Extramedullary myeloid cell tumours localised to the mediastinum: a rare clinicopathological entity with unique karyotypic features

Extramedullary myeloid cell tumour (EMMT) localised to the mediastinum is a rare manifestation of acute myeloid leukaemia, forming less than 4% of all cases of EMMT. In contrast to other types of EMMT, cytogenetic characteristics of this rare entity are relatively unknown. This report describes a patient with EMMT who had evidence of superior vena cava syndrome and normal peripheral blood counts at diagnosis. The results from an initial biopsy specimen were consistent with a diagnosis of mediastinal large B cell lymphoma. A diagnosis of acute myeloid leukaemia was made three months after initial diagnosis by bone marrow examination. Review of the initial biopsy specimen showed strong positivity for myeloperoxidase, revealing that the patient had been initially misdiagnosed as having large B cell lymphoma. Cytogenetic studies revealed a near triploid and near tetraploid karyotype with structural abnormalities in 12 and three metaphases, respectively. Review of the literature showed that a near tetraploid or triploid karyotype is found in most of the reported cases of mediastinal EMMT. Thus, the presence of a near triploid/tetraploid karyotype and mediastinal EMMT may represent a specific subset of EMMT. The biological relevance of this observation is discussed.     

Ultimate tensile strength of dentin: Evidence for a damage mechanics approach to dentin failure

Dentin structure and properties are known to vary with orientation and location. The present study explored the variation in the ultimate tensile strength (UTS) of dentin with location in the tooth. Hourglass specimens were prepared from dentin located in the center, under cusps, and in the cervical regions of human molar teeth. These were tested in tension at various distances from the pulp. Median tensile strengths ranged from 44.4 MPa in the inner dentin near the pulp, to 97.8 MPa near the dentino-enamel junction (DEJ). This increase in the median UTS with distance from the pulp to the DEJ was statistically significant (P <.001). Of particular importance was the observation that the UTS measurements followed a Weibull probability distribution, with a Weibull modulus of about 4.5. The Weibull behavior of the UTS data strongly suggests that the large variances in fracture strength data result from a distribution of preexisting defects in the dentin. These findings justify a damage-mechanics approach to studies of dentin failure.     

The Schizosaccharomyces pomberfc3 + gene encodes a homologue of the human hRFC36 and Saccharomyces cerevisiae Rfc3 subunits of replication factor C

In the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe replication factor C (RF-C) plays key roles both in chromosomal DNA replication and in DNA replication checkpoint function. At the replication fork, the five-subunit RF-C complex functions to load the trimeric polymerase accessory factor PCNA onto DNA. PCNA then acts as a sliding clamp, tethering Pol δ to the DNA to maximise its processivity. Here we describe the cloning of the S. pomberfc3 ⁺ gene, encoding a homologue of the S. cerevisiae Rfc3 and human hRFC36 proteins. The 1026 bp rfc3 ⁺ ORF is interrupted by five introns, ranging in size from 49 to 165 bp. The spliced ORF is predicted to encode a 342 amino-acid protein that is approximately 50% identical at the amino acid sequence level to the S. cerevisiae Rfc3 and human hRFC36 proteins. As expected, S. pomberfc3 ⁺ is an essential gene, with rfc3Δ cells being defective for DNA replication. Loss of rfc3 ⁺ function can be rescued by heterologous expression of either the S. cerevisiae Rfc3 or human hRFC36 proteins in S. pombe. Received: 15 October 1999     

Recognition surfaces of MHC class I

Summary: Recent crystallographic results have provided dose to atomic resolution views of the recognition events mediated by MHC class I molecules. The specificity-conferring interaction of MHC class I/peptide with a T-cell antigen receptor (TCR) appears dependent on certain key interactions with the MHC scaffold. These interactions, in particular those of the TCR Va domain, define a standard orientation for TCR binding. Previous studies on biologically significant variations in the TCR recognition surface presented by a series of MHC/variant peptide complexes can be reassessed in the light of this TCR-building mode. The interaction of CDS with MHC class I resembles that between antibody and antigen in the use of loops from the CD8 structure. The interaction is of very low affinity and buries equivalent surface area to that between the TCR and MHC class I but while the TCR/MHC interface shows poor surface shape complementarity the match in the conservative interaction between MHC and CDS is precise.     

