Eli J. Holtzman

Loss-of-Function Mutations of CYP24A1, the Vitamin D 24-Hydroxylase Gene, Cause Long-standing Hypercalciuric Nephrolithiasis and Nephrocalcinosis

PURPOSE Hypercalciuria is the most common cause of kidney stone disease and genetic factors have an important role in nearly half of these cases. Recently loss-of-function mutations of CYP24A1, the gene encoding vitamin D 24-hydroxylase, were identified in idiopathic infantile hypercalcemia. We describe the clinical and molecular basis of severe long-standing kidney stone disease in adults caused by CYP24A1 mutations. MATERIALS AND METHODS Three subjects from 2 Israeli families with nephrolithiasis and nephrocalcinosis were clinically characterized. Genomic DNA was isolated from peripheral blood and sequencing of CYP24A1 was performed. RESULTS All subjects presented with severe kidney stone disease, the cause of which was not discovered for decades despite extensive evaluation. They all had hypercalciuria, nephrocalcinosis and intermittent hypercalcemia, and chronic kidney insufficiency developed in the oldest subject. All patients had a typical pattern of test results, including normal-high serum calcium, low parathyroid hormone levels, high vitamin D 25-(OH)D3 and 1,25-(OH)2D3, and low 24,25-(OH)2D3. Overall 3 CYP24A1 loss-of-function mutations were identified, including a homozygous deletion (delE143) in consanguinous family 1, and compound heterozygous mutations L409S and the novel W268-stop in family 2. CONCLUSIONS Loss-of-function mutations of CYP24A1 gene, encoding for 1,25-dihydroxyvitamin D3 24-hydroxylase, cause severe hypercalciuric nephrolithiasis and nephrocalcinosis. The mutations may present in adults and may lead to chronic renal insufficiency. Our results support a recessive mode of inheritance. CYP24A1 mutations should be considered in the differential diagnosis of hypercalciuric nephrolithiasis, especially as many adults are now prescribed supplemental oral vitamin D.

Late Diagnosis of Primary Hyperoxaluria Type 2 in the Adult: Effect of a Novel Mutation in GRHPR Gene on Enzymatic Activity and Molecular Modeling

PURPOSE Genetic causes of nephrolithiasis are underestimated. Primary hyperoxaluria type 2 is a rare autosomal recessive disease caused by mutations in the GRHPR gene, leading to an accumulation of oxalate and L-glycerate with recurrent kidney stone formation and nephrocalcinosis, and the later development of renal failure and systemic oxalate depositions. We studied the effects of a novel GRHPR mutation on GRHPR enzymatic activity and molecular modeling. MATERIALS AND METHODS Genomic DNA from a 50-year-old male with a late diagnosis of primary hyperoxaluria type 2 was extracted, analyzed and compared with the established human GRHPR gene sequence. Restriction enzyme analysis of the patient, 30 healthy controls and 30 patients with nephrolithiasis of various causes was done to confirm the presence of the mutation. GRHPR activity was analyzed by site directed mutagenesis of WT and mutant clones. We studied the effects of the mutation on enzymatic molecular modeling. RESULTS We found the novel homozygous single missense mutation A975G in exon 9, creating an amino acid change from asparagine to aspartic acid in position 312. No mutations were detected in restriction enzyme analysis in all 30 healthy controls and 30 patients with nephrolithiasis of various causes. Transfected cells with the mutant clone showed abolished GRHPR activity. Molecular modeling studies revealed that the mutation was likely to disrupt the correct folding of the GRHPR substrate binding domain, hence affecting the enzyme active site. CONCLUSIONS Primary hyperoxaluria type 2 should be considered in patients at adult stone clinics who have had a history of nephrolithiasis since childhood, especially in those with consanguineous parents. Biochemical analysis followed by mutation identification should be the approach for making the definitive diagnosis of primary hyperoxaluria type 2.

Chronic hypercalcaemia from inactivating mutations of vitamin D 24-hydroxylase (CYP24A1): implications for mineral metabolism changes in chronic renal failure

