Liddle's syndrome caused by a novel missense mutation (P617L) of the epithelial sodium channel beta subunit.

OBJECTIVE: The aim of the study was to search for mutations of SCNN1B and SCNN1G in an Italian family with apparently dominant autosomal transmission of a clinical phenotype consistent with Liddle's syndrome. METHODS: Genetic analysis was performed in the proband, his relatives, and 100 control subjects. To determine the functional role of the mutation identified in the proband, we expressed the mutant or wild-type epithelial sodium channel in Xenopus laevis oocytes. RESULTS: A novel point mutation, causing an expected substitution of a leucine residue for the second proline residue of the conserved PY motif (PPP x Y) of the beta subunit was identified in the proband. The functional expression of the mutant epithelial sodium channel in X. laevis oocytes showed a three-fold increase in the amiloride-sensitive current as compared with that of the wild-type channel. CONCLUSION: This newly identified mutation adds to other missense mutations of the PY motif of the beta subunit of the epithelial sodium channel, thus confirming its crucial role in the regulation of the epithelial sodium channel. To our knowledge, this is the first report of Liddle's syndrome in the Italian population, confirmed by genetic and functional analysis, with the identification of a gain-of-function mutation not previously reported.

Variable phenotypic expressivity in a Swiss family with autosomal dominant retinitis pigmentosa due to a T494M mutation in the PRPF3 gene.

PURPOSE: To characterize the clinical, psychophysical, and electrophysiological phenotypes in a five-generation Swiss family with dominantly inherited retinitis pigmentosa caused by a T494M mutation in the Precursor mRNA-Processing factor 3 (PRPF3) gene, and to relate the phenotype to the underlying genetic mutation. METHODS: Eleven affected patients were ascertained for phenotypic and genotypic characterization. Ophthalmologic evaluations included color vision testing, Goldmann perimetry, and digital fundus photography. Some patients had autofluorescence imaging, Optical Coherence Tomography, and ISCEV-standard full-field electroretinography. All affected patients had genetic testing. RESULTS: The age of onset of night blindness and the severity of the progression of the disease varied between members of the family. Some patients reported early onset of night blindness at age three, with subsequent severe deterioration of visual acuity, which was 0.4 in the best eye after their fifties. The second group of patients had a later onset of night blindness, in the mid-twenties, with a milder disease progression and a visual acuity of 0.8 at age 70. Fundus autofluorescence imaging and electrophysiological and visual field abnormalities also showed some degree of varying phenotypes. The autofluorescence imaging showed a large high-density ring bilaterally. Myopia (range: -0.75 to -8) was found in 10/11 affected subjects. Fundus findings showed areas of atrophy along the arcades. A T494M change was found in exon 11 of the PRPF3 gene. The change segregates with the disease in the family. CONCLUSIONS: A mutation in the PRPF3 gene is rare compared to other genes causing autosomal dominant retinitis pigmentosa (ADRP). Although a T494M change has been reported, the family in our study is the first with variable expressivity. Mutations in the PRPF3 gene can cause a variable ADRP phenotype, unlike in the previously described Danish, English, and Japanese families. Our report, based on one of the largest affected pedigree, provides a better understanding as to the phenotype/genotype description of ADRP caused by a PRPF3 mutation.

A hypomorphic mutation in lpin1 induces progressively improving neuropathy and lipodystrophy in the rat.

The Lpin1 gene encodes the phosphatidate phosphatase (PAP1) enzyme Lipin 1, which plays a critical role in lipid metabolism. In this study we describe the identification and characterization of a rat model with a mutated Lpin1 gene (Lpin1(1Hubr)), generated by N-ethyl-N-nitrosourea mutagenesis. Lpin1(1Hubr) rats are characterized by hindlimb paralysis and mild lipodystrophy that are detectable from the second postnatal week. Sequencing of Lpin1 identified a point mutation in the 5'-end splice site of intron 18 resulting in mis-splicing, a reading frameshift, and a premature stop codon. As this mutation does not induce nonsense-mediated decay, it allows the production of a truncated Lipin 1 protein lacking PAP1 activity. Lpin1(1Hubr) rats developed hypomyelination and mild lipodystrophy rather than the pronounced demyelination and adipocyte defects characteristic of Lpin1(fld/fld) mice, which carry a null allele for Lpin1. Furthermore, biochemical, histological, and molecular analyses revealed that these lesions improve in older Lpin1(1Hubr) rats as compared with young Lpin1(1Hubr) rats and Lpin1(fld/fld) mice. We observed activation of compensatory biochemical pathways substituting for missing PAP1 activity that, in combination with a possible non-enzymatic Lipin 1 function residing outside of its PAP1 domain, may contribute to the less severe phenotypes observed in Lpin1(1Hubr) rats as compared with Lpin1(fld/fld) mice. Although we are cautious in making a direct parallel between the presented rodent model and human disease, our data may provide new insight into the pathogenicity of recently identified human LPIN1 mutations.

