Dynamic stability of human walking in visually and mechanically destabilizing environments.

Understanding how humans remain stable during challenging locomotor activities is critical to developing effective tests to diagnose patients with increased fall risk. This study determined if different continuous low-amplitude perturbations would induce specific measureable changes in measures of dynamic stability during walking. We applied continuous pseudo-random oscillations of either the visual scene or support surface in either the anterior-posterior or mediolateral directions to subjects walking in a virtual environment with speed-matched optic flow. Floquet multipliers and short-term local divergence exponents both increased (indicating greater instability) during perturbed walking. These responses were generally much stronger for body movements occurring in the same directions as the applied perturbations. Likewise, subjects were more sensitive to both visual and mechanical perturbations applied in the mediolateral direction than to those applied in the anterior-posterior direction, consistent with previous experiments and theoretical predictions. These responses were likewise consistent with subjects' anecdotal perceptions of which perturbation conditions were most challenging. Contrary to the Floquet multipliers and short-term local divergence exponents, which both increased, long-term local divergence exponents decreased during perturbed walking. However, this was consistent with specific changes in the mean log divergence curves, which indicated that subjects' movements reached their maximum local divergence limits more quickly during perturbed walking. Overall, the Floquet multipliers were less sensitive, but reflected greater specificity in their responses to the different perturbation conditions. Conversely, the short-term local divergence exponents exhibited less specificity in their responses, but were more sensitive measures of instability in general.

Walking variability during continuous pseudo-random oscillations of the support surface and visual field.

Walking on uneven surfaces or while undergoing perturbations has been associated with increased gait variability in both modeling and human studies. Previous gait research involving continuous perturbations has focused on sinusoidal oscillations, which can result in individuals predicting the perturbation and/or entraining to it. Therefore, we examined the effects of continuous, pseudo-random support surface and visual field oscillations on 12 healthy, young participants. Participants walked in a virtual reality environment under no perturbation (NOP), anterior-posterior (AP) walking surface and visual oscillation and mediolateral (ML) walking surface and visual oscillation conditions. Participants exhibited shorter (p< or =0.005), wider (p<0.001) and faster (p<0.001) steps relative to NOP during ML perturbations and shorter (p< or =0.005) and wider (p<0.001) steps during AP perturbations. Step length variability and step width variability both increased relative to NOP during all perturbation conditions (p<0.001) but exhibited greater increases for the ML perturbations (p<0.001). Participants exhibited greater trunk position variability and trunk velocity variability in the ML direction than in the AP direction during ML perturbations relative to NOP (p<0.001). Significantly greater variability in the ML direction indicates that to maintain stability, participants needed to exert greater control in the ML direction. This observation is consistent with prior modeling predictions. The large and consistent responses observed during ML visual and walking surface perturbations suggest potential for application during gait training and patient assessment.

Mutation detection in the ABCC6 gene and genotype-phenotype analysis in a large international case series affected by pseudoxanthoma elasticum.

BACKGROUND: Pseudoxanthoma elasticum (PXE), an autosomal recessive disorder with considerable phenotypic variability, mainly affects the eyes, skin and cardiovascular system, characterised by dystrophic mineralization of connective tissues. It is caused by mutations in the ABCC6 (ATP binding cassette family C member 6) gene, which encodes MRP6 (multidrug resistance-associated protein 6). OBJECTIVE: To investigate the mutation spectrum of ABCC6 and possible genotype-phenotype correlations. METHODS: Mutation data were collected on an international case series of 270 patients with PXE (239 probands, 31 affected family members). A denaturing high-performance liquid chromatography-based assay was developed to screen for mutations in all 31 exons, eliminating pseudogene coamplification. In 134 patients with a known phenotype and both mutations identified, genotype-phenotype correlations were assessed. RESULTS: In total, 316 mutant alleles in ABCC6, including 39 novel mutations, were identified in 239 probands. Mutations were found to cluster in exons 24 and 28, corresponding to the second nucleotide-binding fold and the last intracellular domain of the protein. Together with the recurrent R1141X and del23-29 mutations, these mutations accounted for 71.5% of the total individual mutations identified. Genotype-phenotype analysis failed to reveal a significant correlation between the types of mutations identified or their predicted effect on the expression of the protein and the age of onset and severity of the disease. CONCLUSIONS: This study emphasises the principal role of ABCC6 mutations in the pathogenesis of PXE, but the reasons for phenotypic variability remain to be explored.

