Optically Tunable Electrical Oscillations in Oxide-Based Memristors for Neuromorphic Computing

The application of hardware-based neural networks can be enhanced by integrating sensory neurons and synapses that enable direct input from external stimuli. This work reports direct optical control of an oscillatory neuron based on volatile threshold switching in V3O5. The devices exhibit electroforming-free operation with switching parameters that can be tuned by optical illumination. Using temperature-dependent electrical measurements, conductive atomic force microscopy (C-AFM), in situ thermal imaging, and lumped element modelling, it is shown that the changes in switching parameters, including threshold and hold voltages, arise from overall conductivity increase of the oxide film due to the contribution of both photoconductive and bolometric characteristics of V3O5, which eventually affects the oscillation dynamics. Furthermore, V3O5 is identified as a new bolometric material with a temperature coefficient of resistance (TCR) as high as -4.6% K-1 at 423 K. The utility of these devices is illustrated by demonstrating in-sensor reservoir computing with reduced computational effort and an optical encoding layer for spiking neural network (SNN), respectively, using a simulated array of devices.

Effect of Interdiffusion and Crystallization on Threshold Switching Characteristics of Nb/Nb2O5/Pt Memristors

The resistive switching response of two terminal metal/oxide/metal devices depends on the stoichiometry of the oxide film, and this is commonly controlled by using a reactive metal electrode to reduce the oxide layer. Here, we investigate compositional and structural changes induced in Nb/Nb2O5 bilayers by thermal annealing at temperatures in the range of 573-973 K and its effect on the volatile threshold switching characteristics of Nb/Nb2O5/Pt devices. Changes in the stoichiometry of the Nb and Nb2O5 films are determined by Rutherford backscattering spectrometry and energy-dispersive X-ray (EDX) mapping of sample cross sections, while the structure of the films is determined by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy (TEM). Such analysis shows that the composition of the Nb and Nb2O5 layers is homogenized by interdiffusion at temperatures less than the crystallization temperature (i.e., >773 K) but that this effectively ceases once the films crystallize. This is explained by comparison with the predictions of a simple diffusion model which shows that the compositional changes are dominated by oxygen diffusion in the amorphous oxide, which is much faster than that in the crystalline phases. We further show that these compositional and structural changes have a significant effect on the electroforming and threshold switching characteristics of the devices, the most significant being a marked increase in their reliability and endurance after crystallization of the oxide films. Finally, we examine the effect of annealing on the quasistatic negative differential resistance characteristics and oscillator dynamics of devices and use a lumped element model to show that this is dominated by changes in the device capacitance resulting from interdiffusion.

Design and Application of Memristive Balanced Ternary Univariate Logic Circuit

This paper proposes a unique memristor-based design scheme for a balanced ternary digital logic circuit. First, a design method of a single-variable logic function circuit is proposed. Then, by combining with a balanced ternary multiplexer, some common application-type combinational logic circuits are proposed, including a balanced ternary half adder, multiplier and numerical comparator. The above circuits are all simulated and verified in LTSpice, which demonstrate the feasibility of the proposed scheme.

Thermal transport in metal-NbOx-metal cross-point devices and its effect on threshold switching characteristics

Volatile threshold switching and current-controlled negative differential resistance (NDR) in metal-oxide-metal (MOM) devices result from thermally driven conductivity changes induced by local Joule heating and are therefore influenced by the thermal properties of the device-structure. In this study, we investigate the effect of the metal electrodes on the threshold switching response of NbO_x-based cross-point devices. The electroforming and switching characteristics are shown to be strongly influenced by the thickness and thermal conductivity of the top-electrode due to its effect on heat loss from the NbO_x film. Specifically, we demonstrate a 40% reduction in threshold voltage and a 75% reduction in threshold power as the thickness of the top Au electrode is reduced from 125 nm to 25 nm, and a 24% reduction in threshold voltage and 64% reduction in threshold power when the Au electrode is replaced by a Pt electrode of the same thickness of NbO_x film, due to its lower thermal conductivity. Lumped element and finite element modelling of the devices show that these improvements are due to a reduction in heat loss to the electrodes, which is dominated by lateral heat flow within the electrode. These results clearly demonstrate the importance of the electrodes in determining the electroforming and threshold switching characteristics of MOM cross point devices.

Physical Origin of Negative Differential Resistance in V3 O5 and Its Application as a Solid-State Oscillator

Oxides that exhibit an insulator-metal transition can be used to fabricate energy-efficient relaxation oscillators for use in hardware-based neural networks but there are very few oxides with transition temperatures above room temperature. Here the structural, electrical, and thermal properties of V₃ O₅ thin films and their application as the functional oxide in metal/oxide/metal relaxation oscillators are reported. The V₃ O₅ devices show electroforming-free volatile threshold switching and negative differential resistance (NDR) with stable (<3% variation) cycle-to-cycle operation. The physical mechanisms underpinning these characteristics are investigated using a combination of electrical measurements, in situ thermal imaging, and device modeling. This shows that conduction is confined to a narrow filamentary path due to self-confinement of the current distribution and that the NDR response is initiated at temperatures well below the insulator-metal transition temperature where it is dominated by the temperature-dependent conductivity of the insulating phase. Finally, the dynamics of individual and coupled V₃ O₅ -based relaxation oscillators is reported, showing that capacitively coupled devices exhibit rich non-linear dynamics, including frequency and phase synchronization. These results establish V₃ O₅ as a new functional material for volatile threshold switching and advance the development of robust solid-state neurons for neuromorphic computing.

High Spatial Resolution Thermal Mapping of Volatile Switching in NbOx-Based Memristor Using In Situ Scanning Thermal Microscopy

Temperature mapping by in situ thermoreflectance thermal imaging (TRTI) or midwave infrared spectroscopy has played an important role in understanding the origins of threshold switching and the effect of insulator-metal transitions in oxide-based memrsitive devices. In this study, we use scanning thermal microscopy (SThM) as an alternative thermal mapping technique that offers high spatial resolution imaging (∼100 nm) and is independent of material. Specifically, SThM is used to map the temperature distribution in NbO_x-based cross-bar and nanovia devices with Pt top electrodes. The measurements on cross-bar devices reproduce the current redistribution and confinement processes previously observed by TRTI but without the need to coat the electrodes with a material of high thermo-reflectance coefficient (e.g., Au), while those on the nanovia devices highlight the spatial resolution of the technique. The measured temperature distributions are compared with those obtained from physics-based finite-element simulations and suggest that thermal boundary resistance plays an important role in heat transfer between the active device volume and the top electrode.

Thermal Conductivity of Amorphous NbOx Thin Films and Its Effect on Volatile Memristive Switching

Metal-oxide-metal (MOM) devices based on niobium oxide exhibit threshold switching (or current-controlled negative differential resistance) due to thermally induced conductivity changes produced by Joule heating. A detailed understanding of the device characteristics therefore relies on an understanding of the thermal properties of the niobium oxide film and the MOM device structure. In this study, we use time-domain thermoreflectance to determine the thermal conductivity of amorphous NbO_x films as a function of film composition and temperature. The thermal conductivity is shown to vary between 0.86 and 1.25 W·m^-1·K^-1 over the composition (x = 1.9 to 2.5) and temperature (293 to 453 K) ranges examined, and to increase with temperature for all compositions. The impact of these thermal conductivity variations on the quasistatic current-voltage (I-V) characteristics and oscillator dynamics of MOM devices is then investigated using a lumped-element circuit model. Understanding such effects is essential for engineering functional devices for nonvolatile memory and brain-inspired computing applications.

