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Biomedical subjects

S J Clark

Publications and source records attributed to S J Clark.

At least 91 records · Page 5Linked to original sources
PubMed1997

Extensive DNA methylation spanning the Rb promoter in retinoblastoma tumors.

The retinoblastoma gene (Rb) is one of the best characterized tumor suppressor genes, and its inactivation is associated with a number of cancers. Previous studies have shown, by restriction enzyme analysis, that the promoter region of the Rb gene is methylated in a significant proportion of primary retinoblastoma tumors. We now report the first detailed methylation sequence analysis of the CpG island spanning the retinoblastoma promoter from hypermethylated retinoblastoma tumors. Our results show methylation is not confined to a specific CpG site, as detected by restriction enzyme studies, but extends to essentially all 27 CpG dinucleotides spanning the retinoblastoma CpG island, including the core promoter. The methylation pattern from each tumor DNA sample is different, ranging from densely to sparsely methylated profiles. Single CpG sites, in particular the E2F transcription factor binding site, as well as blocks of CpGs, were undermethylated in some tumor samples. Possible interference of methylation could be due to the binding of sequence-specific protein factors at these sites in the tumor cells. This study highlights that the dynamics of DNA methylation in cancer cells are clearly different from normal cells and gives an insight into the mechanism of abnormal methylation of CpG islands in cancer cells.

Base Sequence↗
PubMed1997

Impact of a new universal purchase vaccine program in North Carolina.

OBJECTIVE: To explore the effects of state universal purchase (UP) of vaccines for all children, regardless of income or insurance status, on North Carolina physicians and families. DESIGN: Cross-sectional survey. PARTICIPANTS: Pediatricians and family physicians (N = 2163) were surveyed in 1995 to compare immunization charges in North Carolina (new UP) with those of Massachusetts (UP) and Texas (free market). MAIN OUTCOME MEASURES: Patient charges for immunizations and well-child visits and physician perceptions of the effects of state immunization programs. Models were devised to simulate the net effect of the North Carolina UP program on immunization revenue for physicians and on families' out-of-pocket costs for well-child care. RESULTS: Physician participation rates in the 2 UP programs were very high. North Carolina physicians reported substantial decreases in immunization charges and reduced referrals to public clinics, but thought that UP increased their administrative burden. Sixty percent of North Carolina physicians increased charges for well-child visits, nearly twice that in the 2 control states. Families who previously had received immunizations from public clinics but chose to remain in the private-sector "medical home" for immunizations after implementation of UP had increased out-of-pocket expenses that varied by their insurance status. CONCLUSIONS: The North Carolina UP program is effective in decreasing patient immunization charges and reducing referrals to public clinics. However, UP does not eliminate cost as a barrier to immunization, nor does it enable all children to remain in their medical homes. Underinsured children still may face considerable financial barriers to immunization in a UP system.

Cross-Sectional Studies↗
PubMed1997

Serum free thyroxine concentration is not reduced in premature infants with respiratory distress syndrome.

OBJECTIVE: We used improved methods of assay to determine whether pituitary-thyroid function is altered in premature infants with respiratory distress syndrome (RDS) during the first week of postnatal life. METHODS: Serum free thyroxine (T4) was measured by direct equilibrium dialysis, total thyroxine (TT4) by radioimmunoassay, and thyrotropin by a sensitive immunometric assay in 90 premature infants (45 healthy control subjects and 45 with RDS) during their first week of life after 25 to 30 weeks of gestation. Infants in the RDS group received exogenous surfactant therapy. RESULTS: Free T4 and thyrotropin concentrations of infants were not significantly different between RDS and control groups. As expected, infants with RDS had significantly lower serum total T4 concentrations compared with control infants (p < 0.001). This difference was present even after stratification for gestational age (25- to 27-week group, p = 0.012; 28- to 30-week group, p = 0.002). Lower total T4 concentrations were attributable to lower T4 binding to serum proteins among infants with RDS compared with control subjects, especially in the 25- to 27-week gestation group (p = 0.0075). CONCLUSION: These data indicate that pituitary-thyroid function is not altered in premature infants with RDS. The low total T4 state in these premature infants is attributable solely to reduced serum T4 binding, as is often seen in acute nonthyroidal illnesses.

Case-Control Studies↗
PubMed1997

Public-sector immunization coverage in 11 states: the status of rural areas.

