Functional analysis of secreted and transmembrane proteins critical to mouse development.

We describe the successful application of a modified gene-trap approach, the secretory trap, to systematically analyze the functions in vivo of large numbers of genes encoding secreted and membrane proteins. Secretory-trap insertions in embryonic stem cells can be transmitted to the germ line of mice with high efficiency and effectively mutate the target gene. Of 60 insertions analyzed in mice, one-third cause recessive lethal phenotypes affecting various stages of embryonic and postnatal development. Thus, secretory-trap mutagenesis can be used for a genome-wide functional analysis of cell signaling pathways that are critical for normal mammalian development and physiology.

Rethinking the genetic architecture of schizophrenia.

BACKGROUND: For many years, the prevailing paradigm has stated that in each individual with schizophrenia (SZ) the genetic risk is due to a combination of many genetic variants, individually of small effect. Recent empirical data are prompting a re-evaluation of this polygenic, common disease-common variant (CDCV) model. Evidence includes a lack of the expected strong positive findings from genome-wide association studies and the concurrent discovery of many different mutations that individually strongly predispose to SZ and other psychiatric disorders. This has led some to adopt a mixed model wherein some cases are caused by polygenic mechanisms and some by single mutations. This model runs counter to a substantial body of theoretical literature that had supposedly conclusively rejected Mendelian inheritance with genetic heterogeneity. Here we ask how this discrepancy between theory and data arose and propose a rationalization of the recent evidence base. METHOD: In light of recent empirical findings, we reconsider the methods and conclusions of early theoretical analyses and the explicit assumptions underlying them. RESULTS: We show that many of these assumptions can now be seen to be false and that the model of genetic heterogeneity is consistent with observed familial recurrence risks, endophenotype studies and other population-wide parameters. CONCLUSIONS: We argue for a more biologically consilient mixed model that involves interactions between disease-causing and disease-modifying variants in each individual. We consider the implications of this model for moving SZ research beyond statistical associations to pathogenic mechanisms.

Balloon valvuloplasty of valvular pulmonary stenosis in a neonatal foal.

In a 1-day old filly with a loud heart murmur, transthoracic echocardiography revealed right ventricular hypertrophy associated with severe pulmonary valvular stenosis and a transvalvular pressure gradient (between right ventricle and pulmonary artery) of 125 mmHg. Computed tomographic angiography confirmed the finding, with no evidence of other relevant concurrent abnormalities. Balloon valvuloplasty was performed using a single balloon technique. The foal recovered well from anaesthesia. Following the procedure, the right ventricle-pulmonary artery transvalvular gradient decreased to 38 mmHg. At follow up examinations after 1 month, 1 year and 2 years, the filly showed normal exercise capacity and echocardiography confirmed the persistent substantial improvement in the transvalvular outflow gradient.

Quantification of left atrial wall motion in healthy horses using two-dimensional speckle tracking.

INTRODUCTION: The mechanical function of the left atrium (LA) plays a pivotal role in modulation of left ventricular filling. Assessment of LA function might be a clinically useful prognostic tool for horses with mitral regurgitation or atrial fibrillation. However, the most accurate, reliable, and clinically useful methods to assess LA myocardial function are yet to be determined. The objective of this study was to describe the methods for quantification of LA wall motion using two-dimensional speckle tracking (2DST) echocardiography in healthy Warmblood horses to quantify measurement variability, to calculate reference intervals for 2DST variables, and to investigate their relationship to sex, age, body weight, and heart rate. ANIMALS, MATERIALS, AND METHODS: Twenty-six healthy Warmblood horses were included. 2DST analyses of LA wall motion were performed on digitally stored cine-loop recordings of a standardized right-parasternal four-chamber view focusing on the LA. Longitudinal strain, longitudinal strain rate, and time to peak LA contraction were measured to characterize LA contractile, reservoir, and conduit function. Intraobserver and interobserver measurement variability was quantified, and reference intervals were calculated. RESULTS: The coefficient of variation for intraobserver and interobserver measurement variability ranged between 2.0-11.1% and 5.1-15.4%, respectively, for global strain, strain rate, and time to peak LA contraction. Reference intervals for healthy Warmblood horses were reported. CONCLUSION: This study shows that 2DST is a feasible and reliable method to quantify LA wall motion throughout the cardiac cycle in healthy Warmblood horses. Further studies are required to establish the clinical value of 2DST for assessment of LA function.

