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Biomedical subjects

K A Schneider

Publications and source records attributed to K A Schneider.

At least 19 recordsLinked to original sources
PubMed2006

Does competitive divergence occur if assortative mating is costly?

Most models of sympatric speciation have assumed that assortative mating has no costs. A few studies, however, have shown that the costs for being choosy can prevent such speciation. Here, we investigate the role of the strength of assortment and of the costs for being choosy for a simple genetic model of a single ('magic') trait that mediates both intraspecific competition for a continuum of resources and assortative mating, which is induced by choosy females who preferentially mate with males of similar phenotype. Choosiness may be costly if it is difficult to find a mating partner. Such magic trait models are considered to be most conducive of sympatric speciation. We consider a sexually reproducing population of haploid individuals that is density regulated. The trait is determined by a single locus with multiple alleles. The strength of stabilizing selection (caused by a unimodal resource distribution), the strength of competition, the degree of assortment and the costs for being choosy are independent parameters. We investigate analytically and numerically how these parameters determine the equilibrium and stability structure. In particular, we identify conditions under which no polymorphism at all is maintained as well as conditions under which strong competitive divergence occurs, or the population even splits into two reproductively isolated classes of highly diverse phenotypes. If costs are absent or moderate, genetic variability tends to be minimized at intermediate strengths of assortment, and reproductively isolated classes of phenotypes are a likely result of evolution only for intermediate or strong competition and for very strong assortment. The likelihood of divergence depends relatively weakly on the costs as long as they are not high. With high costs, however, increasingly strong assortment rapidly depletes all genetic variation, and strong competitive divergence is prevented.

Evolution, Molecular↗
PubMed2000

BRCA1 testing and informed consent in a woman with mild retardation.

Cancer predisposition testing can pose complex genetic counseling issues. This case report discusses whether it is appropriate to provide BRCA1 testing to a woman with limited intellectual capacity and documented psychological distress. This case is one of several cancer counseling cases presented to our Genetic Counseling Supervision Group over the past three and a half years. The Supervision Group provided valuable feedback and support to proceed with this challenging case.

Adult↗
PubMed2000

Anticipated versus actual emotional reactions to disclosure of results of genetic tests for cancer susceptibility: findings from p53 and BRCA1 testing programs.

PURPOSE: We examined the ability of individuals undergoing genetic testing for cancer susceptibility in two structured research protocols to accurately anticipate emotional reactions to disclosure of their test result. We explored whether accuracy of emotional anticipation was associated with postdisclosure psychologic adjustment. METHODS: Data from 65 individuals were analyzed; 24 members of Li-Fraumeni cancer syndrome families were tested for p53 mutations (all 24 were unaffected), and 41 subjects with hereditary breast-ovarian cancer susceptibility were tested for BRCA1 mutations (34 were unaffected and seven were affected). Subjects were from families in which a germline mutation had been previously identified. At the pretest session, subjects rated the extent to which they anticipated feeling each of six emotional states (relief, happiness, sadness, guilt, anger, and worry) after disclosure that they did or did not carry the familial mutation. After receiving their test result, they rated their feelings on the same scale of emotions for the appropriate condition. Extent of accuracy and association with psychologic distress at 6 months, as assessed with standardized measures, were evaluated. RESULTS: Overall, mean levels of emotional reactions after receiving test results were not different from those anticipated before result disclosure. However, affected BRCA1 carriers experienced higher levels of anger and worry than they had anticipated. Underestimation of subsequent distress emotions related to test result was associated with a significant increase in general psychologic distress at 6 months. CONCLUSION: Unaffected individuals in cancer-predisposition testing programs are generally accurate in anticipating emotional reactions to test results. However, cancer patients may underestimate their distress after disclosure of positive results and could benefit from intervention strategies.

Adult↗
PubMed2000

Behavioral risk factors among women presenting for genetic testing.

Considerable research attention has been given to the impact of genetic testing on psychological outcomes. Participation in genetic testing also may impact on health behaviors that increase the risk of cancer and other chronic diseases. The purpose of this study is to describe behavioral cancer risk factors of women who requested genetic testing for breast and ovarian cancer susceptibility (BRCA1, BRCA2). Before participation in a genetic testing program, 119 women completed a series of questionnaires designed to assess their health behaviors, perception of risk, and depressive symptomatology. Eight percent of participants were current smokers, 27% did not engage in at least moderate exercise, 46% did not regularly protect themselves from the sun, 39% did not consume at least five servings of fruits and vegetables per day, and 9% drank at least one alcoholic beverage per day. Poisson regression analysis revealed that age was the only predictor of behavioral risk profiles, with older women having fewer cancer risk behaviors. These patients who presented for genetic testing generally had better health behaviors than the general population. However, given their possible high-risk status, these patients should consider further improving their preventable cancer risk factors and, in particular, their diet, sun protection, and physical activity levels. Inclusion of behavioral risk factor counseling in the context of the genetic testing process may be an important opportunity to reach this at-risk population.