Engineering the Threshold Switching Response of Nb2O5-Based Memristors by Ti Doping

Two terminal metal-oxide-metal devices based on niobium oxide thin films exhibit a wide range of non-linear electrical characteristics that have applications in hardware-based neuromorphic computing. In this study, we compare the threshold-switching and current-controlled negative differential resistance (NDR) characteristics of cross-point devices fabricated from undoped Nb₂O₅ and Ti-doped Nb₂O₅ and show that doping offers an effective means of engineering the device response for particular applications. In particular, doping is shown to improve the device reliability and to provide a means of tuning the threshold and hold voltages, the hysteresis window, and the magnitude of the negative differential resistance. Based on temperature-dependent current-voltage characteristics and lumped-element modelling, these effects are attributed to doping-induced reductions in the device resistance and its rate of change with temperature (i.e., the effective thermal activation energy for conduction). Significantly, these studies also show that a critical activation energy is required for devices to exhibit NDR, with doping providing an effective means of engineering the current-voltage characteristics. These results afford an improved understanding of the physical mechanisms responsible for threshold switching and provide new insights for designing devices for specific applications.

Fly ash and zinc slag blended geopolymer: Immobilization of hazardous materials and development of paving blocks

The potential for practical application of fly ash, zinc slag and their blends for geopolymer synthesis at ambient temperature have been investigated in this paper. Fly ash is an alumino-silicate byproduct suitable for geopolymer reaction, but its low reactivity at ambient condition is the restriction of its bulk utilization. Above limitation can be overcome by blending with zinc slag (ZS). Additionally, ZS contains heavy and toxic metals (Pb, Zn, Cr, Cd, As), which can be stabilize in Al-Si based geopolymer network structure. Isothermal conduction calorimetry (ICC) is used to monitor the geopolymer reaction with time. Slag rich specimens are characterized with higher rate of reaction with augmented peak. The mineralogy and microstructure of the geopolymers have been examined through X-ray diffraction and scanning electron microscope. The detected chief reaction product is N-(C)-A-S-H and C-(N)-A-S-H¹ type hydrated gel. Continual improvement of compressive strength of the geopolymers with increasing slag content is explained with higher degree of reaction, formation of more reaction products and development of compact microstructure. According to toxicity characteristic leaching procedure (TCLP), toxic metals leaching is within permissible limit. Paver blocks using 40-80 wt% ZS has been developed, which meets IS 15,658: 2006 standard and comply with US-EPA specification.

Metal-oxide interface reactions and their effect on integrated resistive/threshold switching in NbO x

Reactive metal electrodes (Nb, Ti, Cr, Ta, and Hf) are shown to play an important role in controlling the volatile switching characteristics of metal/Nb₂O₅/Pt devices. In particular, devices are shown to exhibit stable threshold switching under negative bias but to have a response under positive bias that depends on the choice of metal. Three distinct responses are highlighted: Devices with Nb and Ti top electrodes are shown to exhibit stable threshold switching with symmetric characteristics for both positive and negative polarities; devices with Cr top electrodes are shown to exhibit stable threshold switching but with asymmetric hysteresis windows under positive and negative polarities; and devices with Ta and Hf electrodes are shown to exhibit an integrated threshold-memory (1S1M) response. Based on thermodynamic data and lumped element modelling these effects are attributed to the formation of a metal-oxide interlayer and its response to field-induced oxygen exchange. These results provide important insight into the physical origin of the switching response and pathways for engineering devices with reliable switching characteristics.

Epidemiology and outcome of trauma victims admitted in trauma centers of tertiary care hospitals - A multicentric study in India

Background:

Roadside trauma in India is an increasingly significant problem, particularly because of bad roads, irregular road signs, overcrowding, overspeeding, and bad traffic etiquettes. Adequate information on the characteristics of victims, causes of accidents, frequency, vehicles involved, alcohol intake, and outcome of management is essential for understanding and planning for better management.

Aim:

This study aimed to determine the characteristics of trauma (roadside accidents) victims admitted to various trauma centers in India. The purpose of this study is to examine the epidemiology of trauma within a local community in India through data gained from the different emergency centers and to analyze trauma patients to find the predictors that led to the deaths of trauma patients.

Materials and Methods:

The present observational study involved trauma victims over 1-year period in three centers. Demographical details recorded were age, sex, alcohol intake, systolic blood pressure on arrival, respiratory rate, Glasgow Coma Scale (GCS) score, the interval between injury and admission, Injury Severity Score (ISS) risk factors, hospital stay, and outcome.

Results:

A total of 2650 injuries were recorded in 2466 patients. The mean age was 42.45 ± 15.7 years, the mean ISS was 13.82 ± 6.2, and the mean GCS was 12.20 ± 4.1. The mean time to admission at different trauma centres was 48.41 ± 172.8 h. The head injury was the most common (29.52%).

Conclusion:

Road side accidents due to overspeeding was the most common cause whereas driving under the effect of alcohol was the second most common cause. Accidents are common because of bad traffic etiquette on Indian roads.

Electric Field- and Current-Induced Electroforming Modes in NbOx

Electroforming is used to initiate the memristive response in metal/oxide/metal devices by creating a filamentary conduction path in the oxide film. Here, we use a simple photoresist-based detection technique to map the spatial distribution of conductive filaments formed in Nb/NbO_x/Pt devices, and correlate these with current-voltage characteristics and in situ thermoreflectance measurements to identify distinct modes of electroforming in low- and high-conductivity NbO_x films. In low-conductivity films, the filaments are randomly distributed within the oxide film, consistent with a field-induced weakest-link mechanism, while in high-conductivity films they are concentrated in the center of the film. In the latter case, the current-voltage characteristics and in situ thermoreflectance imaging show that electroforming is associated with current bifurcation into regions of low and high current density. This is supported by finite element modeling of the current distribution and shown to be consistent with predictions of a simple core-shell model of the current distribution. These results clearly demonstrate two distinct modes of electroforming in the same material system and show that the dominant mode depends on the conductivity of the film, with field-induced electroforming dominant in low-conductivity films and current bifurcation-induced electroforming dominant in high-conductivity films.

Effect of variation in signal amplitude and transit time on reliability analysis of ultrasonic time of flight diffraction characterization of vertical and inclined cracks

The variation of amplitude and transit time of the diffracted signal from the crack-tip in complex geometry components and their resulting effect on the probability of detection (POD) and probability of sizing (POS) was studied. The diffracted signal amplitude has been evaluated from the standard expressions for diffraction coefficient, spatial attenuation and the transit time from the respective mathematical models for both vertical and inclined cracks. The same parameters namely the signal amplitude and the transit time have been measured through experiments conducted on simulated test specimens. It has been observed that the analytical and experimental results compare well with each other. Based on this result the trend and shape (width of the transition zone) of the POD/POS curves can be predicted.