Neural projections of the preoptic-suprachiasmatic region to the median eminence in the rat: A quantitative autoradiographic study

The possibility of a preferential distribution of projections from the preoptic-suprachiasmatic region (POA-Sch) to the median eminence in the male rat was studied using autoradiographic and computer procedures. A cocktail of [3H]leucine-[3H]proline was injected into the POA-Sch. Animals were killed after either 1, 4, or 24 h of incorporation time (IT). The number of silver grains per 25-micron square was counted throughout the median eminence. Squares with silver grain densities at or above the 75 percentile of the population for any given IT group were labeled as "concentrating areas." The distribution of these concentrating areas in median eminence tissue was analyzed utilizing univariate procedures. Visual inspection of the distribution of silver grain densities in a rostrocaudal fashion indicated the likelihood of uneven distribution; however, these differences were not statistically significant. In the dorsoventral plane, results indicated that the highest silver grain density was at 50 to 75 micron from the floor of the 3rd ventricle. Such distribution was apparent both ipsi- and contralateral to the injection site, but was greater on the ipsilateral side.     

Electroconvulsive Therapy in Two Former Neurosurgical Patients: Skull Prosthesis and Ventricular Shunt

Electroconvulsive therapy (ECT) was successfully used to treat patients with prior neurosurgical history. The first patient had undergone surgery for a meningioma with subsequent insertion of a plate in the cranium. The second patient had a history of normal pressure hydrocephalus which was treated with a ventriculoperitoneal shunt procedure. Both patients received ECT and in both cases the presenting symptoms of depression abated. Treatment was considered both uneventful and successful.     

Maturational topography of the visual evoked potential in fetal lambs

The normal maturational course of the visual evoked potential (VEP) in human newborns and infants is well documented. Unfortunately, there is a paucity of data about VEP maturation in the normal preterm infant. Since this population is at risk to develop many abnormalities affecting the VEP (intraventricular hemorrhage, hydrocephalus, and retinopathy of prematurity), one must question whether such VEP data collected from this group is representative of normal maturation. To provide normative parametric developmental data we have been studying VEP development in fetal lambs. Six fetal lambs between 105 and 120 days gestational age were externalized and surgically instrumented with subcutaneous recording electrodes placed over the occipital and parietal regions. High-intensity light-emitting diodes (LEDs) externalized fiberoptic cables were secured adjacent to the orbit. from 108 to 141 days gestation, fetal VEPs were recorded in response to bright flash stimulation and the maturational topography was investigated.Over the occipital regions, the emergence of major positivities at P400 and P650 were observed beginning around 120 days gestation. Over the parietal area, the emergence of P200 and P500 components was observed by 128 days gestation. The latency-maturation functions revealed that the slope of the parietal function was steeper than the occipital counterpart, suggesting that the maturation of parietal neurons occurs at a faster rate than neuronal development in the occipital regions.     

Incidence and specificity of interference in two-site immunoassays

Using a modified "two-site" immunoradiometric assay, termed an "interference assay," we have demonstrated the occurrence of non-analyte antibody-binding substances in approximately 40% of serum samples. These substances multivalently bind antibodies from any of several species at a site other than the antigen-binding site. Using a two-site immunoradiometric assay for human choriogonadotropin, we have investigated their effect on analyte quantification. In this system these antibody-binding substances mimic the presence of analyte; when analyte is actually present, they can also cause over- or underestimates. Addition of excess nonspecific immunoglobulin from an appropriate species eliminates this interference. However, the amount of nonspecific immunoglobulin added to an assay system may not always be enough to block interference in all samples.     

Informed consent: patient information forms in chemotherapy trials

Documentation of informed consent by patients entering clinical trials is an ethical and legal necessity. Federal regulations and judicial opinions have led to increasingly lengthy, detailed "consent" forms, yet published studies demonstrate that patients remain confused about the nature and anticipated consequences of study entry. It has been suggested that more detail may even alarm or further confuse patients. Seventy-five women undergoing chemotherapy for advanced breast cancer participated in this study which assessed patient preference for long-, medium-, or short-form length, and whether form length preference correlated with patient characteristics or indicators of patient autonomy in decision-making or physician dependency. Patient preferences for information were not predicted by the patient autonomy or physician dependency scores or by age, marital status, or level of education. The majority of patients expressed a preference for more detailed information about their treatment, yet a majority of patients given detailed forms answered questions basic to the study design incorrectly, irrespective of educational level. The increased detail included in the long forms was not reported to increase stress compared to the short forms. Patient information forms are a principal tool for informing patients for consent but if they are to perform their desired function they must be designed more carefully and evaluated more thoroughly than in the past.