FtsK from Escherichia coli is a fast and sequence-directed DNA translocase with roles in chromosome dimer resolution, segregation, and decatenation. From the movement of single FtsK particles on defined DNA substrates and an analysis of skewed DNA sequences in bacteria, we identify GNGNAGGG, its complement, or both as a sequence motif that controls translocation directionality. GNGNAGGG is skewed so that it is predominantly on the leading strand of chromosomal replication. Translocation across this octamer from the 3' side of the G-rich strand causes FtsK to pause, turn around, and translocate in the opposite direction. Only 39 +/- 4% of the encounters between FtsK and the octamer result in a turnaround, congruent with our optimum turnaround probability prediction of 30%. The probability that the observed skew of GNGNAGGG within 1 megabase of dif occurred by chance in E. coli is 1.7 x 10(-57), and similarly dramatic skews are found in the five other bacterial genomes we examined. The fact that FtsK acts only in the terminus region and the octamer skew extends from origin to terminus implies that this skew is also important in other basic cellular processes that are common among bacteria. Finally, we show that the FtsK translocase is a powerful motor that is able to displace a triplex-forming oligo from a DNA substrate.

Cognitive screening tests and items have been found to perform differently across groups that differ in terms of education, ethnicity and race. Despite the profound implications that such bias holds for studies in the epidemiology of dementia, little research has been conducted in this area. Using the methods of modern psychometric theory (in addition to those of classical test theory), we examined the performance of the Attention subscale of the Mattis Dementia Rating Scale. Several item response theory models, including the two- and three-parameter dichotomous response logistic model, as well as a polytomous response model were compared. (Log-likelihood ratio tests showed that the three-parameter model was not an improvement over the two-parameter model.) Data were collected as part of the ten-study National Institute on Aging Collaborative investigation of special dementia care in institutional settings. The subscale KR-20 estimate for this sample was 0.92. IRT model-based reliability estimates, provided at several points along the latent attribute, ranged from 0.65 to 0.97; the measure was least precise at the less disabled tail of the distribution. Most items performed in similar fashion across education groups; the item characteristic curves were almost identical, indicating little or no differential item functioning (DIF). However, four items were problematic. One item (digit span backwards) demonstrated a large error term in the confirmatory factor analysis; item-fit chi-square statistics developed using BIMAIN confirm this result for the IRT models. Further, the discrimination parameter for that item was low for all education subgroups. Generally, persons with the highest education had a greater probability of passing the item for most levels of theta. Model-based tests of DIF using MULTILOG identified three other items with significant, albeit small, DIF. One item, for example, showed non-uniform DIF in that at the impaired tail of the latent distribution, persons with higher education had a higher probability of correctly responding to the item than did lower education groups, but at less impaired levels, they had a lower probability of a correct response than did lower education groups. Another method of detection identified this item as having DIF (unsigned area statistic=3.05, p<0.01, and 2.96, p<0.01). On average, across the entire score range, the lower education group's probability of answering the item correctly was 0.11 higher than the higher education group's probability. A cross-validation with larger subgroups confirmed the overall result of little DIF for this measure. The methods used for detecting differential item functioning (which may, in turn, be indicative of bias) were applied to a neuropsychological subtest. These methods have been used previously to examine bias in screening measures across education and ethnic and racial subgroups. In addition to the important epidemiological applications of ensuring that screening measures and neuropsychological tests used in diagnoses are free of bias so that more culture-fair classifications will result, these methods are also useful for the examination of site differences in large multi-site clinical trials. It is recommended that these methods receive wider attention in the medical statistical literature.

BACKGROUND

In Europe it is common for outcome measures to be translated for use in other languages. This adaptation may be complicated by culturally specific approaches to certain tasks; for example, bathing. In this context the issue of cross-cultural validity becomes paramount.

OBJECTIVE

To facilitate the pooling of data in international studies, a project set out to evaluate the cross-cultural validity of impairment and activity limitation measures used in rehabilitation from the perspective of the Rasch measurement model.

