Jameela A. Kari

ADCK4 mutations promote steroid-Resistant nephrotic syndrome through CoQ10 biosynthesis disruption

Identification of single-gene causes of steroid-resistant nephrotic syndrome (SRNS) has furthered the understanding of the pathogenesis of this disease. Here, using a combination of homozygosity mapping and whole human exome resequencing, we identified mutations in the aarF domain containing kinase 4 (ADCK4) gene in 15 individuals with SRNS from 8 unrelated families. ADCK4 was highly similar to ADCK3, which has been shown to participate in coenzyme Q10 (CoQ10) biosynthesis. Mutations in ADCK4 resulted in reduced CoQ10 levels and reduced mitochondrial respiratory enzyme activity in cells isolated from individuals with SRNS and transformed lymphoblasts. Knockdown of adck4 in zebrafish and Drosophila recapitulated nephrotic syndrome-associated phenotypes. Furthermore, ADCK4 was expressed in glomerular podocytes and partially localized to podocyte mitochondria and foot processes in rat kidneys and cultured human podocytes. In human podocytes, ADCK4 interacted with members of the CoQ10 biosynthesis pathway, including COQ6, which has been linked with SRNS and COQ7. Knockdown of ADCK4 in podocytes resulted in decreased migration, which was reversed by CoQ10 addition. Interestingly, a patient with SRNS with a homozygous ADCK4 frameshift mutation had partial remission following CoQ10 treatment. These data indicate that individuals with SRNS with mutations in ADCK4 or other genes that participate in CoQ10 biosynthesis may be treatable with CoQ10.

Metabolic syndrome and chronic kidney disease.

Purpose of review The association of the metabolic syndrome (MetS) with cardiovascular risk, mortality, type 2 diabetes mellitus, stroke, nonfatty liver disease and gout is well known. However, the association of the MetS with chronic kidney disease (CKD) is now emerging. This review discusses the epidemiology, pathology and potential mechanisms for the relationship of MetS with CKD. Recent findings Studies show that patients with MetS have a 2.5-fold higher risk of developing CKD. The risk of microalbuminuria is also increased two-fold in the MetS. Renal dysfunction becomes apparent long before the appearance of hypertension or diabetes in MetS. Compared with healthy controls, patients with MetS have increased microvascular disease-tubular atrophy, interstitial fibrosis, arterial sclerosis and global and segmental sclerosis. Studies suggest that the renal fibrosis seen in MetS might be caused by a constellation of insulin resistance, hypertension, dyslipidemias and inflammation, and result in a heightened expression of adipocytokines, angiotensin and inflammatory cytokines such as interleukin-6 and tumour necrosis factor-alpha. Summary Despite the strong association of MetS with CKD, a causal relationship has not been proven. More studies are needed to precisely elucidate the mechanisms that might lead upstream factors such as insulin resistance, hypertension, dyslipidemia and inflammation to cause renal fibrosis.

CLDN16 Genotype Predicts Renal Decline in Familial Hypomagnesemia with Hypercalciuria and Nephrocalcinosis

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is a rare autosomal recessive tubular disorder caused by CLDN16 mutations. CLDN16 encodes the renal tight junction protein claudin-16, which is important for the paracellular reabsorption of calcium and magnesium in the thick ascending limb of Henle’s loop. That FHHNC is frequently associated with progressive renal failure suggests additional roles for claudin-16 in the maintenance of tight junction integrity. An investigation of 32 patients with FHHNC and 17 different mutations was previously reported; here, the analysis is expanded to 39 additional patients and 12 new mutations. Expression studies revealed that five of the12 new mutations led to partial loss of claudin-16 function and the remaining seven led to complete loss of function. The 23 patients who had mutations resulting in complete loss of function of both alleles were significantly younger at the onset of symptoms than the 46 patients who had at least one mutant allele providing partial function (2.2 versus 5.6 years; P _ 0.01). In addition, those with complete loss of function had a more rapid decline in GFR (7.3 versus 2.9 ml/min per 1.72 m2/y; P _ 0.01), leading to 54% requiring renal replacement therapy by age 15 compared with 20% of those with residual function (P _0.05). These data suggest that residual function of claudin-16 may delay the progression of renal failure in FHHN

Nineteen novel NPHS1 mutations in a worldwide cohort of patients with congenital nephrotic syndrome (CNS)

