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Biomedical subjects

B Issa

Publications and source records attributed to B Issa.

14 recordsLinked to original sources
PubMed1998

Variegated aneuploidy in two siblings: phenotype, genotype, CENP-E analysis, and literature review.

Cytogenetic studies of 2 sisters with mild microcephaly, growth deficiency, and mild errors of morphogenesis demonstrated a unique combination of multiple trisomies, most often involving chromosomes 8 and 18 either together as sole trisomies or in combination with other chromosomes. Since neither sib has phenotypic anomalies associated with trisomy 8 or 18 mosaicism, the trisomies likely did not occur during embryogenesis, but later possibly due to a predisposition for mitotic instability. To determine if the observed chromosome instability may be related to centromere function, metaphase cells were characterized by immunofluorescence of the centromere protein, CENP-E. Hybridization of CENP-E antibodies, in combination with in situ hybridization of a chromosome 8 or 18 alpha-satellite probe, showed hybridization to chromosomes 8 and 18 in both normal and aneuploid cells from each patient. These data indicate that the chromosomes in each child contain functional and active centromeres. The clinical and cytogenetic findings in these 2 individuals are compared with 7 other previously reported individuals, each of whom have similar findings. Together, these studies support the notion that a recessive mitotic mutant may be responsible for the chromosomal mosaicism and for the resulting clinical phenotype.

Centromere↗
PubMed1997

Demonstration of changes in fetal liver erythropoiesis using echo-planar magnetic resonance imaging.

This study investigated the variation in magnetic resonance characteristics of the fetal liver during a time of changing erythropoietic function. Echo-planar imaging was carried out in 25 normal pregnant women at 20 and 26 wk gestation. The signal intensity from regions of the fetal liver, background image, and maternal back muscle and the highest signal intensity from the maternal spinal cord were measured and compared with the signal intensity of amniotic fluid. Data are expressed as ratios, in arbitrary units (median pixel values; interquartile range shown in parentheses), and analyzed with the use of Wilcoxon's signed-rank test. At 20 wk, the signal intensity ratio of liver to amniotic fluid was 0.309 (0.231-0.365). At 26 wk, the ratio was 0.544 (0.429-0.616). The change was highly significant (P < 0.0001). No change in the signal intensity ratios of amniotic fluid compared with other measured parameters was noted. These data are consistent with known changes in fetal liver erythropoiesis occurring between 20 and 26 wk gestation and have potential use in early noninvasive physiological assessment of the fetus.

Adult↗
PubMed1996

A microscopic model of fluid transport in porous rocks.

NMR measurements of water velocity flowing through two different porous rocks, Bentheimer and Clashach, have been made using the PEPI sequence. Random changes of localised velocity occur in both materials even though the average velocities across the core cross-sections follow Darcy's Law. The velocity distributions are approximately Gaussian and the velocity variance follows a linear relationship with mean velocity as predicted in the stochastic theory of Mansfield and Issa. The origin of the large fluctuations in localised velocity is thought to be hydrodynamic and a detailed theory of intervoxel coupling is presented, which accounts for such behaviour in a coupled voxel array. In this work the intervoxel coupling is restricted to isolated voxel pairs.

Echo-Planar Imaging↗
PubMed1996

Transient flow through porous rocks studied by PEPI.

The transient behaviour of fluid flow through porous rocks is examined using the high speed pi-modified echo-planar imaging technique (PEPI). Spatially resolved flow maps show the change in velocity, as the bulk flow rate is increased or decreased in large steps in the approach to steady state for two sandstone samples of different porosity and permeability. Different rise and fall settling times are observed for these rocks. In addition, the area occupied by significant flow and the variance of the velocity distributions are calculated during the transient state.

Echo-Planar Imaging↗
PubMed1996

Simulating MRI flow maps in porous rocks: a new approach.

The Mansfield and Issa model of voxel pair coupling is extended using electrical circuit simulation to interacting voxel clusters comprising all configurations of contiguous voxels up to and including four voxels. This information is used to simulate flow through porous rock samples by calculating the expected velocity distributions found in porous rocks using the PEPI rapid NMR imaging technique.

Computer Simulation↗
PubMed1996

Desensitisation of somatostatin, TRH and GHRH responses to glucose in the diabetic (Goto-Kakizaki) rat hypothalamus.

We have studied the effects of glucose on the release of somatostatin (SS), TRH and GHRH from incubated hypothalami of normal and genetically diabetic, Goto-Kakizaki (GK) rats. The active isomer D-glucose caused a dose-related inhibition of SS, TRH and GHRH from normal rat hypothalami over a 20-min incubation period in vitro. In contrast, in GK rats the effects of glucose on TRH and SS were significantly reduced and the effects on GHRH were abolished. These data indicate that the sensitivity of SS-, TRH- and GHRH-producing hypothalamic neurones is reduced in diabetic rats. The effect is most pronounced for GHRH release as there was no change in the release of this peptide with increasing glucose concentrations. In conclusion, it appears that the diabetic state in GK rats causes differential desensitisation (GHRH > TRH and SS) of neuronal responses to subsequent changes in glucose concentrations in vitro. This may be due to alterations in the neurotransmitter control and/or a reduction in number, affinity or function of glucose transporters on these peptidergic neurones or other intermediary neuronal pathways.

Animals↗
PubMed1995

Cytogenetic findings in a case of congenital mesoblastic nephroma.