METHODS

Cross-cultural validity is assessed through an analysis of Differential Item Functioning (DIF) within the context of additive conjoint measurement expressed through the Rasch model. Data from patients undergoing rehabilitation for stroke was provided from 62 centers across Europe. Two commonly used outcome measures, the Mini-Mental State Examination (MMSE) and the Functional Independence Measure (FIM) motor scale are used to illustrate the approach.

RESULTS

Pooled data from 3 countries for the MMSE were shown to fit the Rasch model with only 1 item displaying DIF by country. In contrast, many items from the FIM expressed DIF and misfit to the model. Consequently they were allowed to be unique across countries, so resolving the lack of fit to the model.

CONCLUSIONS

Where data are to be pooled for international studies, analysis of DIF by culture is essential. Where DIF is observed, adjustments can be made to allow for cultural differences in outcome measurement.

We report an efficient, controllable, site-specific replication roadblock that blocks cell proliferation, but which can be rapidly and efficiently reversed, leading to recovery of viability. Escherichia coli replication forks of both polarities stalled in vivo within the first 500 bp of a 10 kb repressor-bound array of operator DNA-binding sites. Controlled release of repressor binding led to rapid restart of the blocked replication fork without the participation of homologous recombination. Cytological tracking of fork stalling and restart showed that the replisome-associated SSB protein remains associated with the blocked fork for extended periods and that duplication of the fluorescent foci associated with the blocked operator array occurs immediately after restart, thereby demonstrating a lack of sister cohesion in the region of the array. Roadblocks positioned near oriC or the dif site did not prevent replication and segregation of the rest of the chromosome.

Genetic recombination is central to DNA metabolism. It promotes sequence diversity and maintains genome integrity in all organisms. However, it can have perverse effects and profoundly influence the cell cycle. In bacteria harbouring circular chromosomes, recombination frequently has an unwanted outcome, the formation of chromosome dimers. Dimers form by homologous recombination between sister chromosomes and are eventually resolved by the action of two site-specific recombinases, XerC and XerD, at their target site, dif, located in the replication terminus of the chromosome. Studies of the Xer system and of the modalities of dimer formation and resolution have yielded important knowledge on how both homologous and site-specific recombination are controlled and integrated in the cell cycle. Here, we briefly review these advances and highlight the important questions they raise.

The bacterial septum-located DNA translocase FtsK coordinates circular chromosome segregation with cell division. Rapid translocation of DNA by FtsK is directed by 8-base-pair DNA motifs (KOPS), so that newly replicated termini are brought together at the developing septum, thereby facilitating completion of chromosome segregation. Translocase functions reside in three domains, alpha, beta and gamma. FtsKalphabeta are necessary and sufficient for ATP hydrolysis-dependent DNA translocation, which is modulated by FtsKgamma through its interaction with KOPS. By solving the FtsKgamma structure by NMR, we show that gamma is a winged-helix domain. NMR chemical shift mapping localizes the DNA-binding site on the gamma domain. Mutated proteins with substitutions in the FtsKgamma DNA-recognition helix are impaired in DNA binding and KOPS recognition, yet remain competent in DNA translocation and XerCD-dif site-specific recombination, which facilitates the late stages of chromosome segregation.

BACKGROUND

The quality of clinical specimens is a crucial determinant for virological diagnosis.

OBJECTIVE

We compared the viral diagnostic yield for influenza A and respiratory syncytial virus (RSV) from the recently developed nasopharyngeal flocked swabs (NPFS) with nasopharyngeal aspirates (NPA) collected in parallel from 196 hospitalized children with acute respiratory infection during the peak period of influenza A and RSV activity in Hong Kong. Specimens were tested by RT-PCR for influenza A and RSV and viral load determined. They were also tested by direct immunofluorescence (DIF) for influenza A and B, RSV, parainfluenza types 1-3 and adenovirus.

