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Biomedical subjects

G Stevens

Publications and source records attributed to G Stevens.

At least 37 records · Page 2Linked to original sources
PubMed2000

Identification of P gene mutations in individuals with oculocutaneous albinism in sub-Saharan Africa.

Oculocutaneous albinism (OCA) is an inherited disorder resulting in hypopigmentation of the skin, hair, and eyes. OCA type 2 (tyrosinase-positive) is the most common recessively inherited disorder among southern African Blacks. OCA2 is also seen in southern African Caucasoids, but is less frequent. The gene responsible for this type of albinism, P, is the human homolog of the mouse pink-eyed dilution gene. Mutations at this locus are also responsible for the milder hypopigmentation phenotype seen in individuals with brown oculocutaneous albinism (BOCA). A common African P mutation was identified in Black OCA2 individuals, and has since been shown to occur in Black individuals with brown OCA as well. This mutation is a 2.7 kb interstitial deletion. In this study, we undertook to screen the coding region of the P gene for mutations in the non-2.7 kb deletion alleles of OCA2 patients who did not carry the deletion allele in either one or both of their P genes. We identified four mutations (A334V, 614delA, 683insG [corrected], 727insG) in a group of 39 unrelated Black OCA2 patients with a total of 52 non-2.7 kb deletion OCA2 genes. When taking all OCA2 cases into consideration, including those homozygous for the 2.7 kb deletion mutation, these account for a further 1.7% of OCA2 mutations in southern African Blacks, increasing the overall mutation detection rate to 78.7%. Three mutations (E678K, L688F, I370T) were identified in a group of 15 Black patients with an initially unclassified type of OCA and another three mutations (IVS 14-2 (a-->g), V350M, P743L) were identified in nine Caucasoid OCA patients. Relatively few mutations, all with low frequency, were identified in the non-2.7 kb deletion OCA genes. We propose that other mutations may lie either within intronic sequence or within the promoter region of the gene.

Africa South of the Sahara↗
PubMed2000

Epithelial ingrowth in a corneal graft treated by laser in situ keratomileusis: light and electron microscopy.

PURPOSE: To demonstrate progressive epithelial ingrowth histopathologically in a human cornea after laser in situ keratomileusis (LASIK) and review its pathophysiology. SETTING: Department of Ophthalmology, Medical College of Virginia Campus, Virginia Commonwealth University, and the Veterans Affairs Medical Center, Richmond, Virginia, USA. METHODS: Tissue from a corneal transplant specimen was examined 6 weeks after LASIK by light and transmission electron microscopy. RESULTS: Epithelial ingrowth in the flap interface with connection to the surface corneal epithelium was evident on light microscopy. In areas without epithelial ingrowth, the flap interface was imperceptible. Electron microscopy revealed minimal disruption of the stromal collagenous lamellae. CONCLUSION: Progressive epithelial ingrowth occurred with a continuous sheet of epithelium to the flap edge. Location of epithelial ingrowth and cytokine epithelial-stromal interaction appear to be important factors in this complication. Histopathological changes in the cornea after LASIK are difficult to detect in areas with normal wound healing.

Adult↗
PubMed2000

Contaminated drinking water in one town manifesting as an outbreak of cryptosporidiosis in another.

In early 1992 we identified an outbreak of cryptosporidiosis in Oregon and sought to identify and control its source. We used a series of studies to identify risk factors for illness: (i) a case-control study among employees of a long-term-care facility (LTCF); (ii) a matched case-control study of the general community; (iii) a cohort study of wedding attendees; and (iv) a cross-sectional survey of the general community. Drinking Talent water was associated with illness in the LTCF (OR = 22.7, 95 % CI = 2.7-1009.0), and in the community (matched OR = 9.5, 95% CI 2.3-84.1). Drinking Talent water was associated with illness only among non-Talent residents who attended the wedding (P < 0.001) and in the community (RR = 6.5, 95 % CI 3.3-12.9). The outbreak was caused by contaminated municipal water from Talent in the absence of a discernible outbreak among Talent residents, suggesting persons exposed to contaminated water may develop immunity to cryptosporidiosis.

