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Mutations in 11 genes that encode ion channels or their associated proteins cause inherited long QT syndrome (LQTS) and account for [approximately equal to] 75-80% of cases (LQT1-11). Direct sequencing of SNTA1, the gene encoding [alpha]1-syntrophin, was performed in a cohort of LQTS patients that were negative for mutations in the 11 known LQTS-susceptibility genes. A missense mutation (A390V-SNTA1) was found in a patient with recurrent syncope and markedly prolonged QT interval (QTc, 530 ms). SNTA1 links neuronal nitric oxide synthase (nNOS) to the nNOS inhibitor plasma membrane Ca-ATPase subtype 4b (PMCA4b); SNTA1 also is known to associate with the cardiac sodium channel SCN5A. By using a GST-fusion protein of the C terminus of SCN5A, we showed that WT-SNTA1 interacted with SCN5A, nNOS, and PMCA4b. In contrast, A390VSNTA1 selectively disrupted association of PMCA4b with this complex and increased direct nitrosylation of SCN5A. A390V-SNTA1 expressed with SCN5A, nNOS, and PMCA4b in heterologous cells increased peak and late sodium current compared with WT-SNTA1, and the increase was partially inhibited by NOS blockers. Expression of A390V-SNTA1 in cardiac myocytes also increased late sodium current. We conclude that the A390V mutation disrupted binding with PMCA4b, released inhibition of nNOS, caused S-nitrosylation of SCNSA, and was associated with increased late sodium current, which is the characteristic biophysical dysfunction for sodium-channel-mediated LQTS (LQT3). These results establish an SNTAl-based nNOS complex attached to SCN5A as a key regulator of sodium current and suggest that SNTA 1 be considered a rare LQTS-susceptibility gene. cardiac arrhythmia | ion channel | nitrosylation | plasma membrane Ca-ATPase | sodium current

A mutation in the human FXYD2 polypeptide (Na-K-ATPase [gamma] subunit) that changes a conserved transmembrane glycine to arginine is linked to dominant renal hypomagnesemia. Xenopus laevis oocytes injected with wild-type FXYD2 or the mutant G41R cRNAs expressed large nonselective ion currents. However, in contrast to the wild-type FXYD2 currents, inward rectifying cation currents were induced by hyperpolarization pulses in oocytes expressing the G41R mutant. Injection of EDTA into the oocyte removed inward rectification in the oocytes expressing the mutant, but did not alter the nonlinear current-voltage relationship of the wild-type FXYD2 pseudo-steady-state currents. Extracellular divalent ions, [Ca.sup.2+] and [Ba.sup.2+], and trivalent cations, [La.sup.3+], blocked both the wild-type and mutant FXYD2 currents. Site-directed mutagenesis of G41 demonstrated that a positive charge at this site is required for the inward rectification. When the wild-type FXYD2 was expressed in Madin-Darby canine kidney cells, the cells in the presence of a large apical-to-basolateral [Mg.sup.2+] gradient and at negative potentials had an increase in transepithelial current compared with cells expressing the G41R mutant or control transfected cells. Moreover, this current was inhibited by extracellular [Ba.sup.2+] at the basolateral surface. These results suggest that FXYD2 can mediate basolateral extrusion of magnesium from cultured renal epithelial cells and provide new insights into the understanding of the possible physiological roles of FXYD2 wild-type and mutant proteins. ion currents; mutant proteins; inward rectification; Na-K-ATPase

Exocytosis of neurotransmitters and hormones occurs through the fusion of secretory vesicles with the plasma membrane. This highly regulated process involves key proteins, such as SNAREs, and specific lipids at the site of membrane fusion. Phospholipase D (PLD) has recently emerged as a promoter of membrane fusion in various exocytotic events potentially by providing fusogenic cone-shaped phosphatidic acid. We show here that PLD1 is regulated by ribosomal S6 kinase 2 (RSK2)-dependent phosphorylation. RSK2 is activated by a high [K.sup.+]-induced rise in cytosolic calcium. Expression of inactive RSK2 mutants or selective knockdown of endogenous RSK2 dramatically affects the different kinetic components of the exocytotic response in chromaffin cells. RSK2 physically interacts with and stimulates PLD activity through the phosphorylation of Thr-147 in the PLD1 amino-terminal phox homology domain. Expression of PLD1 phosphomimetic mutants fully restores secretion in cells depleted of RSK2, suggesting that RSK2 is a critical upstream signaling element in the activation of PLD1 to produce the lipids required for exocytosis. We propose that PLD-related defects in neuronal and endocrine activities could contribute to the effect observed after the loss-of-function mutations in Rsk2 that lead to Coffin-Lowry syndrome, an X-linked form of growth and mental retardation.

