Elisabeth A. M. Cornelissen

C14ORF179 encoding IFT43 is mutated in Sensenbrenner syndrome

Background Sensenbrenner syndrome is a heterogeneous ciliopathy that is characterised by skeletal and ectodermal anomalies, accompanied by chronic renal failure, heart defects, liver fibrosis and other features. Objective To identify an additional causative gene in Sensenbrenner syndrome. Methods Single nucleotide polymorphism array analysis and standard sequencing techniques were applied to identify the causative gene. The effect of the identified mutation on protein translation was determined by western blot analysis. Antibodies against intraflagellar transport (IFT) proteins were used in ciliated fibroblast cell lines to investigate the molecular consequences of the mutation on ciliary transport. Results Homozygosity mapping and positional candidate gene sequence analysis were performed in two siblings with Sensenbrenner syndrome of a consanguineous Moroccan family. In both siblings, a homozygous mutation in the initiation codon of C14ORF179 was identified. C14ORF179 encodes IFT43, a subunit of the IFT complex A (IFT-A) machinery of primary cilia. Western blots showed that the mutation disturbs translation of IFT43, inducing the initiation of translation of a shorter protein product from a downstream ATG. The IFT-A protein complex is implicated in retrograde ciliary transport along axonemal microtubules. It was shown that in fibroblasts of one of the siblings affected by Sensenbrenner syndrome, disruption of IFT43 disturbs this transport from the ciliary tip to its base. As anterograde transport in the opposite direction apparently remains functional, the IFT complex B proteins accumulate in the ciliary tip. Interestingly, similar results were obtained using fibroblasts from a patient with Sensenbrenner syndrome with mutations in WDR35/IFT121, encoding another IFT-A subunit. Conclusions The results indicate that Sensenbrenner syndrome is caused by disrupted IFT-A-mediated retrograde ciliary transport.

Autosomal-Recessive Mutations in SLC34A1 Encoding Sodium-Phosphate Cotransporter 2A Cause Idiopathic Infantile Hypercalcemia

Idiopathic infantile hypercalcemia (IIH) is characterized by severe hypercalcemia with failure to thrive, vomiting, dehydration, and nephrocalcinosis. Recently, mutations in the vitamin D catabolizing enzyme 25-hydroxyvitamin D3-24-hydroxylase (CYP24A1) were described that lead to increased sensitivity to vitamin D due to accumulation of the active metabolite 1,25-(OH)2D3. In a subgroup of patients who presented in early infancy with renal phosphate wasting and symptomatic hypercalcemia, mutations in CYP24A1 were excluded. Four patients from families with parental consanguinity were subjected to homozygosity mapping that identified a second IIH gene locus on chromosome 5q35 with a maximum logarithm of odds (LOD) score of 6.79. The sequence analysis of the most promising candidate gene, SLC34A1 encoding renal sodium-phosphate cotransporter 2A (NaPi-IIa), revealed autosomal-recessive mutations in the four index cases and in 12 patients with sporadic IIH. Functional studies of mutant NaPi-IIa in Xenopus oocytes and opossum kidney (OK) cells demonstrated disturbed trafficking to the plasma membrane and loss of phosphate transport activity. Analysis of calcium and phosphate metabolism in Slc34a1-knockout mice highlighted the effect of phosphate depletion and fibroblast growth factor-23 suppression on the development of the IIH phenotype. The human and mice data together demonstrate that primary renal phosphate wasting caused by defective NaPi-IIa function induces inappropriate production of 1,25-(OH)2D3 with subsequent symptomatic hypercalcemia. Clinical and laboratory findings persist despite cessation of vitamin D prophylaxis but rapidly respond to phosphate supplementation. Therefore, early differentiation between SLC34A1 (NaPi-IIa) and CYP24A1 (24-hydroxylase) defects appears critical for targeted therapy in patients with IIH.

A Randomized Controlled Crossover Trial with Delayed-Release Cysteamine Bitartrate in Nephropathic Cystinosis: Effectiveness on White Blood Cell Cystine Levels and Comparison of Safety

BACKGROUND AND OBJECTIVES Immediate-release cysteamine bitartrate (Cystagon; Mylan Pharmaceuticals, Canonsburg, PA) may prevent or delay kidney transplantation and other serious outcomes in patients with cystinosis, but has never been subjected to a prospective clinical trial. Cystagon efficacy requires strict lifelong dosing every 6 hours. Such a dosing schedule and Cystagon-associated side effects are often cited by patients as reasons for nonadherence. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS This open-label, randomized, controlled, crossover trial was powered to show that a new delayed-release formulation of cysteamine bitartrate, RP103, taken every 12 hours, was noninferior to Cystagon for maintenance of white blood cell (WBC) cystine at levels associated with optimal outcomes in the disease. RESULTS Forty-three patients were randomized. Using a mixed-effects statistical analysis model, the least-squares mean peak value of WBC cystine level was 0.62±0.05 nmol 1/2 cystine/mg protein after 12 hours under RP103 and 0.54±0.05 nmol 1/2 cystine/mg protein after 6 hours under Cystagon, a difference of 0.08±0.04 nmol 1/2 cystine/mg protein (95.8% confidence interval, 0-0.16). The average steady-state total daily dose of RP103 was 82% of the incoming steady-state total daily dose of Cystagon. There were three-fold more gastrointestinal side effects compared with using Cystagon. CONCLUSIONS A new delayed-release Q12H formulation of cysteamine bitartrate is not inferior to the Q6H formulation (Cystagon) in maintaining low WBC cystine levels in patients with cystinosis but at a lower total daily dose.