BACKGROUND Loss-of-function mutations of vitamin D-24 hydroxylase have recently been recognized as a cause of hypercalcaemia and nephrocalcinosis/nephrolithiasis in infants and adults. True prevalence and natural history of this condition are still to be defined. METHODS We describe two adult patients with homozygous mutations and six related heterozygous carriers. Mineral and hormonal data in these patients were compared with that in 27 patients with stage 2-3 chronic kidney disease and 39 healthy adult kidney donors. RESULTS Probands had recurrent nephrolithiasis, chronic hypercalcaemia with depressed parathyroid hormone (PTH) and increased 1,25(OH)(2)D levels; carriers had nephrolithiasis (two of six), hypercalciuria (two of six) and high or normal-high 1,25(OH)(2)D (four of four). Corticosteroids did not reduce plasma and urine calcium levels, but ketoconazole did, indicating that 1,25(OH)(2)D production is not maximally depressed despite coexisting hypercalcaemia, high 1,25(OH)(2)D and depressed PTH, and that 1,25(OH)(2)D degradation through vitamin D-24 hydroxylase is a regulator of plasma 1,25(OH)(2)D levels. Both probands had vascular calcifications and high bone mineral content. One developed stage 3b renal failure: in this patient 1,25(OH)(2)D decreased within normal limits as glomerular filtration rate (GFR) fell and PTH rose to high-normal values, yet hypercalcaemia persisted and the ratio of 1,25(OH)(2)D to GFR remained higher than normal for any degree of GFR. CONCLUSIONS This natural model indicates that vitamin D-24 hydroxylase is a key physiologic regulator of calcitriol and plasma calcium levels, and that balanced reduction of 1,25(OH)(2)D and GFR is instrumental for the maintenance of physiologic calcium levels and balance in chronic kidney diseases.

Urinary organic anion transporter protein profiles in AKI

BACKGROUND Organic anion transporters (OATs) are located on either the basolateral or the apical membrane of the proximal tubule cell and mediate the absorption and secretion of various drugs and endogenous metabolites. It has been shown that cellular damage in acute kidney injury (AKI) involves three forms of injury: sublethal damage resulting in loss of cell polarity, cell death through apoptosis and necrosis. We hypothesize that cellular mistargeting of OAT proteins in AKI will change the profile of OAT proteins in urine. METHODS Thirty AKI patients were included in the study. AKI was defined by clinical course, daily urine output, response to fluid repletion, urinary sediment, fractional excretion of sodium (FeNa) and urine osmolality. Urinary OAT1, OAT3 and OAT4 protein abundance was measured from semiquantitative immunoblots of urine membrane fraction samples (exosome) collected from patients with AKI and from control subjects. RESULTS Although all patients studied reached a similar severity of renal failure measured by serum creatinine, some of them recovered from AKI with supportive care only, while others required renal replacement therapy (RRT). OAT1 and OAT3, which are normally localized in the basolateral membrane of the proximal tubule cell, were detected at low levels in urine from control subjects and were increased significantly in all patients with AKI. OAT4 protein, which is normally localized in the luminal membrane of proximal tubule cells, was present in abundance in urine of control subjects. Interestingly, in patients with AKI who eventually recovered, urinary OAT4 was found to be significantly lower than in controls, while in patients who needed RRT, it was higher than in controls. CONCLUSIONS We have shown that OATs are mistargeted in AKI. The urinary OAT protein profile can help us to learn about the pathophysiology of the disease and might be a marker of AKI severity. AKI patients with early reversible proximal tubular damage will have high urine OAT1 and OAT3 and low OAT4, while patients with severe AKI will have high urine OAT1, OAT3 and OAT4.

Truncating mutations in the chloride/proton ClC-5 antiporter gene in Seven Jewish Israeli families with Dent's 1 disease.

Dent’s disease is an X-linked hereditary renal tubular disorder characterized by low-molecular-weight proteinuria (LMWP), hypercalciuria, nephrocalcinosis, nephrolithiasis, rickets and progressive renal failure. About 60% of patients have mutations in the CLCN5 gene (Dent 1), which encodes a kidney-specific chloride/proton antiporter, and 15% of patients have mutations in the OCRL1 gene (Dent 2). The aim of the study was to identify CLCN5 mutations in Jewish Israeli families with Dent‘s disease and to characterize the associated clinical syndromes. We studied 17 patients from 14 unrelated Israeli families with a clinical diagnosis of Dent’s disease. LMWP was detected in all patients. Most of the affected individuals had hypercalciuria and nephrocalcinosis. Renal stones were found in 1 patient, and renal insufficiency developed in 2 patients. We identified six different truncating CLCN5 mutations that were segregated with the disease in 7 families: three nonsense mutations (Arg28stop, Arg467stop and Arg637stop), one deletion mutation (505delA) and two novel mutations, consisted of one deletion mutation (1493delG) and one insertion mutation (409insC). All the mutations cause premature termination of protein translation and result in a non-functional truncated protein. The clinical characteristics of patients with different mutations were, in general, similar.

Peritoneal dialysis in patients with refractory congestive heart failure: potential prognostic factors.

