on chromosome 19p13, which is linked to Type 1 diabetes (T1D). ICAM‐1 expression is related to development of T1D and diabetic nephropathy. The present study aims to evaluate the genetic influence of ICAM‐1 gene polymorphisms on the development of T1D and diabetic nephropathy.

The endothelial nitric oxide synthase gene and risk of diabetic nephropathy and development of cardiovascular disease in type 1 diabetes

Nitric oxide (NO) is important in the maintenance of vascular tone and regulation of blood pressure. NO may also play a role in the development of both nephropathy and cardiovascular disease (CVD) in patients with diabetes. The susceptibility to nephropathy and CVD depends to some extent on genetic factors, therefore polymorphisms in the gene coding for endothelial NO-synthase, NOS3, can affect the risk of developing these diseases. Type 1 diabetes patients attending the Steno Diabetes Center, Denmark, between 1993 and 2001 were enrolled in this study. A total of 458 cases with diabetic nephropathy (albumin excretion >300 mg/24h) and 319 controls with persistent normoalbuminuria (<30 mg/24h), despite > or =20 years of diabetes duration at follow-up were identified. Patients were followed until death or end of the study. Associations between seven NOS3-gene polymorphisms and nephropathy, progression of nephropathy and CVD were studied. There was significant association between the rs743507 TT-genotype and diabetic nephropathy. When including age at diabetes onset, diabetes duration at follow-up, baseline Hb(A1c), sex and ever smoking in the analysis the OR was 1.43 (95% CI=1.03-2.00), P=0.035. In analyses of CVD development using Cox-regression the rs1799983 GG-genotype was a significant protective factor in normoalbuminuric patients, HR=0.32 (0.12-0.82), P=0.018, but not in patients with macroalbuminuria (covariates were; age at follow-up, baseline Hb(A1c), baseline systolic blood pressure, baseline cholesterol, sex and ever smoking). Our conclusion is that the NOS3-gene may be involved in the development of diabetic nephropathy in patients with type 1 diabetes and can be predictive of CVD during follow-up.

Genetic polymorphisms in the renin-angiotensin system confer increased risk of stroke independently of blood pressure : a nested case-control study.

Objective The renin–angiotensin system has a pathophysiological role in cardiovascular disease through a variety of processes. Polymorphisms in involved genes have been described and implicated in stroke. The aim of this study was to investigate two polymorphisms in two genes in the renin–angiotensin system and the risk of stroke. Design A nested case–control study using baseline data obtained from population-based surveys in northern Sweden was performed. There were 275 individuals without major concomitant disease who suffered a first ever stroke during follow-up and 549 controls matched for age, sex and domicile. Methods Blood samples obtained at baseline were analyzed for potential risk factors including the A1166C polymorphism of the angiotensin II type I receptor (AT1R) gene and the functional insertion/deletion polymorphism of the angiotensin-converting enzyme gene. Results Individuals with the AA genotype of the AT1R gene were at increased risk of ischemic stroke (odds ratio = 1.60; P = 0.005) compared with those with the AC and CC genotypes. The D allele of the angiotensin-converting enzyme insertion/deletion polymorphism was associated with a higher risk of stroke (odds ratio = 1.58; P = 0.014). Conclusion In this prospective study, there was an association between A1166C polymorphism in the angiotensin II receptor gene and ischemic stroke. We also replicated previous observations that the D allele of the angiotensin-converting enzyme insertion/deletion polymorphism was associated with increased risk of stroke. The observed elevated stroke risks conferred by these two polymorphisms are independent of each other and common risk factors such as blood pressure, diabetes, smoking and high cholesterol levels.

Glu298Asp and NOS4ab polymorphisms in diabetic nephropathy.