Neonatal onset autosomal dominant polycystic kidney disease (ADPKD) in a patient homozygous for a PKD2 missense mutation due to uniparental disomy

Autosomal dominant polycystic kidney disease (ADPKD), due to a heterozygous mutation in PKD1 or PKD2, is usually an adult onset disease. Renal cystic disease is generally milder in PKD2 patients than in PKD1 patients. Recently, several PKD1 patients with a severe renal cystic phenotype due to a second modifying PKD1 allele, or carrying two incomplete penetrant PKD1 alleles, have been described. This study reports for the first time a patient with neonatal onset of PKD homozygous for an incomplete penetrant PKD2 missense variant due to uniparental disomy.

Proteomic profiling and identification in peritoneal fluid of children treated by peritoneal dialysis

BACKGROUND Proteomic technologies offer a high-throughput analysis of the expression of proteins in biological samples. The global analysis of the proteins in peritoneal dialysis (PD) fluid will provide a better understanding of the biological processes of the peritoneal membrane. METHODS The dialysate of nine paediatric PD patients was collected from peritoneal equilibrium tests with 3.86% glucose. Proteins were separated on a 10% SDS-PAGE gel and in-gel digested with trypsin. Peptide mixtures were analysed using nanoLC-MS/MS and results were searched against the NCBI database. RESULTS A total number of 189 proteins were identified in the PD fluid of nine patients, with 88 proteins shared by all patients. These 88 proteins accounted for 47% of the identified proteins and >90% of the total protein content in the analysed samples. Proteins were subdivided into eight different classes according to function. CONCLUSIONS This study gives a representative overview of the proteins present in PD fluid. The proteins in PD fluid reflect plasma proteins as well as local peritoneal processes. Potentially interesting proteins are revealed.

Transition to the adult nephrologist does not induce acute renal transplant rejection

BACKGROUND In spite of the overall increased renal graft survival, long-term allograft survival has remained least successful in adolescent recipients. A major change in their care is the transition from the paediatric to the adult nephrology unit. METHODS To analyse the effect of transition on the acute rejection frequency and graft survival, we performed a historical cohort study in all patients transplanted at the paediatric unit between 1980 and 2004. Data were obtained by reviewing medical charts in two of the four Dutch pediatric renal transplantation centers from time of transplantation until 3 years after transition. For analysis, we used a Cox proportional hazards model. RESULTS The cohort consisted of 162 patients: 133 native Dutch and 29 immigrant patients. Transition occurred at a mean age of 18 years (range 14-22). At transition, 72% had a functioning allograft. Acute rejections occurred in 92/162 patients before (median follow-up 4.8 years, range 0.2-12.8) and in 15/116 patients after transition (median follow-up 3.0 years, range 1.6-3.0). Most rejections (62%) occurred within the first year after transplantation. The relative risk of acute rejections after transition in comparison to before transition was 0.10 [95% confidence interval (95% CI) 0.04-0.28] in Dutch patients and 0.69 (95% CI 0.33-1.40) in immigrant patients. In the 3 years before transition, 28/154 patients (18%) experienced graft failure compared to 19/116 patients (16%) in the 3 years after transition. CONCLUSIONS The risk for acute rejection decreases after transition to the adult unit. There is less risk reduction in immigrant patients. Nephrologists should pay special attention to these patients.

Copper deficiency in patients with cystinosis with cysteamine toxicity

OBJECTIVES To assess whether copper deficiency plays a role in the recently described cysteamine toxicity in patients with cystinosis, and to examine whether polymorphisms in copper transporters, lysyl oxidase, and/or type I procollagen genes could be responsible for the occurrence of cysteamine toxicity in a small subset of patients with cystinosis. STUDY DESIGN Thirty-six patients with cystinosis were included: 22 with Fanconi syndrome (including 7 with cysteamine toxicity), 12 after renal transplantation, 1 receiving hemodialysis, and 1 with ocular cystinosis. Serum copper and ceruloplasmin levels and urinary copper/creatinine ratio were measured. Genes ATP7A and CTR1 (encoding copper transporters), LOX (encoding lysyl oxidase), and COL1A1 and COL1A2 (encoding type I procollagen) were analyzed in patients with (n = 6) and without (n = 5) toxicity. Fibroblast (pro)collagen synthesis was compared in patients with (n = 3) and those without (n = 2) cysteamine toxicity. RESULTS All 22 patients with Fanconi syndrome had increased urinary copper excretion. Serum copper and ceruloplasmin levels were decreased in 9 patients, including all 7 patients with cysteamine toxicity. No specific sequence variations were associated with toxicity. All fibroblasts exhibited normal (pro)collagen synthesis. CONCLUSION Patients with cystinosis with cysteamine toxicity demonstrate copper deficiency. This can cause decreased activity of lysyl oxidase, the enzyme that generates the aldehydes required for collagen cross-linking. Thus, copper supplementation might prevent cysteamine toxicity.