BACKGROUND Recessive mutations in the NPHS1 gene encoding nephrin account for approximately 40% of infants with congenital nephrotic syndrome (CNS). CNS is defined as steroid-resistant nephrotic syndrome (SRNS) within the first 90 days of life. Currently, more than 119 different mutations of NPHS1 have been published affecting most exons. METHODS We here performed mutational analysis of NPHS1 in a worldwide cohort of 67 children from 62 different families with CNS. RESULTS We found bi-allelic mutations in 36 of the 62 families (58%) confirming in a worldwide cohort that about one-half of CNS is caused by NPHS1 mutations. In 26 families, mutations were homozygous, and in 10, they were compound heterozygous. In an additional nine patients from eight families, only one heterozygous mutation was detected. We detected 37 different mutations. Nineteen of the 37 were novel mutations (approximately 51.4%), including 11 missense mutations, 4 splice-site mutations, 3 nonsense mutations and 1 small deletion. In an additional patient with later manifestation, we discovered two further novel mutations, including the first one affecting a glycosylation site of nephrin. CONCLUSIONS Our data hereby expand the spectrum of known mutations by 17.6%. Surprisingly, out of the two siblings with the homozygous novel mutation L587R in NPHS1, only one developed nephrotic syndrome before the age of 90 days, while the other one did not manifest until the age of 2 years. Both siblings also unexpectedly experienced an episode of partial remission upon steroid treatment.

Rapid detection of monogenic causes of childhood-onset steroid-resistant nephrotic syndrome.

BACKGROUND AND OBJECTIVES In steroid-resistant nephrotic syndrome (SRNS), >21 single-gene causes are known. However, mutation analysis of all known SRNS genes is time and cost intensive. This report describes a new high-throughput method of mutation analysis using a PCR-based microfluidic technology that allows rapid simultaneous mutation analysis of 21 single-gene causes of SRNS in a large number of individuals. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS This study screened individuals with SRNS; samples were submitted for mutation analysis from international sources between 1996 and 2012. For proof of principle, a pilot cohort of 48 individuals who harbored known mutations in known SRNS genes was evaluated. After improvements to the method, 48 individuals with an unknown cause of SRNS were then examined in a subsequent diagnostic study. The analysis included 16 recessive SRNS genes and 5 dominant SRNS genes. A 10-fold primer multiplexing was applied, allowing PCR-based amplification of 474 amplicons in 21 genes for 48 DNA samples simultaneously. Forty-eight individuals were indexed in a barcode PCR, and high-throughput sequencing was performed. All disease-causing variants were confirmed via Sanger sequencing. RESULTS The pilot study identified the genetic cause of disease in 42 of 48 (87.5%) of the affected individuals. The diagnostic study detected the genetic cause of disease in 16 of 48 (33%) of the affected individuals with a previously unknown cause of SRNS. Seven novel disease-causing mutations in PLCE1 (n=5), NPHS1 (n=1), and LAMB2 (n=1) were identified in <3 weeks. Use of this method could reduce costs to 1/29th of the cost of Sanger sequencing. CONCLUSION This highly parallel approach allows rapid (<3 weeks) mutation analysis of 21 genes known to cause SRNS at a greatly reduced cost (1/29th) compared with traditional mutation analysis techniques. It detects mutations in about 33% of childhood-onset SRNS cases.

What is the calcineurin inhibitor of choice for pediatric renal transplantation

Abstract:  Cyclosporine microemulsion (CyA) and tacrolimus (Tac) are the principal immunosuppressants prescribed for adult and pediatric renal transplantation. In the majority of patients, these calcineurin inhibitors have been used in combination with other immunosuppressive drugs, such as azathioprine or mycophenolate mofetil (MMF). In this review we will address the question of what calcineurin inhibitor we should use in an individual pediatric renal transplant patient. Well‐designed randomized studies in children showed no difference in short‐term patient and graft survival with cyclosporine microemulsion and tacrolimus. However Tac is significantly more effective than CyA microemulsion in preventing acute rejection after renal transplantation in a pediatric population when used in conjunction with azathioprine and corticosteroids. This difference disappears when calcineurin inhibitors are used in combination with MMF as both Tac and CyA produce similar rejection rates and graft survival. However, Tac is associated with improved graft function at 1 and 2 yr post‐transplant. Adverse events of hypomagnesaemia and diarrhea seem to be higher in Tac group whereas hypertrichosis, flu syndrome and gum hyperplasia occurs more frequently in the CyA group. The incidence of post‐transplant diabetes mellitus was almost identical between Tac and CyA treated patients. The recommendation drawn from the available data is that both CyA and Tac can be used safely and effectively in children. However Tac may be preferable to CyA because of steroid sparing effect and less hirsutism. We recommend that cyclosporine should be chosen when patients experience Tac‐related adverse events. Nevertheless, the best calcineurin inhibitor should be decided on individual patients according to variable risk factors, such as risk of rejection in sensitized patient or delayed graft function. The possibility of adverse events should also be considered.

Chronic Kidney Disease in the Arab World: A Call for Action

Chronic kidney disease (CKD) is an emerging non-communicable disease worldwide. The Arab countries have a high prevalence of CKD risk factors, e.g. diabetes, obesity and hypertension. Unfortunately, the magnitude of CKD in the Arab world has not been studied well. This review presents the current data on CKD in the Arab world and proposes a call for action to address this rising epidemic.