The effect of substitution of Mn by Fe and Cr on the martensitic transition in the Ni50Mn34In16 alloy

The potential shape memory alloy Ni(50)Mn(34)In(16) is studied with partial substitution of Mn with Fe and Cr to investigate the effect of such substitution on the martensitic transition in the Ni-Mn-In alloy system. The results of ac susceptibility, magnetization and electrical resistivity measurements show that while the substitution with Cr increases the martensitic transition temperature, the substitution with Fe decreases it. Possible reasons for this shift in martensitic transition are discussed. Evidence of kinetic arrest of the austenite to martensite phase transition in the Fe substituted alloys is also presented. Unlike the kinetic arrest of the austenite to martensite phase transition in the parent Ni(50)Mn(34)In(16) alloy which takes place in the presence of high external magnetic field, the kinetic arrest of the austenite to martensite phase transition in the Fe doped alloy occurs even in zero magnetic field. The Cr substituted alloys, on the other hand, show no signature of kinetic arrest of this phase transition.

Genetic associations of LYN with systemic lupus erythematosus

We targeted LYN, a src-tyosine kinase involved in B-cell activation, in case-control association studies using populations of European-American, African-American and Korean subjects. Our combined European-derived population, consisting of 2463 independent cases and 3131 unrelated controls, shows significant association with rs6983130 in a female-only analysis with 2254 cases and 2228 controls (P=1.1 x 10(-4), odds ratio (OR)=0.81 (95% confidence interval: 0.73-0.90)). This single nucleotide polymorphism (SNP) is located in the 5' untranslated region within the first intron near the transcription initiation site of LYN. In addition, SNPs upstream of the first exon also show weak and sporadic association in subsets of the total European-American population. Multivariate logistic regression analysis implicates rs6983130 as a protective factor for systemic lupus erythematosus (SLE) susceptibility when anti-dsDNA, anti-chromatin, anti-52 kDa Ro or anti-Sm autoantibody status were used as covariates. Subset analysis of the European-American female cases by American College of Rheumatology classification criteria shows a reduction in the risk of hematological disorder with rs6983130 compared with cases without hematological disorders (P=1.5 x 10(-3), OR=0.75 (95% CI: 0.62-0.89)). None of the 90 SNPs tested show significant association with SLE in the African American or Korean populations. These results support an association of LYN with European-derived individuals with SLE, especially within autoantibody or clinical subsets.

Patients with familial and sporadic onset SLE have similar clinical profiles but vary profoundly by race

Few large, multi-ethnic studies have examined the clinical and serologic differences between familial and sporadic SLE patients. Understanding these similarities and differences is critical for interpreting genetic studies and developing therapeutic strategies. We compiled information on 1915 patients with SLE in a large multi-racial cohort, including general demographics, pedigree structure and the specific American College of Rheumatology (ACR) criteria met. One patient was randomly selected from each multiplex family for analysis, yielding 554 European-Americans (EA), 373 African-Americans (AA), 193 Hispanics (HI) and 237 patients of other of mixed races. When comparing familial and sporadic patients stratified by race, lupus erythematosus (LE) cells and arthritis were increased in white familial cases ( P = 5.5 × 10−6 and P = 0.028, respectively), but no other significant differences between familial and sporadic patients were found. We found that there were profound differences in clinical profiles between races. For example, photosensitivity and malar rash were decreased in AA ( P = 1.3 × 10−13 and 1.4 × 10−7, respectively), whereas discoid rash was increased in AA ( P = 5.5×10−6). EA had significantly less renal disease ( P = 5.4×10−13), proteinuria ( P = 4 × 10−12) and anti-Sm ( P = 1.7 × 10−12) than AA or HI. We, therefore, conclude that familial and sporadic onset patients may be treated similarly with respect to clinical and genetic studies.

TCF7L2 polymorphisms are associated with type 2 diabetes in Khatri Sikhs from North India: genetic variation affects lipid levels

Recently, the transcription factor-7-like 2 (TCF7L2) gene has been identified as the most important type 2 diabetes mellitus (T2DM) susceptibility gene. Common intronic polymorphisms in this gene have been found to be strongly associated with T2DM susceptibility showing marked reproducibility in multiple populations. The purpose of this study was to confirm the reported association of six TCF7L2 variants in a Khatri Sikh diabetic sample from North India. We genotyped six-associated SNPs in a case-control sample consisting of 556 T2DM cases and 537 controls. We also examined the impact of these variants on body mass index (BMI), waist to hip ratio (WHR), fasting insulin, and glucose and lipid levels. We report replication of association of four of the six SNPs with T2DM in this Khatri Sikh sample [rs7903146, (p = 0.010); rs11196205, (p = 0.011); rs10885409, (p = 0.002) and rs4918789, (p = 0.029)], under a dominant model conferring odds ratios (ORs) of 1.39, 1.44, 1.57 and 1.36, respectively. Haplotype analysis provided further evidence of association by showing a significant difference between cases and controls as revealed by the global omnibus test (chi(2)= 19.36; p = 0.0036). Multiple linear regression analysis also revealed the risk allele carriers of three of four significant SNPs (rs7903146, rs11196205, rs10885409) to be significantly associated with increased fasting total cholesterol (p value = 0.019, 0.025, 0.006) and LDL cholesterol levels (p value = 0.021, 0.018, 0.005), respectively. Our findings confirm that the TCF7L2 gene is a major risk factor for development of T2DM in Khatri Sikhs. It also provides new information about the significant impact of TCF7L2 gene variants on plasma cholesterol levels that appear to be independent of BMI.

APRIL polymorphism and systemic lupus erythematosus (SLE) susceptibility

OBJECTIVE

Two novel non-synonymous polymorphisms of the APRIL gene, codon 67 (rs11552708) and 96 (rs3803800), were recently identified and tested for disease association. The 67G allele was reported to be associated with systemic lupus erythematosus (SLE) in a Japanese population. The aim of the study is to investigate whether the APRIL polymorphism associated with susceptibility to SLE in a Japanese population is associated with the susceptibility to SLE in other ethnic groups.

METHODS

Three hundred and forty-eight SLE patients (204 European-American, 103 African-American and 41 Hispanic) and 345 ethnicity-matched controls (201 European-American, 104 African-American and 40 Hispanic) were included from the Lupus Multiplex Registry and Repository (LMRR) and evaluated for genetic association. The APRIL codon 67 and codon 96 were genotyped by a 3-base extension method. Statistical evaluations were performed using both chi-square and logistic regression analysis.

RESULTS

Both the single-nucleotide polymorphisms (SNPs) were in Hardy-Weinberg equilibrium in cases and controls within each ethnic group. The APRIL codon 67 was significantly associated with SLE risk under the dominant model adjusted by ethnicity (odds ratio, 95% confidence interval and P-values were 1.45 and 1.02-2.06 and 0.036, respectively). Race-specific analysis also showed a trend for association in African-American and Hispanic SLE subjects. CONCLUSION The APRIL codon G67R polymorphism associated with SLE in a Japanese population may also be associated with SLE in other populations.

The PTPN22 C1858T functional polymorphism and autoimmune diseases--a meta-analysis

OBJECTIVE

To assess whether combined evidence shows the association between the protein tyrosine phosphatase non-receptor 22 (PTPN22) C1858T polymorphism and autoimmune diseases, and to summarize the effect size of the polymorphism associated with susceptibility of autoimmune diseases.

