Modeling GFR trajectories in diabetic nephropathy

American Indian chronic Renal insufficiency cohort study (AI-CRIC study)

BACKGROUND

Chronic kidney disease (CKD) is an increasing epidemic globally that is associated with adverse health outcomes including end stage kidney disease (ESKD), cardiovascular disease (CVD), and death. American Indians (AIs) have a higher prevalence of CKD than most other racial/ethnic groups, due in part to a high prevalence of type 2 diabetes. Other genetic and environmental factors not yet identified may also contribute to the disproportionate burden of CKD in AIs.

METHOD

We will establish 3 clinical centers to recruit AIs from the Southwest United States (US) to expand the Chronic Renal Insufficiency Cohort (CRIC) study. We will follow the current CRIC protocol for kidney and cardiovascular measures and outcomes, which include ambulatory monitoring of kidney function and the use of mobile health technologies for CVD sub-phenotyping, and compare the outcomes in AIs with those in other racial/ethnic groups in CRIC.

DISCUSSION

AI-CRIC will identify the role of various risk factors for rapid loss of kidney function among AIs of the Southwest US. In addition, to better understand the natural history of CKD and CVD in this high-risk population, we will identify unique risk factors for CKD and CVD progression in AIs. We will also compare event rates and risk factors for kidney and cardiovascular events in AIs with the other populations represented in CRIC.

Markers and risk factors for chronic kidney disease in sub-Saharan Africans: baseline levels and 12-month trajectories in newly referred patients in Cameroon

Background

Little is known about the changes in disease makers and risk factors in patients with chronic kidney disease (CKD) under nephrological care in Africa. This study aimed to evaluate the baseline level of markers of CKD and their 12-month time-trend in newly referred patients in a tertiary hospital in Cameroon.

Methods

This was a retrospective cohort study including 420 patients referred for CKD between 2006 and 2012 to the nephrology unit of the Douala General Hospital in the littoral region of Cameroon. Their disease and risk profile was assessed at baseline and every 3 months for 1 year. Estimated glomerular filtration rate (eGFR) was based on MDRD and Schwartz equations. CKD was diagnosed in the presence of eGFR< 60 ml/min/1.73 m² and/or proteinuria> 1+ and/or abnormal renal ultrasound persisting for ≥3 months. Data analysis used mixed linear regressions.

Results

Of the 420 patients included, 66.9% were men and mean age was 53.8 (15.1) years. At referral, 37.5% of the participants were at CKD Stage 3, 30.8% at stage 4 and 26.8% at stage 5. There was 168 (40%) diabetic and 319 (75.9%) hypertensive patients. After some improvement during the first 3 months, eGFR steadily decreased during the first year of follow-up, and this pattern was robust to adjustment for many confounders. Systolic and diastolic blood pressure levels significantly fluctuated during the first twelve months of follow-up. Changes in the levels of other risk factors and markers of disease severity over time were either borderline or non-significant.

Conclusion

Patients with CKD in African settings are referred to the nephrologist at advanced stages. This likely translates into a less beneficial effects of specialised care on the course of the disease.

Increased lipogenesis and impaired β-oxidation predict type 2 diabetic kidney disease progression in American Indians