Effect of enteral feeding on lipid subfractions in children with chronic renal failure

Abstract. The anorexia of chronic renal failure (CRF) is frequently managed with enteral feeds using combinations of commercial preparations, glucose polymers and fat emulsions. Such feeds might predispose to atherogenic blood lipid profiles. Our aim, therefore, was to compare the blood lipid profiles of enterally fed and non-enterally fed children. Plasma lipid subfractions were measured in 37 children with CRF managed conservatively and 10 managed with peritoneal dialysis (PD); 10 of the children were tube fed, 5 of whom were on PD. Results were compared between these groups. Overall, triglycerides (TGs, mean ± SD) were high (2.3±1.4 mmol/l) and total cholesterol (TC) was at the upper limit of normal (5.2±1.5 mmol/l). Low-density lipoprotein (LDL), high-density lipoprotein (HDL), apoprotein A1 (apo A1), A2 (apo A2) and B (apo B), and lipoprotein (a) [Lp(a)] were within the normal range. There was an inverse correlation between TGs and glomerular filtration rate (P = 0.0001). There were no differences in the levels of TC, TG, LDL, HDL, apo A1, apo A2 or Lp(a) between tube-fed and non-tube-fed children. We conclude that enteral feeding does not enhance hyperlipidaemia.The anorexia of chronic renal failure (CRF) is frequently managed with enteral feeds using combinations of commercial preparations, glucose polymers and fat emulsions. Such feeds might predispose to atherogenic blood lipid profiles. Our aim, therefore, was to compare the blood lipid profiles of enterally fed and non-enterally fed children. Plasma lipid subfractions were measured in 37 children with CRF managed conservatively and 10 managed with peritoneal dialysis (PD); 10 of the children were tube fed, 5 of whom were on PD. Results were compared between these groups. Overall, triglycerides (TGs, mean ± SD) were high (2.3±1.4 mmol/l) and total cholesterol (TC) was at the upper limit of normal (5.2±1.5 mmol/l). Low-density lipoprotein (LDL), high-density lipoprotein (HDL), apoprotein A1 (apo A1), A2 (apo A2) and B (apo B), and lipoprotein (a) [Lp(a)] were within the normal range. There was an inverse correlation between TGs and glomerular filtration rate (P = 0.0001). There were no differences in the levels of TC, TG, LDL, HDL, apo A1, apo A2 or Lp(a) between tube-fed and non-tube-fed children. We conclude that enteral feeding does not enhance hyperlipidaemia.

Infantile nephrotic syndrome and congenital glaucoma.

Abstract. A case of infantile nephrotic syndrome (NS) with advanced membranoproliferative glomerulonephritis (MPGN), type I, and bilateral congenital glaucoma, is presented. The patient also had persistent thrombocytopenia and subclinical hypothyroidism. The parents were second-degree cousins and the affected infant had a sibling who was born with congenital glaucoma. His mother had an aunt and uncle on the maternal side who were born with congenital glaucoma. In addition, there was a history of infantile death in five family members of unknown causes (pedigree). To the best of our knowledge, the association of congenital glaucoma and infantile NS due to MPGN has not been reported previously.

Whole exome sequencing frequently detects a monogenic cause in early onset nephrolithiasis and nephrocalcinosis

The incidence of nephrolithiasis continues to rise. Previously, we showed that a monogenic cause could be detected in 11.4% of individuals with adult-onset nephrolithiasis or nephrocalcinosis and in 16.7-20.8% of individuals with onset before 18 years of age, using gene panel sequencing of 30 genes known to cause nephrolithiasis/nephrocalcinosis. To overcome the limitations of panel sequencing, we utilized whole exome sequencing in 51 families, who presented before age 25 years with at least one renal stone or with a renal ultrasound finding of nephrocalcinosis to identify the underlying molecular genetic cause of disease. In 15 of 51 families, we detected a monogenic causative mutation by whole exome sequencing. A mutation in seven recessive genes (AGXT, ATP6V1B1, CLDN16, CLDN19, GRHPR, SLC3A1, SLC12A1), in one dominant gene (SLC9A3R1), and in one gene (SLC34A1) with both recessive and dominant inheritance was detected. Seven of the 19 different mutations were not previously described as disease-causing. In one family, a causative mutation in one of 117 genes that may represent phenocopies of nephrolithiasis-causing genes was detected. In nine of 15 families, the genetic diagnosis may have specific implications for stone management and prevention. Several factors that correlated with the higher detection rate in our cohort were younger age at onset of nephrolithiasis/nephrocalcinosis, presence of multiple affected members in a family, and presence of consanguinity. Thus, we established whole exome sequencing as an efficient approach toward a molecular genetic diagnosis in individuals with nephrolithiasis/nephrocalcinosis who manifest before age 25 years.