METHODS

We surveyed studies on the PTPN22 C1858T polymorphism and autoimmune diseases using comprehensive Medline search and review of the references. Meta-analysis was performed for genotypes T/T (recessive effect), T/T + C/T (dominant effect) and T-allele in random effects models.

RESULTS

Twenty-nine studies with 43 comparisons including 13 rheumatoid arthritis (RA), six systemic lupus erythematosus (SLE), six type-1 DM (T1D), three Grave's disease (GD), four inflammatory bowel diseases (IBD), three juvenile idiopathic arthritis (JIA), two psoriasis, two multiple sclerosis, two Addison's disease and two Celiac disease were available for the meta-analysis. The overall odds ratios (ORS) for T-allele, T/T and T/T + C/T genotypes were significantly increased in RA, SLE, GD and T1D (OR for T-allele = 1.58, 1.49, 1.85, 1.61, respectively, P < 0.00001). This meta-analysis showed the association between the T-allele and the T/T genotype and JIA (OR = 1.34, P = 0.03; OR = 1.97, P = 0.02) but did not reveal the association between the PTPN22 C1858T polymorphism and IBD, psoriasis, multiple sclerosis, Addison's disease and Celiac disease.

CONCLUSION

This meta-analysis demonstrates that the PTPN22 1858T allele confers susceptibility to RA, SLE, GD, T1D and JIA, supporting evidence of association of the PTPN22 gene with subgroup of autoimmune diseases.

Linkage analysis of SLE susceptibility: confirmation of SLER1 at 5p15.3

We detected a novel susceptibility gene, SLER1, for systemic lupus erythematosus (SLE) at 5p15.3.(1) This finding was based on a selected subgroup of SLE families, where two or more family members have had alleged rheumatoid arthritis (SLE-RA). The main objective of this study was to replicate the linkage at 5p15.3 based on an independent data set of 88 SLE-RA families. Heterogeneity in the genetic model led us to use a nonparametric allele-sharing method. Since our a priori hypothesis of linkage at 5p15.3 was fixed, we genotyped six markers at the linked region. Our new results replicate the initial linkage at 5p15.3 (Zlr=2.58, P<0.005, LOD=1.45). Moreover, evidence of linkage was sustained when analysis was restricted to the subset of SLE families who had 3 or more individuals with alleged RA (Zlr=3.32, P=0.008, LOD=2.40) The results of our previous findings, together with these new results, confirm the SLER1 linkage at 5p15.3. Our results also demonstrate the utility of clinically defined subgroup analysis for detecting susceptibility loci for complex genetic diseases, such as SLE.

Genetic linkage of systemic lupus erythematosus with chromosome 11q14 (SLEH1) in African-American families stratified by a nucleolar antinuclear antibody pattern

Systemic lupus erythematosus (SLE) is an autoimmune disease with complex genetics. We evaluated pedigrees multiplex for SLE that had an affected with antinucleolar antibodies to increase the homogeneity for genetic linkage analysis. We found a significant linkage effect on chromosome 11q14 at marker D11S2002 in African-American Pedigrees. This effect produced a maximum LOD score of 5.62 using a dominant inheritance model with 95% penetrance in males and 99% penetrance in females. The results were supported by multipoint linkage analysis. Fine mapping of the region with two additional markers within 6 cM of D11S2002 further provided evidence of linkage in this region. Linkage at D11S2002, named SLEH1, was previously found in some of these same African-American pedigrees multiplex for SLE, but who were stratified by hemolytic anemia (Kelly et al, submitted). In conclusion, an important SLE susceptibility gene, SLEH1 at 11q14, is identified in African-Americans when stratifying pedigrees by antinucleolar autoantibodies.

Genome scan stratified by the presence of anti-double-stranded DNA (dsDNA) autoantibody in pedigrees multiplex for systemic lupus erythematosus (SLE) establishes linkages at 19p13.2 (SLED1) and 18q21.1 (SLED2)

Anti-double-stranded DNA (anti-dsDNA) is arguably one of the most specific autoantibodies in systemic lupus erythematosus (SLE). This antibody is associated with more severe SLE and with glomerulonephritis. From 196 pedigrees multiplex for SLE, we selected those that had any SLE affected positive for anti-dsDNA by the Crithidia luciliae kinetoplast imunofluorescence assay. This stratification strategy tested the hypothesis that anti-dsDNA would identify a more genetically homogeneous group of pedigrees, in which previously undetected linkage effects could be established. A genome screen data for linkage to SLE was available at 307 microsatellite markers for this selected group of 71 pedigrees: 37 European-American, 29 African-American, and five others. The most significant results were obtained at 19p13.2 (LOD(max) = 4.93), named SLED1, in the 37 European-American pedigrees using a dominant model with mixed penetrances (92% for females and 49% for males) at 100% homogeneity (theta = 0). A second linkage effect, SLED2, was established in the 29 African-American pedigrees at 18q21.1 (LOD(max) = 3.40) using a recessive model with 100% penetrance (theta = 0.1). Parametric and non-parametric multipoint analyses were performed, which provided further evidence and support of susceptibility genes residing in these regions. In conclusion, two powerful linkages have been detected with SLE based on the presence of anti-dsDNA. These findings show SLE to be a richly complicated disease phenotype that is now ripe for important new discovery through a genetic approach.

Two-trait-locus linkage analyses of asthma susceptibility

A genome-wide search was conducted to identify chromosomal regions likely to harbor genes for asthma susceptibility. One hundred and twelve Caucasian families ascertained through a proband with a diagnosis of asthma by the Collaborative Study on the Genetics of Asthma (CSGA) were used for this search. Genotype data on 323 polymorphic markers were analyzed via parametric and nonparametric linkage analysis in an initial genome scan to identify potential asthma susceptibility region(s). The regions where hold or nonparametric linkage scores were greater than 2.0 were selected for further investigation using two-trait-locus linkage analysis models.

Comparison of three methods for obtaining principal components from family data in genetic analysis of complex disease

Three multivariate techniques used to derive principal components (PCs) from family data were compared for their ability to model family data and power to detect linkage. Using the simulated data from Genetic Analysis Workshop 12, the five quantitative traits were first adjusted for age, sex, and environmental factors 1 and 2. Then, standard PCs, PCs obtained from between-family covariance, and PCs obtained from within-family genetic covariance were derived and subjected to multivariate sib pair linkage analysis. The standard PCs obtained from the overall correlation matrix allowed identification of key features of the true genetic model more readily than did the other methods. For detection of linkage, standard PCs and PCs obtained from the between-family genetic covariance performed similarly in terms of both power and type 1 error, and both methods performed better than the PCs obtained from within-family genetic covariance.

Evidence for a susceptibility gene, SLEV1, on chromosome 17p13 in families with vitiligo-related systemic lupus erythematosus

Both systemic lupus erythematosus (SLE) and vitiligo are autoimmune disorders that have strong evidence of complex genetic contributions to their etiology, but, to date, efforts using genetic linkage to find the susceptibility genes for either phenotype have met with limited success. Since autoimmune diseases are thought to share at least some of their genetic origins, and since only a small minority (16 of 92) of the European-American pedigrees multiplex for SLE in our collection have one or more affected members with vitiligo, we hypothesized that these pedigrees might be more genetically homogeneous at loci important to both SLE and vitiligo and, hence, have increased power for detection of linkage. We therefore evaluated genomewide microsatellite-marker-scan data for markers at an average marker density of approximately 11 cM in these 16 European-American pedigrees and identified a significant linkage at 17p13, where the maximum multipoint parametric LOD score was 3.64 (P<4.3x10(-5)) and the nonparametric linkage score was 4.02 (P<2.8x10(-5)), respectively. The segregation behavior of this linkage suggests a recessive mode of inheritance with a virtually homogeneous genetic effect in these 16 pedigrees. These results support the hypotheses that SLE and vitiligo may share important genetic effects and that sampling on the basis of clinical covariates dramatically improves power to identify genetic effects.