Adolescent↗
PubMed2000

Thyroid surgery and anaesthesia following head and neck irradiation for childhood malignancy.

BACKGROUND: Increasing numbers of adolescents and young adults are undergoing thyroid surgery because of the risk of malignancy following previous irradiation for childhood malignancy. Irradiation to the head and/or neck regions may induce changes in the soft tissues and larynx that are far from normal with respect to both size and mobility. The aim of the present study was to evaluate the possible impact of such changes on both surgical and anaesthetic technique during thyroidectomy. METHODS: This was a retrospective ease study. Thirty consecutive patients undergoing total thyroidectomy following previous irradiation for childhood malignancy formed the study group. RESULTS: There were no permanent surgical or anaesthetic complications in the group. In particular there were no cases of either permanent recurrent laryngeal nerve palsy or permanent hypoparathyroidism. Twenty-eight patients had an uneventful intubation and two were unable to be intubated directly, one requiring fibre-optic bronchoscopic intubation and the other having surgery performed with a laryngeal mask following failed bronchoscopy. Both of these patients had received high-dose direct irradiation to the larynx for solid tumours. CONCLUSIONS: Despite potential difficulties associated with the heavily irradiated larynx, thyroid surgery and anaesthesia can be performed safely with minimal complications in experienced hands.

Adolescent↗
PubMed2000

Rectal cancer: changing patterns of referral for radiation therapy 1982-1997.

BACKGROUND: The purpose of the present study was to evaluate the changing role of radiation therapy in rectal cancer and to determine the patterns of referral of patients during a 15-year period. METHODS: From 1982 to 1997, 464 patients with carcinoma of the rectum were referred to the Department of Radiation Oncology, Royal Prince Alfred Hospital: 79% of patients had locoregional disease alone and 21% had distant metastasis. Radiation therapy consisted of irradiation (definitive or palliative) alone to the primary tumour in 9.7% of cases; preoperative radiation in 7.3% of cases: preoperative chemoradiation in 7.5% of patients: postoperative radiation in 15.3% of patients: postoperative chemoradiation in 12.31% of patients: treatment of pelvic recurrence in 23.5% of patients and treatment of metastases in 9.1% of patients. The remainder were treated elsewhere (1.9%) or not treated (13.4%). RESULTS: There was an average annual 14% increase in referrals over the accrual period. Recurrent rectal cancer decreased from approximately 30% of referrals during 1982-91 to approximately 10% in 1995-7. The use of postoperative adjuvant radiation reached a peak of 50% in 1993. The use of preoperative radiation increased suddenly in 1994 from < 10% to a sustained rate of approximately 30% of referrals. The use of chemoradiation commenced in 1990 for postoperative adjuvant treatment and in 1994 for preoperative treatment. The median survival time from initial diagnosis was 35 months, with 2- and 5-year survival rates of 62 and 28%, respectively. Survivals at 5 years for patients treated with preoperative and postoperative radiation (with or without chemotherapy) and with recurrent disease were 56, 44 and 21%, respectively. CONCLUSIONS: The present study illustrates the changing role of radiation therapy in the management of rectal cancer. The increase in referrals over the observation period was due to increased multidisciplinary input into the initial management of these patients, based on reported clinical trials. The steady increase in the use of adjuvant therapy has paralleled a decrease in referrals for treatment of recurrence and reflects current clinical results. The sequencing of adjuvant therapy is changing currently, with greater emphasis on preoperative adjuvant treatment. Currently most adjuvant therapy includes chemotherapy.

Adenocarcinoma↗
PubMed1999

Different molecular basis for spinal muscular atrophy in South African black patients.

