Nanosecond X-ray diffraction from biological samples with a laser-produced plasma source.

By using 4.45-angstrom radiation generated by Cl+15 ions in a laser plasma and nanosecond exposures, low-angle x-ray diffraction patterns were obtained from dried rat spinal nerves and a powder of cholesterol. Three to four 400-picosecond, 45-joule pulses were required for the exposure. This new technique should have wide application in structural kinetic studies.

Bright-field microscopy of semitransparent objects.

We examine theoretically and experimentally the characteristics of in-focus and out-of-focus images of simple, well-defined phase objects. Theoretical calculations are based on the theory of partial coherence, and a simple calculation for imaging with coherent light demonstrates distinctive aspects of bright-field images. Experiments are performed with a well-corrected microscope, equipped for the precise control of illumination conditions and focus position. Theoretical and experimental results agree, although the contrast in the experimental images is often lower than expected. Also verified by experiment is a (to our knowledge) previously uninvestigated linear response in the intensity modulation of defocused, coherent images of thin, phase objects. The near-focus behavior of phase object images differs in symmetry from the more-familiar behavior of opaque object images.

Time-resolved x-ray diffraction study of photostimulated purple membrane.

A nanosecond resolution laser-driven x-ray source has been used to perform a time-resolved, x-ray diffraction study of the purple membrane of the Halobacterium halobium. Alterations in diffraction patterns have been observed 1 ms after photostimulation, and are interpreted to show disorder of bacteriorhodopsin packing in the plane of the membrane with little bacteriorhodopsin structural change.

IgA antibodies to human tissue transglutaminase: audit of routine practice confirms high diagnostic accuracy.

BACKGROUND: The diagnostic accuracy of IgA tissue transglutaminase antibodies (TGA) for coeliac disease (CD) has been assessed following the introduction of the test into routine practice in 2002. METHODS: Specificity was assessed in serum samples received from 1554 adults for routine coeliac serology. The population for assessing sensitivity was 75 consecutive new adult diagnoses of CD. TGA was measured by enzyme-linked immunoassay using human tissue transglutaminase as antigen. Concordance between TGA and endomysial antibody (EMA) was also assessed. RESULTS: The prevalence of new diagnoses of CD in the population tested was 2.8% with similar proportions of new diagnoses in males and females. The positive predictive values at a cut-off of 3 units/mL were 0.77 for samples from Primary Care and 0.92 for samples from Hospital sources, with a sensitivity of 92%. At TGA <3 units/mL, EMA was usually negative; when TGA was >4.9 units/mL, EMA was rarely negative. CONCLUSIONS: We have assessed the role of TGA in routine clinical practice and confirmed high diagnostic accuracy. Sensitivity (92%) is identical to the sensitivity for EMA. IgA deficiency should be excluded in samples showing low absorbance readings in the TGA assay and interference from monoclonal and polyclonal IgA should be excluded in samples with slightly raised TGA levels and negative EMA. TGA is recommended as the first-line serological test for coeliac disease.

Co-existence of lysosomal storage diseases in a consanguineous family.

Lysosomal storage diseases are rare and coexistence of more than one in a family can present a diagnostic challenge as illustrated by this study. The index case born to consanguineous Asian parents presented with developmental delay. Investigations led to an incidental finding of Fabry disease. After numerous additional investigations over a year, a second diagnosis of aspartylglucosaminuria (AGU) was made. A family history of renal disease and developmental delay was disclosed. The sister and first cousin of the index case were diagnosed as homozygous for AGU, but do not have Fabry disease. The younger brother has since been diagnosed with both Fabry disease and AGU. Another cousin has learning difficulties and fits, but is heterozygous for AGU, and possibly has another uncharacterised autosomal recessive disorder. In a family with consanguinity when the clinical picture in an individual is not fully explained by the presence of one rare metabolic disease, it is essential to investigate further for the presence of others.