Linkage disequilibrium analysis of biallelic DNA markers, human quantitative trait loci, and threshold-defined case and control subjects

Linkage disequilibrium (LD) mapping has been applied to many simple, monogenic, overtly Mendelian human traits, with great success. However, extensions and applications of LD mapping approaches to more complex human quantitative traits have not been straightforward. In this article, we consider the analysis of biallelic DNA marker loci and human quantitative trait loci in settings that involve sampling individuals from opposite ends of the trait distribution. The purpose of this sampling strategy is to enrich samples for individuals likely to possess (and not possess) trait-influencing alleles. Simple statistical models for detecting LD between a trait-influencing allele and neighboring marker alleles are derived that make use of this sampling scheme. The power of the proposed method is investigated analytically for some hypothetical gene-effect scenarios. Our studies indicate that LD mapping of loci influencing human quantitative trait variation should be possible in certain settings. Finally, we consider possible extensions of the proposed methods, as well as areas for further consideration and improvement.

NHE2 contains subdomains in the COOH terminus for growth factor and protein kinase regulation

The cloned epithelial cell-specific Na+/H+ exchanger (NHE) isoform NHE2 is stimulated by fibroblast growth factor (FGF), phorbol 12-myristate 13-acetate (PMA), okadaic acid (OA), and fetal bovine serum (FBS) through a change in maximal velocity of the transporter. In the present study, we used COOH-terminal truncation mutants to delineate specific domains in the COOH terminus of NHE2 that are responsible for growth factor and/or protein kinase regulation. Five truncation mutants (designated by the amino acid number at the truncation site) were stably expressed in NHE-deficient PS120 fibroblasts. The effects of PMA, FGF, OA, FBS, and W-13 [a Ca2+/calmodulin (CaM) inhibitor] were studied. Truncation mutant E2/660, but not E2/573, was stimulated by PMA. OA stimulated E2/573 but not E2/540. FGF stimulated E2/540 but not E2/499. The most truncated mutant, E2/499, was stimulated by FBS. W-13 stimulated the basal activity of the wild-type NHE2. However, W-13 had no effect on E2/755. By monitoring the emission spectra of dansylated CaM fluorescence, we showed that dansylated CaM bound directly to a purified fusion protein of glutathione S-transferase and the last 87 amino acids of NHE2 in a Ca2+-dependent manner, with a stoichiometry of 1:1 and a dissociation constant of 300 nM. Our results showed that the COOH terminus of NHE2 is organized into separate stimulatory and inhibitory growth factor/protein kinase regulatory subdomains. This organization of growth factor/protein kinase regulatory subdomains is very similar to that of NHE3, suggesting that the tertiary structures of the putative COOH termini of NHE2 and NHE3 are very similar despite the minimal amino acid identity in this part of the two proteins.

Squalamine, a novel cationic steroid, specifically inhibits the brush-border Na+/H+ exchanger isoform NHE3

Squalamine, an endogenous molecule found in the liver and other tissues of Squalus acanthias, has antibiotic properties and causes changes in endothelial cell shape. The latter suggested that its potential targets might include transport proteins that control cell volume or cell shape. The effect of purified squalamine was examined on cloned Na+/H+ exchanger isoforms NHE1, NHE2, and NHE3 stably transfected in PS120 fibroblasts. Squalamine (1-h pretreatment) decreased the maximal velocity of rabbit NHE3 in a concentration-dependent manner (13, 47, and 57% inhibition with 3, 5, and 7 micrograms/ml, respectively) and also increased K'[H+]i. Squalamine did not affect rabbit NHE1 or NHE2 function. The inhibitory effect of squalamine was 1) time dependent, with no effect of immediate addition and maximum effect with 1 h of exposure, and 2) fully reversible. Squalamine pretreatment of the ileum for 60 min inhibited brush-border membrane vesicle Na+/H+ activity by 51%. Further investigation into the mechanism of squalamine's effects showed that squalamine required the COOH-terminal 76 amino acids of NHE3. Squalamine had no cytotoxic effect at the concentrations studied, as indicated by monitoring lactate dehydrogenase release. These results indicate that squalamine 1) is a specific inhibitor of the brush-border NHE isoform NHE3 and not NHE1 or NHE2, 2) acts in a nontoxic and fully reversible manner, and 3) has a delayed effect, indicating that it may influence brush-border Na+/H+ exchanger function indirectly, through an intracellular signaling pathway or by acting as an intracellular modulator.

Schizophrenia susceptibility loci on chromosomes 13q32 and 8p21

Schizophrenia is a common disorder characterized by psychotic symptoms; diagnostic criteria have been established. Family, twin and adoption studies suggest that both genetic and environmental factors influence susceptibility (heritability is approximately 71%; ref. 2), however, little is known about the aetiology of schizophrenia. Clinical and family studies suggest aetiological heterogeneity. Previously, we reported that regions on chromosomes 22, 3 and 8 may be associated with susceptibility to schizophrenia, and collaborations provided some support for regions on chromosomes 8 and 22 (refs 9-13). We present here a genome-wide scan for schizophrenia susceptibility loci (SSL) using 452 microsatellite markers on 54 multiplex pedigrees. Non-parametric linkage (NPL) analysis provided significant evidence for an SSL on chromosome 13q32 (NPL score=4.18; P=0.00002), and suggestive evidence for another SSL on chromosome 8p21-22 (NPL=3.64; P=0.0001). Parametric linkage analysis provided additional support for these SSL. Linkage evidence at chromosome 8 is weaker than that at chromosome 13, so it is more probable that chromosome 8 may be a false positive linkage. Additional putative SSL were noted on chromosomes 14q13 (NPL=2.57; P=0.005), 7q11 (NPL=2.50, P=0.007) and 22q11 (NPL=2.42, P=0.009). Verification of suggestive SSL on chromosomes 13q and 8p was attempted in a follow-up sample of 51 multiplex pedigrees. This analysis confirmed the SSL in 13q14-q33 (NPL=2.36, P=0.007) and supported the SSL in 8p22-p21 (NPL=1.95, P=0.023).

The effect of L-glutamine on salt and water absorption: a jejunal perfusion study in cholera in humans

OBJECTIVES

To assess the efficacy of an L-glutamine solution on jejunal salt and water absorption in cholera patients.

DESIGN

A randomized double-blind jejunal perfusion study.

SETTING

International Centre for Diarrhoeal Disease Research, Bangladesh.

PATIENTS

Nineteen adults with acute cholera.

INTERVENTIONS

Perfusion of balanced salt solutions alternated with defined glucose salt solution and glutamine glucose salt or alanine glucose salt solutions.

MAIN OUTCOME MEASURES

Net jejunal water and sodium secretion.

