Genomic organization and chromosomal localization of the murine 2 P domain potassium channel gene Kcnk8: conservation of gene structure in 2 P domain potassium channels.

A 2 P domain potassium channel expressed in eye, lung, and stomach, Kcnk8, has recently been identified. To initiate further biochemical and genetic studies of this channel, we assembled the murine Kcnk8 cDNA sequence, characterized the genomic structure of the Kcnk8 gene, determined its chromosomal localization, and analyzed its activity in a Xenopus laevis oocyte expression system. The composite cDNA has an open reading frame of 1029 bp and encodes a protein of 343 amino acids with a predicted molecular mass of 36 kDa. Structure analyses predict 2 P domains and four potential transmembrane helices with a potential single EF-hand motif and four potential SH3-binding motifs in the COOH-terminus. Cloning of the Kcnk8 chromosomal gene revealed that it is composed of three exons distributed over 4 kb of genomic DNA. Genome database searching revealed that one of the intron/exon boundaries identified in Kcnk8 is present in other mammalian 2 P domain potassium channels genes and many C. elegans 2P domain potassium channel genes, revealing evolutionary conservation of gene structure. Using fluorescence in situ hybridization, the murine Kcnk8 gene was mapped to chromosome 19, 2B, the locus of the murine dancer phenotype, and syntenic to 11q11-11q13, the location of the human homologue. No significant currents were generated in a Xenopus laevis oocyte expression system using the composite Kcnk8 cDNA sequence, suggesting, like many potassium channels, additional channel subunits, modulator substances, or cellular chaperones are required for channel function

Potential and pitfalls in the genetic diagnosis of kidney diseases

Next-generation sequencing has dramatically decreased the cost of gene sequencing, facilitating the simultaneous analysis of multiple genes at the same time; obtaining a genetic result for an individual patient has become much easier. The article by Ars and Torra in this issue of the Clinical Kidney Journal provides examples of the ever-increasing ability to understand a given patient's disease on the molecular level, so that in some cases not only the causative variants in a disease gene are identified, but also potential modifiers in other genes. Yet, with increased sequencing, a large number of variants are discovered that are difficult to interpret. These so-called 'variants of uncertain significance' raise important questions: when and how can pathogenicity be clearly attributed? This is of critical importance, as there are potentially serious consequences attached: decisions about various forms of treatment and even about life and death, such as termination of pregnancy, may hinge on the answer to these questions. Geneticists, thus, need to use the utmost care in the interpretation of identified variants and clinicians must be aware of this problem. We here discuss the potential of genetics to facilitate personalized treatment, but also the pitfalls and how to deal with them

Hypomagnesemia and increased risk of new-onset diabetes mellitus after transplantation in pediatric renal transplant recipients

Background: New onset diabetes after transplantation (NODAT) is a significant co-morbidity following kidney transplantation. Lower post-transplant serum magnesium levels have been found to be an independent risk factor for NODAT in adult kidney transplant recipients. / Methods: We undertook a retrospective analysis of risk factors for NODAT in pediatric renal transplant recipients at our institution with the aim of determining if hypomagnesemia confers a significant risk of developing NODAT in children. / Results: One hundred and seventy three children with median age at transplantation 7.0 (range: 1.3 – 17.5) years were included. Hypomagnesemia was a significant independent risk factor for NODAT (p = 0.01). High trough tacrolimus levels were also independently associated with NODAT (p < 0.001). There was no significant association between NODAT and children’s BMI at the time of transplantation, monthly cumulative steroid dose or post transplant CMV viremia (p = 0.9, 0.6 and 0.7 respectively). / Conclusions: This study identifies hypomagnesemia as a significant independent risk factor for developing NODAT in pediatric renal transplant recipients. Given the clear association between hypomagnesemia and NODAT in both adults and children following renal transplantation, further studies are merited to clarify the etiology of this association, and to examine the effect of magnesium supplementation on NODAT

Cyclophosphamide and rituximab in frequently relapsing/steroid-dependent nephrotic syndrome

BACKGROUND: Steroid-sensitive nephrotic syndrome is the most common form of nephrotic syndrome in childhood, defined by the response to treatment with glucocorticoids with consequent remission. While most children eventually experience spontaneous resolution of the disease, some have a difficult course with frequent relapses or steroid dependence nephrotic syndrome (FRSDNS). The consequent steroid toxicity often prompts administration of other immunosuppressive drugs, traditionally cyclophosphamide. Recently, rituximab has been reported as effective in this disorder, but long-term experience is lacking. METHODS: Retrospective note review of all children with FRSDNS treated with a first course of cyclophosphamide and/or rituximab in our center between December 2006 and April 2015. We reviewed time to first relapse after treatment, co-medications, and side effects. RESULTS: A total of 102 children were treated with cyclophosphamide (79) and/or rituximab (42). Of these, 34 received cyclophosphamide prior to rituximab. Median time to first relapse was 7 months after cyclophosphamide and 14 months after rituximab. Documented side effects of cyclophosphamide included neutropenia, hair loss, and hemorrhagic cystitis (1). Rituximab was associated with an allergic reaction at infusion in two patients. CONCLUSIONS: Rituximab was used in children with the most difficult to treat FRSDNS, yet was associated with longer remission time and less side effects than cyclophosphamide. A randomized controlled trial is needed to directly compare these drugs

EAST syndrome: Clinical, pathophysiological, and genetic aspects of mutations in KCNJ10

EAST syndrome is a recently described autosomal recessive disorder secondary to mutations in KCNJ10 (Kir4.1), a gene encoding a potassium channel expressed in the brain, eye, ear and kidney. This condition is characterized by 4 cardinal features; Epilepsy, Ataxia, Sensorineural deafness, and (a renal salt-wasting) Tubulopathy, hence the acronym EAST syndrome. Here we review reported clinical manifestations, in particular the neurological signs and symptoms which typically have the most impact on the quality of life of patients. In addition we review the pathophysiology and genetic aspects of the disease. So far 14 different KCNJ10 mutations have been published which either directly affect channel function or may lead to mislocalisation. Investigations of the pathophysiology may provide clues to potential treatments