Evolutionary branching in deme-structured populations.

Adaptive dynamics shows that a continuous trait under frequency dependent selection may first converge to a singular point followed by spontaneous transition from a unimodal trait distribution into a bimodal one, which is called "evolutionary branching". Here, we study evolutionary branching in a deme-structured population by constructing a quantitative genetic model for the trait variance dynamics, which allows us to obtain an analytic condition for evolutionary branching. This is first shown to agree with previous conditions for branching expressed in terms of relatedness between interacting individuals within demes and obtained from mutant-resident systems. We then show this branching condition can be markedly simplified when the evolving trait affect fecundity and/or survival, as opposed to affecting population structure, which would occur in the case of the evolution of dispersal. As an application of our model, we evaluate the threshold migration rate below which evolutionary branching cannot occur in a pairwise interaction game. This agrees very well with the individual-based simulation results.

Mutation spectrum of MLL2 in a cohort of Kabuki syndrome patients.

ABSTRACT: BACKGROUND: Kabuki syndrome (Niikawa-Kuroki syndrome) is a rare, multiple congenital anomalies/mental retardation syndrome characterized by a peculiar face, short stature, skeletal, visceral and dermatoglyphic abnormalities, cardiac anomalies, and immunological defects. Recently mutations in the histone methyl transferase MLL2 gene have been identified as its underlying cause. METHODS: Genomic DNAs were extracted from 62 index patients clinically diagnosed as affected by Kabuki syndrome. Sanger sequencing was performed to analyze the whole coding region of the MLL2 gene including intron-exon junctions. The putative causal and possible functional effect of each nucleotide variant identified was estimated by in silico prediction tools. RESULTS: We identified 45 patients with MLL2 nucleotide variants. 38 out of the 42 variants were never described before. Consistently with previous reports, the majority are nonsense or frameshift mutations predicted to generate a truncated polypeptide. We also identified 3 indel, 7 missense and 3 splice site. CONCLUSIONS: This study emphasizes the relevance of mutational screening of the MLL2 gene among patients diagnosed with Kabuki syndrome. The identification of a large spectrum of MLL2 mutations possibly offers the opportunity to improve the actual knowledge on the clinical basis of this multiple congenital anomalies/mental retardation syndrome, design functional studies to understand the molecular mechanisms underlying this disease, establish genotype-phenotype correlations and improve clinical management.

La rate: entre mystères et découvertes [The spleen: between mysteries and discoveries].

Mainly because it is possible to live without it, the spleen has always been considered a secondary and mysterious organ. However, recent observations have revealed new unsuspected functions for this organ whose patho-physiological importance should be reconsidered. Much less known than the hypersplenism, the hyposplenism corresponds historically to the loss or the insufficiency of the two principal functions of spleen: the filtration of faded or senescent elements from the blood and the fight against infections. In this article, after a short recall of the physiological functions of spleen, three innovations relating to hyposplenism will be explored: the vascular complications, the loss of the splenic pool of regenerating monocytes and the loss of the splenic pool of pluripotent mesenchymal stem cell.

Autosomal-dominant distal myopathy associated with a recurrent missense mutation in the gene encoding the nuclear matrix protein, matrin 3.

Distal myopathies represent a heterogeneous group of inherited skeletal muscle disorders. One type of adult-onset, progressive autosomal-dominant distal myopathy, frequently associated with dysphagia and dysphonia (vocal cord and pharyngeal weakness with distal myopathy [VCPDM]), has been mapped to chromosome 5q31 in a North American pedigree. Here, we report the identification of a second large VCPDM family of Bulgarian descent and fine mapping of the critical interval. Sequencing of positional candidate genes revealed precisely the same nonconservative S85C missense mutation affecting an interspecies conserved residue in the MATR3 gene in both families. MATR3 is expressed in skeletal muscle and encodes matrin 3, a component of the nuclear matrix, which is a proteinaceous network that extends throughout the nucleus. Different disease related haplotype signatures in the two families provided evidence that two independent mutational events at the same position in MATR3 cause VCPDM. Our data establish proof of principle that the nuclear matrix is crucial for normal skeletal muscle structure and function and put VCPDM on the growing list of monogenic disorders associated with the nuclear proteome.