Dense core secretory vesicles revealed as a dynamic Ca(2+) store in neuroendocrine cells with a vesicle-associated membrane protein aequorin chimaera.

The role of dense core secretory vesicles in the control of cytosolic-free Ca(2+) concentrations ([Ca(2+)](c)) in neuronal and neuroendocrine cells is enigmatic. By constructing a vesicle-associated membrane protein 2-synaptobrevin.aequorin chimera, we show that in clonal pancreatic islet beta-cells: (a) increases in [Ca(2+)](c) cause a prompt increase in intravesicular-free Ca(2+) concentration ([Ca(2+)]SV), which is mediated by a P-type Ca(2+)-ATPase distinct from the sarco(endo) plasmic reticulum Ca(2+)-ATPase, but which may be related to the PMR1/ATP2C1 family of Ca(2+) pumps; (b) steady state Ca(2+) concentrations are 3-5-fold lower in secretory vesicles than in the endoplasmic reticulum (ER) or Golgi apparatus, suggesting the existence of tightly bound and more rapidly exchanging pools of Ca(2+); (c) inositol (1,4,5) trisphosphate has no impact on [Ca(2+)](SV) in intact or permeabilized cells; and (d) ryanodine receptor (RyR) activation with caffeine or 4-chloro-3-ethylphenol in intact cells, or cyclic ADPribose in permeabilized cells, causes a dramatic fall in [Ca(2+)](SV). Thus, secretory vesicles represent a dynamic Ca(2+) store in neuroendocrine cells, whose characteristics are in part distinct from the ER/Golgi apparatus. The presence of RyRs on secretory vesicles suggests that local Ca(2+)-induced Ca(2+) release from vesicles docked at the plasma membrane could participate in triggering exocytosis.

Genetic analysis of Netrin genes in Drosophila: Netrins guide CNS commissural axons and peripheral motor axons.

Two tandem Netrin genes in Drosophila are expressed at the midline of the developing CNS and in different subsets of neurons, muscles, and epidermal patches. In embryos carrying a small deficiency that deletes both genes, CNS axon commissures are partially missing or thinner. This phenotype is rescued by expressing either Netrin gene at the midline. Pan-neural expression of either gene causes disruption of commissural and longitudinal tracts, indicating that the pattern of Netrin expression is crucial and that Netrins function as instructive cues. The double mutant also shows defects in motor axon projections. Expression of either Netrin gene in all muscles also results in aberrant motor projections. Thus, Drosophila Netrins are required for the guidance of commissural axons at the midline, and of motor axons to their target muscles.

Plasma homocysteine concentrations in healthy horses and horses with atrial fibrillation.

INTRODUCTION: Homocysteine (HCY) is an amino acid produced from methionine metabolism. Plasma homocysteine concentrations ([HCY]p) are elevated (>13 µmol/L) in people with atrial fibrillation (AF) and can predict the recurrence of AF after cardioversion. This study aimed to validate a commercially available human HCY assay for use in horses to develop reference intervals for [HCY]p and compare [HCY]p in healthy horses and horses with AF. ANIMALS: Healthy horses (n = 27) and horses with AF (n = 55, 34 of which were cardioverted using transvenous electrical cardioversion). MATERIALS AND METHODS: Blood samples were analysed for HCY using an automated enzyme-cycling assay (Homocysteine Cobas C, Integra, Roche) and creatinine (compensated Jaffe method). Assay linearity and precision were assessed, reference intervals calculated and [HCY]p and creatinine compared between groups. RESULTS: The assay was precise (coefficient of variation 1.6-4.3%, n = 10 repetitions) and provided linear results (r = 0.99 for spiked and natural samples) for a range of [HCY]p. The reference interval for [HCY]p was 1.5-7.8 µmol/L. The plasma concentration of homocysteine was 4.65 ± 1.5 µmol/L (mean ± standard deviation) in healthy horses and 4.65 ± 1.72 µmol/L in horses with AF (p=0.99); [HCY]p was not associated with recurrence of AF (n = 18, p=0.97). A weak, positive correlation between plasma creatinine and [HCY]p was detected (r = 0.295, p=0.008, r2 = 0.11). CONCLUSIONS: This assay allows precise measurement of [HCY]p in horses. Unlike in people, [HCY]p is not increased in horses with AF and cannot predict AF recurrence. This might be due to differences in the underlying pathological mechanisms of AF development in people and horses.

