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J C Leonard

Publications and source records attributed to J C Leonard.

At least 37 records · Page 2Linked to original sources
PubMed1995

The 18q- syndrome: analysis of chromosomes by bivariate flow karyotyping and the PCR reveals a successive set of deletion breakpoints within 18q21.2-q22.2.

The 18q- syndrome is one of several terminal deletion disorders that occur in humans. Previous G-banding studies suggest that the loss of a critical band, 18q21.3, results in mental retardation, craniofacial anomalies, and metabolic defects. However, it is difficult to reconcile the consistent loss of a single region with the large variability in clinical phenotype. The purpose of this study was to reassess the extent of chromosomal loss in a cohort of 17 18q- syndrome patients by using fluorescent-activated chromosome sorting, PCR, and FISH. Bivariate flow karyotypes revealed heterogeneity among the deletions; they ranged in size from 9 to 26 Mb. To confirm this heterogeneity at a molecular level, deleted and normal chromosomes 18 of six patients were collected by flow sorting, preamplified by random priming, and assayed for marker content by the PCR. This analysis defined five unique breakpoints among the six patients. We conclude that the terminal deletions in the 18q- syndrome occur over a broad region spanning the interval from 18q21.2 to 18q22.2. Our results suggest that the variability in clinical phenotype may be more representative of a contiguous-gene syndrome with a baseline deficit of 18q22.2-qter than of the loss of a single critical region within 18q21.3.

Chromosome Deletion↗
PubMed1993

Alanine-scanning mutagenesis of the epidermal growth factor-like domains of human thrombomodulin identifies critical residues for its cofactor activity.

Thrombomodulin (TM) is an endothelial cell surface-bound cofactor in thrombin-dependent formation of activated protein C, a potent anticoagulant. Cofactor activity has been localized to the carboxyl-terminal half of the six epidermal growth factor-like (EGF) domains of TM (TME). To identify residues in TME that are critical for activity, 77 alanine point mutants were made between Cys-333 and Cys-462 by site-directed mutagenesis (all residues except Ala, Cys, Gly, and Pro). Mutants were expressed in Escherichia coli and cofactor activity measured directly in periplasmic extracts obtained by osmotic shock. Critical residues were defined as those which when mutated had less than 25% cofactor activity of a reference TME. Western blots of non-reduced samples confirmed that alanine substitutions did not significantly decrease expression levels or result in the formation of multimers. In EGF4, which is essential for protein C activation by the thrombin-TM complex, critical residues were: Asp-349, Glu-357, Tyr-358, and Phe-376. In EGF5-EGF6, critical residues within a proposed acidic thrombin-binding region were: Glu-408, Tyr-413, Ile-414, Leu-415, Asp-416, Asp-417, Asp-423, Ile-424, Asp-425, and Glu-426. A potential Ca(2+)-binding site, which is comprised of residues Asp-423, Asp-425, Glu-426, Asn-439, Leu-440, and Phe-444, was also identified and overlaps the thrombin-binding region. Asp-461, in the C-loop of EGF6 previously shown to be critical for thrombin binding, was also critical. Asp-398, Asp-400, Asn-402, and Asn-429 in EGF5 were also critical. Thus, rapid alanine-scanning mutagenesis of TME has identified 22 critical residues in the region comprising EGF4-6, which is essential for thrombin binding and protein C activation by the thrombin-TM complex.

Alanine↗
PubMed1993

Bone scan findings in craniometaphyseal dysplasia.

Craniometaphyseal dysplasia is a rare genetic bone disorder characterized by undertubulation of the long bones, especially in the lower extremities, and sclerosis of the skull base. Differentiation from other sclerosing bone dysplasias, including metaphyseal dysplasia (Pyle's disease), craniodiaphyseal dysplasia, and diaphyseal dysplasia is based largely on characteristic radiographic findings. Radionuclide bone scans usually are not necessary for diagnosis, but are helpful in demonstrating the abnormal bone metabolism. The authors report the first whole-body bone images in a patient with craniometaphyseal dysplasia, demonstrating the abnormal bone activity over time.

Bone Diseases, Developmental↗
PubMed1992

Clastogenicity of lead chromate particles in hamster and human cells.