BACKGROUNDIn this study, we identified the lipidomic predictors of early type 2 diabetic kidney disease (DKD) progression, which are currently undefined.METHODSThis longitudinal study included 92 American Indians with type 2 diabetes. Serum lipids (406 from 18 classes) were quantified using mass spectrometry from baseline samples when iothalamate-based glomerular filtration rate (GFR) was at least 90 mL/min. Affymetrix GeneChip Array was used to measure renal transcript expression. DKD progression was defined as at least 40% decline in GFR during follow-up.RESULTSParticipants had a mean age of 45 ± 9 years and median urine albumin/creatinine ratio of 43 (interquartile range 11-144). The 32 progressors had significantly higher relative abundance of polyunsaturated triacylglycerols (TAGs) and a lower abundance of C16-C20 acylcarnitines (ACs) (P < 0.001). In a Cox regression model, the main effect terms of unsaturated free fatty acids and phosphatidylethanolamines and the interaction terms of C16-C20 ACs and short-low-double-bond TAGs by categories of albuminuria independently predicted DKD progression. Renal expression of acetyl-CoA carboxylase-encoding gene (ACACA) correlated with serum diacylglycerols in the glomerular compartment (r = 0.36, and P = 0.006) and with low-double-bond TAGs in the tubulointerstitial compartment (r = 0.52, and P < 0.001).CONCLUSIONCollectively, the findings reveal a previously unrecognized link between lipid markers of impaired mitochondrial β-oxidation and enhanced lipogenesis and DKD progression in individuals with preserved GFR. Renal acetyl-CoA carboxylase activation accompanies these lipidomic changes and suggests that it may be the underlying mechanism linking lipid abnormalities to DKD progression.TRIAL REGISTRATIONClinicalTrials.gov, NCT00340678.FUNDINGNIH R24DK082841, K08DK106523, R03DK121941, P30DK089503, P30DK081943, and P30DK020572.

Progression of diabetic kidney disease and trajectory of kidney function decline in Chinese patients with Type 2 diabetes

Diabetes is a major cause of end stage renal disease (ESRD), yet the natural history of diabetic kidney disease is not well understood. We aimed to identify patterns of estimated GFR (eGFR) trajectory and to determine the clinical and genetic factors and their associations of these different patterns with all-cause mortality in patients with type 2 diabetes. Among 6330 patients with baseline eGFR >60 ml/min per 1.73 m² in the Hong Kong Diabetes Register, a total of 456 patients (7.2%) developed Stage 5 chronic kidney disease or ESRD over a median follow-up of 13 years (incidence rate 5.6 per 1000 person-years). Joint latent class modeling was used to identify different patterns of eGFR trajectory. Four distinct and non-linear trajectories of eGFR were identified: slow decline (84.3% of patients), curvilinear decline (6.5%), progressive decline (6.1%) and accelerated decline (3.1%). Microalbuminuria and retinopathy were associated with accelerated eGFR decline, which was itself associated with all-cause mortality (odds ratio [OR] 6.9; 95% confidence interval [CI]: 5.6-8.4 for comparison with slow eGFR decline). Of 68 candidate genetic loci evaluated, the inclusion of five loci (rs11803049, rs911119, rs1933182, rs11123170, and rs889472) improved the prediction of eGFR trajectories (net reclassification improvement 0.232; 95% CI: 0.057--0.406). Our study highlights substantial heterogeneity in the patterns of eGFR decline among patients with diabetic kidney disease, and identifies associated clinical and genetic factors that may help to identify those who are more likely to experience an accelerated decline in kidney function.

A molecular morphometric approach to diabetic kidney disease can link structure to function and outcome

Diabetic kidney disease is the leading cause of kidney failure. However, studies of molecular mechanisms of early kidney damage are lacking. Here we examined for possible linkage between transcriptional regulation and quantitative structural damage in early diabetic kidney disease in Pima Indians with type 2 diabetes. Tissue obtained from protocol kidney biopsies underwent genome-wide compartment-specific gene expression profiling and quantitative morphometric analysis. The ultrastructural lesion most strongly associated with transcriptional regulation was cortical interstitial fractional volume (VvInt), an index of tubule-interstitial damage. Transcriptional co-expression network analysis identified 1843 transcripts that correlated significantly with VvInt. These transcripts were enriched for pathways associated with mitochondrial dysfunction, inflammation, migratory mechanisms, and tubular metabolic functions. Pathway network analysis identified IL-1β as a key upstream regulator of the inflammatory response and five transcription factors cooperating with p53 to regulate metabolic functions. VvInt-associated transcripts showed significant correlation with the urine albumin to creatinine ratio and measured glomerular filtration rate 10 years after biopsy, establishing a link between the early molecular events and long-term disease progression. Thus, molecular mechanisms active early in diabetic kidney disease were revealed by correlating intrarenal transcripts with quantitative morphometry and long-term outcomes. This provides a starting point for identification of urgently needed therapeutic targets and non-invasive biomarkers of early diabetic kidney disease.

