Biomedical subjects
Publications and source records attributed to A L Williams.
CT images and anatomic slices of two brains containing numerous demyelinated plaques were correlated. Demyelinated plaques smaller than 0.7 cm were not detected by CT. Some larger plaques were misinterpreted as normal structures. These and other considerations suggest that chronic cerebral demyelination cannot be excluded by negative nonenhanced CT scan.
To justify CT purchases and document certificates of need, the clinical effectiveness of CT scanners with different cost and resolution must be compared. The diagnostic accuracy and anatomic detail in three scanners with different resolution were studied. Seventeen patients were studied with both a first or a second generation CT scanner and a third-generation scanner. Appearance of normal and pathologic structures was compared. Cerebral sulci, corticomedullary discrimination, basal cistern vessels, and some pathologic lesions were seen in third generation images that were not seen in the others. Higher resolution scans provide significantly better anatomic detail and accuracy in detecting pathologic processes.
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Valyl-, isoleucyl-, and leucyl-tRNA synthetase activities were examined in an Escherichia coli K-12 strain that possessed a deletion of three genes of the ilv gene cluster, ilvD, A, and C, and in a strain with the same deletion that also carried the lambdadilvCB bacteriophage. It was observed that the branched-chain tRNA synthetase activities of both strains were considerably less than those of the normal strain during growth in unrestricted medium. Furthermore, during an isoleucine limitation, there was a further reduction in isoleucyl-tRNA synthetase activity and an absence of the isoleucine-mediated derepression of valyl-tRNA synthetase formation in both of these mutants, as compared with the normal strain. In addition, it was observed that these branched-chain synthetase activities were reduced in steady-state cultures of several ilvA point mutants. However, upon the introduction of the ilv operon to these ilvA mutants by use of lambda bacteriophage, there was a specific increase in the branched-chain synthetase activities to levels comparable to those of the normal strain. These results support our previous findings that the stability and repression control of synthesis of these synthetases require some product(s) missing in the ilvDAC deletion strain and strongly suggest this component is some form of the ilvA gene product, threonine deaminase.
The effectiveness of prophylactic intrathecal methylprednisone (MP) in preventing arachnoiditis from iocarmate myelography was studied. Monkeys were injected intrathecally with locarmate, MP, or a combination of the two. Twelve weeks later the severity of arachnoiditis was determined in each animal. There was no significant prophylactic effect of intrathecal MP on arachnoiditis from locarmate. Some arachnoiditis was found in control animals treated with MP alone.
A collapsing cord in six patients with hydromyelia and a collapsing intraspinal arachnoid cyst in one patient are demonstrated. The authors describe the technique for two-position gas myelography and demonstrate that both intra- and extra-medullary intraspinal processes may collapse during myelography.
Myelography with meglumine iocarmate, a dilute meglumine iocarmate solution, or gas was performed in macaque monkeys. Twelve weeks later the animals were examined myelographically and histologically for evidence of arachnoiditis. Arachnoiditis in the animals treated with dilute meglumine iocarmate and gas was significantly less than in those treated with meglumine iocarmate.
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HLA phenotypes of 66 parents of 33 infants succumbing to the sudden infant death syndrome (SIDS) were determined using a standard microlymphocytotoxicity method. Heterogeneity testing over all locus antigens revealed a significant difference between the parents and a control group consisting of blood donors and healthy unrelated volunteers. This heterogeneity was still evident when maternal and paternal groups were considered separately with the controls and when compared with each other. Individual A locus antigens displaying frequency deviation from control values included A9 (decreased in husbands), A10 (increased in wives and total parent group), and A28 (increased in wives). The increase in frequency of A10 became highly significant when only parents of children with evidence of laryngitis at post mortem were used for comparison with control values. No difference in B locus antigens between any of the groups was observed. The results obtained are compatible with the view that SIDS is the result of a hypersensitivity reaction to one or more allergens and that genes coding for these specific responses are linked to the HLA complex. Differences observed between the maternal and paternal groups may be explained on the basis of maternal antibody, passively acquired by the infant, which serves a protective role in the respiratory tract, prior to the development of immunocompetence. The production of these antibodies is also dependent on genes linked to the maternal HLA complex.
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Studies by Thompson, 1 Carter et al, 2 MacDonald et al. and McCrae 4 have all shown a high familial frequency of coeliac disease (CD). The diagnostic criteria differed in each study; in Thompson's patients the diagnosis was based on clinical or historical data alone; in Carter's study response to a gluten-free diet was required, while in MacDonald's and McCrae's studies the diagnostic criteria included the demonstration of the lesion of CD by small bowel biopsy. In MacDonald's study some asymptomatic cases were discovered and a few of these had normal fat balance results. No hereditary pattern emerged from these studies though MacDonald postulated a dominant gene with variable penetrance while McCrae suggested that susceptibility to CD is inhereited multifactorially and that enviromental factors other than dietary gluten are of aetiological importance. Hoffman et al. 5, on the other hand, have described discordance for CD in identical twins.
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The arginyl-transfer ribonucleic acid (Arg-tRNA) synthetase (EC 6.1.1.13, arginine: RNA ligase adenosine monophosphate) mutants, exhibiting nonrepressible synthesis of arginine by exogenous arginine, were employed in studies of several biochemical properties. Two of these mutants possessed Arg-tRNA synthetases with a reduced affinity for arginine, and this enzyme of another mutant had a reduced affinity for arginine-tRNA (tRNA(arg)). The mutant possessing an Arg-tRNA synthetase with an altered K(m) for tRNA(arg) was found to have reduced in vivo aminoacylation of two of the five isoaccepting species of tRNA(arg) and complete absence of aminoacylation of one of the isoaccepting species.
In this study, we have extended our earlier observations indicating in vitro inhibition of arginyl-transfer ribonucleic acid synthetase (EC 6.1.13, arginine: soluble ribonucleic acid ligase, adenosine monophosphate) activity by the arginine biosynthetic precursors ornithine, citrulline, and argininosuccinate. Furthermore, we report evidence which suggest that this enzyme activity is inhibited by these arginine precursors in vivo and that this inhibition of activity results in a derepression of arginine biosynthesis.