RESULTS

Both NPA and NPFS had excellent sensitivity (100%) for detecting influenza A by RT-PCR but NPA was slightly more sensitive than NPFS for detecting RSV by both RT-PCR (100% vs. 92.3%) and DIF (87.2% vs. 84.6%) and for detecting influenza A by DIF (90.2% vs. 82.9%). Viral load for influenza A in NPA and NPFS was not significantly different but that for RSV was higher in NPA.

CONCLUSIONS

NPA remains the optimal specimen for diagnosis of respiratory infections by RT-PCR and DIF. However, collection of NPFS is easier to perform in an out-patient setting, was more acceptable to parents and less likely to generate aerosols than NPA engendering potentially less infection control hazard.

Assessment of test bias is important to establish the construct validity of tests. Assessment of differential item functioning (DIF) is an important first step in this process. DIF is present when examinees from different groups have differing probabilities of success on an item, after controlling for overall ability level. Here, we present analysis of DIF in the Cognitive Assessment Screening Instrument (CASI) using data from a large cohort study of elderly adults. We developed an ordinal logistic regression modelling technique to assess test items for DIF. Estimates of cognitive ability were obtained in two ways based on responses to CASI items: using traditional CASI scoring according to the original test instructions as well as using item response theory (IRT) scoring. Several demographic characteristics were examined for potential DIF, including ethnicity and gender (entered into the model as dichotomous variables), and years of education and age (entered as continuous variables). We found that a disappointingly large number of items had DIF with respect to at least one of these demographic variables. More items were found to have DIF with traditional CASI scoring than with IRT scoring. This study demonstrates a powerful technique for the evaluation of DIF in psychometric tests. The finding that so many CASI items had DIF suggests that previous findings of differences between groups in cognitive functioning as measured by the CASI may be due to biased test items rather than true differences between groups. The finding that IRT scoring diminished the impact of DIF is discussed. Some preliminary suggestions for how to deal with items found to have DIF in cognitive tests are made. The advantages of the DIF detection techniques we developed are discussed in relation to other techniques for the evaluation of DIF.

OBJECTIVE

The aim of this study is to assess the structural and cross-cultural validity of the KIDSCREEN-27 questionnaire.

METHODS

The 27-item version of the KIDSCREEN instrument was derived from a longer 52-item version and was administered to young people aged 8-18 years in 13 European countries in a cross-sectional survey. Structural and cross-cultural validity were tested using multitrait multi-item analysis, exploratory and confirmatory factor analysis, and Rasch analyses. Zumbo's logistic regression method was applied to assess differential item functioning (DIF) across countries. Reliability was assessed using Cronbach's alpha.

RESULTS

Responses were obtained from n = 22,827 respondents (response rate 68.9%). For the combined sample from all countries, exploratory factor analysis with procrustean rotations revealed a five-factor structure which explained 56.9% of the variance. Confirmatory factor analysis indicated an acceptable model fit (RMSEA = 0.068, CFI = 0.960). The unidimensionality of all dimensions was confirmed (INFIT: 0.81-1.15). Differential item functioning (DIF) results across the 13 countries showed that 5 items presented uniform DIF whereas 10 displayed non-uniform DIF. Reliability was acceptable (Cronbach's alpha = 0.78-0.84 for individual dimensions).

CONCLUSIONS

There was substantial evidence for the cross-cultural equivalence of the KIDSCREEN-27 across the countries studied and the factor structure was highly replicable in individual countries. Further research is needed to correct scores based on DIF results. The KIDSCREEN-27 is a new short and promising tool for use in clinical and epidemiological studies.

OBJECTIVE

To use the polymerase chain reaction (PCR) to detect Chlamydia pneumoniae and Chlamydia psittaci in sputum samples.

METHODS

A nested PCR was developed, the first stage of which amplified DNA from both C pneumoniae and C psittaci while the second stage targeted specifically at C pneumoniae, allowing the two species to be differentiated. The primers were designed not to amplify sequences from C trachomatis. A panel of 26 sputum samples from patients with community acquired pneumonia evaluated previously by enzyme linked immunosorbent assay (ELISA), direct immunofluorescence (DIF), and culture was tested blind by PCR. Most of these specimens also had accompanying serial serum samples which were tested for species specific antibodies using microimmunofluorescence (micro-IF).

