Faculty Bibliography

Background: CSF have lower HRQoL compared to US Standard Population. We have shown previously that HRQoL results need to be controlled for the last stone event and comorbidities. We now show the first longitudinal HRQoL domain profiles for baseline and two yearly follow-ups.
Method(s): CSF were enrolled from the RKSC registry. HRQoL was measured with the generic non-disease specific SF-36v2. Results were calculated as norm-based scores (NBS) based on US Standard Population (Domain score mean = 50). We selected 3 stone frequency groups (SFG): low (stone-free during observation period), medium (minimum of one stone event between 31-365 days) and high (stone event always present within 30 days of the survey), and compared the groups' HRQoL at baseline and second follow-up.
Result(s): We scored 386 surveys. 78 participants (32 males and 46 females) were compared at baseline and 2 follow-up assessments. Mean age was 45 years (male 44/ female 46). Repeated measure ANOVA showed no difference within each SFG over time (Fig 1). However, domain scores were significantly different between SFG's (p<0.05) at each time point, with low>medium>high stone frequency. Whether surgical intervention was required, and type, were not predictors of HRQoL outcomes. Better HRQoL tracked with lower cystine excretion per liter on 24h urine collections; lower cystine capacity and higher citrate doses were underpowered (NS).
Conclusion(s): CSF with high stone event rates experience worse HRQoL over time, while CSF with no stone events achieved better HRQoL than US standard. Clinnical data suggest that the high SFG is undertreated

Background: About 60-80% of kidney stones are composed of calcium oxalate (CaOx); idiopathic CaOx kidney stones (CaOPx), primary hyperoxaluria (PH) and enteric hyperoxaluria (EH) are diseases predisposing to stones. Oxalobacter formigenes (Oxf) is a human gut commensal that depends on oxalate for its carbon and energy, and may be protective against CaOx stones. We hypothesize that the microbiome community structure differs between patients with CaOx, PH, EH and normal subjects (NS). We also expect that Oxf isolates from PH patients will result in further reduction in urinary oxalate when compared to Oxf reference strain CC13, in a germ-free (GF) mouse model.
Method(s): We collected fecal specimens from 34 subjects (mean age: 39.1 +/- 11.9 years) with PH (n=6), CaOPx (n=10), EH (n= 5) and NS (n=13) in a cross-sectional observational study, and tested fecal samples from the groups by: 1)16S rRNA sequencing to determine the microbiome community structure, 2)PCR and qPCR for Oxf colonization and, 3) culturing in high oxalate selective media for indication of Oxf presence and subsequent isolation. We isolated Oxf from 4 PH (Oxf PH) subjects. We gavaged a growing culture of PH Oxf (n=6), Oxf reference strain CC13 (Oxf CC13) (n=5), and sham (n=6) into adult C5B6 GF mice, observing them for 4 weeks. We collected urine from mice for 48 hours before sacrifice to be tested for oxalate and creatinine (Uox/cr).
Result(s): Oxf was detected in 6 (46%) of 13 NS, 1 (10%) of 10 CaOPx, 0 (0%)of 4 EH, and 5 (83%) of 6 PH. Microbiome analysis revealed that the 4 groups differed in beta diversity, based on Bray-Curtis dissimilarity (p=0.08). Alpha diversity analysis trended toward lower Shannon and phylogenetic diversity index in the CaOPx and EH subjects compared to PH and NS. Introducing the PH Oxf to GF mice led to lower Uox/cr than in uninoculated controls (0.68 +/- 0.14, and 2.26 +/-0.49, respectively, p=0.04 by Mann-Whitney U test), but not significantly different from the Oxf CC13-innoculated mice (0.68 +/- 0.14, and 0.91 +/-0.24, respectively, p=0.26 by Mann-Whitney U test).
Conclusion(s): These studies provide evidence of differences in Oxf colonization rates and in microbiome composition in patients with CaOx stones and show the functional capacity of a PH Oxf strain to ameliorate hyperoxaluria. Studies to expand these patient groups are on-going