Adult↗
PubMed1997

Genetic counseling for BRCA1/BRCA2 testing.

Genetic counseling plays a key role in the BRCA1/BRCA2 testing process. The initial genetic counseling encounter will determine the appropriateness of the test by collecting a detailed family history and determining the likelihood that the family has a BRCA1 or BRCA2 mutation. Once the test is offered, then genetic counseling discussions center around the possible test results, implications of the results to the patient and other relatives, and risks and benefits of testing. The goal of this pre-test genetic counseling session is to ensure that patients have sufficient information with which to make a decision about being tested. At results disclosure, individuals can learn their results along with information about cancer risks and medical management options. Follow-up genetic counseling services can provide continued support and help arrange consultations with other medical care providers as needed. All clinical BRCA1/BRCA2 testing programs should include pre- and post-test genetic counseling.

BRCA2 Protein↗
PubMed1993

Influence of dietary sodium restriction on lipid metabolism.

The possible increase in total and low-density lipoprotein cholesterol following severe restriction of dietary NaCl was reported in 1990 and and 1991 from three experiments, one in the United States and two in Germany. Each of these experiments lasted only 1 week. To evaluate the clinical side effects we analyzed data collected from patients who completed a course of NaCl-restricted weight reduction at the Duke Diet and Fitness Center. Observations of lipid changes are not available for periods of less than 3 weeks; however, we were able to collect data on lipid and lipoprotein changes from 556 participants 25 days after they were referred for weight reduction. Total cholesterol, low-density lipoprotein cholesterol, and triglyceride levels returned to normal in the majority of obese patients. In our slightly longer observation period in patients on a 1000 mg NaCl restricted diet we found no evidence of hyperlipidemic side effects. We believe that the hyperlipidemia resulting from severe sodium restriction in non-hypertensive, normal-weight individuals is not relevant to the problem of nonpharmacological and diuretic treatment of obese hypertensive patients. In clinically healthy, normal-weight, normotensive individuals severe salt restriction serves no practical or therapeutic purpose.

Cholesterol↗
PubMed1991

Issues in cerebrospinal fluid management. CSF Venereal Disease Research Laboratory testing.

Three policies for decreasing unnecessary cerebrospinal fluid (CSF) management Venereal Disease Research Laboratory (VDRL) tests were compared. The first policy attempted to educate physicians about the use of serologic tests for diagnosing neurosyphilis but allowed the CSF VDRL to be performed either as a screening test or as a retrospective test. The second policy required that the CSF VDRL be performed as a retrospective test without regard to the patient's serologic status. The third policy required that a patient be seropositive by either rapid plasma reagin (RPR) or fluorescent treponemal antibody absorbance (FTA-ABS) before a CSF VDRL could be performed. Before these policies were instituted, VDRL testing was performed on 18.2% of all CSF samples. The optional and required retrospective policies decreased the CSF VDRL rate to 13.0% and 8.5%, respectively, but the percentages of seropositive patients for whom these procedures were performed were only 7.3% and 12.9%. The third policy decreased the CSF VDRL test rate to 1.8% (P less than 0.001) with seropositivity improving to 90%. To assure serologic tests are obtained in the evaluation of neurosyphilis, requirement for seropositivity must be implemented with the use of retrospective CSF VDRL testing.

Antibodies, Bacterial↗
PubMed1991

Issues in cerebrospinal fluid management. Acid-fast bacillus smear and culture.

Meningeal tuberculosis is an uncommon disease in the United States with an annual incidence of fewer than 200 cases. This study evaluates three approaches to improving the use of the cerebrospinal (CSF) acid-fast bacillus (AFB) smear and culture procedure: (1) education alone; (2) optional screening by which physicians can select to have the AFB analysis stopped if the initial CSF findings are unremarkable; and (3) mandatory screening before the performance of all CSF AFB analyses. With education alone, the CSF AFB culture rate decreased from 20.6% of all CSF acquisitions to 15.7% (P less than 0.001); however, the effect may have been related to a decrease in all types of AFB testing. Optional screening had no impact on the AFB testing rate. Mandatory screening significantly decreased the CSF AFB rate to 6.7% (P less than 0.001), unrelated to changes in other types of AFB testing. Laboratories that employ mandatory screening should report the screening results immediately and have a mechanism whereby physicians can bypass the screen, providing CSF AFB analysis on unremarkable fluid from high-risk patients.

Adolescent↗
PubMed1991

Effectiveness of education-screening on cholesterol levels of students.

Increases of cholesterol levels from the age of 16 years have been demonstrated in community-based studies. Cholesterol education to students aged 15-17 years in 5 high schools was presented prior to cholesterol screening with the Reflotron. First screening took place in March 1987. An identical program was repeated 11 months later, again followed by screening in March 1988. Of the 5 schools, 2 were assigned to involve teachers. There was a significant cholesterol reduction in these 2 schools, i.e., -17 and -19 mg/dl (p less than 0.05). The effectiveness of the physicians' education and the compliance of the students with the teachers' recommendations certainly must have been enhanced by a different family environment with a higher socioeconomic stratum prevailing in these 2 high schools. However, these factors did not influence the baseline in all 5 schools. In the 3 remaining schools no increases in cholesterol levels expected for this age were observed.