RESULTS

PCR detected C pneumoniae DNA in 10 of the 26 samples and C psittaci DNA in four. There was good concordance between ELISA, DIF, micro-IF and PCR in the C pneumoniae group. Two of the C psittaci identified by PCR were labelled C pneumoniae by DIF but the PCR results were supported by serology or a history of bird contact. Of the PCR negative group: six were true negative results; two contained C trachomatis. There were four discrepant results.

CONCLUSIONS

The data suggest that PCR is effective in the detection of C pneumoniae. The sensitivity for C psittaci is inevitably lower due to the strategy taken but specificity seemed to be good.

In Dictyostelium amoebae, cell-type differentiation, spatial patterning, and morphogenesis are controlled by a combination of cell-autonomous mechanisms and intercellular signaling. A chemotactic aggregation of approximately 10(5) cells leads to the formation of a multicellular organism. Cell-type differentiation and cell sorting result in a small number of defined cell types organized along an anteroposterior axis. Finally, a mature fruiting body is created by the terminal differentiation of stalk and spore cells. Analysis of the regulatory program demonstrates a role for several molecules, including GSK-3, signal transducers and activators of transcription (STAT) factors, and cAMP-dependent protein kinase (PKA), that control spatial patterning in metazoans. Unexpectedly, two component systems containing histidine kinases and response regulators also play essential roles in controlling Dictyostelium development. This review focuses on the role of cAMP, which functions intracellularly to mediate the activity of PKA, an essential component in aggregation, cell-type specification, and terminal differentiation. Cytoplasmic cAMP levels are controlled through both the regulated activation of adenylyl cyclases and the degradation by a phosphodiesterase containing a two-component system response regulator. Extracellular cAMP regulates G-protein-dependent and -independent pathways to control aggregation as well as the activity of GSK-3 and the transcription factors GBF and STATa during multicellular development. The integration of these pathways with others regulated by the morphogen DIF-1 to control cell fate decisions are discussed.

Plasmid pSC101 harbors a 28-bp sequence which is homologous to dif, the target site of the XerC/XerD-dependent recombination system in Escherichia coli. Using a technique which allows very sensitive detection of plasmid loss, we show that recombination at this site, termed psi for pSC101 stabilized inheritance, causes a moderate increase in pSC101 stability. The role of the psi sequence in site-specific recombination has been explored in two other contexts. It was cloned in a derivative of plasmid p15A and inserted into the chromosome in place of dif. In the first situation, psi activity requires accessory sequences and results in multimer resolution; in the second situation, it suppresses the effects of the dif deletion and can promote intermolecular exchanges. Thus, psi is a site whose recombinational activity depends on the context, the first in the cer/dif family known to exhibit such flexibility.

Strain AK127 is a developmental mutant of Dictyostelium discoideum that was isolated by restriction enzyme-mediated integration (REMI). Mutant cells aggregate normally but are unable to proceed past the loose aggregate stage. The cloned gene, lagC (loose aggregate C), encodes a novel protein of 98 kD that contains an amino-terminal signal sequence and a putative carboxy-terminal transmembrane domain. The mutant strain AK127 shows no detectable lagC transcript upon Northern analysis, indicating that the observed phenotype is that of a null allele. Expression of the lagC cDNA in AK127 cells complements the arrest at the loose aggregate stage, indicating that the mutant phenotype results from disruption of the lagC gene. In wild-type cells, lagC mRNA is induced at the loose aggregate stage and is expressed through the remainder of development. lagC- null cells aggregate but then disaggregate and reaggregate to form small granular mounds. Mature spores are produced at an extremely low efficiency (< 0.1% of wild type), appearing only after approximately 72 hr, whereas wild-type strains produce mature spores by 26 hr. lagC- null cells accumulate reduced levels of transcripts for the prestalk-enriched genes rasD and CP2 and do not express the DIF-induced prestalk-specific gene ecmA or the cAMP-induced prespore-specific gene SP60 to significant levels. In chimeric organisms resulting from the coaggregation of lagC- null and wild-type cells, cell-type-specific gene expression is rescued in the lagC- null cells; however, lagC- prespore cells are localized to the posterior of the prespore region and do not form mature spores, suggesting that LagC protein has both no cell-autonomous and cell-autonomous functions. Overexpression of lagC from an actin promoter in both wild-type and lagC- cells causes a delay at the tight aggregate stage, the first stage requiring LagC activity. These results suggest that the LagC protein functions as a nondiffusible cell-cell signaling molecule that is required for multicellular development.