Quality of Life is Improved and Kidney Function Preserved in Patients with Nephropathic Cystinosis Treated for 2 Years with Delayed-Release Cysteamine Bitartrate *

Objectives To determine the long-term effects of delayed-release cysteamine bitartrate (DR-CYS) based on our previous work that established the short-term noninferiority of DR-CYS every 12 hours compared with immediate-release cysteamine bitartrate every 6 hours. Study design We conducted a prospective, controlled, open label, single-arm study of DR-CYS for 2 years in 40 patients to assess efficacy in depletion of cystine in peripheral white blood cells, to assess the dose required to maintain white blood cell content of cystine <1 nmol ½ cystine/mg protein, to measure quality of life using the Pediatric Quality of Life Inventory, change in estimated glomerular filtration rate, and change in height Z-score. Results Through 24 months of study, the mean white blood cell content of cystine was always <1 nmol ½ cystine/mg protein, and the dose of DR-CYS decreased from 43.5-40.1 mg/kg/d (P = .05), and the significant improvement in social function, school function, and in total function scores on the Pediatric Quality of Life Inventory remained. The estimated glomerular filtration rate was maintained and growth velocity was maintained at 24 months compared with the baseline height Z-score. Conclusions The use of a DR-CYS administered every 12 hours to patients with cystinosis is of great benefit to their quality of life and to important biomarkers of disease control, when studied in a prospective, controlled fashion. We suggest that DR-CYS should be considered for substrate depletion in patients with cystinosis.

Controversies and research agenda in nephropathic cystinosis: conclusions from a “Kidney Disease: Improving Global Outcomes” (KDIGO) Controversies Conference

Nephropathic cystinosis is an autosomal recessive metabolic, lifelong disease characterized by lysosomal cystine accumulation throughout the body that commonly presents in infancy with a renal Fanconi syndrome and, if untreated, leads to end-stage kidney disease (ESKD) in the later childhood years. The molecular basis is due to mutations in CTNS, the gene encoding for the lysosomal cystine-proton cotransporter, cystinosin. During adolescence and adulthood, extrarenal manifestations of cystinosis develop and require multidisciplinary care. Despite substantial improvement in prognosis due to cystine-depleting therapy with cysteamine, no cure of the disease is currently available. Kidney Disease: Improving Global Outcomes (KDIGO) convened a Controversies Conference on cystinosis to review the state-of-the-art knowledge and to address areas of controversies in pathophysiology, diagnostics, monitoring, and treatment in different age groups. More importantly, promising areas of investigation that may lead to optimal outcomes for patients afflicted with this lifelong, systemic disease were discussed with a research agenda proposed for the future.

A retrospective study of focal segmental glomerulosclerosis: clinical criteria can identify patients at high risk for recurrent disease after first renal transplantation.

BackgroundFocal segmental glomerulosclerosis (FSGS) is a frequent cause of end-stage renal disease. Renal transplantation in patients with FSGS is often complicated by disease recurrence, which is associated with poor outcome. There are no tests that reliably predict recurrence of FSGS after transplantation. The aim of this study was to evaluate if clinical criteria can identify patients at high risk for recurrent disease.MethodsWe retrospectively studied 94 patients who received a first renal transplant at a median age of 37 years (range 5–69 years). Patients were assigned to one of three groups: familial or genetic FSGS (group I; n=18), secondary FSGS (group II; n=10) and idiopathic FSGS (group III; n=66). Pretransplant clinical characteristics were analyzed to determine predictors of a recurrence after transplantation.ResultsFSGS only recurred in patients with idiopathic FSGS (group III; 42%). Patients with a recurrence had a significantly lower serum albumin, higher 24-hour proteinuria and higher estimated glomerular filtration rate at diagnosis. Serum albumin at diagnosis was the only independent predictor of a recurrence in patients with idiopathic FSGS. Patients with recurrent FSGS had more acute rejection episodes (54% vs. 27%, P =0.02) and lower five year graft survival compared to patients without a recurrence (50 vs. 82%, P <0.01).ConclusionsClinical criteria allow identification of patients at high risk of recurrent FSGS after renal transplantation. This information can be used in the counseling and management of patients with FSGS.