Background: Peritoneal dialysis (PD) is increasingly used for long-term management of refractory congestive heart failure (CHF). In this study, we investigated the outcome of patients with refractory CHF treated with PD, aiming to identify potential prognostic factors for long term-survival. Methods: This was a prospective observational study over a period of 42 months which included 37 refractory CHF patients. Results: Median survival on PD was 14 months (1-41 months). Long survivors had serum sodium >132 mEq/l (p < 0.001), serum albumin >3.2 g/dl (p < 0.001) and hospitalization rate <2 days per month a year before starting the treatment (p = 0.008). Patients in the lowest survival quartile had lower serum albumin (2.8 vs. 3.5 g/dl in longer survivors, p = 0.003) and serum sodium (126 vs. 137 mEq/l, p < 0.0001), higher serum leukocyte count (7,500 vs. 6,800/μl in long survivors, p = 0.033), higher glomerular filtration rate (39.4 vs. 29.9 ml/min/1.73 m2, p = 0.035), had more hospitalization before starting the treatment (3.4 vs. 1.9 days per month, p = 0.003) and lower estimated left ventricular mass index (113 vs. 137 g/m2, p = 0.035). Long-term survivors demonstrated significant improvement in the New York Heart Association functional class by a median of one class, reduced hospitalization rate by 55% and decrease in dependence on intravenous diuretics and vasoactive medications (73% drop in CHF day care visits during the first year of treatment). Conclusions: Survival of patients with refractory CHF treated with PD is highly variable. Serum sodium, serum albumin and hospitalization rate are important prognostic factors for long-term survival. Long survivors demonstrated improved functional status, reduced hospitalization and mortality rates.

Mycobacterium chelonae peritonitis in peritoneal dialysis. Literature review

Non-tuberculous mycobacteria are a rare but serious cause of peritoneal dialysis-related peritonitis. There are no clear guidelines for treating non-tuberculous mycobacteria peritoneal dialysis-associated infections. It has been recommended that at least two antibiotics be given for a prolonged period and peritoneal catheter should be removed. This paper describes the clinical course and treatment of a patient with M. chelonae peritoneal dialysis-related peritonitis and reviews the previously published cases.

Molecular Study of Proteinuria in Patients Treated with B12 Supplements: Do Not Forget Megaloblastic Anemia Type 1

Background/Aims: Current consensus supports the notion that proteinuria is a marker of renal disease with prognostic implications. Whereas most chronic kidney disease patients with proteinuria would often require antiproteinuric agents, there are some exceptions. Megaloblastic anemia type 1 (MGA1) is characterized by megaloblastic anemia due to congenital selective vitamin B12 malabsorption and proteinuria. In the present study, we describe 2 Israeli Jewish patients with MGA1 and isolated proteinuria. Methods: Because of their origin, the patients were screened for the presence of the already studied Tunisian AMN mutation, by direct sequencing the corresponding region from genomic DNA. PCR products were purified and sequenced. Results: Genomic DNA sequencing of the AMN gene of both patients confirmed that the acceptor splice site in intron 3 was changed from CAG to CGG (208-2A→G). Conclusion: We determined the molecular basis of MGA1 in both patients and discuss the involvement of the cubilin/AMN complex in this pathology and its role in the development of the proteinuria. We also discuss the questionable significance of antiproteinuric treatment for these patients.

Incidence, aetiology and mortality secondary to hypertensive emergencies in a large-scale referral centre in Israel (1991–2010)

Hypertensive emergency (HE) is a life-threatening condition that requires immediate blood pressure (BP) reduction. Although it has been on the decline, the incidence of HE has recently increased in a few countries. The aim of the present retrospective study was to evaluate the incidence, aetiology and 1-year mortality of HE in a large medical centre over a 20-year period (1991–2010). The electronic medical records of all patient files who were hospitalized in the Chaim Sheba Medical Center in Israel from 1991 to 2010 with a primary diagnosis (at admission or discharge) of Malignant Hypertension, Hypertensive Emergency or Accelerated Hypertension were retrieved and analysed. The study interval was divided into four periods of 5 years each. Among 306 files reviewed, only 142 patients had a true HE. Average age at presentation was 63.3±16.5 years. Men were younger than women (59±16 vs 68±16 years; P<0.001). At presentation, most patients (80.3%) had been diagnosed with essential hypertension previously and were undertreated. Average maximum mean arterial pressure (MAP) was higher in men (169±22 mm Hg) than in women (161±17 mm Hg; P=0.026). The rate of HE decreased over the course of the study, from 12.7/100 000 admissions during 1991–1995 to 6.2/100 000 admissions (2006–2010). Similarly, 1-year mortality decreased from 16.7 to 3.6%. The rate of HE has decreased and the prognosis has improved over the last two decades. Appropriate BP control of patients with essential hypertension may further decrease the risk of HE.

Severe and long-lasting hypotension occuring immediately after parathyroidectomy in hypertensive hemodialysis patients: a case series.

Severe and long-lasting hypotension occuring immediately after parathyroidectomy in hypertensive hemodialysis patients: a case series