Analytic Considerations for Repeated Measures of eGFR in Cohort Studies of CKD

Repeated measures of various biomarkers provide opportunities for us to enhance understanding of many important clinical aspects of CKD, including patterns of disease progression, rates of kidney function decline under different risk factors, and the degree of heterogeneity in disease manifestations across patients. However, because of unique features, such as correlations across visits and time dependency, these data must be appropriately handled using longitudinal data analysis methods. We provide a general overview of the characteristics of data collected in cohort studies and compare appropriate statistical methods for the analysis of longitudinal exposures and outcomes. We use examples from the Chronic Renal Insufficiency Cohort Study to illustrate these methods. More specifically, we model longitudinal kidney outcomes over annual clinical visits and assess the association with both baseline and longitudinal risk factors.

Patterns of progression of chronic kidney disease at later stages

Background

At later stages of chronic kidney disease (CKD), a pattern of linear and irreversible renal function decline is thought to be the most common. The objective of this study was to describe the characteristics of the different patterns of CKD progression, and to investigate potentially modifiable factors associated with the rate of decline of renal function.

Methods

This was a retrospective, observational study in a cohort of adult patients with CKD Stage 4 or 5 not on dialysis. Decline in renal function was estimated as the slope of the individual linear regression line of estimated glomerular filtration rate (eGFR) over time. The following patterns of CKD progression were considered: unidentifiable, linear, nonlinear (curvilinear) and positive (improvement of renal function).

Results

The study group consisted of 915 patients (mean ±SD age 65 ± 14 years, 48% females, median follow-up time 16 months). A linear pattern was observed in 38%, unidentifiable in 23%, nonlinear in 24% and positive in 15% of the study patients. The mean eGFR slope was: −3.35 ± 4.45 mL/min/year. Linear and unidentifiable patterns were associated with more rapid loss of renal function. By multiple linear and logistic regression analysis, the magnitude of proteinuria, the systolic blood pressure and the treatment with dual renin–angiotensin system blockade were associated with more rapid CKD progression. On the contrary, older age and discontinuation of commonly prescribed medication with potential influence on renal function or eGFR measurements were associated with slower CKD progression.

Conclusions

A majority of patients with advanced CKD show patterns of renal function decline different from linear, and several of the main determinants of CKD progression are potentially modifiable.

Intrarenal Resistive Index in Patients with Type 2 Diabetes Mellitus with and without Microalbuminuria

Diabetic nephropathy affects a subset of about 30% of patients with type 1 Diabetes Mellitus (DM); it also develops in a less defined percentage (20–30%) of patients with type 2, after a period of 15–20 years. It is usually divided into stages. The aim of this study is to assess the usefulness of duplex sonography with Doppler wave form analysis in the evaluation of early diabetic nephropathy, in order to detect patients at risk for irreversible renal disease. 262 patients (61 males, 201 females; age range: 48–81 years) with type 2 diabetes mellitus were studied; 100 healthy volunteers with no evidence of diabetes mellitus (74 females, 26 males; age range: 50–80 years) composed the control group. All of them underwent duplex Doppler sonography of the kidneys; a scanner with a 3.5 MHz transducer (Toshiba 270 SSA) was used, Pulsatily Index (P.I.) and Resistive Index (R.I.) of Doppler waveform were obtained at the intrarenal arteries; the average value of 3 bilateral measurements was taken. Doppler sonography was done by the same authors without knowledge of the patient group (case or control). Both indexes (PI. and R.I.) resulted to be higher in patients with DM compared to controls in patients with microalbuminuria: PI. = 1.49 +/- 0.34 vs. 1.07 +/- 0.06, p< 0.05; R.I. = 0.79 +/- 0.15 vs 0.60 +/- 0.03, p<0.05. Even if our data have to be confirmed by further studies, they suggest that duplex Doppler sonography may be a useful complementary test in the evaluation of diabetic nephropathy, especially in the early stages, in order to identify more patients at risk of developing diabetic nephropathy.