Adolescent↗
PubMed1991

Effect of thiazide-based therapy on serum alkaline phosphatase. Hypertension Detection and Follow-up Group.

This study reports a correlation of alkaline phosphatase (AP) with diastolic blood pressure (DBP), and a reduction of alkaline phosphatase after chlorthalidone therapy that reached a nadir at three years of therapy, then gradually returned toward, but not reaching, baseline values. The data is from the baseline examination and follow-up of 3928 initially untreated stepped-care patients in the Hypertension Detection and Follow-up Program. In multiple regression analysis, both age and DBP were significantly correlated with increased AP in males and females. After initiation of therapy with chlorthalidone, AP levels fell progressively until the third year, when they were reduced by 11 +/- 15 IU in the males and 14 +/- 15 IU in the females. The data are compatible with the interpretation that thiazide-induced reduction in urinary calcium excretion has led to a more positive calcium balance and reduction of bone turnover, and suggests that a beneficial effect of thiazide-based antihypertensive therapy could be decreased osteoporosis.

Adult↗
PubMed1990

Development and persistence of catecholaminergic neurons in cultured explants of fetal murine vagus nerves and bowel.

Transient catecholaminergic (TC) cells have been found to appear in the vagal pathway and bowel of fetal mice and rats. It has been proposed that these cells are migrating vagal crest-derived precursors of enteric neurons that lose their catecholaminergic properties when they terminally differentiate. In the current experiments, segments of fetal mouse gut were explanted before (day E9) TC cells or any neural markers could be detected in situ. Tyrosine hydroxylase (TH)-immunoreactive neurons developed in vitro in 4/12 such explants; therefore, cells with a catecholaminergic potential are present in the gut of at least some animals prior to the in situ expression of this phenotype. The neurogenic potential of cells in the vagal pathway was similarly tested by studying cultures of explanted vagus nerves (day E11). These studies revealed that neural precursors were present in the vagi and gave rise in vitro to neurons that displayed acetylcholinesterase (AChE) activity and neuron-specific enolase (NSE) immunoreactivity. A subset of these neural precursors were capable of migrating and formed satellite ganglia at a distance from the explants. Coincident expression of NSE and TH immunoreactivities was observed, indicating that at least some of the neurons that developed in vitro were derived from TC cells. Vagal TC cells, therefore, are neurogenic. Catecholaminergic cells did not disappear from cultured explants of vagus nerves or gut provided that these tissues contained TC cells at the time of explantation. Instead, catecholaminergic neurons developed and persisted in vitro for as long as cultures were maintained. These neurons contained aromatic L-amino acid decarboxylase as well as TH, NSE and neurofilament immunoreactivities. In contrast, if the bowel was explanted after the in situ disappearance of TC cells, catecholaminergic cells did not arise in the cultures. These experiments indicate that the period of time during which a catecholaminergic phenotype is expressed by neural precursors in the fetal vagal pathway and gut is not fixed, but can be changed by altering the environment of the cells as occurs when the bowel is grown in vitro; moreover, contact with non-neuronal cells within the bowel is not by itself sufficient to inactivate catecholaminergic expression. The nature of the signal responsible for loss of the catecholaminergic phenotype in situ remains to be determined; however, the persistence of catecholaminergic expression in vitro should facilitate the investigation of this signal.

Acetylcholinesterase↗
PubMed1990

Obesity and hypertension: epidemiological aspects of the relationship.

A large proportion of hypertensive men and women in Europe and North America are overweight. In obesity, the expanded blood volume increases cardiopulmonary volume, cardiac filling, left ventricular preload, stroke volume and, thereby, left ventricular work. Given enough exposure time, it is probable that all obese persons in the Western hemisphere would become hypertensive unless they succumb to competing causes of death. A postulated causal role of obesity in hypertension is based on epidemiological observations. In prospective studies weight gainers in adolescence are more often hypertensive than weight stable individuals. In the lower socio-economic strata of industrialized countries there is a higher prevalence of obesity and hypertension. Persons with high body weight show the greatest rise of BP with age. More relevant demonstration of a causal relationship is weight reduction in hypertensive patients. The evidence from a variety of sources, a) risk factor reduction and enhanced BP reduction in the Hypertension Detection and Follow-up Program patients on antihypertensive medication who experienced modest weight loss, b) clinical observations of formerly obese hypertensives who can forego BP lowering drugs, and c) the reversibility of haemodynamic change found in many overweight hypertensive patients after losing 10 kg, strongly suggests that the impact of obesity on hypertension is considerable.

Adult↗