Background: Kidney stones represent a disease of worldwide prevalence with significant public health implications. About 60-80% of stones are composed of calcium oxalate (CaOx); hyperoxaluria is a major risk factor for CaOx stones. Oxalate is an endproduct of mammalian digestion and as with urea, must be excreted. We obtain oxalate from diet, or from endogenous production. Certain intestinal bacteria have the ability to degrade oxalate, protecting against oxalate nephropathy, including nephrolithiasis. To understand the role of the gut microbiome in oxalate metabolism, we compared conventional mice with germ-free mice (that lack a microbiota). In addition to the stress of endogenous oxalate production, we challenged groups with dietary and metabolic (via hydroxyproline (Hyp) supplementation) oxalate loads.
Method(s): Conventional (CO) and germ-free (GF) mice were fed normal chow diets supplemented with either 1% Oxalate (Ox), 1% Hydroxyproline (Hyp) or were unsupplemented (NC) for 6 weeks (n=3-4/mice group). After 6 weeks, we obtained 48-hour urine collections for measurement of the oxalate/creatinine ratio (Uox/cr).
Result(s): In CO mice, Uox/cr increased with the Ox diet compared with NC (0.57 + 0.17 vs 0.16 + 0.05, p= 0.03 by Student's t test), but not with the Hyp diet (0.14 +0.03 vs 0.16 +0.05, p=ns). However, in germ-free mice, both dietary Hyp and Ox led to increased Uox/ cr compared to NC diet (0.50 +/- 0.04, 0.85 +/- 0.11, vs. 0.31+/- 0.06, p<0.05 by ANOVA, respectively). Uox/Cr was lower in CO mice than GF mice when receiving Hyp (p=0.01, by Student's t test), Ox (p=0.06), and NC diets (0.06).
Conclusion(s): In conclusion, oxalate excretion was higher in the germ-free than in the conventional mice under all three dietary conditions (Ox, Hyp, NC), providing direct evidence that the normal gut microbiome plays a protective (symbiotic) role in oxalate metabolism. With the metabolic stress of the Hyp diet, the CO mice but not the germfree mice could compensate. Since mice are not colonized with O. formigenes, this work indicates that other members of their microbiota have the functional capacity to alter oxalate metabolism

Background: Behavioral methods enhance the effectiveness of lifestyle interventions, but are often resource intensive. Although mobile health (mHealth) technology can help create lower input interventions, their feasibility, acceptability and efficacy have not been adequately evaluated in hemodialysis (HD) patients.
Method(s): Maintenance HD patients with persistent hyperphosphatemia (n=40) were randomized to receive: (1) educational (Edu) videos (EDU), (2) Edu + mobile selfmonitoring (SM) with MyNetDiary (MON), or (3) Edu + SM + social cognitive theory (SCT)-based behavioral counseling videos (SCT) over a 12-week period with videos for each group delivered using iPads. Serum phosphorus concentrations (sPO4) were measured at baseline, 12 and 24 weeks, and a 5-point Likert scale survey on the mHealth technology was completed at 24-weeks. Two participants in the EDU group with no follow-up sPO4 measurements were excluded; missing sPO4 measurements at 12-and 24-weeks were imputed by carrying forward the most recent sPO4 values.
Result(s): At the end of the intervention phase (12-weeks), there was a non-significant trend towards greater decreases in sPO4 in the MON (-0.5+/-1.6 mg/dL, p=0.32) and SCT (-0.3+/-2.1 mg/dL, p=0.56) groups compared to the EDU group (+0.2+/-1.4 mg/dL), but these differences had mostly disappeared by the end of the monitoring phase (24-weeks) (EDU +0.1+/-1.2 mg/dL, MON -0.1+/-1.9 mg/dL, SCT -0.1+/-2.1 mg/dL). Most participants agreed or strongly agreed that the iPads were convenient (64%), and SM helped them stay motivated (68%), take binders (61%), and limit phosphorus intake (68%). Relatively few participants reported that they agreed or strongly agreed that they sometimes "got lost" maneuvering the iPad programs (24%), felt that SM wasn't worthwhile (16%), or would have preferred face-to-face meetings offsite (4%).
Conclusion(s): Many HD patients are willing, able and report benefits of engaging in technology-supported behavioral interventions involving SM and SCT. Although these programs are easy to disseminate with limited resources once developed, any benefits for phosphorus management in HD patients may last only as long as the intervention is active