This report uses county-level immunization data generated by state public health agencies to explore the rural-urban variation in the delivery of childhood immunizations in the public sector. Public health department-documented immunization coverage rates for 1995 were obtained from 882 counties in 11 states east of the Mississippi River. To assess the possible association between public health department immunization coverage rates and county rurality, descriptive statistics were calculated. A multiple regression model then was estimated. In all states except West Virginia, nonmetropolitan counties averaged higher completion rates than metropolitan counties. Consistent with the descriptive statistics, in the regression analysis nonmetropolitan counties had average immunization rates 2.47 percentage points higher than metropolitan counties, even when controlling for county socioeconomic characteristics. For the 11 states in the analysis, rural children immunized in the public sector had higher completion rates compared with urban children. These data reflect the dependence of rural families on the public health system and the potential for successful health care delivery through public clinics. As new health care systems are brought into rural areas, the success of this existing avenue for care must not be overlooked.

Adolescent↗
PubMed1996

HIV-specific cellular and humoral immune responses in primary HIV infection.

Primary human immunodeficiency virus (HIV) infection is characterized by a high-titer viremia that declines precipitously within weeks, most likely as a result of host immune responses. Peripheral blood mononuclear cells (PBMCs) and plasma of four recently HIV-infected individuals were examined to assess the humoral and cellular immune responses potentially involved in early suppression of viral replication. Neutralizing antibodies against autologous viral isolates were low or undetectable in three subjects studied. Cellular cytotoxicity was assayed using Epstein-Barr virus (EBV)-transformed B lymphoblastoid cell lines (B-LCLs) infected with recombinant vaccinia that express HIV-1 proteins. HIV envelope-specific cytotoxicity, which was not mediated by CD8+ cells nor human leukocyte antigen (HLA) class I restricted, developed in PBMCs of all four subjects early after primary infection, but was not correlated with declines in viremia. Gag-specific cytotoxic T lymphocyte (CTL) activity was observed in freshly isolated PBMCs of two subjects, and HIV-specific CTL cell lines were cultured from PBMCs of three subjects shortly after HIV infection. Antibody-dependent cellular cytotoxicity (ADCC) developed early in all four subjects, and was temporally correlated with declines in viremia in two subjects in whom viral load was well characterized. These data suggest that both CTL responses and ADCC may be critical to control of viral replication in acute HIV infection.

Adult↗
PubMed1996

Variation in patient charges for vaccines and well-child care.

BACKGROUND: Several state and federal programs have attempted to boost immunization rates by reducing or eliminating provider vaccine costs. The relation between patient vaccine and well-child visit charges and vaccine financing systems is unknown. OBJECTIVES: To determine patient charges for vaccines and well-child visits in three states with varying vaccine financing systems and to examine the effects of a short-term reduction in provider vaccine costs. DESIGN: Cross-sectional survey study of a random sample of physicians in three states. PARTICIPANTS: A total of 2797 pediatricians and family physicians in North Carolina, Texas, and Massachusetts were surveyed. MAIN OUTCOME MEASURES: Current charges to patients for diphtheria-tetanus-pertussis vaccine (DTP), measles-mumps-rubella vaccine, Haemophilus influenzae type b vaccine (Hib), and combined DPT-Hib vaccine for well-child visits; changes in charges over the previous 8 months. RESULTS: Response rate was 62%. Vaccine and well-child visit charges were comparable in North Carolina and Texas. Massachusetts' average charges for well-child visits were higher than in the other states, although vaccine charges were lower; with the use of combined DPT-Hib vaccine, total simulated charges for vaccines and well-child care during the first 6 months of life averaged only 10% less in Massachusetts vs Texas and North Carolina. Neither regional variation in cost of living nor Medicaid reimbursement rates explained this difference. CONCLUSIONS: The average cost and composition of charges for well-child care in Massachusetts, a state with universal purchase of vaccines, compared with the other states, warrant further study to explore whether physicians shift costs to other preventive services to compensate for lower allowable immunization charges. If such cost shifting occurs, current federal immunization initiatives that lower or eliminate provider cost may not provide increased access to preventive services.

Child↗
PubMed1996

Methods and outcomes of breastfeeding instruction for nursing students.

Support from nurses can influence breastfeeding rates, but many nurses are not well-informed about breastfeeding topics. Surveys were used to assess the breastfeeding instruction provided in five nursing programs. Most students attended breastfeeding lectures, but only one-fourth received breastfeeding information during clinical activities. After completing their maternity rotation, less than 25 percent had as many as three clinical opportunities to teach breastfeeding techniques or counsel about lactation problems. Completion of maternity rotation did not improve student's knowledge of breastfeeding health benefits or clinical advice. Previous personal breastfeeding experience was associated with more accurate clinical advice and rating breastfeeding instruction as inadequate. We conclude that nursing education may not prepare students for effective breastfeeding promotion, and we suggest solutions for lactation consultants.