RESULTS

Perfusion of glutamine in the presence of glucose significantly reduced net water secretion (JnetH2O = -2.6 +/- 1.3 ml/h/cm) and also reduced net sodium secretion (JnetNa = -213 +/- 153 mumol/h/cm). Similar results were observed during the perfusion of solutions that contained alanine in addition to glucose (JnetH2O = -4.2 +/- 1.1 ml/h/cm and JnetNa = -444 U +/- 142 mumol/h/cm, respectively) or glucose alone (JnetH2O = -4.3 +/- 1.7 ml/h/cm and JnetNa = -452 +/- 212 mumol/h/cm, respectively). In addition, a higher basal secretion was associated with a greater stimulation of water absorption (F = 17, P < 0.001).

CONCLUSION

Glutamine in the presence of glucose significantly reduces net water secretion and also reduces sodium secretion; higher basal secretion is associated with greater water absorption. As glutamine is able to stimulate water absorption to the same degree as glucose and alanine, and because it has the theoretical advantage of providing fuel for the mucosa, the inclusion of glutamine as the sole substrate in oral rehydration solution warrants further study.

Brush border phosphatidylinositol 3-kinase mediates epidermal growth factor stimulation of intestinal NaCl absorption and Na+/H+ exchange

In terminally differentiated ileal villus Na+-absorptive cells, epidermal growth factor (EGF) stimulates NaCl absorption and its component brush border Na+/H+ exchanger, acting via basolateral membrane receptors, and as we confirm here, a brush border tyrosine kinase. In the present study we show that brush border phosphatidylinositol 3-kinase (PI 3-kinase) is involved in EGF stimulation of NaCl absorption and brush border Na+/H+ exchange. In rabbit ileum studied with the Ussing chamber-voltage clamp technique, EGF stimulation of active NaCl absorption is inhibited by the selective PI 3-kinase inhibitor wortmannin. PI 3-kinase, a largely cytosolic enzyme, translocates specifically to the brush border of ileal absorptive cells following EGF treatment. This translocation occurs as early as 1 min after EGF treatment and remains increased at the brush border for at least 15 min. EGF also causes a rapid (1 min) and large (4-5-fold) increase in brush border PI 3-kinase activity. Involvement of PI 3-kinase activity in intestinal Na+ absorption is established further by studies done in the human colon cancer cell line, Caco-2, stably transfected with the intestinal brush border isoform of the Na+/H+ exchanger, NHE3 (Caco-2/NHE3 cells). Brush border Na+/H+ exchange activity was measured using the pH-sensitive fluorescent dye 2'7'-bis(carboxyethyl)5-(6)-carboxyfluorescein. EGF added to the basolateral surface but not apical surface of Caco-2/NHE3 cells increased brush border Na+/H+ exchange activity. The EGF-induced increase in brush border Na+/H+ exchange activity was completely abolished in cells pretreated with wortmannin. EGF treatment caused increased tyrosine phosphorylation of PI 3-kinase in both ileal brush border membranes and Caco-2/NHE3 cells, suggesting that a tyrosine kinase upstream of the PI 3-kinase is involved in the EGF effects on Na+ absorption. In conclusion, the present study provides evidence in two separate intestinal models, the ileum and a human colon cancer cell line, that PI 3-kinase is an intermediate in EGF stimulation of intestinal Na+ absorption.

Hyperosmolarity inhibits the Na+/H+ exchanger isoforms NHE2 and NHE3: an effect opposite to that on NHE1

The effect of hyperosmolarity on cloned Na+/H+ exchanger (NHE) isoforms NHE2 and NHE3 was studied in stably transfected PS120 fibroblasts. Na+/H+ exchanger activity was determined spectrofluorometrically in acidified cells that were exposed to isosmolar (300 mosmol/kg) or hyperosmolar (450 mosmol/kg) media, in which the only difference is the presence or absence of 150 mM mannitol. Hyperosmolar solution reversibly inhibited NHE2 and NHE3 with a delay of approximately 15 s. Hyperosmolarity significantly reduced their maximal reaction velocity compared with isosmolar medium but did not alter their Michaelis-Menten constant for intracellular H+. The Michaelis-Menten constant of the exchangers for extracellular Na+ in hyperosmolar medium was not different from that in isosmolar medium. Pretreatment of PS120/NHE3 cells with the protein kinase C inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, the tyrosine kinase inhibitor genistein, and the serine/threonine protein phosphatase inhibitor okadaic acid did not affect the hyperosmolar inhibition of NHE3. Hyperosmolar inhibition of Na+/H+ exchanger activity was also observed in PS120 cells transfected with truncated NHE3 cDNAs (E3/585, E3/543, E3509, and E3/475) and NHE2 cDNA (E2/499). We conclude that 1) hyperosmolarity inhibits NHE2 and NHE3, in contrast to the stimulatory effect on the housekeeping isoform NHE1, 2) this inhibition is reversible, and 3) the COOH termini of NHE2 and NHE3 are not necessary for hyperosmolar inhibition of NHE2 and NHE3.

Ribotyping of nosocomial methicillin-resistant Staphylococcus aureus isolates from a Canadian hospital

OBJECTIVE

To evaluate the clonality of methicillin-resistant Staphylococcus aureus (MRSA) strains among hospitalized patients.

SETTING

University-affiliated, 465-bed tertiary-care teaching hospital with adjacent cancer clinic in Hamilton, Ontario, Canada.

DESIGN

Thirty-five colonized and 30 infected patients from January 2, 1992, through August 31, 1993, were investigated retrospectively. Analysis by restriction fragment-length polymorphisms of ribosomal RNA genes (ie, ribotyping) of 103 nosocomial isolates of MRSA from these 65 patients and of 25 selected unrelated strains was completed. Ribotyping results were compared with the phage typing data obtained prospectively during the course of prospective MRSA surveillance.

RESULTS

HindIII ribotyping was more discriminating than phage typing when epidemiologically unrelated strains were differentiated by these methods (19 different ribotypes versus 14 page types; P < .005). Two early index cases were identified. Isolates from the index cases were two different strains, identified by ribotyping analysis as ribotype A (clonal group 1) and ribotype B (clonal group 2), respectively. These two ribotypes were not found when typing the unrelated control strains. Thirty-six colonized and infected patients (55%) had clonal group 1 isolates, and 20 (31%) had clonal group 2 isolates. These two clones emerged in the hospital in January and February 1992 and dominated the entire investigated period. There also were six patients with an additional clonal group (group 4) that emerged and disappeared in the second quarter of 1993.

CONCLUSIONS

This study highlights the utility of ribotyping in investigating nosocomial MRSA. Three MRSA clones caused nosocomial colonization or infection in patients at this hospital. Two of these MRSA clones, once introduced, were maintained among our patients throughout the study period.

Mammalian Na+/H+ exchanger gene family: structure and function studies

Na+/H+ exchangers are integral plasma membrane proteins that exchange extracellular Na+ for intracellular H+ with a stoichiometry of one for one. They are inhibitable by the diuretic amiloride and have multiple cellular functions, including intracellular pH homeostasis, cell volume control, and electroneutral NaCl absorption in epithelia. The presence of multiple forms of the exchangers was demonstrated by the recent cloning of four mammalian Na+/H+ exchangers, NHE1, NHE2, NHE3, and NHE4. All of these cloned Na+/H+ exchangers have 10-12 putative transmembrane helixes and a long cytoplasmic carboxyl domain. Despite the structural similarity, these Na+/H+ exchanger isoforms differ in their tissue distribution, kinetic characteristics, and response to external stimuli. The present review deals with the recent developments in the molecular identification of the Na+/H+ exchanger gene family, the functional characteristics, and the short-term regulation of Na+/H+ exchange at molecular and cellular levels.