Echocardiographic Assessment of Left Ventricular Function in Healthy Horses and in Horses with Heart Disease Using Pulsed-Wave Tissue Doppler Imaging.

BACKGROUND: Assessment of left ventricular (LV) function by tissue Doppler imaging (TDI) is not well established in horses with heart disease. OBJECTIVES: To describe the use of pulsed-wave (PW) TDI for the assessment of LV function, establish reference intervals, investigate effects of mitral regurgitation (MR), aortic regurgitation (AR), and primary myocardial disease (MD), and provide proof of concept for the use of PW TDI in Warmblood horses with heart disease. ANIMALS: Thirty healthy horses, 38 horses with MR, 25 with AR, 8 with MD. METHODS: Echocardiograms were retrospectively analyzed. Reference intervals were calculated. PW TDI indices of healthy horses and horses with MR, AR, and MD were compared by one-way ANOVA and Dunnett's test. RESULTS: A complete set of PW TDI variables could be obtained in 94 of 101 horses. Variables corresponding to isovolumic intervals were most difficult to measure. Valvular regurgitation influenced variables describing isovolumic contraction and ejection. Horses with MD had significantly shortened ETm (-118.5 [-154.1 to -82.9] ms; mean difference [95% CI of difference of means]), increased PEPm /ETm (0.11 [0.05 to 0.17]), prolonged IMPm (0.28 [0.18 to 0.37]), increased S1 (8.9 [5.2 to 12.6] cm/s), and decreased E1 (-2.6 [-4.7 to -0.5] cm/s), Em (-14.2 [-19.9 to -8.5] cm/s), and Em /Am ratio (-1.6 [-2.6 to -0.6]). CONCLUSIONS AND CLINICAL IMPORTANCE: Pulsed-wave TDI might be useful for detection of LV dysfunction in horses with primary MD. The clinical value of TDI in horses with MR and AR remains uncertain.

Rural-urban differences in the presentation, management and survival of breast cancer in Western Australia.

From all women diagnosed with invasive breast cancer in 1999 in Western Australia, rural and urban women were compared with regard to mode of detection, tumour characteristics at presentation, diagnostic investigations, treatment and survival. Women from rural areas with breast cancer (n=206, 23%) were less likely to have open biopsy with frozen section (P<0.001), breast-conserving surgery (P<0.001), adjuvant radiotherapy (P=0.004) and hormonal therapy (P=0.03), and were less likely to be treated by a high caseload breast cancer surgeon (P<0.001). Adjusting for age and tumour characteristics, rural women had an increased likelihood of death within 5 years of breast cancer diagnosis (HR 1.62, 95% CI 1.10-2.38). This difference was not significant after adjustment for treatment factors (HR 1.36, 95% CI 0.90-2.04).

Echocardiographic Assessment of Left Atrial Size and Function in Warmblood Horses: Reference Intervals, Allometric Scaling, and Agreement of Different Echocardiographic Variables.

BACKGROUND: Echocardiographic assessment of left atrial (LA) size and function in horses is not standardized. OBJECTIVES: The aim of this study was to establish reference intervals for echocardiographic indices of LA size and function in Warmblood horses and to provide proof of concept for allometric scaling of variables and for the clinical use of area-based indices. ANIMALS: Thirty-one healthy Warmblood horses and 91 Warmblood horses with a primary diagnosis of mitral regurgitation (MR) or aortic regurgitation (AR). METHODS: Retrospective study. Echocardiographic indices of LA size and function were measured and scaled to body weight (BWT). Reference intervals were calculated, the influence of BWT, age, and valvular regurgitation on LA size and function was investigated and agreement between different measurements of LA size was assessed. RESULTS: Allometric scaling of variables of LA size allowed for correction of differences in BWT. Indices of LA size documented LA enlargement with moderate and severe MR and AR, whereas most indices of LA mechanical function were not significantly altered by valvular regurgitation. Different indices of LA size were in fair to good agreement but still lead to discordant conclusions with regard to assessment of LA enlargement in individual horses. CONCLUSIONS AND CLINICAL IMPORTANCE: Allometric scaling of echocardiographic variables of LA size is advised to correct for differences in BWT among Warmblood horses. Assessment of LA dimensions should be based on an integrative approach combining subjective evaluation and assessment of multiple measurements, including area-based variables. The clinical relevance of indices of LA mechanical function remains unclear when used in horses with mitral or aortic regurgitation.