Structural Predictors of Loss of Renal Function in American Indians with Type 2 Diabetes

BACKGROUND AND OBJECTIVES

Diabetes is the leading cause of kidney failure in the United States, but early structural determinants of renal function loss in type 2 diabetes are poorly defined. We examined the association between morphometrically determined renal structural variables and loss of renal function in 111 American Indians with type 2 diabetes who volunteered for a research kidney biopsy at the end of a 6-year clinical trial designed to test the renoprotective efficacy of losartan versus placebo. Participants were subsequently followed in an observational study, in which annual measurements of GFR (iothalamate) initiated during the clinical trial were continued.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Renal function loss was defined as ≥40% loss of GFR from the research examination performed at the time of kidney biopsy. Associations with renal function loss were evaluated by Cox proportional hazards regression. Hazard ratios (HRs) were reported per 1-SD increment for each morphometric variable.

RESULTS

Of 111 participants (82% women; baseline mean [±SD] age, 46 years old [±10]; diabetes duration, 16 years [±6]; hemoglobin A1c =9.4% [±2.2]; GFR=147 ml/min [±56]; median albumin-to-creatinine ratio, 41 mg/g [interquartile range, 13-158]), 51 (46%) developed renal function loss during a median follow-up of 6.6 years (interquartile range, 3.1-9.0). Fourteen had baseline GFR <90 ml/min, and three had baseline GFR <60 ml/min. Higher mesangial fractional volume (HR, 2.27; 95% confidence interval [95% CI], 1.58 to 3.26), percentage of global glomerular sclerosis (HR, 1.63; 95% CI, 1.21 to 2.21), nonpodocyte cell number per glomerulus (HR, 1.50; 95% CI, 1.10 to 2.05), glomerular basement membrane width (HR, 1.48; 95% CI, 1.05 to 2.08), mean glomerular volume (HR, 1.42; 95% CI, 1.02 to 1.96), and podocyte foot process width (HR, 1.28; 95% CI, 1.03 to 1.60); lower glomerular filtration surface density (HR, 0.62; 95% CI, 0.41 to 0.94); and fewer endothelial fenestrations (HR, 0.68; 95% CI, 0.48 to 0.95) were each associated with GFR decline after adjustment for baseline age, sex, duration of diabetes, hemoglobin A1c, GFR, and treatment assignment during the clinical trial.

CONCLUSIONS

Quantitative measures of glomerular structure predict loss of renal function in type 2 diabetes.

High body mass index reduces glomerular filtration rate decline in type II diabetes mellitus patients with stage 3 or 4 chronic kidney disease

Whether high body mass index (BMI) has an effect on progressive diabetic nephropathy in type II diabetes mellitus (DM) patients with chronic kidney disease (CKD) stage 3 or 4 remains unclear. This prospective study aimed to investigate the relationship between BMI and progression of renal function deterioration in type II DM patients with CKD stage 3 or 4.A total of 105 type II DM patients with CKD stage 3 or 4 participated in this 24-month prospective observational study. Patients were divided into 3 groups according to BMI as follows: normal group, BMI of 18.5-22.9 kg/m; overweight group, BMI of 23-24.9 kg/m; and obese group, BMI of ≥25 kg/m. The primary end point was a 2-fold elevation in serum creatinine levels (measured twice with a 1-month interval) from baseline values, need for long-term dialysis, or death during the 24-month observation period.In the linear regression analysis with the stepwise method, each 1 kg/m increase in BMI led to an increase of 0.32 mL min × 1.73 m in the estimated glomerular filtration rate (95% confidence interval, CI, 0.01-0.62; P = 0.04) during the 24-month study period. Moreover, multivariate Cox regression analysis showed that compared with the obese group, the normal BMI group (hazard ratio = 2.76, 95% CI : 1.27-6; P = 0.01) achieved the primary outcome after adjusting for other factors.In this 24-month prospective observational study, we showed that BMI of ≥25 kg/m was a protective factor for renal function deterioration in type II DM patients with CKD stage 3 or 4.