BACKGROUND

Several techniques have been developed to detect differential item functioning (DIF), including ordinal logistic regression (OLR). This study compared different criteria for determining whether items have DIF using OLR.

OBJECTIVE

To compare and contrast findings from three different sets of criteria for detecting DIF using OLR. General distress and physical functioning items were evaluated for DIF related to five covariates: age, marital status, gender, race, and Hispanic origin.

METHODS

Cross-sectional study.

METHODS

1,714 patients with cancer or HIV/AIDS.

METHODS

A total of 23 items addressing physical functioning and 15 items addressing general distress were selected from a pool of 154 items from four different health-related quality of life questionnaires.

RESULTS

The three sets of criteria produced qualitatively and quantitatively different results. Criteria based on statistical significance alone detected DIF in almost all the items, while alternative criteria based on magnitude detected DIF in far fewer items. Accounting for DIF by using demographic-group specific item parameters had negligible effects on individual scores, except for race.

CONCLUSIONS

Specific criteria chosen to determine whether items have DIF have an impact on the findings. Criteria based entirely on statistical significance may detect small differences that are clinically negligible.

OBJECTIVE

To develop a social health measurement framework, to test items in diverse populations and to develop item response theory (IRT) item banks.

METHODS

A literature review guided framework development of Social Function and Social Relationships sub-domains. Items were revised based on patient feedback, and Social Function items were field-tested. Analyses included exploratory factor analysis (EFA), confirmatory factor analysis (CFA), two-parameter IRT modeling and evaluation of differential item functioning (DIF).

RESULTS

The analytic sample included 956 general population respondents who answered 56 Ability to Participate and 56 Satisfaction with Participation items. EFA and CFA identified three Ability to Participate sub-domains. However, because of positive and negative wording, and content redundancy, many items did not fit the IRT model, so item banks do not yet exist. EFA, CFA and IRT identified two preliminary Satisfaction item banks. One item exhibited trivial age DIF.

CONCLUSIONS

After extensive item preparation and review, EFA-, CFA- and IRT-guided item banks help provide increased measurement precision and flexibility. Two Satisfaction short forms are available for use in research and clinical practice. This initial validation study resulted in revised item pools that are currently undergoing testing in new clinical samples and populations.

BACKGROUND

MicroRNAs (miRNAs) are small non-coding RNAs that participate in the spatiotemporal regulation of messenger RNA (mRNA) and protein synthesis. Recent studies have shown that some miRNAs are involved in the progression of nasopharyngeal carcinoma (NPC). However, the aberrant miRNAs implicated in different clinical stages of NPC remain unknown and their functions have not been systematically studied.

METHODS

In this study, miRNA microarray assay was performed on biopsies from different clinical stages of NPC. TargetScan was used to predict the target genes of the miRNAs. The target gene list was narrowed down by searching the data from the UniGene database to identify the nasopharyngeal-specific genes. The data reduction strategy was used to overlay with nasopharyngeal-specifically expressed miRNA target genes and complementary DNA (cDNA) expression data. The selected target genes were analyzed in the Gene Ontology (GO) biological process and Kyoto Encyclopedia of Genes and Genomes (KEGG) biological pathway. The microRNA-Gene-Network was build based on the interactions of miRNAs and target genes. miRNA promoters were analyzed for the transcription factor (TF) binding sites. UCSC Genome database was used to construct the TF-miRNAs interaction networks.