Brugada syndrome is a genetic disease associated with sudden cardiac death that is characterized by ventricular fibrillation and right precordial ST segment elevation on ECG. Loss-of-function mutations in SCN5A, which encodes the predominant cardiac sodium channel [alpha] subunit [Na.sub.V]1.5, can cause Brugada syndrome and cardiac conduction disease. However, SCN5A mutations are not detected in the majority of patients with these syndromes, suggesting that other genes can cause or modify presentation of these disorders. Here, we investigated SCN1B, which encodes the function-modifying sodium channel [beta]1 subunit, in 282 probands with Brugada syndrome and in 44 patients with conduction disease, none of whom had SCN5A mutations. We identified 3 mutations segregating with arrhythmia in 3 kindreds. Two of these mutations were located in a newly described alternately processed transcript, [beta]1B. Both the canonical and alternately processed transcripts were expressed in the human heart and were expressed to a greater degree in Purkinje fibers than in heart muscle, consistent with the clinical presentation of conduction disease. Sodium current was lower when [Na.sub.V]1.5 was coexpressed with mutant [beta]1 or [beta]1B subunits than when it was coexpressed with WT subunits. These findings implicate SCN1B as a disease gene for human arrhythmia susceptibility., Introduction Voltage-gated sodium channels are critical for the generation and propagation of the cardiac action potential, and mutations in SCN5A, the gene encoding the major pore-forming sodium channel [alpha] subunit [...]

Phenotypic overlap of type 3 long QT syndrome (LQT3) with Brugada syndrome (BrS) is observed in some carriers of mutations in the Na channel SCN5A. While this overlap is important for patient management, the clinical features, prevalence, and mechanisms underlying such overlap have not been fully elucidated. To investigate the basis for this overlap, we genotyped a cohort of 44 LQT3 families of multiple ethnicities from 7 referral centers and found a high prevalence of the E1784K mutation in SCN5A. Of 41 E1784K carriers, 93% had LQT3, 22% had BrS, and 39% had sinus node dysfunction. Heterologously expressed E1784K channels showed a 15.0-mV negative shift in the voltage dependence of Na channel inactivation and a 7.5-fold increase in flecainide affinity for resting-state channels, properties also seen with other LQT3 mutations associated with a mixed clinical phenotype. Furthermore, these properties were absent in Na channels harboring the T1304M mutation, which is associated with LQT3 without a mixed clinical phenotype. These results suggest that a negative shift of steady-state Na channel inactivation and enhanced tonic block by class IC drugs represent common biophysical mechanisms underlying the phenotypic overlap of LQT3 and BrS and further indicate that class IC drugs should be avoided in patients with Na channels displaying these behaviors., Introduction Congenital long QT syndrome (LQTS) is characterized by the prolongation of the QT interval on surface ECGs and an increased risk of potentially fatal ventricular arrhythmias, especially torsade de [...]

The [Ca.sup.2+] release channel ryanodine receptor 2 (RyR2) is required for excitation-contraction coupling in the heart and is also present in the brain. Mutations in RyR2 have been linked to exercise-induced sudden cardiac death (catecholaminergic polymorphic ventricular tachycardia [CPVT]). CPVT-associated RyR2 mutations result in "leaky" RyR2 channels due to the decreased binding of the calstabin2 (FKBP12.6) subunit, which stabilizes the closed state of the channel. We found that mice heterozygous for the R2474S mutation in Ryr2 (Ryr2-R2474S mice) exhibited spontaneous generalized tonic-clonic seizures (which occurred in the absence of cardiac arrhythmias), exercise-induced ventricular arrhythmias, and sudden cardiac death. Treatment with a novel RyR2-specific compound (S107) that enhances the binding of calstabin2 to the mutant Ryr2-R2474S channel inhibited the channel leak and prevented cardiac arrhythmias and raised the seizure threshold. Thus, CPVT-associated mutant leaky Ryr2-R2474S channels in the brain can cause seizures in mice, independent of cardiac arrhythmias. Based on these data, we propose that CPVT is a combined neurocardiac disorder in which leaky RyR2 channels in the brain cause epilepsy, and the same leaky channels in the heart cause exercise-induced sudden cardiac death., Introduction Pharmacological seizure models have implicated abnormalities in intracellular [Ca.sup.2+] cycling of inhibitory interneurons and/or astrocytes as a mechanism of seizure generation (1), (2), and the inositol 1,4,5-trisphosphate receptor (IP3R), [...]