Regression methods for investigating risk factors of chronic kidney disease outcomes: the state of the art

Background

Chronic kidney disease (CKD) is a progressive and usually irreversible disease. Different types of outcomes are of interest in the course of CKD such as time-to-dialysis, transplantation or decline of the glomerular filtration rate (GFR). Statistical analyses aiming at investigating the association between these outcomes and risk factors raise a number of methodological issues. The objective of this study was to give an overview of these issues and to highlight some statistical methods that can address these topics.

Methods

A literature review of statistical methods published between 2002 and 2012 to investigate risk factors of CKD outcomes was conducted within the Scopus database. The results of the review were used to identify important methodological issues as well as to discuss solutions for each type of CKD outcome.

Results

Three hundred and four papers were selected. Time-to-event outcomes were more often investigated than quantitative outcome variables measuring kidney function over time. The most frequently investigated events in survival analyses were all-cause death, initiation of kidney replacement therapy, and progression to a specific value of GFR. While competing risks were commonly accounted for, interval censoring was rarely acknowledged when appropriate despite existing methods. When the outcome of interest was the quantitative decline of kidney function over time, standard linear models focussing on the slope of GFR over time were almost as often used as linear mixed models which allow various numbers of repeated measurements of kidney function per patient. Informative dropout was accounted for in some of these longitudinal analyses.

Conclusions

This study provides a broad overview of the statistical methods used in the last ten years for investigating risk factors of CKD progression, as well as a discussion of their limitations. Some existing potential alternatives that have been proposed in the context of CKD or in other contexts are also highlighted.

Nonlinear trajectory of GFR in children before RRT

GFR decline in patients with CKD has been widely approximated using linear models, but this linearity assumption is not well validated. We conducted a matched case-control study in children from the Chronic Kidney Disease in Children (CKiD) cohort ages 1-16 years with mild to moderate CKD to assess whether GFR decline follows a nonlinear trajectory as CKD approaches ESRD. Children (n=125) who initiated RRT (cases) during follow-up were individually matched by CKD stage at baseline and glomerular/nonglomerular diagnosis with children (n=125) who remained RRT-free when the corresponding case initiated RRT (controls). GFR trajectories were compared using log-linear and piecewise log-linear mixed effects models adjusted for baseline characteristics. From study entry to 18 months before RRT, GFR declined 7% faster among cases compared with controls. However, GFR declined 26% faster among cases compared with controls (P<0.001) during the 18 months before RRT. Nonlinearity in the rate of kidney function loss, which was shown in this cohort, may preclude accurate clinical prediction of the timing of RRT and adequate patient preparation. This study should prompt the characterization of predictive factors that may contribute to an acceleration of kidney function decline.

Diabetic nephropathy in a sibling and albuminuria predict early GFR decline: a prospective cohort study

BACKGROUND

Diabetic nephropathy is a growing clinical problem, and the cause for >40% of incident ESRD cases. Unfortunately, few modifiable risk factors are known. The objective is to examine if albuminuria and history of diabetic nephropathy (DN) in a sibling are associated with early DN progression or mortality.

METHODS

In this longitudinal study of adults >18 yrs with diabetes monitored for up to 9 yrs (mean 4.6 ± 1.7 yrs), 435 subjects at high risk (DN family history) and 400 at low risk (diabetes >10 yrs, normoalbuminuria, no DN family history) for DN progression were evaluated for rate of eGFR change using the linear mixed effects model and progression to ESRD. All-cause mortality was evaluated by Kaplan-Meier analyses while controlling for baseline covariates in a Cox proportional hazards model. Covariates included baseline eGFR, age, gender, race, diabetes duration, blood pressure, hemoglobin A1c and urine albumin:creatinine ratio. Propensity score matching was used to identify high and low risk group pairs with balanced covariates. Sensitivity analyses were employed to test for residual confounding.