Spinal muscular atrophy (SMA) is an autosomal recessive disorder occurring at a rate of between 1/5,000 and 1/10,000 births in most European countries. The phenotype results from the degeneration of the anterior horn cells of the spinal cord, resulting in symmetrical muscle weakness and wasting. The disorder can be classified according to the severity of the disease and the age of onset into three major types. Two candidate SMA genes, NAIP and SMN, isolated from the 5q13 region, have been reported to be homozygously deleted in approximately 30% and >95% of SMA patients, respectively. Black SMA patients have been reported to have facial muscle weakness more commonly. This study aimed to determine the molecular basis of SMA in South African black SMA patients. The SMN gene was found to be homozygously deleted in 65.5% (19/29) of patients, significantly less frequently than in previous studies. Similarly, the NAIP gene was homozygously deleted in a smaller number, 14% (4/29) of patients; 47% (9/19) of SMN deletion patients appeared to have deletions of telomeric exon 7, but not exon 8. In at least six of these patients a gene conversion event has occurred. No detectable deletions were found in 35% (10/29) of patients. Haplotype analysis in the nondeletion patients, using six closely linked markers, provided no evidence for a founder mutation. No mutations were found in exons 3 and intron 6 through exon 8 by sequence analysis of these nondeletion patients. It is proposed that the differences in the SMA phenotype observed in black patients may in part be explained by a different molecular basis.

Black People↗
PubMed1999

Isolation and characterisation of oxygen evolving thylakoids from the marine prokaryote Prochloron didemni.

The present study describes the first successful attempt to isolate oxygen evolving thylakoids and thylakoid fragments from the marine prokaryote Prochloron didemni, a member of the recently discovered group of prochlorophytes. Oxygen evolving thylakoid membranes and fragments were isolated from seawater suspended cells of Prochloron didemni by passage of the cells through a Yeda press and subsequent differential centrifugation of the broken material. Three fractions were collected at 1000 x g, 5000 x g, and 3000 x g and identified by light microscopy as cells (and their fragments), thylakoids and membrane fragments, respectively. Pigment content, oxygen evolution rate and 77 K fluorescence spectra of these fractions were virtually identical. This finding indicates that the membrane fragments obtained are not enriched in photosystem II. The P680+* reduction kinetics of thylakoid membrane fragments were determined by monitoring flash induced absorption changes at 830 nm and analysing the time course of their decay. The multiphasic relaxation kinetics and their modification by NH2OH were found to be similar to those observed in cyanobacteria and plants. These findings provide an independent line of evidence for the idea of a high conservation of the basic structural and functional pattern of the water oxidising complex in all organisms that perform oxygenic photosynthesis.

Chlorophyll↗
PubMed1999

Cochlear implants: response to therapeutic irradiation.

PURPOSE: To determine the response of cochlear implants ("bionic ears") to therapeutic irradiation. METHODS AND MATERIALS: A patient with a cochlear implant was referred for palliative cranial irradiation. As there were no published or manufacturer's data available regarding the response to radiation, implants were tested for functional changes following irradiation. Cochlear implants were supplied by Cochlear Ltd. Two units each of models CI22M, CI22M (with the second generation integrated circuit) and CI24M were irradiated with 4 MV X-rays, and an unirradiated unit of each model was used as a control. The implants were irradiated initially with 25 daily fractions to 50 Gy. To determine the response at higher doses, 10 Gy fractions were delivered to the same implants to 100 Gy, followed by a final fraction of 50 Gy (total dose 150 Gy). The implants were tested after each 10 Gy, up to 1100 Gy, and at 150 Gy. Several indicators of functionality were assessed, including RF (radio frequency) link range, and stimulator output current. The radiation shielding effect of the implants was also assessed. RESULTS: Within the dose range < or = 50 Gy, the stimulator output current of the CI22M units was the only parameter to change. At higher doses (to 150 Gy), changes in current output continued, and gradual loss of RF link range occurred in the CI22M units. The CI24M units showed changes in output current to 100 Gy, and large changes at 150 Gy. Dose attenuation by the implants was measured at 6% for ipsilateral single field 4 MV X-rays. CONCLUSION: Our results suggest that patients with these cochlear implants can receive cranial irradiation with a low risk of implant failure. Changes in stimulator output current can be compensated simply by reprogramming the speech map after the course of radiation treatment.

Adenocarcinoma↗
PubMed1999

Radiotherapy for bone metastases: a critical appraisal of outcome measures.