Autophagy is the principal cellular pathway for degradation of long-lived proteins and organelles and regulates cell fate in response to stress. Recently, autophagy has been implicated in neurodegeneration, but whether it is detrimental or protective remains unclear. Here we report that beclin 1, a protein with a key role in autophagy, was decreased in affected brain regions of patients with Alzheimer disease (AD) early in the disease process. Heterozygous deletion of beclin 1 (Becn1) in mice decreased neuronal autophagy and resulted in neurode-generation and disruption of lysosomes. In transgenic mice that express human amyloid precursor protein (APP), a model for AD, genetic reduction of Becn1 expression increased intraneuronal amyloid [beta] (A[beta]) accumulation, extracellular A[beta] deposition, and neurodegeneration and caused microglial changes and profound neuronal ultrastructural abnormalities. Administration of a lentiviral vector expressing beclin 1 reduced both intracellular and extracellular amyloid pathology in APP transgenic mice. We conclude that beclin 1 deficiency disrupts neuronal autophagy, modulates APP metabolism, and promotes neurodegeneration in mice and that increasing beclin 1 levels may have therapeutic potential in AD., Introduction Familial Alzheimer disease (AD) mutations increase the toxicity and amyloidogenicity of the amyloid [beta] (A[beta]) peptide, placing disruption of amyloid precursor protein (APP) metabolism and A[beta] production at the [...]

Germline activation of H-RAS oncogenes is the primary cause of Costello syndrome (CS), a neuro-cardio-facio-cutaneous developmental syndrome. Here we describe the generation of a mouse model of CS by introduction of an oncogenic Gly12Val mutation in the mouse H-Ras locus using homologous recombination in ES cells. Germline expression of the endogenous H-[Ras.sup.G12V] oncogene, even in homozygosis, resulted in hyperplasia of the mammary gland. However, development of tumors in these mice was rare. H-[Ras.sup.G12V] mutant mice closely phenocopied some of the abnormalities observed in patients with CS, including facial dysmorphia and cardiomyopathies. These mice also displayed alterations in the homeostasis of the cardiovascular system, including development of systemic hypertension, extensive vascular remodeling, and fibrosis in both the heart and the kidneys. This phenotype was age dependent and was a consequence of the abnormal upregulation of the renin--Ang II system. Treatment with captopril, an inhibitor of Ang II biosynthesis, prevented development of the hypertension condition, vascular remodeling, and heart and kidney fibrosis. In addition, it partially alleviated the observed cardiomyopathies. These mice should help in elucidating the etiology of CS symptoms, identifying additional defects, and evaluating potential therapeutic strategies., Introduction Costello syndrome (CS) (1), (2) belongs to a group of neuro-cardio-facio-cutaneous (NCFC) developmental syndromes that include Noonan syndrome (NS), cardio-facio-cutaneous (CFC) syndrome, and LEOPARD syndrome (LS) as well as [...]

Permanent neonatal diabetes mellitus (PNDM) is a rare disorder usually presenting within 6 months of birth. Although several genes have been linked to this disorder, in almost half the cases documented in Italy, the genetic cause remains unknown. Because the Akita mouse bearing a mutation in the Ins2 gene exhibits PNDM associated with pancreatic [beta] cell apoptosis, we sequenced the human insulin gene in PNDM subjects with unidentified mutations. We discovered 7 heterozygous mutations in 10 unrelated probands. In 8 of these patients, insulin secretion was detectable at diabetes onset, but rapidly declined over time. When these mutant proinsulins were expressed in HEK293 cells, we observed defects in insulin protein folding and secretion. In these experiments, expression of the mutant proinsulins was also associated with increased Grp78 protein expression and XBP1 mRNA splicing, 2 markers of endoplasmic reticulum stress, and with increased apoptosis. Similarly transfected INS-1E insulinoma cells had diminished viability compared with those expressing WT proinsulin. In conclusion, we find that mutations in the insulin gene that promote proinsulin misfolding may cause PNDM., Introduction Neonatal diabetes is a rare monogenic disorder associated with defects of pancreatic [beta] cell mass and/or function. The disorder is distinguished by 2 clinical variants--transient and permanent--caused by specific [...]