Background and aims. The risk of diabetic nephropathy (DN) increases with increase in intraglomerular pressure, which may partly be regulated by nitric oxide (NO). NO‐production can be affected by polymorphisms in the endothelial NO‐synthase gene (NOS3), hyperglycaemia and smoking. We therefore studied association between DN and two polymorphisms in NOS3, Glu298Asp and NOS4ab, in Caucasian type 1 diabetes (T1D) patients. Patients and methods. A total of 1510 Finnish and Swedish T1D patients were included in a cross‐sectional case‐control study. Incipient DN was defined as an albumin excretion rate (AER) of 20–200 µg/min (n = 336). Overt DN = AER>200 µg/min or renal replacement therapy (n = 619). All patients with DN were considered as cases. The controls were T1D patients with diabetes duration ⩾20 years, AER<20 µg/min and without antihypertensive treatment (n = 555). The genetic markers studied were a 27 bp repeat (NOS4ab) and Glu298Asp (rs1799983). Results. Age at onset of diabetes, male sex, duration of diabetes, HbA1c, blood pressure and smoking were assessed as possible confounders in the logistic regression analysis, which showed that homozygosity for the Glu‐allele of the Glu298Asp‐polymorphism was independently associated with increased risk of DN (OR = 1.46; 95% CI = 1.12–1.91). The variables smoking (OR = 2.13; 95% CI = 1.63–2.78), male sex (OR = 1.61; 95% CI = 1.23–2.10), HbA1c (OR per % increase above upper limit of the normal reference range = 1.02; 95% CI = 1.02–1.03), systolic (OR = 1.05; 95% CI = 1.04–1.06) and diastolic blood pressure (OR = 1.04; 95% CI = 1.02–1.05) also significantly and independently increased the risk of DN when taking age at diabetes onset and diabetes duration into account. The NOS4 a‐allele was not associated with DN. Conclusions. The Glu/Glu‐genotype of the NOS3 Glu298Asp polymorphism may increase the risk of developing DN independently of other known risk factors.

The effect of polymorphisms in the renin-angiotensin-aldosterone system on diabetic nephropathy risk

OBJECTIVES The risk of diabetic nephropathy (DN) can be increased by elevated intraglomerular pressure and glomerular filtration rate, leading to glomerular damage. This can be controlled by the renin-angiotensin-aldosterone (RAA) system, which has an important function regulating both systemic and intrarenal blood pressure. Smoking increases the risk of DN, but not all diabetic patients who smoke develop DN. There is a possibility that smoking has different effects depending on the different genotypes of the individual. We investigated the association of DN with seven polymorphisms in the RAA system and their possible interaction with smoking. SUBJECTS AND METHODS In the present case-control study, type 1 diabetic patients with diabetes duration > or =20 years, without albuminuria and without antihypertensive treatment (n=197), were included as controls. An albumin excretion rate (AER) of 20-200 microg/min (n=73) was considered as incipient DN, and an AER >200 microg/min was considered as overt DN (n=48). Smoking habits were obtained from questionnaires. RESULTS Homozygosity for the A allele, of the angiotensin II type 1 receptor (AGTR1) A1166C polymorphism, was associated with increased risk of overt DN (OR=3.04; 99% CI=1.02-9.06), independently of the other associated variables: age, duration of diabetes, ever smoking, HbA1c, and sex. The effect of the AA genotype was enhanced to a four times risk increase among ever-smoking patients. Two alleles of the microsatellite marker adjacent to the angiotensinogen gene were less common among nephropathy cases than among controls, but this was not significant when controlling for the same variables as above. CONCLUSIONS The risk of having overt DN was increased in patients homozygous for the A1166 allele, and smoking seemed to enhance the effect of the AGTR1 genotype.

Distribution of neuropeptide Y Leu7Pro polymorphism in patients with type 1 diabetes and diabetic nephropathy among Swedish and American populations

OBJECTIVE The distribution of Leu7Pro polymorphism in the neuropeptide Y gene shows a geographical north to south gradient of decreasing frequency, suggesting that it may be a population-specific causal variant. This polymorphism is found to be associated with diabetic nephropathy (DN) and coronary heart disease in Finnish women with type 1 diabetes (T1D). The present study aims to evaluate the susceptibility of this polymorphism to the development of DN in two different populations. DESIGN One sample set consists of 174 (females 98 and males 76) Swedish T1D patients with DN and 249 (females 132 and males 117) patients without DN. Another sample set includes 597 (females 356 and males 241) American T1D patients without DN and 577 (females 264 and males 313) patients with DN, who were descents of European Caucasians and were from the Genetics of Kidneys in Diabetes (GoKinD) Study. METHODS Genotyping of Leu7Pro polymorphism was performed by dynamic allele-specific hybridization. RESULTS The C allele frequencies of Leu7Pro polymorphism in T1D patients between Swedish and American GoKinD populations were significantly different (6.3 vs 4.0%; P=0.006). Particularly, the C allele frequency in Swedish female T1D patients with DN was significantly higher in comparison with T1D patients without DN (10.2 vs 4.2%; P=0.011, OR=2.614, 95% confidence intervals: 1.249-5.467). No significant association of this polymorphism with DN was observed in Swedish male T1D patients and the patients from GoKinD. CONCLUSIONS The present study provides further evidence that Leu7Pro polymorphism confers the susceptibility to the development of DN in Swedish female T1D patients.