Pain from bone metastases is a common problem in patients with advanced cancer, and radiotherapy plays an important role in its palliation. Single fraction treatments are often prescribed, but there is no clear consensus on this issue and clinical practice shows significant variability. This situation is unsatisfactory for all patients--the patient, the clinician, and the health care administrator. Randomized trials may use poor outcome measures and this contributes to practice variability. The credibility of outcome studies is often reduced due to poor study design, small sample sizes, and the use of endpoints that are both unreliable and unsuitable. The endpoints used have been narrowly defined, the patient's perspective has generally been overlooked, and quality of life has only once been used as an endpoint. A review of the current literature suggests that instruments specific to bone metastases are required. These must be based on patient experience, and rely on self-report. In addition, there is a need to understand the relative priority that patients attribute to treatment outcomes. The use of better instruments and methodologies in future trials will enhance the credibility of results and reduce practice variations.

Bone Neoplasms↗
PubMed1999

Erbium:YAG laser cataract removal: role of fiber-optic delivery system.

PURPOSE: To review the properties of energy delivery systems and to evaluate the efficiency of zirconium-fluoride-based and sapphire fibers delivering erbium:YAG (Er:YAG) laser energy in a clinical laser cataract surgery system. SETTING: Department of Ophthalmology, Medical College of Virginia Campus of Virginia Commonwealth University, and Veterans Affairs Medical Center, Richmond, Virginia, USA. METHODS: Thirty-two patients had Er:YAG laser cataract extraction. Preoperative visual acuity ranged between finger counting and 20/40 secondary to cataract. The endothelial cell count was measured preoperatively and 6 weeks after surgery. A zirconium-fluoride-based fiber was used in 23 patients and a sapphire fiber in 9 patients. RESULTS: Of the patients examined after 3 months (n = 31), 90.3% (n = 28) had a visual acuity of 20/30 or better and 9.7% (n = 3), of 20/40 or 20/50. Mean endothelial cell loss at 6 weeks was 7.6% +/- 12.8 (SD). Posterior capsule rupture with vitreous loss occurred in 3 cases; 1 was attributed to laser damage to the capsule. Conversion to ultrasound phacoemulsification was required in 13 cases. Suitable fiber materials for Er:YAG laser delivery are sapphire, zirconium fluoride, silica, and germanium oxide. Toxicity of the latter is under investigation. CONCLUSION: The Er:YAG laser emulsified the lens nucleus safely and effectively. These early results include a higher than acceptable posterior capsule rupture rate and reflect the surgeon's learning curve with a new technology. Effective power delivery can be achieved with sapphire- and zirconium-fluoride-based fiber optics through a silica tip. The optimal energy delivery system has not been determined.

Aged↗
PubMed1999

Faculty of Radiation Oncology survey of work practices.

The aim of the present paper was to determine the current working conditions of practising radiation oncologists (RO) in Australasia and their attitudes towards their work and work environment. The authors were requested by the Faculty of Radiation Oncology to conduct a survey of Fellows' work conditions and attitudes. The need for such a survey arose from a workshop of the Faculty held in Sydney in 1995, to determine future directions of the Faculty. Issues of potential interest were identified at the workshop and supplemented by the authors into a survey consisting of both directed and open questions. Respondents were free to remain anonymous. An address list of RO was supplied by the Royal Australian and New Zealand College of Radiologists (RANZCR). Two mailouts were performed to increase the response rate. The survey was completed during the second half of 1996 and analysed in 1997. The response rate was 79% (63-100% according to state/country). The age range was 30-69 years (median: 43 years; mean: 44 years), and 78% of the respondents were male. A public centre was identified as the sole or main place of work for 84% of respondents. The number of RO per practice varied from one to 25 (median: 5). The estimated hours worked per week ranged from 20 to 79 (mean: 52 h; median: 50 h). There were significant differences in allocation of hours between public and private (more clinical hours for private (P = 0.008), more teaching hours for public (P = 0.007)) but no difference in total hours. The responses for clinical work profile were: 'general' 39%, 'largely subspecialty' 37% and both 2% (23% did not respond). The proportion whose practice was 'largely subspecialty' differed between public and private (53% vs 13%, respectively; P = 0.06), and varied according to the number of RO in the practice (62% for > five RO vs 35% for < or = five RO, P = 0.03). The need for subspecialization for the treatment of common tumours (breast, gynaecological etc.) was held by 78% of respondents and was related to the number of RO in the practice (100% for > five RO vs 81% for < or = five RO, P = 0.002). The number of new patients seen per RO in 1995 ranged from 0 to 700 (mean: 342; median: 350), with a significant difference between the mean numbers seen in public versus private settings (331 vs 409, respectively; P = 0.008). Administration of cytotoxics was supervised by 36% of RO across Australasia but was dependent strongly on the state/country of practice (P = 0.0002). The current and preferred roles in clinical management were scored as means of 7.9 and 8.7, respectively, on a linear scale from 1 (mainly technical role) to 10 (significant role in overall management). A total of 40% of RO were content with their current time allocation; the remainder generally wished to reduce clinical time and increase self-education and/or clinical research. Most indicated that they wanted some 'protected time'. Most were content to be called a 'radiation oncologist' and wished to retain this title; the most common alternative was 'clinical oncologist'. Much of the general comment related to perceived loss of control of clinical and academic aspects of oncology to other specialties. The present survey is the first to define current work practices and to explore attitudes to work. It is clear that many RO consider clinical workloads to be excessive, to the exclusion of other work-related activities. There was a strong feeling that significant changes will be required if RO are to maintain the role in cancer management for which they are trained.