Intravenous infusion of recombinant human activated Factor VII (FVIIa) has been used for over a decade in the successful management of bleeding episodes in patients with inhibitory antibodies to Factor VIII or Factor IX. Previously, we showed that expression of murine FVIIa (mFVIIa) from an adeno-associated viral (AAV) vector corrected abnormal hemostatic parameters in hemophilia B mice. To pursue this as a therapeutic approach, we sought to define safe and effective levels of FVIIa for continuous expression. In mice transgenic for mFVIIa or injected with AAV-mFVIIa, we analyzed survival, expression levels, in vitro and in vivo coagulation tests, and histopathology for up to 16 months after birth/mFVIIa expression. We found that continuous expression of mFVIIa at levels at or below 1.5 [mu]g/ml was safe, effective, and compatible with a normal lifespan. However, expression levels of 2 [mu]g/ml or higher were associated with thrombosis and early mortality, with pathologic findings in the heart and lungs that were rescued in a low--factor X (low-FX) mouse background, suggesting a FX-mediated effect. The findings from these mouse models of continuous FVIIa expression have implications for the development of a safe gene transfer approach for hemophilia and are consistent with the possibility of thromboembolic risk of continuously elevated FVIIa levels., Introduction Hemophilia results from mutations in either of 2 genes, F8 or F9, which encode proteins in the intrinsic pathway of coagulation. The current approach to therapy is intravenous infusion [...]

In humans, hereditary inactivation of either [p22.sup.phox] or [gp91.sup.phox] leads to chronic granulomatous disease (CGD), a severe immune disorder characterized by the inability of phagocytes to produce bacteria-destroying ROS. Heterodimers of [p22.sup.phox] and [gp91.sup.phox] proteins constitute the superoxide-producing cytochrome core of the phagocyte NADPH oxidase. In this study, we identified the nmf333 mouse strain as what we believe to be the first animal model of [p22.sup.phox] deficiency. Characterization of nmf333 mice revealed that deletion of [p22.sup.phox] inactivated not only the phagocyte NADPH oxidase, but also a second cytochrome in the inner ear epithelium. As a consequence, mice of the nmf333 strain exhibit a compound phenotype consisting of both a CGD-like immune defect and a balance disorder caused by the aberrant development of gravity-sensing organs. Thus, in addition to identifying a model of [p22.sup.phox]-dependent immune deficiency, our study indicates that a clinically identifiable patient population with an otherwise cryptic loss of gravity-sensor function may exist. Thus, [p22.sup.phox] represents a shared and essential component of at least 2 superoxide-producing cytochromes with entirely different biological functions. The site of [p22.sup.phox] expression in the inner ear leads us to propose what we believe to be a novel mechanism for the control of vestibular organogenesis., Introduction The superoxide-producing NADPH oxidase (Nox) complex of phagocytes (Phox) is critical for the elimination of invading bacteria and fungi. The enzymatic core of Phox is a heterodimeric flavocytochrome composed [...]

A fundamental property of leukemic stem cells is clonal dominance of the bone marrow microenvironment. Truncation mutations of CSF3R, which encodes the G-CSF receptor (G-CSFR), are implicated in leukemic progression in patients with severe congenital neutropenia. Here we show that expression of a truncated mutant Csf3r in mice confers a strong clonal advantage at the HSC level that is dependent upon exogenous G-CSF. G-CSF--induced proliferation, phosphorylation of Stat5, and transcription of Stat5 target genes were increased in HSCs isolated from mice expressing the mutant Csf3r. Conversely, the proliferative advantage conferred by the mutant Csf3r was abrogated in myeloid progenitors lacking both Stat5A and Stat5B, and HSC function was reduced in mice expressing a truncated mutant Csf3r engineered to have impaired Stat5 activation. These data indicate that in mice, inappropriate Stat5 activation plays a key role in establishing clonal dominance by stem cells expressing mutant Csf3r., Introduction There is accumulating evidence suggesting that most leukemia is initiated by rare cancer stem cells, referred to as leukemic stem cells (LSCs). LSCs are functionally defined as cells able [...]