Separate C-terminal domains of the epithelial specific brush border Na+/H+ exchanger isoform NHE3 are involved in stimulation and inhibition by protein kinases/growth factors

NHE3, a cloned intestinal and renal brush border Na+/H+ exchanger, has previously been shown to be both stimulated and inhibited by different protein kinases/growth factors. For instance, NHE3 is stimulated by serum and fibroblast growth factor (FGF) and inhibited by protein kinase C. In the present study, we used a series of NHE3 C terminus truncation mutants to identify separate regions of the C-terminal cytoplasmic tail responsible for stimulation and inhibition by protein kinases/growth factors. Five NHE3 C terminus truncation mutant stable cell lines were generated by stably transfecting NHE3 deletion cDNAs into PS120 fibroblasts, which lack any endogenous Na+/H+ exchanger. Using fluorometric techniques, the effects of the calcium/calmodulin (CaM) inhibitor W13, calcium/CaM kinase inhibitor KN-62, phorbol myristate acetate, okadaic acid, FGF, and fetal bovine serum on Na+/H+ exchange were studied in these transfected cells. Inhibition of basal activity of full-length NHE3 is mediated by CaM at a site C-terminal to amino acid 756; this CaM effect occurs through both kinase dependent and independent mechanisms. There is another independent inhibitory domain for protein kinase C between amino acids 585 and 689. In addition, there are at least three stimulatory regions in the C-terminal domain of NHE3, corresponding to amino acids 509-543 for okadaic acid, 475-509 for FGF, and a region N-terminal to amino acid 475 for fetal bovine serum. We conclude that separate regions of the C terminus of NHE3 are involved with stimulation or inhibition of Na+/H+ exchange activity, with both stimulatory and inhibitory domains having several discrete subdomains. A conservative model to explain the way these multiple domains in the C terminus of NHE3 regulate Na+/H+ exchange is via an effect on associated regulatory proteins.

Genetic epidemiology of vitiligo: multilocus recessivity cross-validated

Vitiligo is a dermatological disorder characterized by hypopigmentary patches that tend to become progressive over time. There are reports of extensive familial aggregation. A genetic model for this disorder was earlier proposed by us. This model postulates that recessive alleles at multiple unlinked autosomal loci interact epistatically in the pathogenesis of vitiligo. The present family study was primarily undertaken to cross-validate the proposed genetic model. Data on 194 families from the United States were collected. Each family was ascertained through an affected proband. Analyses of these data reveal that approximately 20% of probands have at least one first-degree relative afflicted with vitiligo. All types of first-degree relatives of probands show a significant risk of developing vitiligo. Results of segregation and robustness analyses reveal that the genetic model postulated by us previously is the most parsimonious model for the present family data set.

A sustained outbreak of Clostridium difficile in a general hospital: persistence of a toxigenic clone in four units

OBJECTIVE

To evaluate the endemicity and epidemiology of toxigenic Clostridium difficile in a sustained outbreak of antibiotic-associated diarrhea.

SETTING

University-affiliated, 465-bed tertiary care teaching hospital with adjacent cancer clinic in Hamilton, Ontario.

DESIGN

From August 8, 1991, through August 31, 1993, a total of 187 cases were investigated for epidemiologic analysis of toxigenic C difficile from stool cultures, to identify the endemic clone(s). To assess the nature of contamination, cultures of inanimate surfaces in the patient environment from the four most affected units (medical teaching, nonteaching medical, hematologic oncology, and the intensive care unit) were processed for C difficile. The 229 clinical strains and 24 environmental strains isolated were typed by numerical analysis of SDS-PAGE protein patterns.

RESULTS

A majority (81%) of cases in the epidemiologic analysis were associated with a toxigenic electrophoretic (EP) type 1 C difficile that was identical to the strain first isolated from an index case that occurred 18 months before the start of this study. Culture and typing of the C difficile strains from the inanimate surfaces in the four most affected units showed that the patient environment was contaminated with the toxigenic EP type 1 organism. Six other strains that occurred infrequently among cases also were found in the environment.

CONCLUSIONS

A single predominant toxigenic clone has been implicated in a sustained outbreak of antibiotic-associated diarrhea that affected elderly patients. The "endemic" clone transmitted for the 25-month study period was linked to an index case shedding a toxigenic EP type 1 strain that occurred 21 months prior to the initial outbreak on the medical teaching unit. The patient environment in the affected units was found to be contaminated with the same clone, possibly due to shedding of organisms by fecally incontinent symptomatic patients. The extrinsic factors contributing to the endemic transmission of this one clone still are not well understood.

Relation between chloride secretion and intracellular cyclic adenosine monophosphate in a cloned human intestinal cell line HT-29 cl 19A

The relation between the intracellular cyclic adenosine monophosphate (cAMP) content and the electrogenic chloride secretion induced by cholera toxin was studied in secretory HT-29 cl 19A cell monolayers. Cells were treated by the mucosal addition of cholera toxin (5 micrograms/ml) for 10, 45, or 90 minutes in Ussing chambers. After 10 minutes, the mean (SEM) intracellular cAMP content (3.2 (0.2) pmol/mg protein) and short circuit current (Isc) (1.9 (0.3) microA.cm-2) did not differ significantly from the corresponding basal values. At 45 minutes, a significant increase in the Isc (22.2 (5.7) microA.cm-2) was accompanied by a significant elevation in cAMP (10(1.7) pmol/mgh protein). At 90 minutes, when the stimulated Isc plateaued (35.2 (5.2) microA.cm-2), the cAMP value (99.2 (23.8) pmol/mg protein) increased further. The protein kinase C (PKC) activity of the cells was not affected by cholera toxin. Treatment of cell monolayers by different concentrations of DbcAMP (10(5), 5 x 10(-5), 10(-3) M) showed that the minimal concentration of DbcAMP (serosal) which significantly increased the Isc (delta 4.5 microA.cm-2) was 10(-4) M, and that this was accompanied by an increase in cAMP of delta 6.7 pmol/mg protein: Compared with DbcAMP, cholera toxin stimulated the Isc (at 45 minutes) to a much higher degree with a comparable elevation of cAMP. It is concluded that in cl 19A cells there is a threshold value of increase in intracellular cAMP that induces chloride secretion. Cholera toxin stimulated chloride secretion can be explained predominantly by an increase in intracellular cAMP that is unrelated to PKC activity.