Comparison of the glomerular filtration rate in children by the new revised Schwartz formula and a new generalized formula.

The most widely used formula for estimating glomerular filtration rate (eGFR) in children is the Schwartz formula. It was revised in 2009 using iohexol clearances with measured GFR (mGFR) ranging between 15 and 75 ml/min × 1.73 m(2). Here we assessed the accuracy of the Schwartz formula using the inulin clearance (iGFR) method to evaluate its accuracy for children with less renal impairment comparing 551 iGFRs of 392 children with their Schwartz eGFRs. Serum creatinine was measured using the compensated Jaffe method. In order to find the best relationship between iGFR and eGFR, a linear quadratic regression model was fitted and a more accurate formula was derived. This quadratic formula was: 0.68 × (Height (cm)/serum creatinine (mg/dl))-0.0008 × (height (cm)/serum creatinine (mg/dl))(2)+0.48 × age (years)-(21.53 in males or 25.68 in females). This formula was validated using a split-half cross-validation technique and also externally validated with a new cohort of 127 children. Results show that the Schwartz formula is accurate until a height (Ht)/serum creatinine value of 251, corresponding to an iGFR of 103 ml/min × 1.73 m(2), but significantly unreliable for higher values. For an accuracy of 20 percent, the quadratic formula was significantly better than the Schwartz formula for all patients and for patients with a Ht/serum creatinine of 251 or greater. Thus, the new quadratic formula could replace the revised Schwartz formula, which is accurate for children with moderate renal failure but not for those with less renal impairment or hyperfiltration.

Increasing lactate turnover rate during exercise by means of altitude training and fructose ingestion : effects on substrate metabolism and endurance performance