Patients with X-linked hypophosphatemia (XLH) and the hyp-mouse, a model of XLH characterized by a deletion in the Phex gene, manifest hypophosphatemia, renal phosphate wasting, and rickets/osteomalacia. Cloning of the PHEX/Phex gene and mutations in affected patients and hyp-mice established that alterations in PHEX/Phex expression underlie XLH. Although PHEX/Phex expression occurs primarily in osteoblast lineage cells, transgenic Phex expression in hyp-mouse osteoblasts fails to rescue the phenotype, suggesting that Phex expression at other sites underlies XLH. To establish whether abnormal Phex in osteoblasts and/or osteocytes alone generates the HYP phenotype, we created mice with a global Phex knockout ([Cre-Phex.sup.[Delta]flox/y] mice) and conditional osteocalcin-promoted (OC-promoted) Phex inactivation in osteoblasts and osteocytes ([OC-Cre-Phex.sup.[Delta]flox/y]). Serum phosphorus levels in [Cre-Phex.sup.[Delta]flox/y], [OC-Cre-Phex.sup.[Delta]flox/y], and hyp-mice were lower than those in normal mice. Kidney cell membrane phosphate transport in [Cre-Phex.sup.[Delta]flox/y], [OC-Cre-Phex.sup.[Delta]flox/y], and hyp-mice was likewise reduced compared with that in normal mice. Abnormal renal phosphate transport in [Cre-Phex.sup.[Delta]flox/y] and [OC-Cre-Phex.sup.[Delta]flox/y] mice was associated with increased bone production and serum FGF-23 levels and decreased kidney membrane type IIa sodium phosphate cotransporter protein, as was the case in hyp-mice. In addition, [Cre-Phex.sup.[Delta]flox/y], [OC-Cre-Phex.sup.[Delta]flox/y], and hyp-mice manifested comparable osteomalacia. These data provide evidence that aberrant Phex function in osteoblasts and/or osteocytes alone is sufficient to underlie the hyp-mouse phenotype., Introduction X-linked hypophosphatemia (XLH) is the archetypal vitamin D-resistant disease in humans and the most common form of inherited rickets, with an incidence of approximately 1 in 20,000 live births. [...]

Neurodegeneration in familial amyotrophic lateral sclerosis (ALS) is associated with enhanced redox stress caused by dominant mutations in superoxide dismutase-1 (SOD1). SOD1 is a cytosolic enzyme that facilitates the conversion of superoxide ([O.sub.2.sup.*-]) to [H.sub.2][O.sub.2]. Here we demonstrate that SOD1 is not just a catabolic enzyme, but can also directly regulate NADPH oxidase--dependent (Nox-dependent) [O.sub.2.sup.*-] production by binding Rac1 and inhibiting its GTPase activity. Oxidation of Rac1 by [H.sub.2][O.sub.2] uncoupled SOD1 binding in a reversible fashion, producing a self-regulating redox sensor for Nox-derived [O.sub.2.sup.*-] production. This process of redox-sensitive uncoupling of SOD1 from Rac1 was defective in SOD1 ALS mutants, leading to enhanced Rac1/Nox activation in transgenic mouse tissues and cell lines expressing ALS SOD1 mutants. Glial cell toxicity associated with expression of SOD1 mutants in culture was significantly attenuated by treatment with the Nox inhibitor apocynin. Treatment of ALS mice with apocynin also significantly increased their average life span. This redox sensor mechanism may explain the gain-of-function seen with certain SOD1 mutations associated with ALS and defines new therapeutic targets., Introduction Superoxide dismutase-1 (SOD1) is a ubiquitously expressed cytosolic enzyme that facilitates the conversion of superoxide ([O.sub.2.sup.*-]) to [H.sub.2][O.sub.2] (1). Inherited dominant mutations in SOD1 lead to progressive motor neuron [...]

Otitis media is an extremely common pediatric inflammation of the middle ear that often causes pain and diminishes hearing. Vulnerability to otitis media is due to eustachian tube dysfunction as well as other poorly understood factors, including genetic susceptibility. As EYA4 mutations cause sensorineural hearing loss in humans, we produced and characterized Eya4-deficient (Eya4-/-) mice, which had severe hearing deficits. In addition, all Eya4-/- mice developed otitis media with effusion. Anatomic studies revealed abnormal middle ear cavity and eustachian tube dysmorphology; thus, Eya4 regulation is critical for the development and function of these structures. We suggest that some human otitis media susceptibility reflects underlying genetic predisposition in genes like EYA4 that regulate middle ear and eustachian tube anatomy., Introduction Otitis media, an inflammation of the middle ear, accounts for 24 million pediatric office visits annually (1), is responsible for over $4 billion in annual health care costs, and [...]