RESULTS

Forty-eight miRNAs with significant change were obtained by Multi-Class Dif. The most enriched GO terms in the predicted target genes of miRNA were cell proliferation, cell migration and cell matrix adhesion. KEGG analysis showed that target genes were significantly involved in adherens junction, cell adhesion molecules, p53 signalling pathway et al. Comprehensive analysis of the coordinate expression of miRNAs and mRNAs reveals that miR-29a/c, miR-34b, miR-34c-3p, miR-34c-5p, miR-429, miR-203, miR-222, miR-1/206, miR-141, miR-18a/b, miR-544, miR-205 and miR-149 may play important roles on the development of NPC. We proposed an integrative strategy for identifying the miRNA-mRNA regulatory modules and TF-miRNA regulatory networks. TF including ETS2, MYB, Sp1, KLF6, NFE2, PCBP1 and TMEM54 exert regulatory functions on the miRNA expression.

CONCLUSIONS

This study provides perspective on the microRNA expression during the development of NPC. It revealed the global trends in miRNA interactome in NPC. It concluded that miRNAs might play important regulatory roles through the target genes and transcription factors in the stepwise development of NPC.

Mammals and insects employ similar Rel/NF-kappaB signaling cascades in their humoral immune responses. The mammalian interleukin-1 type I receptor (IL-1R) is one way of activating this cascade. The Drosophila Toll protein, whose cytoplasmic domain shows striking similarity to that of the IL-1R, acts in the humoral antimicrobial response. Here we demonstrate that a second IL-1R-related Drosophila protein, 18-Wheeler (18W), is a critical component of the humoral immune response. 18-wheeler is expressed in the larval fat body, the primary organ of antimicrobial peptide synthesis. In the absence of the 18W receptor, larvae are more susceptible to bacterial infection. Nuclear translocation of the Rel protein Dorsal-like immunity factor (Dif) is inhibited, though nuclear translocation of another Rel protein, Dorsal, is unaffected. Induction of several antibacterial genes is reduced following infection, relative to wild-type: attacin is reduced by 95%, cecropin by 65% and diptericin by 12%. Finally, 18-wheeler (18w) expression is induced in response to infection and, in addition to the receptor form, four immune-specific transcripts and proteins are produced.

PKCALC, an interactive computer program written in BASIC, facilitates: initial statistical analysis of multisubject data sets, pharmacokinetic analysis of experimental data, transfer of data between commercially available electronic spread-sheets (e.g., LOTUS 123) and the pharmacokinetic programs ESTRIP and PCNONLIN, and rapid preparation of graphs of data. Concentration versus time data can be entered into the program manually, from a data interchange format (DIF) file, or from a data file previously generated by PKCALC. The program has a main menu listing nine options. These include, but are not limited to, setting up a data file which can subsequently be read by PCNONLIN, chaining to a copy of ESTRIP augmented to read PKCALC data files, stripping curves manually, and utilizing the CRT and a line printer to graph polyexponential equations and/or subject data on linear or semilogarithmic axes. PKCALC runs on the IBM PC, IBM XT, IBM AT, and COMPAQ personal computers.

FtsK and topoisomerase (Topo) IV are both involved in chromosome segregation in Escherichia coli. The former protein resides at the septal ring and is required for resolution of chromosome dimers. The latter protein is the chromosomal decatenase. We have demonstrated recently that Topo IV activity is concentrated at the septal proximal regions of the nucleoids late in the cell cycle. Here we demonstrate that FtsK and Topo IV physically and functionally interact. Topo IV was recovered in immunoprecipitates of FtsK. Two-hybrid analysis and immunoblotting showed that this interaction was mediated by the ParC subunit of Topo IV. In addition, we show that the C-terminal motor domain of FtsK stimulates the decatenation activity of Topo IV but not that of DNA gyrase, the other type II topoisomerase in the cell. Topo IV and FtsK appear to cooperate in the cell as well. Rescue of a parE temperature-sensitive mutation by overproduction of DnaX, which leads to stabilization of the temperature-sensitive Topo IV, required both the C-terminal domain of FtsK and dif, whereas rescue by overproduction of Topo III, which bypasses Topo IV function, did not. The interaction between FtsK and Topo IV may provide a means for concentrating the latter enzyme at the cell center.