Disrupted in schizophrenia 1 (DISC1) L100P mutants have impaired activity-dependent plasticity in vivo and in vitro.

Major neuropsychiatric disorders are genetically complex but share overlapping etiology. Mice mutant for rare, highly penetrant risk variants can be useful in dissecting the molecular mechanisms involved. The gene disrupted in schizophrenia 1 (DISC1) has been associated with increased risk for neuropsychiatric conditions. Mice mutant for Disc1 display morphological, functional and behavioral deficits that are consistent with impairments observed across these disorders. Here we report that Disc1 L100P mutants are less able to reorganize cortical circuitry in response to stimulation in vivo. Molecular analysis reveals that the mutants have a reduced expression of PSD95 and pCREB in visual cortex and fail to adjust expression of such markers in response to altered stimulation. In vitro analysis shows that mutants have impaired functional reorganization of cortical neurons in response to selected forms of neuronal stimulation, but there is no altered basal expression of synaptic markers. These findings suggest that DISC1 has a critical role in the reorganization of cortical plasticity and that this phenotype becomes evident only under challenge, even at early postnatal stages. This result may represent an important etiological mechanism in the emergence of neuropsychiatric disorders.

Intolerance of eight ounces of milk in healthy lactose-intolerant teen-agers.

The ability of lactose-intolerant individuals to tolerate 8 ounces of milk was determined in healthy teen-agers. Thirty-two blacks were studied with 50-gm lactose tolerance tests. Nineteen (59%) had a flat blood sugar curve and 13 (39%) also developed bloating, cramps, loose stools, or diarrhea with the test. These latter 13 were defined as lactose-intolerant. Seven of the 13 lactose-intolerant teen-agers (54%) developed abdominal bloating and/or cramps after drinking 8 ounces of milk (half-pint). None had diarrhea. Eight were symptomatic with the equivalent amount of lactose (12 gm) while only one had symptoms with the monosaccharide components of lactose, glucose and galactose. The symptoms with milk and 12 gm of lactose were less severe than with the 50-gm tolerance test. A history of a prior awareness of milk intolerance was obtained from 11 of the 13 lactose-intolerant subjects. At least one half of lactose intolerant teen-agers might be expected to be symptomatic after drinking 8 ounces of milk without other food. Milk intolerance should be considered in the nutritional planning for teen-agers with special attention to members of population groups with a high prevalence of lactose intolerance.

fMRI evidence of age-related hippocampal dysfunction in feature binding in working memory.

Richly detailed memories for particular events depend on processes that bind individual features of experience together. Previous cognitive behavioral research indicates that older adults have more difficulty than young adults in conditions requiring feature binding. We used functional magnetic resonance imaging (fMRI) during a working memory task to identify neural substrates of this age-related deficit in feature binding. For young, but not older, adults there was greater activation in left anterior hippocampus on combination trials (remember objects together with their locations) than on trials in which participants were told to remember only which objects or only which locations occurred. The results provide neuroimaging evidence for an age-related hippocampal dysfunction in feature binding in working memory.

Traditional predictors of performance in medical school.

This paper addresses the predictive value for performance in medical school of undergraduate grades, the Medical College Admission Test (MCAT), information on the selectivity of the undergraduate institution, and selected transcript data. The performance data examined were basic science grades; clinical science grades; scores on National Board of Medical Examiners examinations, Parts I, II, and III; and information on academic difficulty. Methodological sources of differences in validity data, including restriction in range, criterion attenuation, and method specificity, are discussed. Reported validity data affirm the substantial value of traditional academic predictors of performance in medical school. Selection committees should, nevertheless, supplement academic data with nonacademic and interview information. Their inclusion is particularly important for minority and disadvantaged applicants. Medical schools should assess the validity of their selection systems. Additional research on the relations between academic predictors and performance-based indexes of clinical competence and on the role of traditional predictors with regard to the recently declining medical school applicant pool is suggested.

Score reporting for the 1991 Medical College Admission Test.