Homozygote varitint-waddler (Va) mice, expressing a mutant isoform (A419P) of TRPML3 (mucolipin 3), are profoundly deaf and display vestibular and pigmentation deficiencies, sterility, and perinatal lethality. Here we show that the varitint-waddler isoform of TRPML3 carrying an A419P mutation represents a constitutively active cation channel that can also be identified in native varitint-waddler hair cells as a distinct inwardly rectifying current. We hypothesize that the constitutive activation of TRPML3 occurs as a result of a helix-breaking proline substitution in transmembranespanning domain 5 (TM5). A proline substitution scan demonstrated that the inner third of TRPML3's TM5 is highly susceptible to proline-based kinks. Proline substitutions in TM5 of other TRP channels revealed that TRPML1, TRPML2, TRPV5, and TRPV6 display a similar susceptibility at comparable positions, whereas other TRP channels were not affected. We conclude that the molecular basis for deafness in the varitint-waddler mouse is the result of hair cell death caused by constitutive TRPML3 activity. To our knowledge, our study provides the first direct mechanistic link of a mutation in a TRP ion channel with mammalian hearing loss. cation channel | cochlea | hair cell | inner ear | TRPchannel

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous disorder that results in retinal degeneration, obesity, cognitive impairment, polydactyly, renal abnormalities, and hypogenitalism. Of the 12 known BBS genes, BBS1 is the most commonly mutated, and a single missense mutation (M390R) accounts for [approximately equal to] 80% of BBS1 cases. To gain insight into the function of BBS1, we generated a Bbs[1.sup.M390R/M390R] knockin mouse model. Mice homozygous for the M390R mutation recapitulated aspects of the human phenotype, including retinal degeneration, male infertility, and obesity. The obese mutant mice were hyperphagic and hyperleptinemic and exhibited reduced locomotor activity but no elevation in mean arterial blood pressure. Morphological evaluation of Bbs1 mutant brain neuroanatomy revealed ventriculomegaly of the lateral and third ventricles, thinning of the cerebral cortex, and reduced volume of the corpus striatum and hippocampus. Similar abnormalities were also observed in the brains of Bbs[2.sup.-/-], Bbs[4.sup.-/-], and Bbs[6.sup.-/-] mice, establishing these neuroanatomical defects as a previously undescribed BBS mouse model phenotype. Ultrastructural examination of the ependymal cell cilia that line the enlarged third ventricle of the Bbs1 mutant brains showed that, whereas the 9 + 2 arrangement of axonemal microtubules was intact, elongated cilia and cilia with abnormally swollen distal ends were present. Together with data from transmission electron microscopy analysis of photoreceptor cell connecting cilia, the Bbs1 M390R mutation does not affect axonemal structure, but it may play a role in the regulation of cilia assembly and/or function.

Mutations in MECP2 cause the autism-spectrum disorder Rett syndrome. MeCP2 is predicted to bind to methylated promoters and silence transcription. However, the first large-scale mapping of neuronal MeCP2-binding sites on 26.3 Mb of imprinted and non-imprinted loci revealed that 59% of MeCP2-binding sites are outside of genes and that only 6% are in CpG islands. Integrated genome-wide promoter analysis of MeCP2 binding, CpG methylation, and gene expression revealed that 63% of MeCP2-bound promoters are actively expressed and that only 6% are highly methylated. These results indicate that the primary function of MeCP2 is not the silencing of methylated promoters. chromatin | DNA methylation | epigenetics | genomics | Rett syndrome

A number of mutations have been linked to diseases for which the underlying mechanisms are poorly understood. An example is Timothy Syndrome (TS), a multi-system disorder that includes severe cardiac arrhythmias. Here we employ theoretical simulations to examine the effects of a TS mutation in the L-type [Ca.sup.2+] channel on cardiac dynarmcs over multiple scales, from a gene mutation to protein, cell, tissue, and finally the ECG, to connect a defective [Ca.sup.2+] channel to arrhythmia susceptibility. Our results indicate that 1) the TS mutation disrupts the rate-dependent dynamics in a single cardiac cell and promotes the development of alternans; 2) in coupled tissue, concordant alternans is observed at slower heart rates in mutant tissue than in normal tissue and, once initiated, rapidly degenerates into discordant alternans and conduction block; and 3) the ECG computed from mutant-simulated tissue exhibits prolonged QT intervals at physiological rates and with small increases in pacing rate, T-wave alternans, and alternating T-wave inversion. At the cellular level, enhanced [Ca.sup.2+] influx due to the TS mutation causes electrical instabilities. In tissue, the interplay between faulty [Ca.sup.2+] influx and steep action potential duration restitution causes arrhythmogenic discordant alternans. The prolongation of action potentials causes spatial dispersion of the [Na.sup.+] channel excitability, leading to inhomogeneous conduction velocity and large action potential spatial gradients. Our model simulations are consistent with the ECG patterns from TS patients, which suggest that the TS mutation is sufficient to cause the clinical phenotype and allows for the revelation of the complex interactions of currents underlying it. modeling; Timothy Syndrome

