Gait Initiation in Children with Rett Syndrome

Rett syndrome is an X-linked neurodevelopmental condition mainly characterized by loss of spoken language and a regression of purposeful hand use, with the development of distinctive hand stereotypies, and gait abnormalities. Gait initiation is the transition from quiet stance to steady-state condition of walking. The associated motor program seems to be centrally mediated and includes preparatory adjustments prior to any apparent voluntary movement of the lower limbs. Anticipatory postural adjustments contribute to postural stability and to create the propulsive forces necessary to reach steady-state gait at a predefined velocity and may be indicative of the effectiveness of the feedforward control of gait. In this study, we examined anticipatory postural adjustments associated with gait initiation in eleven girls with Rett syndrome and ten healthy subjects. Muscle activity (tibialis anterior and soleus muscles), ground reaction forces and body kinematic were recorded. Children with Rett syndrome showed a distinctive impairment in temporal organization of all phases of the anticipatory postural adjustments. The lack of appropriate temporal scaling resulted in a diminished impulse to move forward, documented by an impairment in several parameters describing the efficiency of gait start: length and velocity of the first step, magnitude and orientation of centre of pressure-centre of mass vector at the instant of (swing-)toe off. These findings were related to an abnormal muscular activation pattern mainly characterized by a disruption of the synergistic activity of antagonistic pairs of postural muscles. This study showed that girls with Rett syndrome lack accurate tuning of feedforward control of gait.     

Quantity versus quality: identifying the most effective pollinators of the hummingbird-pollinated Vriesea rodigasiana (Bromeliaceae)

Although hummingbirds are considered the major bromeliad pollinators, different species may contribute differently to pollination. This study analyses the importance of different hummingbirds to pollination of Vriesea rodigasiana (Bromeliaceae), based on visitation frequency (a quantity component) and germinated pollen load per visit (a quality component) in the Atlantic rainforest of southeastern Brazil. This bromeliad flowers for 3–4 months with a peak in March. Its yellow, tubular flowers last about 13 h and demonstrate approach herkogamy. During flowering peak, Thalurania glaucopis visited more flowers than Ramphodon naevius, whereas by the end of the flowering season the latter visited more. Differences in hummingbird bill length resulted in different pollen placement and stigma contact. The short-billed T. glaucopis received pollen on the top of its head, depositing it on the center of the stigma, while the long-billed R. naevius received it on the proximal part of its bill, depositing it on the lower lobe of the stigma. Flowers visited by T. glaucopis had six times more pollen tubes than those visited by R. naevius. Our results suggest that this functional group of hummingbirds may be split into even smaller groups, namely short-billed and long-billed hummingbirds, based on different sites of pollen placement. Although both species were pollen vectors of V. rodigasiana, the short-billed T. glaucopis was its most effective pollinator in the area supporting Stebbin’s principle, linking floral features and good pollinators.     

Extensive Heterogeneity and Intrinsic Variation in Spatial Genome Organization

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Psychometric Properties of the Participation Scale among Former Buruli Ulcer Patients in Ghana and Benin

Background

Buruli ulcer is a stigmatising disease treated with antibiotics and wound care, and sometimes surgical intervention is necessary. Permanent limitations in daily activities are a common long term consequence. It is unknown to what extent patients perceive problems in participation in social activities. The psychometric properties of the Participation Scale used in other disabling diseases, such as leprosy, was assessed for use in former Buruli ulcer patients.

Methods

Former Buruli ulcer patients in Ghana and Benin, their relatives, and healthy community controls were interviewed using the Participation Scale, Buruli Ulcer Functional Limitation Score, and the Explanatory Model Interview Catalogue to measure stigma. The Participation Scale was tested for the following psychometric properties: discrimination, floor and ceiling effects, internal consistency, inter-item correlation, item-total correlation and construct validity.

Results

In total 386 participants (143 former Buruli ulcer patients with their relatives (137) and 106 community controls) were included in the study. The Participation Scale displayed good discrimination between former Buruli ulcer patients and healthy community controls. No floor and ceiling effects were found. Internal consistency (Cronbach''s alpha) was 0.88. In Ghana, mean inter-item correlation of 0.29 and item-total correlations ranging from 0.10 to 0.69 were found while in Benin, a mean inter-item correlation of 0.28 was reported with item-total correlations ranging from −0.08 to 0.79. With respect to construct validity, 4 out of 6 hypotheses were not rejected, though correlations between various constructs differed between countries.

Conclusion

The results indicate the Participation Scale has acceptable psychometric properties and can be used for Buruli ulcer patients in Ghana and Benin. Future studies can use this Participation Scale to evaluate the long term restrictions in participation in daily social activities of former BU patients.     

Respiratory Pathogens Adopt a Chronic Lifestyle in Response to Bile

Chronic respiratory infections are a major cause of morbidity and mortality, most particularly in Cystic Fibrosis (CF) patients. The recent finding that gastro-esophageal reflux (GER) frequently occurs in CF patients led us to investigate the impact of bile on the behaviour of Pseudomonas aeruginosa and other CF-associated respiratory pathogens. Bile increased biofilm formation, Type Six Secretion, and quorum sensing in P. aeruginosa, all of which are associated with the switch from acute to persistent infection. Furthermore, bile negatively influenced Type Three Secretion and swarming motility in P. aeruginosa, phenotypes associated with acute infection. Bile also modulated biofilm formation in a range of other CF-associated respiratory pathogens, including Burkholderia cepacia and Staphylococcus aureus. Therefore, our results suggest that GER-derived bile may be a host determinant contributing to chronic respiratory infection.     

Comparing mortality in renal patients on hemodialysis versus peritoneal dialysis using a marginal structural model

When comparing the causal effect of peritoneal dialysis (PD) and hemodialysis (HD) treatment on lowering mortality in renal patients, using observational data, it is necessary to adjust for different forms of confounding and informative censoring. Both the type of dialysis treatment that is started with and mortality are affected by baseline covariates. Longitudinal and baseline variables can affect both the probability of switching from one type of dialysis to the other, and mortality. Longitudinal and baseline variables can also affect the probability of receiving a kidney transplant, possibly causing informative censoring. Adjusting for longitudinal variables by including them as covariates in a regression model potentially causes bias, for instance by losing a possible indirect effect of dialysis on mortality via these longitudinal variables. Instead, we fitted a marginal structural model (MSM) to estimate the causal effect of dialysis type, adjusted for confounding and informative censoring. We used the MSM to compare the hazard of death as well as cumulative survival between the potential treatment trajectories "always PD" and "always HD" over time, conditional on age and diabetes mellitus status. We used inverse probability weighting (IPW) to fit the MSM.