OBJECTIVE

To investigate the internal construct validity of a clinician-assessed measure of foot position, the Foot Posture Index (FPI), versions FPI-8 and FPI-6.

METHODS

Rasch analysis of baseline FPI scores from studies conducted during the development of the instrument.

METHODS

A community-based and a hospital-based study, conducted at 2 institutions.

METHODS

Measures were obtained from 143 participants (98 men, 45 women; age range, 8-65y).

METHODS

Not applicable.

METHODS

Rasch analysis was undertaken using RUMM2020 software in order to evaluate the following properties of the FPI: unidimensionality of each item included in the FPI, the differential item functioning (DIF) of each item, and item and person separation indices.

RESULTS

In the developmental draft of the instrument, the 8-item FPI-8 showed some misfit to the Rasch model (chi(16)(2) test=27.63, P=.03), indicating lack of unidimensionality. Two items were identified as problematic in the Rasch modeling: Achilles' tendon insertion (Helbing's sign), which showed illogical response ordering and "congruence of the lateral border of the foot," which showed misfit, indicating that this item may be measuring a different construct (chi(2)(2) test=15.35, P<.01). All FPI-8 items showed an absence of DIF, and the person separation index (PSI) was good (PSI=.88). The revised FPI-6, which does not include the 2 problematic items, showed unidimensionality (chi(12)(2) test=11.49, P=.49), indicating a good overall fit to the model, and improvement over the preliminary version. With the removal of the 2 problematic items, there were no disordered thresholds; all items remained DIF free and all individual items displayed a good fit to the model. The person-separation index for the FPI was similar for both the 8-item (FPI-8=.880) and 6-item (FPI-6=.884) versions.

CONCLUSIONS

The original FPI-8 showed significant mismatching to the model. The 2 items in the FPI-8 that were identified as problematic in clinical validation studies were also found to be contributing to the lack of fit to the Rasch model. The finalized 6-item instrument showed good metric properties, including good individual item fit and good overall fit to the model, along with a lack of differential item functioning. This analysis provides further evidence for the validity of the FPI-6 as a clinical instrument for use in screening studies and shows that it has the potential to be analyzed using parametric strategies.

BACKGROUND

An important part of examining the adequacy of measures for use in ethnically diverse populations is the evaluation of differential item functioning (DIF) among subpopulations such as those administered the measure in different languages. A number of methods exist for this purpose.

OBJECTIVE

The objective of this study was to introduce and demonstrate the identification of DIF using item response theory (IRT) and the likelihood-based model comparison approach.

METHODS

Data come from a sample of community-residing elderly who were part of a dementia case registry. A total of 1578 participants were administered either an English (n = 913) or Spanish (n = 665) version of the 21-item Mini-Mental State Examination. IRT was used to identify language DIF in these items with the likelihood-based model comparison approach.

RESULTS

: Fourteen of the 21 items exhibited significant DIF according to language of administration. However, because the direction of the identified DIF was not consistent for one language version over the other, the impact at the scale level was negligible.

CONCLUSIONS

IRT and the likelihood-based model comparison approach comprise a powerful tool for DIF detection that can aid in the development, refinement, and evaluation of measures for use in ethnically diverse populations.

