A mutation causing pseudohypoaldosteronism type 1 identifies a conserved glycine that is involved in the gating of the epithelial sodium channel.

Pseudohypoaldosteronism type 1 (PHA-1) is an inherited disease characterized by severe neonatal salt-wasting and caused by mutations in subunits of the amiloride-sensitive epithelial sodium channel (ENaC). A missense mutation (G37S) of the human ENaC beta subunit that causes loss of ENaC function and PHA-1 replaces a glycine that is conserved in the N-terminus of all members of the ENaC gene family. We now report an investigation of the mechanism of channel inactivation by this mutation. Homologous mutations, introduced into alpha, beta or gamma subunits, all significantly reduce macroscopic sodium channel currents recorded in Xenopus laevis oocytes. Quantitative determination of the number of channel molecules present at the cell surface showed no significant differences in surface expression of mutant compared with wild-type channels. Single channel conductances and ion selectivities of the mutant channels were identical to that of wild-type. These results suggest that the decrease in macroscopic Na currents is due to a decrease in channel open probability (P(o)), suggesting that mutations of a conserved glycine in the N-terminus of ENaC subunits change ENaC channel gating, which would explain the disease pathophysiology. Single channel recordings of channels containing the mutant alpha subunit (alphaG95S) directly demonstrate a striking reduction in P(o). We propose that this mutation favors a gating mode characterized by short-open and long-closed times. We suggest that determination of the gating mode of ENaC is a key regulator of channel activity.

Vemurafenib in patients with BRAF(V600) mutation-positive melanoma with symptomatic brain metastases: final results of an open-label pilot study.

BACKGROUND & AIM: Brain metastases are frequent in patients with metastatic melanoma, indicating poor prognosis. We investigated the BRAF kinase inhibitor vemurafenib in patients with advanced melanoma with symptomatic brain metastases. METHODS: This open-label trial assessed vemurafenib (960mg twice a day) in patients with BRAF(V600) mutation-positive metastatic melanoma with non-resectable, previously treated brain metastases. The primary end-point was safety. Secondary end-points included best overall response rate, and progression-free and overall survival. RESULTS: Twenty-four patients received vemurafenib for a median treatment duration of 3.8 (0.1-11.3) months. The majority of discontinuations were due to disease progression (n=22). Twenty-three of 24 patients reported at least one adverse event (AE). Grade 3 AEs were reported in four (17%; 95% confidence interval [CI], 4.7-37.4%) patients and included cutaneous squamous cell carcinoma in four patients. Median progression-free survival was 3.9 (95% CI, 3.0-5.5) months, and median survival was 5.3 (95% CI, 3.9-6.6) months. An overall partial response (PR) at both intracranial and extracranial sites was achieved in 10 of 24 (42%; 95% CI, 22.1-63.4) evaluable patients, with stable disease in nine (38%; 95% CI, 18.8-59.4) patients. Of 19 patients with measurable intracranial disease, seven (37%) achieved >30% intracranial tumour regression, and three (16%; 95% CI, 3.4-39.6%) achieved a confirmed PR. Other signs of improvement included reduced need for corticosteroids and enhanced performance status. CONCLUSIONS: Vemurafenib can be safely used in patients with advanced symptomatic melanoma that has metastasised to the brain and can result in meaningful tumour regression.

Novel mutation in the tyrosine kinase domain of FGFR2 in a patient with Pfeiffer syndrome.

Mutations in the fibroblast growth factor receptor 2 (FGFR2) cause a variety of craniosynostosis syndromes. The mutational spectrum tends to be narrow with the majority of mutations occurring in either exon IIIa or IIIc or in the intronic sequence preceding exon IIIc. Mutations outside of this hotspot are uncommon and the few identified mutations have demonstrated wide clinical variability, making it difficult to establish a clear-cut genotype-phenotype correlation. To better delineate the clinical picture associated with these unusual mutations, we describe a severely affected patient with Pfeiffer syndrome and a missense mutation in the tyrosine kinase (TK) domain of FGFR2.

Sex chromosomes and male functions: where do new genes go?

The position of a gene in the genome may have important consequences for its function. Therefore, when a new duplicate gene arises, its location may be critical in determining its fate. Our recent work in humans, mouse, and Drosophila provided a test by studying the patterns of duplication in sex chromosome evolution. We revealed a bias in the generation and recruitment of new gene copies involving the X chromosome that has been shaped largely by selection for male germline functions. The gene movement patterns we observed reflect an ongoing process as some of the new genes are very young while others were present before the divergence of humans and mouse. This suggests a continuing redistribution of male-related genes to achieve a more efficient allocation of male functions. This notion should be further tested in organisms employing other sex determination systems or in organisms differing in germline sex chromosome inactivation. It is likely that the selective forces that were detected in these studies are also acting on other types of duplicate genes. As a result, future work elucidating sex chromosome differentiation by other mutational mechanisms will shed light on this important process.

An ancient founder mutation in PROKR2 impairs human reproduction.