Congenital mesoblastic nephroma (CMN) is a benign, but locally aggressive, renal tumor of early infancy. Few metastases have been reported, but local recurrence is well documented. CMN is histologically distinct from Wilms' tumor and other childhood renal tumors, and is typically treated by surgical excision without adjuvant therapy. Cytogenetic abnormalities in these tumors have been described and are often compared with abnormalities seen in leiomyomas, fibromatoses, and infantile fibrosarcomas. In particular, trisomy 11 has been suggested as a nonrandom occurrence in CMNs. We describe a case of CMN in a 4-month-old female infant. The diagnostic histologic features included a monophasic mesenchymal appearance, prominent staghorn vascular spaces, and extensive infiltration of the adjacent kidney. Cytogenetic analysis showed a hyperdiploid chromosome number and a single structural abnormality involving a translocation between chromosomes 12 and 15. The composite karyotypic interpretation was: 46-47,XX,-X, +8, +11,t(12;15)(p12;q25), +17, +20[cp14]. The significance of karyotypic changes in this tumor is currently unknown. A genetic basis for histologic variability and progression may exist if certain cytogenetic abnormalities, such as trisomy 11 or specific translocations, confer a proliferative advantage. Additional cases are required to correlate cytogenetic findings with the biologic behaviors of CMN. We present this case as a contribution to existing literature describing these relatively rare and interesting renal tumors.

Female↗
PubMed1995

Echo-planar magnetic resonance imaging to assess water volume in the distal small bowel.

PURPOSE: Assessment of fluid volumes and flow through the small intestine has in the past only been possible by means of invasive intubation studies on human volunteers. Intubation very likely disturbs gut motility and stimulates secretion. METHODS: The aim of this study was to utilise the new technique of echo-planar magnetic resonance imaging in order to non-invasively visualise the changing volume of water in the small intestinal lumen. 200 mls of test solution was ingested and water volume assessed using a multi-slice scanning technique on 3 separate days. The solutions were pure water, pure water plus 2.264 or 10 g of mannitol. These were taken on separate days by 8 healthy male volunteers. Regions of interest were constructed in the area of the lower pelvis excluding retroperitoneal structure. RESULTS: The water content of the lower small intestine did not change significantly over the 4 hours after the control solution. By contrast after both mannitol solutions there was an increase in the amount of water in the distal intestine as assessed by the area under the curve of the volume time profile (Control 51 ml.h (SD +/- 47); mannitol 2.264 g/200 ml 72 ml.h (SD +/- 57); 10 g/200 ml mannitol 115 ml.h (SD +/- 56)). Page's L Trend test showed that the trend for the volume to increase with increasing mannitol concentration to be statistically significant at the 1% level (L = 108). CONCLUSIONS: The study highlights the potential of echo-planar magnetic resonance imaging to visualise changes in gastrointestinal physiology in a noninvasive manner.

Adult↗
PubMed1994

Multiple congenital anomalies in a man with (X;6) translocation.

X;autosome translocations in humans, often associated with congenital anomalies or with gonadal dysgenesis syndromes, are informative for the study of X-linked gene expression and of the phenomenon of X chromosome inactivation. When such translocations occur in association with multiple congenital anomaly (MCA) syndromes, the observed phenotypes are not always attributable solely to disruption of specific genes, if X-inactivation spreads onto the translocated autosome, rendering some distal genes inactive. We report on a man with multiple congenital anomalies and a maternally inherited (X;6)(p22.1;p25) translocation. He has abnormalities not described in the Klinefelter or 6p deletion syndromes. His unique findings constitute a recognizable syndrome, which is likely caused by disomy for a region of Xp in conjunction with a partial 6p deletion.

Abnormalities, Multiple↗
PubMed1994

Permeability estimation from T1 mapping.

Fluids permeating a solid matrix can interact strongly with the pores in which they are contained. Enhanced relaxation behaviour over that of the bulk water can ensue due to the presence of paramagnetic centres or to exchange with bound water at the pore surface. In the latter case, the ratio of pore surface to the pore volume is effective in the relaxation behaviour. NMR provides an effective tool for investigating the solid matrix properties (e.g., pore size distribution) via indirect measurement of the fluid NMR parameters. In addition to spin density, we use T1 mapping to provide an estimate of the specific permeability of sandstone for a few samples.

Echo-Planar Imaging↗
PubMed1994

Studies of fluid transport in porous rocks by echo-planar MRI.

Attempts to quantify the permeability constant that appears in Darcy's equation in terms of the porosity, tortuosity and surface area have been made by Kozeny and Carman. These results in turn have been translated by Seevers into expressions involving spin-lattice relaxation times. When this work was done originally in the mid-1960s, NMR imaging and spatially localised T1 maps had not been invented. Therefore, bulk T1 average values were used and it is not surprising to see substantial deviations from predicted permeabilities in bore core material. In this paper we re-examine the Kozeny-Carman and Seevers theories in the light of new techniques development for the localised measurement of both T1 maps and fluid velocity maps. New results show spatially correlated T1 and flow maps obtained from Bentheimer sandstone samples. These are discussed in terms of a localised permeability constant. By this means we show that the relationship between T1 and permeability does not hold at the local level for isolated pixels within a larger specimen.

Echo-Planar Imaging↗
PubMed1989

Prenatal diagnosis of a large heteromorphic region in a chromosome 5: implications for genetic counseling.

We performed an amniotic fluid chromosome study at 16 weeks of gestation because of advanced maternal age. G-band chromosome analysis demonstrated that one 5q was significantly longer than its homologue. The region subjacent to the centromere appeared similar to a 9qh region. Subsequent Giemsa-11 and C-band staining results of this area were positive. Cytogenetic studies in this family demonstrated several other individuals who have the same chromosome 5qh+ as the proposita. All are asymptomatic. The clinical insignificance of the chromosome heteromorphism in this family readily demonstrates the need for special cytogenetic and family chromosome studies before performing genetic counseling.

Centromere↗