RecQ helicases are involved in the processing of DNA structures arising during replication, recombination, and repair throughout all kingdoms of life. Mutations of different RecQ homologues are responsible for severe human diseases, such as Blooms (BLM) or Werner (WRN) syndrome. The loss of RecQ function is often accompanied by hyperrecombination caused by a lack of crossover suppression. In the Arabidopsis genome seven different RecQ genes are present. Two of them (AtRECQ4A and 4B) arose because of a recent duplication and are still nearly 70% identical on a protein level. Knockout of these genes leads to antagonistic phenotypes: the RECQ4A mutant shows sensitivity to DNA-damaging agents, enhanced homologous recombination (HR) and lethality in a mus81 background. Moreover, mutation of RECQ4A partially suppresses the lethal phenotype of an AtTOP3[alpha] mutant, a phenomenon that had previously been demonstrated for RecQ homologues of unicellular eukaryotes only. Together, these facts strongly suggest that in plants RECQ4A is functionally equivalent to SGS1 of Saccharomyces cerevisiae and the mammalian BLM protein. In stark contrast, mutants of the closely related RECQ4B are not mutagen-sensitive, not viable in a mus81 background, and unable to suppress the induced lethality caused by loss of TOP3[alpha]. Moreover, they are strongly impaired in HR. Thus, AtRECQ4B is specifically required to promote but not to suppress crossovers, a role in which it differs from all eukaryotic RecQ homologues known. Blooms syndrome | crossover suppression | Holliday Junction | Mus81 | topoisomerase

In humans, loss-of-function mutations in the gene encoding Wnt1 inducible signaling pathway protein 3 (WISP3) cause the autosomal-recessive skeletal disorder progressive pseudorheumatoid dysplasia (PPD). However, in mice there is no [...]

PTEN is a tumor suppressor gene mutated in many human cancers. We generated a bronchioalveolar epithelium-specific null mutation of Pten in mice [SP-C-rtTA/[(tetO).sub.7]-Cre/[Pten.sup.flox/flox] [(SOPten.sup.flox/flox) mice that was under the control [...]

Patients with Omenn syndrome (OS) have hypomorphic RAG mutations and develop varying manifestations of severe combined immunodeficiency. It is not known which symptoms are caused directly by the RAG mutations [...]

Mutations in presenilins are responsible for approximately 40% of all early-onset familial Alzheimer disease (FAD) cases in which a genetic cause has been identified. In addition, a number of mutations [...]

Abstract The WT1 gene encodes a zinc finger transcription factor involved in kidney and gonadal development and, when mutated, in the occurrence of kidney tumor and glomerular diseases. Patients with [...]

Byline: M. Somaschini (1), S. Wert (2), G. Mangili (1), A. Colombo (1), L. Nogee (3) Keywords: Key words Respiratory distress syndrome; Congenital pulmonary alveolar proteinosis; Surfactant protein B deficiency Abstract: Hereditary surfactant protein B (SP-B) deficiency is an autosomal recessive disease in which affected infants are unable to produce normally functional surfactant, resulting in neonatal respiratory failure and death within the first year of life. The most common cause of SP-B deficiency is a frameshift mutation in exon 4 (121ins2) of the SP-B gene. We report a newborn infant who had onset of respiratory distress during the first days, was unresponsive to exogenous surfactant, corticosteroids, prostacyclin, high frequency oscillatory ventilation and inhaled nitric oxide, and died after 27 days. Immunostaining of lung tissue obtained at biopsy demonstrated absent staining for SP-B, and robust extracellular staining for proSP-C, findings characteristic for SP-B deficiency. DNA analysis revealed the 121ins2 mutation on one of her SP-B alleles and a novel mutation, 122delC, on her other SP-B allele. The proximity of the novel mutation in exon 4 allele found in this infant to the 121ins2 supports the notion that this region may represent a 'hot spot' for SP-B gene mutations and confirms the heterogeneity of mechanisms which lead to SP-B deficiency.APHereditary SP-B deficiency is a rare, newly diagnosable and probably under-recognized disease, which should be suspected in term newborn infants with unexplained respiratory failure. Author Affiliation: (1) Divisione di Patologia Neonatale, Ospedali Riuniti di Bergamo, Bergamo, Italy, IT (2) Division of Neonatology and Pulmonary Biology Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, Ohio 45229--3039, USA, US (3) Division of Neonatology, CMSC 210, John Hopkins University, School of Medicine, 600 N. Wolfe Street, Balitmore, Maryland 21287-3200, USA, US Article note: Received: 20 May 1999/Final revision received 3 November 1999/Accepted: 8 November 1999