Congenital gonadotropin-releasing hormone (GnRH) deficiency manifests as absent or incomplete sexual maturation and infertility. Although the disease exhibits marked locus and allelic heterogeneity, with the causal mutations being both rare and private, one causal mutation in the prokineticin receptor, PROKR2 L173R, appears unusually prevalent among GnRH-deficient patients of diverse geographic and ethnic origins. To track the genetic ancestry of PROKR2 L173R, haplotype mapping was performed in 22 unrelated patients with GnRH deficiency carrying L173R and their 30 first-degree relatives. The mutation's age was estimated using a haplotype-decay model. Thirteen subjects were informative and in all of them the mutation was present on the same ~123 kb haplotype whose population frequency is ≤10%. Thus, PROKR2 L173R represents a founder mutation whose age is estimated at approximately 9000 years. Inheritance of PROKR2 L173R-associated GnRH deficiency was complex with highly variable penetrance among carriers, influenced by additional mutations in the other PROKR2 allele (recessive inheritance) or another gene (digenicity). The paradoxical identification of an ancient founder mutation that impairs reproduction has intriguing implications for the inheritance mechanisms of PROKR2 L173R-associated GnRH deficiency and for the relevant processes of evolutionary selection, including potential selective advantages of mutation carriers in genes affecting reproduction.

HIV-1 Subtype Is an Independent Predictor of Reverse Transcriptase Mutation K65R in HIV-1 Patients Treated with Combination Antiretroviral Therapy Including Tenofovir.

Subtype-dependent selection of HIV-1 reverse transcriptase resistance mutation K65R was previously observed in cell culture and small clinical investigations. We compared K65R prevalence across subtypes A, B, C, F, G, and CRF02_AG separately in a cohort of 3,076 patients on combination therapy including tenofovir. K65R selection was significantly higher in HIV-1 subtype C. This could not be explained by clinical and demographic factors in multivariate analysis, suggesting subtype sequence-specific K65R pathways.

Exome sequencing identifies recurrent somatic MAP2K1 and MAP2K2 mutations in melanoma.

We performed exome sequencing to detect somatic mutations in protein-coding regions in seven melanoma cell lines and donor-matched germline cells. All melanoma samples had high numbers of somatic mutations, which showed the hallmark of UV-induced DNA repair. Such a hallmark was absent in tumor sample-specific mutations in two metastases derived from the same individual. Two melanomas with non-canonical BRAF mutations harbored gain-of-function MAP2K1 and MAP2K2 (MEK1 and MEK2, respectively) mutations, resulting in constitutive ERK phosphorylation and higher resistance to MEK inhibitors. Screening a larger cohort of individuals with melanoma revealed the presence of recurring somatic MAP2K1 and MAP2K2 mutations, which occurred at an overall frequency of 8%. Furthermore, missense and nonsense somatic mutations were frequently found in three candidate melanoma genes, FAT4, LRP1B and DSC1.

Postpacing abnormal repolarization in catecholaminergic polymorphic ventricular tachycardia associated with a mutation in the cardiac ryanodine receptor gene.

BACKGROUND Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an arrhythmogenic disease for which electrophysiological studies (EPS) have shown to be of limited value.OBJECTIVE This study presents a CPVT family in which marked postpacing repolarization abnormalities during EPS were the only consistent phenotypic manifestation of ryanodine receptor (RyR2) mutation carriers.METHODS The study was prompted by the observation of transient marked QT prolongation preceding initiation of ventricular fibrillation during atrial fibrillation in a boy with a family history of sudden cardiac death (SCD). Family members underwent exercise and pharmacologic electrocardiographic testing with epinephrine, adenosine, and flecainide. Noninvasive clinical test results were normal in 10 patients evaluated, except for both epinephrine- and exercise-induced ventricular arrhythmias in 1. EPS included bursts of ventricular pacing and programmed ventricular extrastimulation reproducing short-long sequences. Genetic screening involved direct sequencing of genes involved in long QT syndrome as well as RyR2.RESULTS Six patients demonstrated a marked increase in QT interval only in the first beat after cessation of ventricular pacing and/or extrastimulation. All 6 patients were found to have a heterozygous missense mutation (M4109R) in RyR2. Two of them, presenting with aborted SCD, also had a second missense mutation (I406T- RyR2). Four family members without RyR2 mutations did not display prominent postpacing QT changes.CONCLUSION M4109R- RyR2 is associated with a high incidence of SCD. The contribution of I406T to the clinical phenotype is unclear. In contrast to exercise testing, marked postpacing repolarization changes in a single beat accurately predicted carriers of M4109R- RyR2 in this family.

Mutation identification by direct comparison of whole-genome sequencing data from mutant and wild-type individuals using k-mers.