Mesoscale eddies drive increased silica export in the subtropical Pacific Ocean.

Mesoscale eddies may play a critical role in ocean biogeochemistry by increasing nutrient supply, primary production, and efficiency of the biological pump, that is, the ratio of carbon export to primary production in otherwise nutrient-deficient waters. We examined a diatom bloom within a cold-core cyclonic eddy off Hawaii. Eddy primary production, community biomass, and size composition were markedly enhanced but had little effect on the carbon export ratio. Instead, the system functioned as a selective silica pump. Strong trophic coupling and inefficient organic export may be general characteristics of community perturbation responses in the warm waters of the Pacific Ocean.

Measurement of DNA biomarkers for the safety of tissue-engineered medical products, using artificial skin as a model.

To test the hypothesis that the process of tissue engineering introduces genetic damage to tissue-engineered medical products, we employed the use of five state-of-the-art measurement technologies to measure a series of DNA biomarkers in commercially available tissue-engineered skin as a model. DNA was extracted from the skin and compared with DNA from cultured human neonatal control cells (dermal fibroblasts and epidermal keratinocytes) and adult human fibroblasts from a 55-year-old donor and a 96-year-old donor. To determine whether tissue engineering caused oxidative DNA damage, gas chromatography/isotope-dilution mass spectrometry and liquid chromatography/isotope-dilution mass spectrometry were used to measure six oxidatively modified DNA bases as biomarkers. Normal endogenous levels of the modified DNA biomarkers were not elevated in tissue-engineered skin when compared with control cells. Next, denaturing high-performance liquid chromatography and capillary electrophoresis-single strand conformation polymorphism were used to measure genetic mutations. Specifically, the TP53 tumor suppressor gene was screened for mutations, because it is the most commonly mutated gene in skin cancer. The tissue-engineered skin was found to be free of TP53 mutations at the level of sensitivity of these measurement technologies. Lastly, fluorescence in situ hybridization was employed to measure the loss of Y chromosome, which is associated with excessive cell passage and aging. Loss of Y chromosome was not detected in the tissue-engineered skin and cultured neonatal cells used as controls. In this study, we have demonstrated that tissue engineering (for TestSkin II) does not introduce genetic damage above the limits of detection of the state-of-the-art technologies used. This work explores the standard for measuring genetic damage that could be introduced during production of novel tissue-engineered products. More importantly, this exploratory work addresses technological considerations that need to be addressed in order to expedite accurate and useful international reference standards for the emerging tissue-engineering industry.

Rapid and robust screening of the Menkes disease/occipital horn syndrome gene.

Menkes disease and occipital horn syndrome (OHS) are allelic neurogenetic disorders of copper transport associated with mutations in an X-linked gene, ATP7A. This gene encodes a copper-transporting P-type ATPase. The spectrum of mutations at the Menkes/OHS locus is estimated to include 1% chromosomal rearrangements and 15-20% large deletions, with the remaining defects involving small alterations. There is a compelling need for a rapid and reliable molecular diagnostic approach for patients and families impacted by these conditions. In addition to testing suspected affected males, carrier screening of females in Menkes/OHS families and prenatal evaluation of at-risk pregnancies will be enhanced by the wider availability of robust mutation analysis for this large (23-exon) locus. Here we describe a stepwise approach to mutation screening for these disorders that successfully identified molecular alterations in over 95% of our patient population (n = 49). This genomic DNA-based technique employs multiplex PCR, heteroduplex analysis, and direct sequencing, in a serial fashion. This approach should find application in molecular diagnostic laboratories in the United States and other countries. Currently, only a single European center provides commercial testing for unknown mutations in Menkes/OHS patients, even though these disorders occur worldwide.