Breast Feeding↗
PubMed1996

Cytosine methylation: quantitation by automated genomic sequencing and GENESCAN analysis.

Bisulfite treatment and PCR amplification of genomic DNA permits the methylation analysis of any cytosine residue in a target sequence. By cloning and sequencing the PCR product, the methylation of individual molecules can be determined, whereas direct sequencing of the PCR product can provide an average of the methylation status in the population of molecules. Reliable quantitation of cytosine methylation by direct sequencing, however, has not been possible with current methods. In this paper we describe an accurate and innovative protocol to directly quantitate the methylation of any cytosine residue in the target sequence by fluorescence-based automated genomic sequencing. Only the cytosine and thymine residues of bisulfite-treated and amplified genomic DNA are sequenced. The degree of methylation is obtained by direct comparison of the cytosine and thymine signals, which have been labeled with the same fluorescent dyes. GENESCAN analysis is employed to achieve a fast and accurate estimate of methylation at every cytosine in the target sequence. Combining direct bisulfite genomic sequencing and GENESCAN analysis permits the rapid survey of detailed DNA methylation profiles. Using this approach we have found the unexpected result that multicopy plasmid DNA grown in a Dcm host is not always fully methylated as suggested by restriction enzyme data.

Autoanalysis↗
PubMed1996

Pediatrician and family physician agreement with and adoption of universal hepatitis B immunization.

BACKGROUND: The purpose of this study was to assess (1) rates of agreement with and adoption of the universal hepatitis B vaccine recommendation among practicing pediatricians and family physicians in nine selected states; (2) physicians' attitudes related to hepatitis B immunization; and (3) physicians' perceptions of parental attitudes regarding the hepatitis B vaccine series. METHODS: Self-administered questionnaires were mailed to 3014 pediatricians and family physicians in selected metropolitan areas and non-metropolitan areas of nine states. Outcome variables were agreement with and adoption of the hepatitis B vaccine recommendation. Predictor variables included physicians' characteristics, practice type and location, and proportion of managed care and Medicaid patients. Other variables that were studied include physicians' attitudes related to hepatitis B immunization, sources of immunization recommendation information, personal completion of the hepatitis B immunization series, and physicians' impressions of parental attitudes about the vaccine. RESULTS: Pediatricians were more likely than family physicians to report that they knew "a lot" about the recommendation (95% vs 84%), agreed with it (83% vs 57%), and have adopted it into practice (90% vs 64%). More physicians in both specialties had adopted the recommendation than actually agreed with it. Doubt about long-term protection from the vaccine was a strong predictor of not agreeing with or adopting the recommendation. Parental resistance to or request for hepatitis B vaccine affected the likelihood of physicians adopting it. CONCLUSIONS: Pediatricians and family physicians continue to differ in both agreement with and adoption of universal hepatitis B immunization. Two years after the recommendation was made, less than two thirds of all family physicians have adopted this recommendation. Adoption is likely influenced by practice policy, physician attitudes, and perceived parental opinions. We recommend that as new vaccines are approved and recommended, research be conducted to explore and address issues germane to physician agreement and adoption.

Adult↗
PubMed1995

Virologic and immunologic characterization of symptomatic and asymptomatic primary HIV-1 infection.

To define virologic and immunologic differences in patients with acute symptomatic and asymptomatic primary human immunodeficiency virus type 1 (HIV-1) infection, sequential plasma specimens were obtained longitudinally for 1-2 years postseroconversion from subjects with well-documented time of seroconversion. Thirteen of them had an acute symptomatic primary infection, eight subjects had asymptomatic primary infection and long-term follow-up, and 27 had asymptomatic seroconversion and short-term follow-up. Quantitative plasma HIV-1 RNA levels, CD4+ lymphocyte counts, and levels of antibodies to gp120, p66, p41, p31, p24, and p17 were measured. At the time of seroconversion, there was no significant difference in HIV-1 RNA levels and CD4+ counts between symptomatic (n = 13) and asymptomatic (n = 27) subjects. Subsequently, however, establishment of low levels of plasma HIV-1 RNA was seen significantly more frequently in asymptomatic (n = 8) than in symptomatic (n = 13) primary infection; this correlated with higher levels of some (anti-gp120 and anti-p31) anti-HIV-1 antibodies and a slower decline in CD4+ lymphocyte counts. These results indicate that immunologic control of viremia early after infection may be a critical determinant to subsequent clinical course of HIV-1 infection. They also suggest that persons with acute symptomatic primary infection may generally progress to having acquired immune deficiency syndrome (AIDS) more rapidly than people with low-grade symptoms or asymptomatic primary infection.