Genes underlying mutant phenotypes can be isolated by combining marker discovery, genetic mapping and resequencing, but a more straightforward strategy for mapping mutations would be the direct comparison of mutant and wild-type genomes. Applying such an approach, however, is hampered by the need for reference sequences and by mutational loads that confound the unambiguous identification of causal mutations. Here we introduce NIKS (needle in the k-stack), a reference-free algorithm based on comparing k-mers in whole-genome sequencing data for precise discovery of homozygous mutations. We applied NIKS to eight mutants induced in nonreference rice cultivars and to two mutants of the nonmodel species Arabis alpina. In both species, comparing pooled F2 individuals selected for mutant phenotypes revealed small sets of mutations including the causal changes. Moreover, comparing M3 seedlings of two allelic mutants unambiguously identified the causal gene. Thus, for any species amenable to mutagenesis, NIKS enables forward genetics without requiring segregating populations, genetic maps and reference sequences.

Retinal Dystrophy In The Oculo-auricular Syndrome Due to HMX1 Mutation.

Purpose: To report on the clinical and electrophysiological findings in a patient with oculo-auricular syndrome due to HMX1 mutation, with a follow-up of 12 years. Background: Oculo-auricular syndrome (MIM: 612109) is a rare developmental recessive condition affecting the eye and external ear that results from a mutation in the HMX1 gene. Previously described ocular abnormalities include bilateral microcornea, posterior synechiae, cataract, chorioretinal colobomas and rod-cone dystrophy. Methods: Retrospective chart review of an affected boy followed over a period of 12 years who had serial complete ophthalmologic examinations, fundus photographs, Goldmann perimetry and full-field electroretinograms (ERG). Results: Initial ERG tracings revealed generalized rod more than cone dysfunction. Thereafter, a rapid deterioration in rod and cone function was detected on follow up ERGs. Conclusion: The retinal degeneration in the recessively inherited oculo-auricular syndrome is a progressive rod-cone dystrophy. Visual prognosis is guarded considering the progressive nature of the retinal dystrophy in early infancy.

Prenatal presentation and postnatal evolution of a patient with Jansen metaphyseal dysplasia with a novel missense mutation in PTH1R.

Wave-shaped ribs were detected at prenatal ultrasound in a 20(+1) week female fetus. At birth, skeletal radiographs showed marked hypomineralization and suggested hypophosphatasia. However, elevated blood calcium and alkaline phosphatase excluded hypophosphatasia and raised the possibility of Jansen metaphyseal dysplasia. Molecular analysis of the PTH/PTHrP receptor gene (PTH1R) showed heterozygosity for a previously undescribed transversion variant (c.1373T>A), which predicts p.Ile458Lys. In vitro evaluation of wild type and mutant PTH/PTHrP receptors supported the pathogenic role of the p.Ile458Lys substitution, and confirmed the diagnosis of Jansen metaphyseal dysplasia. This disorder may present prenatally with wavy ribs and in the newborn with hypomineralization, and may therefore be confused with hypophosphatasia. The mottled metaphyseal lesions typically associated with this disease appear only in childhood.

A missense mutation in myelin oligodendrocyte glycoprotein as a cause of familial narcolepsy with cataplexy.

Narcolepsy is a rare sleep disorder characterized by excessive daytime sleepiness and cataplexy. Familial narcolepsy accounts for less than 10% of all narcolepsy cases. However, documented multiplex families are very rare and causative mutations have not been identified to date. To identify a causative mutation in familial narcolepsy, we performed linkage analysis in the largest ever reported family, which has 12 affected members, and sequenced coding regions of the genome (exome sequencing) of three affected members with narcolepsy and cataplexy. We successfully mapped a candidate locus on chromosomal region 6p22.1 (LOD score ¼ 3.85) by linkage analysis. Exome sequencing identified a missense mutation in the second exon of MOG within the linkage region. A c.398C>G mutation was present in all affected family members but absent in unaffected members and 775 unrelated control subjects. Transient expression of mutant myelin oligodendrocyte glycoprotein (MOG) in mouse oligodendrocytes showed abnormal subcellular localization, suggesting an altered function of the mutant MOG. MOG has recently been linked to various neuropsychiatric disorders and is considered as a key autoantigen in multiple sclerosis and in its animal model, experimental autoimmune encephalitis. Our finding of a pathogenic MOG mutation highlights a major role for myelin and oligodendrocytes in narcolepsy and further emphasizes glial involvement in neurodegeneration and neurobehavioral disorders. [corrected].

A dystroglycan mutation associated with limb-girdle muscular dystrophy.

Dystroglycan, which serves as a major extracellular matrix receptor in muscle and the central nervous system, requires extensive O-glycosylation to function. We identified a dystroglycan missense mutation (Thr192→Met) in a woman with limb-girdle muscular dystrophy and cognitive impairment. A mouse model harboring this mutation recapitulates the immunohistochemical and neuromuscular abnormalities observed in the patient. In vitro and in vivo studies showed that the mutation impairs the receptor function of dystroglycan in skeletal muscle and brain by inhibiting the post-translational modification, mediated by the glycosyltransferase LARGE, of the phosphorylated O-mannosyl glycans on α-dystroglycan that is required for high-affinity binding to laminin.