Several insoluble compounds of chromium, such as lead chromate, are respiratory carcinogens in experimental animals and suspected to be so in humans. Lead chromate induces neoplastic transformation in cultured cells but the mechanism of genotoxicity is unknown. We examined the effect of lead chromate on the integrity of chromosomes of Chinese hamster ovary (CHO) and human foreskin fibroblasts (HFF) after a 24-h exposure. At 0.4 microgram/cm2, 0.8 microgram/cm2, 2 microgram/cm2 and 8 microgram/cm2 lead chromate particles reduced survival of CHO cells to 86%, 62%, 2% and less than 1% respectively. These concentrations induced a dose-dependent 4-19-fold increase in the percent metaphases with damage. The HFF cells exhibited higher sensitivity in both cytotoxicity and clastogenicity. The spectrum of damage observed for both cell types was primarily achromatic lesions affecting one or both chromatids. To test for particle dissolution effects, CHO cells were treated for 24 h with either clarified medium that had been incubated for 24 h with lead chromate particles, or clarified medium that had been pre-conditioned by CHO cells treated with lead chromate particles for 24 h. No damage was detected in these cells, indicating that extracellular dissolution into ionic lead and chromate did not contribute to the genotoxicity. This is consistent with a previous study in which scanning electron micrographs illustrated internalization of the particles. These results suggest that clastogenesis may be a mechanism for lead chromate induced carcinogenesis.

Animals↗
PubMed1992

Rapid determination of glomerular filtration rate in infants using Tc-99m DTPA.

Glomerular filtration rate obtained by using Tc-99m DTPA was compared with that obtained from Schwartz's formula using serum creatinine and length in 21 infants (age range, 3 to 348 days). The GFR (mean +/- SD) obtained by Tc-99m DTPA was 76 +/- 37 ml/min per 1.73m2 and by the Schwartz formula was 83 +/- 49 ml/min per 1.73m2. GFR by Tc-99m DTPA method overestimated GFR by 3.6% compared to the Schwartz method. The imaging technique and the advantages are discussed.

Glomerular Filtration Rate↗
PubMed1991

Baseline sister chromatid exchange in human cell lines with different levels of poly(ADP-ribose) polymerase.

Poly(ADP-ribose) polymerase is a chromatin enzyme which adds long chains of ADP-ribose to various acceptor proteins in response to DNA strand breaks. Its primary function is unknown; however, a role in DNA repair and radiation resistance has been postulated based largely on experiments with enzyme inhibitors. Recent reports of mutant cell lines, deficient in poly(ADP-ribose) polymerase activity, have supported previous studies with inhibitors, which suggests the involvement of poly(ADP-ribose) polymerase in maintaining baseline levels of sister chromatid exchanges. Mutant cells with even slightly depressed enzyme levels show large elevation of baseline sister chromatid exchanges. Since intracellular poly(ADP-ribose) polymerase levels can vary greatly between different nonmutant cell lines, we surveyed levels of baseline sister chromatid exchange in normal and tumor human cell lines and compared them with endogenous levels of poly(ADP-ribose) polymerase. Despite 10-fold differences in poly(ADP-ribose) polymerase, the baseline level of sister chromatid exchanges remained relatively constant in the different cell lines (0.13 +/- 0.03 SCE/chromosome), with no indication of a protective effect for cells with high levels of the enzyme.

Humans↗
PubMed1990

Neuroimaging findings in Alexander's disease.

We present the findings from magnetic resonance imaging, computed tomographic scan, and single photon emission computed tomography of the brain in a 2-year-old girl with Alexander's disease. Computed tomographic scans showed prominent low-density white matter throughout the cerebral hemispheres. Magnetic resonance imaging showed increased T2 signal from the cerebral white matter but not the cerebellum or brain stem. Single photon emission computed tomography revealed diminished cerebral metabolism, particularly in the frontal regions, as compared with the cerebellum.

Astrocytes↗
PubMed1989

Absorption of Tc-99m pertechnetate from the augmented bladder during direct nuclear cystography.

A retrospective review comparing bladder absorption of pertechnetate and Tc-99m sulfur colloid from the augmented bladder was performed. Based upon the author's findings, the routine use of Tc-99m sulfur colloid in this patient population is recommended to prevent the erroneous diagnosis of vesicoureteral reflux and miscalculation of GFR due to the presence of background soft-tissue and blood activity.

Glomerular Filtration Rate↗
PubMed1988

Arabinofuranosyl nucleosides induce common fragile sites.

The capacities for fragile site induction of three inhibitors of semiconservative DNA synthesis and DNA repair synthesis, aphidicolin, arabinofuranosyl cytosine, and arabinofuranosyl adenosine were compared. Aphidicolin is known to induce type 4 fragile sites, the largest recognized group of common fragile sites. Although the modes of action of these inhibitors vary, both arabinofuranosyl analogs induce type 4 aphidicolin-sensitive fragile sites. An analysis of variance demonstrates that the three inhibitors are not equally capable of inducing significant breakage (P less than 0.01) at all type 4 fragile sites. Induction of type 4 fragile sites appears to be a general consequence of inhibition of DNA polymerization.

Aphidicolin↗