Genetic defects in the transcription factor fork head box protein P3 (FoxP3) cause immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEx). IPEx is thought to be due to a defect in naturally [...]

Abstract Recent identification of the urate transporter in the kidney (URAT1, encoded by SLC22A12) led to the molecular elucidation of idiopathic renal hypouricemia, which is a predisposition toward exercise-induce acute [...]

Abstract Growth hormone insensitivity (GHI) has been attributable, classically, to mutations in the gene for the GH receptor. After binding to the GH receptor, GH initiates signal transduction through a [...]

Byline: Ilham. Ratbi, Chafai. Elalaoui, Moal. Dastot-Le, Michel. Goossens, Irina. Giurgea, Abdelaziz. Sefiani Mowat-Wilson syndrome is a mental retardation-multiple congenital anomaly syndrome characterized by a typical facies, developmental delay, epilepsy, [...]

Over the last few years, epidemiological evidence has suggested that as men age their odds of having a child with autism, schizophrenia or bipolar disorder might increase. The findings--along with [...]

Individuals with Brugada syndrome and/or cardiac conduction disease are at increased risk of sudden death due to cardiac arrhythmias (irregular heartbeats). Although mutations in the SCN5A gene (which encodes NaV1.5, [...]

Intracellular aggregation of the protein tau is a defining neuropathological characteristic of neurodegenerative tauopathies, a group of heterogeneous dementias and movement disorders including Alzheimer disease (AD) and frontotemporal dementia and [...]

X-linked hypophosphatemia (XLH) is the most common form of inherited rickets. It is caused by loss-of-function mutations in PHEX (phosphate-regulating gene with homologies to endo-peptidases on the X chromosome). Mice [...]

Byline: D. M. Livermore (1) Keywords: Key words Antibiotic resistance; Epidemiology Abstract: Three biological processes contribute to the accumulation of bacterial drug resistance: new selection, gene epidemics and strain epidemics. New resistance emerges by (i) the advantaging of entire species, (ii) by mutation, and (iii) by the escape of resistance genes to mobile DNA. Organisms to have 'benefited' from modern patterns of cephalosporins and quinolone use include enterococci, Clostridium difficile, coagulase-negative staphylococci and Enterobacter spp. Mutational resistance notoriously occurs with certain antibiotic/organsim combinations and allows rapid multifocal accumulation of resistance. At worst, therapy can fail when resistant mutants are selected in individual patients. Escape of new genes to mobile DNA is rare but, having occurred, permits massive 'gene epidemics', as the same genes and plasmids spread into diverse pathogens. Strain epidemics notoriously occur in individual units, reflecting breakdowns of hygiene. Some strains achieve a much wider distribution: thus, much of the MRSA problem in the UK depends on the dissemination of two epidemic strains, APEMRSA15 and 16 penicillin resistant pneumococci of serotypes 6 and 23 have disseminated internationally from Spain and a serotype K25 strain of Klebsiella pneumoniae with SHV-4 [beta]-lactamase has spread widely in France. It remains unknown why some strains and genes achieve wide spread whereas others, equally resistant, fail to do so.APThere is no simple cure for resistance but the best opportunities for control lie in lesser and better use of antibiotics backed by swifter and more accurate microbiology in developing new antibiotics and in protecting old ones from resistance determinants. All this must be supported by good local knowledge of the epidemiology of infections and resistance and of the likelihood of particular antibiotics to select resistance. Author Affiliation: (1) Antibiotic Resistance Monitoring and Reference Laboratory, Central Public Health Laboratory, 61 Colindale Avenue, London NW9 5HT, UK e-mail: DLivermore@phls.nhs.uk Tel.: + 44--181--200--4400 x4223 Fax: + 44-1 81-2 00-74 49, GB