Acquired Immunodeficiency Syndrome↗
PubMed1995

National assessment of physicians' breast-feeding knowledge, attitudes, training, and experience.

OBJECTIVE: Previous reports have demonstrated that physician counseling can improve rates of breast-feeding initiation and duration but suggest that physicians are ill-prepared for this role. It is unclear whether residency training for pediatricians, obstetrician/gynecologists, and family physicians provides the knowledge and skills necessary for effective breast-feeding promotion. DESIGN: Survey. PARTICIPANTS: A national random sample of 3115 residents and 1920 practicing physicians in pediatrics, obstetrics/gynecology, and family medicine. OUTCOMES: Assessment of breast-feeding knowledge, attitudes, training, and experience. RESULTS: Overall response rate was 68%. All groups demonstrated significant deficits in knowledge of breast-feeding benefits and clinical management; for example, less than 50% of residents chose appropriate clinical management for a breast-fed jaundiced infant or a breast abscess. Practicing physicians performed slightly better, but still more than 30% chose incorrect advice for mothers with low milk supply. Residents reported that their breast-feeding instruction consisted mainly of didactic lecture, not patient experience. Only 55% of senior residents recalled even one instance of precepting related to breast-feeding, and less than 20% had demonstrated breast-feeding techniques at least five times during residency. Regarding preparation for breast-feeding counseling, more than 50% of all practicing physicians rated their residency training as inadequate. Overall, physician involvement in breast-feeding promotion was endorsed by 90% of respondents, yet only half rated themselves as effective in counseling breast-feeding patients. The greatest predictor of physician self-confidence was previous personal or spousal breast-feeding experience. CONCLUSIONS: In this national sample of residents and practicing physicians in three specialties, physicians were ill-prepared to counsel breast-feeding mothers. Deliberate efforts must be made to incorporate clinically based breast-feeding training into residency programs and continuing education workshops to better prepare physicians for their role in breast-feeding promotion.

Breast Feeding↗
PubMed1995

Breast-feeding education of obstetrics-gynecology residents and practitioners.

OBJECTIVE: Our purpose was to assess breast-feeding education, knowledge, attitudes, and practices among resident and practicing obstetrician-gynecologists. STUDY DESIGN: A mailed survey was administered to a national sample of resident and practicing obstetrician-gynecologists. RESULTS: Response rates were 64% for residents and 69% for practitioners. Residency training included limited opportunity for direct patient interaction regarding breast-feeding; 60% of practitioners recommended that training devote more time to breast-feeding counseling skills. Only 38% of residents reported that obstetric faculty presented breast-feeding topics; more common sources were nursing staff and other residents. Practitioners rated themselves as more effective in meeting the needs of breast-feeding patients than were residents; prior personal breast-feeding experience was a significant influence on perceived effectiveness. Almost all respondents agreed that obstretician-gynecologists have a role in breast-feeding promotion, but significant deficits in knowledge of breast-feeding benefits and clinical management were found. CONCLUSION: Residency training and continuing education programs should create opportunities to practice breast-feeding promotion skills and emphasize management of common lactation problems.

Breast Feeding↗
PubMed1995

Reference ranges for newer thyroid function tests in premature infants.

OBJECTIVE: To establish reference ranges for recently developed assays of thyroid function in premature infants. METHODS: We measured serum free thyroxine (T4) by direct equilibrium dialysis and serum thyrotropin by a sensitive immunometric method in 104 preterm infants (25 to 36 weeks of gestational age) during the first week of life. RESULTS: The free T4 level correlated positively with gestational age (p < 0.0001; r2 = 0.09) and differed significantly between adjacent gestational age groups (p < 0.05). Free T4 concentrations (mean +/- SD) for the 25- to 27-, 28-to 30-, 31- to 33-, and 34- to 36-week groups were 18.0 +/- 5.2, 25.7 +/- 9.0, 30.9 +/- 9.0, 36.0 +/- 10.3 pmol/L (1.4 +/- 0.4, 2.0 +/- 0.7, 2.8 +/- 0.8 ng/dl), respectively. Two reference ranges for free T4 were determined, one for 25 to 30 weeks (6.4 to 42.5 pmol/L (0.5 to 3.3 ng/dl) and one for 31 to 36 weeks (16.7 to 60.5 pmol/L (1.3 to 4.7 ng/dl)). The logarithm of the value for thyrotropin correlated positively with gestational age (p < 0.001; r2 = 0.08); one reference range of 0.5 to 29 mU/L was determined for thyrotropin. CONCLUSION: This study extends information on thyroid function of preterm infants and establishes reference ranges for this population.

