An Integrative Study of the Genetic, Social and Environmental Determinants of Chronic Kidney Disease Characterized by Tubulointerstitial Damages in the North Central Region of Sri Lanka: Shanika NANAYAKKARA, et al. Department of Health and Environmental Sciences, Graduate School of Medicine, Kyoto University—Objectives: Previous investigations on chronic kidney disease of unknown etiology characterized by tubulointerstitial damages (CKDu) in the North Central Region (NCR) of Sri Lanka have supported the involvement of social, environmental and genetic factors in its pathogenesis. Methods: We conducted a social‐environmental‐ and‐genetic epidemiology study on a male population in NCR to investigate the genetic and environmental contributors. We recruited 311 case‐series patients and 504 control candidates. Of the 504 control candidates, 218 (43%) were eliminated because of the presence of hypertension, proteinuria, high HbA1c, high serum creatinine or high alpha‐1 microglobulin in urine.Results and Discussion: None of 18 metals measured (μg/l) in urine, including Cd, As and Pb, showed significantly higher concentrations in cases compared with controls. As speciation results showed that 75.80% of total urinary As was in the form of arsenobetaine, which is non‐toxic to humans. None of the metal concentrations in drinking water samples exceeded guideline values. A genome‐wide association study (GWAS) was conducted to determine the genetic contributors. The GWAS yielded a genome‐wide significant association with CKDu for a single nucleotide polymorphism (SNP; rs6066043; p=5.23 ~ 10.9 in quantitative trait locus analysis; p=3.73 ~ 10.8 in dichotomous analysis) in SLC13A3 (sodium‐dependent dicarboxylate transporter member 3). The population attributable fraction and odds ratio for this SNP were 50% and 2.13. Genetic susceptibility was identified as the major risk factor for CKDu. However, 43% of the apparently healthy male population suffers from non‐communicable diseases, suggesting their possible influence on CKDu progression.

Chronic kidney disease of uncertain etiology (CKDu) in North Central Province of Sri Lanka has become a key public health concern in the agricultural sector due to the dramatic rise in its prevalence and mortality among young farmers. Although cadmium has been suspected as a causative pathogen, there have been controversies. To date, the pathological characteristics of the disease have not been reported. Histopathological observations of 64 renal biopsies obtained at Anuradhapura General Hospital from October 2008 to July 2009 were scored according to Banff 97 Working Classification of Renal Allograft pathology. The correlations between the histological observations and clinical parameters were statistically analyzed. Interstitial fibrosis and tubular atrophy with or without nonspecific interstitial mononuclear cell infiltration was the dominant histopathological observation. Glomerular sclerosis, glomerular collapse, and features of vascular pathology such as fibrous intimal thickening and arteriolar hyalinosis were also common. Although hypertension was identified as one of the common clinical features among the cases, it did not influence the histopathological lesions in all the cases. This study concludes that tubulointerstitial damage is the major pathological lesion in CKDu. Exposure(s) to an environmental pathogen(s) should be systematically investigated to elucidate such tubulointerstitial damage in CKDu.

Moyamoya disease—an idiopathic vascular disorder of intracranial arteries—is often accompanied by hypertension. RNF213 has been identified as a susceptibility gene for moyamoya disease. In the present study, the association of p.R4810K (G>A) with blood pressure (BP) was investigated in a Japanese population. Three independent study populations, the Nyukawa (n = 984), Noshiro (n = 2,443) and Field (n = 881) studies, joined this study. BP, body weight and height were measured. Past and present symptoms and disease and medication histories were assessed by interview. Associations of p.R4810K (rs112735431, ss179362673) of RNF213 with BP were investigated. Two linkage disequilibrium blocks were constructed for moyamoya patients with p.R4810K (n = 140) and the general population (n = 384) using 39 single nucleotide polymorphisms (SNPs) spanning 390 kb around RNF213. A total of 60 carriers (3 for AA genotype and 57 for GA genotype) were found in these samples, and the minor allele frequencies were 1.4 % in the Nyukawa and Field studies and 0.2 % in the Noshiro study. Regression analyses adjusted for age, sex and body mass index based on an additive model demonstrated significant associations with systolic BP (mmHg/allele): β (standard error) was 8.2 (2.9) in the Nyukawa study (P = 4.7 × 10⁻³), 18.7 (5.4) in the Noshiro study (P = 4.6 × 10⁻⁴) and 8.9 (2.0) (P = 1.0 × 10⁻⁵) in the three populations. In contrast, diastolic BP showed significant associations only in the Noshiro study. Linkage disequilibrium blocks contained none of the BP-associated proxy SNPs reported by previous studies. Our study suggests that p.R4810K of RNF213 is associated strongly with systolic BP.

Background In the North Central Province of Sri Lanka, chronic kidney disease of uncertain etiology (CKDue) has increased markedly over the past 15–20 years. Methods From around 4,700 patients who were followed up, 106 affected patients who visited two local clinics in the endemic area for CKDue on August 10, 2009 and 10 pedigrees of 10 of these cases with familial clustering of CKDue participated in this study. Urine samples, collected from affected patients (n = 106), unaffected relative controls (n = 81), and Japanese controls (n = 50), were analyzed for two tubular markers: α1-microglobulin and N-acetyl-β-d-glucosaminidase. Urine samples from patients with CKDue stages 1–4 (n = 101) and all the samples from unaffected relatives and Japanese controls were analyzed for urinary cadmium concentration. Results Urinary excretion of α1-microglobulin was elevated even in the earliest stage of CKDue compared with its levels in unaffected relative controls. Urinary excretion of N-acetyl-β-d-glucosaminidase was elevated only in stage 5. In contrast, urinary cadmium excretion was similar in CKDue patients and in the unaffected relative controls, and levels in both these groups were significantly lower than the level in the Japanese controls. All levels were below the threshold level for renal toxicity, indicating the absence of any evidence of cadmium toxicity. Conclusions The present study indicates that renal tubular damage occurs in the very early stage of CKDue and demonstrates the existence of familial clustering, suggesting that CKDue is likely to be the outcome of exposure to an unknown nephrotoxin in susceptible subjects in the endemic region.