Investigation of an outbreak of Clostridium difficile infection in a general hospital by numerical analysis of protein patterns by sodium dodecyl sulfate-polyacrylamide gel electrophoresis

One hundred forty-five cultures of Clostridium difficile, including strains from an apparent nosocomial outbreak of infection, were characterized by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins. Each protein pattern was characterized by the presence of one to three dense bands which were highly reproducible. The first 100 strains (in chronological order) were used as the basis for a numerical analysis which divided the strains into 17 phenons (EP types 1 to 17). The protein patterns of the remaining 45 strains were identified to type by comparing their individual patterns against a data base made up of the protein patterns of the first 100 strains. EP type 1 was the most common, with 70 of 139 (50%) patient isolates having this pattern type, and it accounted for 26 of 35 strains (74%) from patients in a medical teaching ward from which the outbreak was believed to have originated. This type was also found as a high proportion of isolations in a number of other medical and oncology wards, but the majority of these isolates occurred subsequent to the isolations on the initial outbreak ward. This technique can therefore provide a method for tracing the possible spread of epidemic strains in hospitals and other institutions and may contribute to a better understanding of the epidemiology of C. difficile.

Pattern of familial aggregation of vitiligo

BACKGROUND AND DESIGN

Vitiligo is a disorder whose cause is not well understood. This study was undertaken to clarify whether genetic factors are involved in the pathogenesis of vitiligo. Data on 160 white kindreds living in the United States have been collected. Each family was ascertained through a proband afflicted with vitiligo. The nature and extent of familial aggregation and other relevant epidemiologic features have been determined.

RESULTS

The mean age at onset of vitiligo is about 19 years in male and about 24 years in female individuals. The percentage of probands reporting one or more first-degree relatives also afflicted with vitiligo is 20%. Children of probands are found to be afflicted about 1.7 times more commonly than other first-degree relatives. The relative risk (RR) for vitiligo is about 7 for parents, about 12 for siblings, and about 36 for children. For second-degree relatives, the RR varies between 1 and 16. Relative risks for all first- and second-degree relatives, except uncles and grandsons, are significant at the 5% level. In families in which one or more relatives of the proband are afflicted with vitiligo, the intrafamilial correlation of ages at onset of vitiligo is moderate (0.6). No statistically significant effect (at the 5% level) of parental age at first childbirth was seen on the proportion of offspring afflicted with vitiligo. No significant association of some commonly related diseases (eg, thyroid disorder or alopecia areata) was observed with vitiligo or with a family history of vitiligo.

CONCLUSIONS

The extent of familial aggregation of vitiligo is statistically significant. The pattern of relationship between RR and degree of kinship indicates involvement of genetic factors, although it is not consistent with single-locus mendelian transmission.

Leu143 in the putative fourth membrane spanning domain is critical for amiloride inhibition of an epithelial Na+/H+ exchanger isoform (NHE-2)

A family of Na+/H+ exchanger isoforms (called NHE1, NHE2, and NHE3) which exhibits a wide range of amiloride sensitivity has recently been cloned and characterized. A part of the domain, which determines amiloride sensitivity in the epithelial Na+/H+ exchanger isoform, NHE2, was identified by site-directed mutagenesis and functional studies using cDNAs stably expressed in a fibroblast cell line. It has previously been reported that AR300, an amiloride resistant mutant of the ubiquitous Na+/H+ exchanger isoform, NHE1, is 30-fold more resistant to methylpropyl amiloride (MPA) compared to NHE1 and contains a single amino acid substitution of L167F in the fourth putative transmembrane helix, which corresponds to L143 in NHE2. Therefore, in the present study point mutational substitutions were introduced into the equivalent of this fourth transmembrane helix of rabbit NHE2 (including Y144F; L143F; L143F and Y144F) to mimic the corresponding amino acids in NHE1, NHE3 (another epithelial isoform) and AR300, respectively. NHE2/L143F (mimicking NHE3) increased the IC50 for amiloride by 5-fold and for ethylisopropyl amiloride (EIPA) by 20-fold. Similarly, NHE2/L143F and Y144F (mimicking AR300) increased the resistance to both amiloride and EIPA by 10-fold. On the other hand, NHE2/Y144F (mimicking NHE1) did not affect the sensitivity to amiloride or EIPA, and this mutant, like wild type NHE2, is partially resistant to EIPA. Thus, amino acid 143 of NHE2 is critical for, but is not the only amino acid responsible for, amiloride and EIPA inhibition of Na+/H+ exchange. That none of the mutations studied altered the Na+ affinity of these Na+/H+ exchangers further suggests that amiloride binding and Na+ transport sites are not identical.

Comparative effects of nicotinic acid and nicotinamide on cholera toxin-induced secretion in rabbit ileum

Nicotinic acid reduces the cholera-toxin induced fluid secretion in experimental animals but its toxicity at high doses prevent its therapeutic use in patients suffering from cholera. This study aimed to determine whether nicotinamide, the non toxic amide derivative of nicotinic acid, is as effective as nicotinic acid in inhibiting cholera toxin induced intestinal secretion in vivo. Four intestinal loops, with their blood supply intact, were isolated in 30 rabbits and injected with either (i) 30 mM mannitol, (ii) 30 mM mannitol + 10 micrograms cholera toxin, (iii) 30 mM glucose, or (iv) 30 mM glucose + 10 micrograms cholera toxin. These rabbits were then randomly assigned to three groups receiving intraluminally either 100 mg/kg of nicotinic acid, 100 mg/kg of nicotinamide, or 10 ml/kg of Ringer solution. Measurement of intestinal fluid accumulation showed that nicotinic acid, but not nicotinamide, significantly reduced cholera toxin induced intestinal secretion.

Rh segregation distortion: an artifact of ascertainment bias?

On the basis of Rh blood group data on mother-child pairs collected from the maternity clinic of a hospital in Chile, Valenzuela and Harb postulated that there is a significant segregation distortion at the Rh locus. For data collected from a hospital, biases of ascertainment cannot be ruled out. For the Rh blood group locus, there is a strong possibility of preferential admission of Rh(-) pregnant women, especially of those Rh(-) women with Rh(+) husbands. We show that the evidence of segregation distortion vanishes when the possibility of such preferential admissions are taken into account.

[15N]- and [14C]glutamine fluxes across rabbit ileum in experimental bacterial diarrhea

L-Glutamine (Gln) fluxes and the effects of Gln on Na and Cl transport were studied across the ileum of healthy and rabbit diarrheagenic Escherichia coli (RDEC-1)-infected weanling rabbits. Stable ([alpha-15N]Gln) and radioisotopic ([U-14C]Gln) tracers provided identical estimates of Gln transport both in healthy (H) and infected (I) rabbits. RDEC-1 infection, however, decreased net Gln flux [Jnet[14C]Gln = 682 +/- 147 (H) vs. 278 +/- 63 (I); Jnet[15N]Gln = 739 +/- 160 vs. 225 +/- 110 nmol.h-1.cm-2] due to a reduction in mucosal-to-serosal flux. After addition of Gln, increases in net Na absorption [delta Jnet[15N]Gln = 1.87 +/- 0.45 (H) vs. 0.70 +/- 0.27 (I) microeq.h-1.cm-2] and short-circuit current (delta Isc) [1.80 +/- 0.40 (H) vs. 0.74 +/- 0.14 (I) microeq.h-1.cm-2] were also reduced in infected rabbits. Addition of glucose after Gln, however, stimulated Na absorption further. These results indicate that 1) Gln is actively absorbed as intact Gln molecule across rabbit ileum; 2) Gln stimulates an electrogenic Na absorption in a 1:2 ratio that may be further stimulated by glucose; and 3) in RDEC-1 infection electroneutral NaCl absorption, intact Gln absorption, and electrogenic stimulation of Na absorption by glutamine are reduced.