RESULTS

Mean baseline eGFR was 74 ml/min/1.73 m2 (86% of cohort >60 ml/min/1.73 m2). Thirty high risk and no low risk subjects developed ESRD. eGFR decline was significantly greater in high compared to low risk subjects. After controlling for confounders, change in eGFR remained significantly different between groups, suggesting that DN family history independently regulates GFR progression. Mortality was also significantly greater in high versus low risk subjects, but after controlling for baseline covariates, no significant difference was observed between groups, indicating that factors other than DN family history more strongly affect mortality. Analyses of the matched pairs confirmed change in eGFR and mortality findings. Sensitivity analyses demonstrated that the eGFR results were not due to residual confounding by unmeasured covariates of a moderate effect size in the propensity matching.

CONCLUSIONS

Diabetic subjects with albuminuria and family history of DN are vulnerable for early GFR decline, whereas subjects with diabetes for longer than 10 years, normoalbuminuria and negative family history, experience slower eGFR decline, and are extremely unlikely to require dialysis. Although we would not recommend that patients with low risk characteristics be neglected, scarce resources would be more sensibly devoted to vulnerable patients, such as the high risk cases in our study, and preferably prior to the onset of albuminuria or GFR decline.

Explorations in statistics: permutation methods

Learning about statistics is a lot like learning about science: the learning is more meaningful if you can actively explore. This eighth installment of Explorations in Statistics explores permutation methods, empiric procedures we can use to assess an experimental result-to test a null hypothesis-when we are reluctant to trust statistical theory alone. Permutation methods operate on the observations-the data-we get from an experiment. A permutation procedure answers this question: out of all the possible ways we can rearrange the observations we got, in what proportion of those arrangements is the sample statistic we care about at least as extreme as the one we got? The answer to that question is the P value.

The early decline in renal function in patients with type 1 diabetes and proteinuria predicts the risk of end-stage renal disease

The risk of end-stage renal disease (ESRD) remains high in patients with type 1 diabetes and proteinuria; however, little is known about the rate of decline in their renal function. To help determine this, we enrolled patients with type 1 diabetes and proteinuria whose estimated glomerular filtration rate (eGFR) was normal (equal to or above 60 ml/min per 1.73 m(2)). Using a minimum of five serial measurements of serum creatinine for 161 patients, we determined individual trajectories of eGFR change and the occurrence of ESRD during 5-18 years of follow-up. The rates were linear for 110 patients, for 24 the nonlinear rate was mild enough to satisfy a linear model, and the rates were clearly nonlinear for only 27 patients. Overall, in more than one-third of patients, the eGFR decline was less than 3.5 ml/min per 1.73 m(2) per year and the lifetime risk of ESRD could be considered negligible. In the remainder of patients, eGFR declined with widely different slopes and ESRD developed within 2 to 18 years. Based on up to 5 years observation, when renal function was within the normal range, the estimates of early eGFR slope predicted the risk of ESRD during subsequent follow-up better than the baseline clinical characteristics of glycated hemoglobin, blood pressure, or the albumin to creatinine ratio. Thus, the early slope of eGFR decline in patients with type 1 diabetes and proteinuria can be used to predict the risk of ESRD.

Early renal function decline in type 2 diabetes

BACKGROUND AND OBJECTIVES

Early decline in GFR may reflect progressive kidney disease in type 1 diabetes, but its predictive value in type 2 diabetes is uncertain.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this longitudinal study, GFR was measured serially over approximately 4.0 years in 195 Pima Indians with type 2 diabetes. Renal function decline (RFD) was defined during this initial period by an average GFR loss ≥3.3%/yr, as defined previously in type 1 diabetes. Subsequently, participants were followed for up to 17.8 years to ESRD onset, death, or December 31, 2010, whichever came first.

RESULTS

RFD prevalence during the initial period was 32% in 68 participants with normal baseline albuminuria (albumin/creatinine ratio [ACR] < 30 mg/g), 42% in 88 with microalbuminuria (ACR 30 to <300 mg/g), and 74% in 39 with macroalbuminuria (ACR ≥300 mg/g; P<0.001). The cumulative incidence of ESRD 10 years after the initial period was 41% in those with RFD and 15% in those without (P<0.001); 41 of the 49 ESRD cases (83.7%) occurred in participants who had or developed macroalbuminuria during the initial period. When adjusted for age, sex, diabetes duration, and hemoglobin A1c, the ESRD hazard rate was 4.78 times (95% confidence interval, 2.39-9.58) as high in those with RFD as in those without; further adjustment for albuminuria attenuated this association (hazard ratio, 1.79; 95% confidence interval, 0.82-3.91).