Background: Cystinuria is an inherited kidney stone disorder caused by mutations to the SLC3A1 and SLC7A9 genes. While most cases are due to biallelic mutations to either gene, monoallelic and digenic families have been described, with overall considerable disease variability. Nevertheless, clear genotype/phenotype correlations have not been described to date.
Method(s): A next generation sequencing (NGS) panel consisting of 90 known and candidate kidney stone genes was developed and validated. A total of 49 unrelated, genetically unscreened individuals with a clinical diagnosis of cystinuria were analyzed using this panel. Preliminary correlations with phenotype were made with the genic groups.
Result(s): The baseline mean (SD) characteristics of the cohort were: age at diagnosis = 19.6y (12.5), number of stones = 5.8 (6.6), cystine excretion = 939.9mg (323.6), eGFR = 82.1ml/min/1.73m² (24.5), with age at last follow up = 43.8y (14). A total of 34 patients (69.4%) had biallelic SLC3A1 and 11 (22.4%) biallelic SLC7A9 mutations. One SLC3A1 and two SLC7A9 cases had a single detected mutation, and one case had no mutations detected. Large rearrangements, detected by LOG2 ratio analysis of the sequence data and confirmed by Multiplex Ligation-dependent Probe Amplification (MLPA), accounted for 31.9% of all SLC3A1 mutations, mainly the common ex5-9 duplication. Other common mutations were the SLC3A1 missense change p.Met467Thr (21.7% alleles) and the nonsense mutation p.Arg270* (18.8%), while for SLC7A9 the missense mutation p.Gly105Arg accounted for 29.2% of pathogenic alleles. Ten novel mutations were identified for each gene. The only detected correlation with genotype was with baseline mean stone number, SLC3A1 = 7.1 (7.1), SLC7A9 = 2.0 (2.1; p=0.05) in this cohort.
Conclusion(s): This analysis shows the utility of a panel-based NGS approach in cystinuria populations and more broadly in patients with suspected monogenic stone disease. Other genetic and/or environmental factors likely also contribute to the observed phenotypic variability

PURPOSE/OBJECTIVE:Treatment of a first-time renal stone consists of acute management followed by medical efforts to prevent stone recurrence. Although nephrolithiasis is roughly 50% heritable, the presence of a family history usually does not affect treatment since most stone disease is regarded as polygenic, ie not attributable to a single gene. Recent evidence has suggested that single mutations could be responsible for a larger proportion of renal stones than previously thought. This intriguing possibility holds the potential to change the management paradigm in stone prevention from metabolically directed therapy to more specific approaches informed by genetic screening and testing. This review synthesizes new findings concerning monogenic kidney stone disease, and provides a concise and clinically useful reference for monogenic causes. It is expected that increased awareness of these etiologies will lead to increased use of genetic testing in recurrent stone formers and further research into the prevalence of monogenic stone disease. MATERIALS AND METHODS/METHODS:We assembled a complete list of genes known to cause or influence nephrolithiasis based on recent reviews and commentaries. We then comprehensively searched PubMed® and Google Scholar™ for all research on each gene having a pertinent role in nephrolithiasis. We determined which genes could be considered monogenic causes of nephrolithiasis. One gene, ALPL, was excluded since nephrolithiasis is a relatively minor aspect of the disorder associated with the gene (hypophosphatasia). We summarized selected studies and assembled clinically relevant details. RESULTS:A total of 27 genes were reviewed in terms of recent findings, mode of inheritance of stone disease, known or supposed prevalence of mutations in the general population of stone patients and specific therapies or considerations. CONCLUSIONS:There is a distinct opportunity for increased use of genetic testing to improve the lives of pediatric and adult stone patients. Several genes first reported in association with rare disease may be loci for novel mutations, heterozygous disease and forme frustes as causes of stones in the broader population. Cases of idiopathic nephrolithiasis should be considered as potentially having a monogenic basis.

Diet is a key determinant of several common and serious disease complications in hemodialysis (HD) patients. The recommended balance and variety of foods in the HD diet is designed to limit high potassium and phosphorus foods while maintaining protein adequacy. In this report, we examine the potassium, phosphorus, and protein content of foods, and identify critical challenges, and potential pitfalls when translating nutrient prescriptions into dietary guidelines. Our findings highlight the importance of individualized counseling based on a comprehensive dietary assessment by trained diet professionals, namely renal dietitians, for managing diet-related complications in HD patients.