In December 1988, a 16-member advisory panel, made up of medical school deans, basic science faculty, clinical scientists, medical education researchers, medical students, premedical advisers, and practicing physicians, completed a full-scale review of the format, content, and score-reporting system of the Medical College Admission Test (MCAT). The advisory panel's recommendations will shape the MCAT to be introduced in 1991. Presented here are data the panel used in deciding to keep the score scale for the upcoming MCAT. Survey data on student selection practices in U.S. and Canadian medical schools and acceptance information for 1987 applicants showed that medical schools used the scores differently within each school and between the schools in deciding whom to admit. The data demonstrated the value of the current reporting system and led the advisory panel to recommend retention of the 15-point MCAT score scale in 1991.

Aging and reflective processes of working memory: binding and test load deficits.

It was hypothesized that age-related deficits in episodic memory for feature combinations (e.g., B. L. Chalfonte & M. K. Johnson, 1996) signal, in part, decrements in the efficacy of reflective component processes (e.g., M. K. Johnson, 1992) that support the short-term maintenance and manipulation of information during encoding (e.g., F. 1. M. Craik. R. G. Morris. & M. L. Gick, 1990; T. A. Salthouse, 1990). Consistent with this, age-related binding deficits in a working memory task were found in 2 experiments. Evidence for an age-related test load deficit was also found: Older adults had greater difficulty than young adults when tested on 2 features rather than 1, even when binding was not required. Thus, disruption of source memory in older adults may involve deficits in both encoding processes (binding deficits) and monitoring processes (difficulty accessing multiple features, evaluating them, or both).

Source ROCs are (typically) curvilinear: comment on Yonelinas (1999).

On the basis of his assumption that recollection is a threshold process, A. P. Yonelinas (1999) predicted linear source-identification receiver operating characteristics (ROCs) and recently reported data that were consistent with this prediction. In this article, the authors present data showing curvilinear source-identification ROCs across various encoding and test conditions. On the basis of the source-monitoring framework (e.g., M. K. Johnson, S. Hashtroudi, & D. S. Lindsay, 1993), the authors argue that curvilinearity of source-identification ROCs is a result of differences in the qualitative characteristics of memories rather than simply the influence of undifferentiated familiarity as the dual-process model might suggest.

Primary malignant small bowel tumors: an atypical abdominal emergency.

Primary malignant tumors of the small bowel are uncommon in the United States. They comprise less than 1% of all gastrointestinal malignancies, with an incidence of 2200 cases per year. The clinical presentation of small bowel tumors is frequently insidious and often overlooked by physicians. The low incidence and lack of pathognomonic symptoms are the reasons that the early diagnosis of malignant small bowel tumor is uncommon. To better understand the clinical presentation, diagnostic evaluation, management, and outcome, a review of Howard University patients with primary malignant small bowel tumors between 1970 and 1990 was conducted. Our experience concurs with the reported literature and supports the conclusion that a high index of suspicion is necessary. The diagnosis of a malignant small bowel tumor should be considered in patients with vague chronic abdominal complaints.

Evaluation of massive volume replacement in the penetrating trauma patient.

The records of 163 penetrating trauma patients who required surgery in a 36-month period between 1988 and 1990 were reviewed. Those patients with head trauma were excluded. Thirty patients were identified as having: similar Injury Severity Scores (ISS), received at least 8 L of crystalloid, and received at least 4 units of packed red blood cells during the first 24 hours after admission. There were 22 (73%) survivors and 8 (27%) nonsurvivors. Charts were reviewed for a variety of variables to determine which characteristics distinguished nonsurvivors from survivors. The mean ISS was 30.5 +/- 5.5. As a group, nonsurvivors received more blood transfusions (14.9 +/- 4.9 versus 5.0 +/- 1.14), had longer durations of shock (55.6 +/- 18 minutes versus 19.3 +/- 11.7 minutes), and had lower core body temperatures (92.6 degrees F +/- 2.2 versus 95.1 degrees F +/- 2.4) than survivors. Nonsurvivors also had lower hemoglobin levels (7.84 +/- 1 versus 9.1 +/- 2.3) and platelet counts (134.2 +/- 14.1 versus 188.6 +/- 6.3) than survivors. In addition, nonsurvivors demonstrated greater incidence of three major risk factors than did the survivors: hypothermia (75% versus 41%), acidosis (100% versus 27%), and coagulopathy (62% versus 4.5%). Therapeutic measures to limit these risk factors for increased mortality may maximize the chance of survival in these patients.