Adult↗
PubMed1999

Ebola hemorrhagic fever, Democratic Republic of the Congo, 1995: determinants of survival.

In May 1995, an international team characterized and contained an outbreak of Ebola hemorrhagic fever in Kikwit, Democratic Republic of the Congo. This study reports the descriptive features of this outbreak along with a statistical analysis of the outbreak data. Proportional hazards analysis was used to examine the effect of age, phase of the outbreak, and sex on the risk of death, and a conditional probability analysis was used to examine the effectiveness of whole blood transfusion from convalescent patients on survival. Two hundred fifty case-patients (80.7%) died. The main predictor of survival in the proportional hazards model was age. No statistical evidence of a survival benefit of transfusion of blood from convalescent patients was evident after adjusting for age, sex, and the days since onset of symptoms (P = .1713).

Adolescent↗
PubMed1999

Utilisation of predictive, prenatal and diagnostic testing for Huntington's disease in Johannesburg.

CONTEXT: Huntington's disease (HD) is a dominantly inherited condition in which the gene defect is known. As such individuals in at-risk families can be tested before symptoms occur, prenatally, or after symptoms appear to confirm the diagnosis. OBJECTIVES: To investigate the utilisation and sequelae of the predictive, prenatal and diagnostic services offered to families with suspected Huntington's disease. DESIGN: A retrospective design was used. The 1975-1997 records of the Department of Human Genetics for all families with a history of HD presenting for genetic counselling and DNA analysis were studied. SETTING: Department of Human Genetics, South African Institute for Medical Research and University of the Witwatersrand, Johannesburg. SUBJECTS: There were 30 at-risk (50% risk) subjects for predictive testing, 7 women (10 pregnancies) for prenatal testing, and 52 subjects for diagnostic testing. OUTCOME MEASURES: These were provided by the results from molecular studies and by the action taken by subjects after a predictive or prenatal result was given. RESULTS: Altogether 15 (50%) subjects for predictive testing had a positive result, but none had serious psychiatric sequelae. Two women were found to be carrying an affected fetus and both requested pregnancy termination. Of 52 diagnostic tests, 33 (63%) were positive. CONCLUSION: The service was used appropriately, and there were no traumatic incidents following positive results. There was no genotypic or sex bias in subjects presenting for testing. Black and white patients were equally likely to be positive for HD on diagnostic testing. The families appreciated the service and found it useful in the detection and prevention of HD.

Female↗
PubMed1999

A century of U.S. censuses and the language characteristics of immigrants.

Since 1890, every U.S. census but one has asked about the language characteristics of the U.S. population. This almost uninterrupted data series, however, has been shaped by contemporaneous presumptions about the ties between language and ethnicity, the likelihood of proficiency in English among various subgroups, and practical constraints. I describe shifts across censuses in the phrasing of questions about language, the coding of responses, and the subpopulations for which the questions were asked and the results were published. I then describe the data generated by these items and discuss their interpretation. I conclude with a summary of the major insights and limitations of a century's worth of data.

Adolescent↗