Summary : With regard to exercise metabolism, lactate was long considered as a dead-end waste product responsible for muscle fatigue and a limiting factor for motor performance. However, a large body of evidence clearly indicates that lactate is an energy efficient metabolite able to link the glycolytic pathway with aerobic metabolism and has endocrine-like actions, rather than to be a dead-end waste product. Lactate metabolism is also known to be quickly upregulated by regular endurance training and is thought to be related to exercise performance. However, to what extent its modulation can increase exercise performance in already endurance-trained subjects is unknown. The general hypothesis of this work was therefore that increasing either lactate metabolic clearance rate or lactate availability could, in turn, increase endurance performance. The first study (Study I) aimed at increasing the lactate clearance rate by means of assumed interaction effects of endurance training and hypoxia on lactate metabolism and endurance performance. Although this study did not demonstrate any interaction of training and hypoxia on both lactate metabolism and endurance performance, a significant deleterious effect of endurance training in hypoxia was shown on glucose homeostasis. The methods used to determine lactate kinetics during exercise exhibited some limitations, and the second study did delineate some of the issues raised (Study 2). The third study (Study 3) investigated the metabolic and performance effects of increasing plasma lactate production and availability during prolonged exercise in the fed state. A nutritional intervention was used for this purpose: part of glucose feedings ingested during the control condition was substituted by fructose. The results of this study showed a significant increase of lactate turnover rate, quantified the metabolic fate of fructose; and demonstrated a significant decrease of lipid oxidation and glycogen breakdown. In contrast, endurance performance appeared to be unmodified by this dietary intervention, being at odds with recent reports. Altogether the results of this thesis suggest that in endurance athletes the relationship between endurance performance and lactate turnover rate remains unclear. Nonetheless, the result of the present study raises questions and opens perspectives on the rationale of using hypoxia as a therapeutic aid for the treatment of insulin resistance. Moreover, the results of the second study open perspectives on the role of lactate as an intermediate metabolite and its modulatory effects on substrate metabolism during exercise. Additionally it is suggested that the simple nutritional intervention used in the third study can be of interest in the investigation on the aforementioned roles of lactate. Résumé : Lorsque le lactate est évoqué en rapport avec l'exercice, il est souvent considéré comme un déchet métabolique responsable de l'acidose métabolique, de la fatigue musculaire ou encore comme un facteur limitant de la performance. Or la littérature montre clairement que le lactate se révèle être plutôt un métabolite utilisé efficacement par de nombreux tissus par les voies oxydatives et, ainsi, il peut être considéré comme un lien entre le métabolisme glycolytique et le métabolisme oxydatif. De plus on lui prête des propriétés endocrines. Il est connu que l'entraînement d'endurance accroît rapidement le métabolisme du lactate, et il est suggéré que la performance d'endurance est liée à son métabolisme. Toutefois la relation entre le taux de renouvellement du lactate et la performance d'endurance est peu claire, et, de même, de quelle manière la modulation de son métabolisme peut influencer cette dernière. Le but de cette thèse était en conséquence d'investiguer de quelle manière et à quel degré l'augmentation du métabolisme du lactate, par l'augmentation de sa clearance et de son turnover, pouvait à son tour améliorer la performance d'endurance de sujets entraînés. L'objectif de la première étude a été d'augmenter la clearance du lactate par le biais d'un entraînement en conditions hypoxiques chez des cyclistes d'endurance. Basé sur la littérature scientifique existante, on a fait l'hypothèse que l'entraînement d'endurance et l'hypoxie exerceraient un effet synergétique sur le métabolisme du lactate et sur la performance, ce qui permettrait de montrer des relations entre performance et métabolisme du lactate. Les résultats de cette étude n'ont montré aucun effet synergique sur la performance ou le métabolisme du lactate. Toutefois, un effet délétère sur le métabolisme du glucose a été démontré. Quelques limitations de la méthode employée pour la mesure du métabolisme du lactate ont été soulevées, et partiellement résolues dans la seconde étude de ce travail, qui avait pour but d'évaluer la sensibilité du modèle pharmacodynamique utilisé pour le calcul du turnover du lactate. La troisième étude a investigué l'effet d'une augmentation de la lactatémie sur le métabolisme des substrats et sur la performance par une intervention nutritionnelle substituant une partie de glucose ingéré pendant l'exercice par du fructose. Les résultats montrent que les composants dynamiques du métabolisme du lactate sont significativement augmentés en présence de fructose, et que les oxydations de graisse et de glycogène sont significativement diminuées. Toutefois aucun effet sur la performance n'a été démontré. Les résultats de ces études montrent que la relation entre le métabolisme du lactate et la performance reste peu claire. Les résultats délétères de la première étude laissent envisager des pistes de travail, étant donné que l'entraînement en hypoxie est considéré comme outil thérapeutique dans le traitement de pathologies liées à la résistance à l'insuline. De plus les résultats de la troisième étude ouvrent des perspectives de travail quant au rôle du lactate comme intermédiaire métabolique durant l'exercice ainsi que sur ses effets directs sur le métabolisme. Ils suggèrent de plus que la manipulation nutritionnelle simple qui a été utilisée se révèle être un outil prometteur dans l'étude des rôles et effets métaboliques que peut revêtir le lactate durant l'exercice.

Transmission of HIV-1 drug resistance in Switzerland: a 10-year molecular epidemiology survey.

OBJECTIVES: Representative prevalence data of transmitted drug-resistant HIV-1 are essential to establish accurate guidelines addressing resistance testing and first-line treatments. METHODS: Systematic resistance testing was carried out in individuals in Switzerland with documented HIV-1 seroconversion during 1996-2005 and available samples with RNA > 1000 copies/ml obtained within 1 year of estimated seroconversion. Resistance interpretation used the Stanford list of mutations for surveillance of transmitted drug resistance and the French National Agency for AIDS Research algorithm. RESULTS: Viral sequences from 822 individuals were available. Risk groups were men having sex with men (42%), heterosexual contacts (32%) and intravenous drug users (20%); 30% were infected with non-B subtype viruses. Overall, prevalence of transmitted resistance was 7.7% [95% confidence interval (CI), 5.9-9.5] for any drug, 5.5% (95% CI, 3.9-7.1) for nucleoside reverse transcriptase inhibitors, 1.9% (95% CI, 1.0-2.8) for non-nucleoside reverse transcriptase inhibitors and 2.7% (95% CI, 1.6-3.8) for protease inhibitors. Dual- or triple-class resistance was observed in 2% (95% CI, 0.8-2.5). No significant trend in prevalence of transmitted resistance was observed over years. There were no differences according to ethnicity, risk groups or gender, but prevalence of transmitted resistance was highest among individuals infected with subtype B virus. CONCLUSIONS: The transmission rate of drug-resistant HIV-1 has been stable since 1996, with very rare transmission of dual- or triple-class resistance. These data suggest that transmission of drug resistance in the setting of easy access to antiretroviral treatment can remain stable and be kept at a low level.