CONCLUSIONS

In type 2 diabetes, loss of GFR often occurs before the onset of macroalbuminuria, but a decline predictive of ESRD is strongly dependent on progression to macroalbuminuria.

Explorations in statistics: the bootstrap

Learning about statistics is a lot like learning about science: the learning is more meaningful if you can actively explore. This fourth installment of Explorations in Statistics explores the bootstrap. The bootstrap gives us an empirical approach to estimate the theoretical variability among possible values of a sample statistic such as the sample mean. The appeal of the bootstrap is that we can use it to make an inference about some experimental result when the statistical theory is uncertain or even unknown. We can also use the bootstrap to assess how well the statistical theory holds: that is, whether an inference we make from a hypothesis test or confidence interval is justified.

Linkage analysis of albuminuria

American Indians have a higher prevalence of albuminuria than the general population, likely resulting from a combination of environmental and genetic risk factors. To localize gene regions influencing variation in urinary albumin-to-creatinine ratio, we performed a linkage analysis and explored gene-by-diabetes, -hypertension, and -obesity interactions in a large cohort of American Indian families. We recruited >3600 individuals from 13 American Indian tribes from three centers (Arizona, North and South Dakota, and Oklahoma). We performed multipoint variance component linkage analysis in each center as well as in the entire cohort after controlling for center effects. We used two modeling strategies: Model 1 incorporated age, gender, and interaction terms; model 2 also controlled for diabetes, BP, body mass index, HDL, LDL, triglycerides, and smoking status. We evaluated interactions with diabetes, hypertension, and obesity using additive, interaction-specific linkage and stratified analyses. Loci suggestive for linkage to urinary albumin-to-creatinine ratio included 1q, 6p, 9q, 18q, and 20p. Gene-by-diabetes interaction was present with a quantitative trait locus specific to the diabetic stratum in the Dakotas isolated on 18q21.2 to 21.3 using model 1 (logarithm of odds = 3.3). Gene-by-hypertension interaction was present with quantitative trait loci specific to the hypertensive stratum in the Dakotas on 7q21.11 using model 1 (logarithm of odds = 3.4) and 10q25.1 using model 2 (logarithm of odds = 3.3). These loci replicate findings from multiple other genome scans of kidney disease phenotypes with distinct populations and are worthy of further study.

Increased Renal Arterial Resistance Predicts the Course of Renal Function in Type 2 Diabetes With Microalbuminuria

Type 2 diabetic patients often die because of end-stage renal failure, but no definitive reliable factor predicting long-term renal outcome has been identified. We tested whether a renal arterial resistance index (R/I) ≥80, using Doppler ultrasound technique, was predictive of worsening renal function. The primary end points of the study were 1) the course of glomerular filtration rate (GFR) and 2) the albumin excretion rate in 157 microalbuminuric, hypertensive, type 2 diabetic patients after a 7.8-year follow-up period (range 7.1–9.2). Kaplan-Meier curves for the primary end point (decrease of GFR ≥−3.0 ml/min per 1.73 m2 per year) was two to three times more frequently observed in patients with R/I ≥80. Four- to fivefold fewer patients showed a regression to normoalbuminuria during the follow-up period from baseline microalbuminuria in the cohort with R/I ≥80. Overt proteinuria did develop in 24% of patients with R/I ≥80 and in 5% of patients with R/I &lt;80 (P &lt; 0.01). In conclusion, intrarenal arterial resistance appears to play a nontrivial role in deteriorating renal function in type 2 diabetic patients. R/I is a noninvasive diagnostic procedure, which strongly predicts the outcome of renal function in type 2 diabetic patients, even when GFR patterns are still normal.