Gestational Age↗
PubMed1995

CpNpG methylation in mammalian cells.

In vertebrate DNA, 3% to 5% of cytosine residues are present as 5-methylcytosine, and it is generally accepted that essentially all of this methylation occurs at cytosines which are contained in the symmetrical dinucleotide CpG. In this report we demonstrate, using bisulphite genomic sequencing, that the methylation machinery of mammalian cells is capable of both maintenance and de novo methylation at CpNpG sites. The existence of inherited CpNpG methylation in mammalian cells has important implications in gene regulation and in the aetiology of disease.

3T3 Cells↗
PubMed1995

Pediatrician involvement in breast-feeding promotion: a national study of residents and practitioners.

OBJECTIVE: Physician support for breast-feeding mothers has been shown to improve breast-feeding rates, but no evaluation of the adequacy of physicians' breast-feeding-related training has been conducted. This study was designed to assess pediatricians' knowledge, attitudes, training, and activities related to breast-feeding promotion. METHODS: Surveys were mailed to a national random sample of pediatric residents (n = 999) and practitioners (n = 610) who were board certified within the previous 3 to 5 years. RESULTS: Response rates were 74% for residents and 69% for practitioners. Although more than 90% of respondents agreed that pediatricians should be involved in breast-feeding promotion, their clinical knowledge and experience did not suggest a high degree of competency. For example, practitioners were only slightly more aware of breast-feeding's protective effect against otitis media (71% vs 60%), and more than one quarter of both groups did not agree that exclusive breast-feeding is the most beneficial form of infant nutrition. Clinical advice often included inappropriate recommendations for breast-feeding termination or formula supplementation; only 64% of practitioners and 52% of residents knew that supplementing during the first few weeks of life may cause breast-feeding failure. For both groups, prior personal breast-feeding experience (ie, respondent or spouse had breast-fed an infant for 2 or more weeks) was a major determinant of improved clinical knowledge, more frequent activity, and greater self-confidence and perceived effectiveness in the area of breast-feeding promotion. Residents reported that the breast-feeding instruction provided during training was primarily in lecture format, with limited clinical opportunities to practice skills needed to assist breast-feeding mothers. Reflecting on their own training, more than 70% of practitioners recommended that more time be devoted to direct patient interaction and practice of counseling and problem-solving skills. CONCLUSIONS: These results indicate that residency training does not adequately prepare pediatricians for their role in breast-feeding promotion. Improvements in residency training and innovative continuing education programs should be implemented to help pediatricians meet the needs of their breast-feeding patients.

Breast Feeding↗
PubMed1995

Breast-feeding education and practice in family medicine.

BACKGROUND: Physician support has been shown to increase breast-feeding rates, but anecdotal reports suggest that physicians are ill prepared for their role in breast-feeding promotion. Inadequate breast-feeding education during residency training may be a contributing factor. METHODS: A self-administered questionnaire mailed to 1099 family medicine residents and 665 recently board-certified family physicians assessed knowledge, attitudes, education, and activity related to breast-feeding promotion. Response rates were 71% for residents and 58% for physicians. RESULTS: Although residents and physicians were strongly convinced that family physicians should be involved in breast-feeding promotion, both groups demonstrated significant deficits in knowledge about breast-feeding benefits and clinical management strategies. Common errors included inappropriate recommendations for breast-feeding termination or formula supplementation, a proven cause of breast-feeding failure. Personal breast-feeding experience was the only factor consistently associated with more frequent breast-feeding promotion activity among residents and increased self-confidence for both groups. Respondents reported only limited opportunities for developing breast-feeding counseling skills during residency training. CONCLUSIONS: Improved breast-feeding education is needed for family medicine residents and physicians. Residency training and continuing education programs should emphasize the benefits of breast-feeding, clinical management strategies, and development of practical counseling skills.

Breast Feeding↗