Background Although intestinal and urinary microbiome perturbations are associated with nephrolithiasis, whether antibiotics are a risk factor for this condition remains unknown.Methods We determined the association between 12 classes of oral antibiotics and nephrolithiasis in a population-based, case-control study nested within 641 general practices providing electronic health record data for >13 million children and adults from 1994 to 2015 in the United Kingdom. We used incidence density sampling to match 25,981 patients with nephrolithiasis to 259,797 controls by age, sex, and practice at date of diagnosis (index date). Conditional logistic regression models were adjusted for the rate of health care encounters, comorbidities, urinary tract infections, and use of thiazide and loop diuretics, proton-pump inhibitors, and statins.Results Exposure to any of five different antibiotic classes 3-12 months before index date was associated with nephrolithiasis. The adjusted odds ratio (95% confidence interval) was 2.33 (2.19 to 2.48) for sulfas, 1.88 (1.75 to 2.01) for cephalosporins, 1.67 (1.54 to 1.81) for fluoroquinolones, 1.70 (1.55 to 1.88) for nitrofurantoin/methenamine, and 1.27 (1.18 to 1.36) for broad-spectrum penicillins. In exploratory analyses, the magnitude of associations was greatest for exposure at younger ages (P<0.001) and 3-6 months before index date (P<0.001), with all but broad-spectrum penicillins remaining statistically significant 3-5 years from exposure.Conclusions Oral antibiotics associated with increased odds of nephrolithiasis, with the greatest odds for recent exposure and exposure at younger age. These results have implications for disease pathogenesis and the rising incidence of nephrolithiasis, particularly among children.

Medullary sponge kidney (MSK) is a cause of nephrocalcinosis, associated with hematuria, renal colic, pyelonephritis. There are rare and atypical MSK cases characterized by chronic severe pain (CP), whose features are unknown, in particular the relationship with the stone disease activity. This study analyzes a cohort of MSK-CP patients belonging to three North-America self-support Facebook groups. Patients had to self-administer an on-line questionnaire (on intensity, progression and MSK-associated conditions, stone-related disease, pain features, drug use), the Brief Pain Inventory, the Fatigue Severity Score, and Wisconsin Quality of Life (WQL) in stone formers questionnaires. Ninety-two patients with a diagnosis of MSK joined our survey. Stone rate was very high (3.1 stones per patient-year, < 15% of patients had ≤ 1 stone per year). Most patients had repeated hospitalizations for stones symptoms (p < 0.001) or pain (p < 0.005). 71% of participants referred a daily pain that interfered strongly with everyday life and quality of life (WQL mean value 29.4). 69% used pain medications daily (70% opioids). In most cases, pain was associated with stone passage, while 15% referred a sine materia pain. We showed how MSK-CP symptoms affect very negatively on the quality of life of these patients. They also have a definite risk of progressing to end-stage kidney disease. Generally, CP seems to be associated with an exceptionally high lithogenic activity, suggesting that a better and earlier metabolic treatment for stone prevention should be the first approach in these patients before mini-invasive treatments to prevent pain.

Expression of Tamm-Horsfall protein (THP or uromodulin) is highly restricted to the kidneys' thick ascending limb (TAL) of loop of Henle. Despite the unique location and recent association of THP gene mutations with hereditary uromodulin-associated kidney disease and THP single nucleotide polymorphisms with chronic kidney disease and hypertension, the physiological function(s) of THP and its pathological involvement remain incompletely understood. By studying age-dependent changes of THP knockout (KO) mice, we show here that young KO mice had significant salt and water wasting but were partially responsive to furosemide, due to decreased luminal translocation of Na-K-Cl cotransporter 2 (NKCC2) in the TAL. Aged THP KO mice were, however, markedly oliguric and unresponsive to furosemide, and their NKCC2 was localized primarily in the cytoplasm as evidenced by lipid raft floatation assay, cell fractionation, confocal and immunoelectron microscopy. These aged KO mice responded to metolazone and acetazolamide, known to target distal and proximal tubules, respectively. They also had marked upregulation of renin in juxtaglomerular apparatus and serum, and they were hypertensive. Finally, the aged THP KO mice had significant upregulation of Na-coupled urate transporters Slc5a8 and Slc22a12 as well as sodium-hydrogen exchanger 3 (NHE3) in the proximal tubule and elevated serum uric acid and allantoin. Collectively, our results suggest that THP deficiency can cause progressive disturbances in renal functions via initially NKCC2 dysfunction and later compensatory responses resulting in prolonged activation of the renin-angiotensin-aldosterone axis and hyperuricema.