Complex signaling pathways regulate the innate immune system of insects, with NF-kappaB transcription factors playing a central role in the activation of antimicrobial peptides and other immune genes. Although numerous studies have characterized the immune responses of insects to pathogens, comparatively little is known about the counter-strategies pathogens have evolved to circumvent host defenses. Among the most potent immunosuppressive pathogens of insects are polydnaviruses that are symbiotically associated with parasitoid wasps. Here, we report that the Microplitis demolitor bracovirus encodes a family of genes with homology to inhibitor kappaB (IkappaB) proteins from insects and mammals. Functional analysis of two of these genes, H4 and N5, were conducted in Drosophila S2 cells. Recombinant H4 and N5 greatly reduced the expression of drosomycin and attacin reporter constructs, which are under NF-kappaB regulation through the Toll and Imd pathways. Coimmunoprecipitation experiments indicated that H4 and N5 bound to the Rel proteins Dif and Relish, and N5 also weakly bound to Dorsal. H4 and N5 also inhibited binding of Dif and Relish to kappaB sites in the promoters of the drosomycin and cecropin A1 genes. Collectively, these results indicate that H4 and N5 function as IkappaBs and, circumstantially, suggest that other IkappaB-like gene family members are involved in the suppression of the insect immune system.

OBJECTIVE

To empirically evaluate the psychometric properties of the 15-item Geriatric Depression Scale (GDS-15); determine the optimal cutoff points and screening performance for the detection of major depression; and examine differential item functioning (DIF) to determine the variability of item responses across sociodemographics in an elderly home care population.

METHODS

A secondary analysis of data collected from a random sample study.

METHODS

Homebound subjects newly admitted over a 2-year-period to a large visiting nurse service agency in Westchester, New York.

METHODS

Five hundred twenty-six subjects over age 65, newly admitted to home care for skilled nursing.

METHODS

Major depression was diagnosed using both patient, Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, and best estimate procedures. Self-report measures included the GDS-15, activities of daily living (ADL), instrumental ADL, and pain intensity. Cognitive impairment was assessed using the Mini-Mental State Examination and medical morbidity using the Charlson Comorbidity Index.

RESULTS

Optimal cutoff (5) yielded sensitivity 71.8% and specificity of 78.2%, however, the accuracy of the GDS-15 was not influenced by severity of medical burden. Persons with a cluster of ailments were twice as likely (Adj odds ratio = 2.47; 95% confidence interval = 1.49-4.09) to be diagnosed with depression. DIF analyses revealed no variability of item responses across sociodemographics.

CONCLUSIONS

Main findings suggest that the accuracy of the GDS-15 was not influenced by severity of clinical or functional factors, or sociodemographics. This has broad implications suggesting that the very old, ill, and diverse populations can be appropriately screened for depression using the GDS-15.

The extracellular matrix fibrils of Myxococcus xanthus are essential for the social lifestyle of this unusual bacterium. These fibrils form networks linking or encasing cells and are tightly correlated with cellular cohesion, development, and social (S) gliding motility. Previous studies identified a set of bacterial chemotaxis homologs encoded by the dif locus. It was determined that difA, difC, and difE, encoding respective homologs of a methyl-accepting chemotaxis protein, CheW, and CheA, are required for fibril production and therefore S motility and development. Here we report the studies of three additional genes residing at the dif locus, difB, difD, and difG. difD and difG encode homologs of chemotaxis proteins CheY and CheC, respectively. difB encodes a positively charged protein with limited homology at its N terminus to conserved bacterial proteins with unknown functions. Unlike the previously characterized dif genes, none of these three newly studied dif genes are essential for fibril production, S motility, or development. The difB mutant showed no obvious defects in any of the processes examined. In contrast, the difD and the difG mutants were observed to overproduce fibril polysaccharides in comparison with production by the wild type. The observation that DifD and DifG negatively regulate fibril polysaccharide production strengthens our hypothesis that the M. xanthus dif genes define a chemotaxis-like signal transduction pathway which regulates fibril biogenesis. To our knowledge, this is the first report of functional studies of a CheC homolog in proteobacteria. In addition, during this study, we slightly modified previously developed assays to easily quantify fibril polysaccharide production in M. xanthus.