Self-determined motivation and physical activity in patients with rheumatoid arthritis: a cross-sectional study.

OBJECTIVE: To identify factors associated with two self-reported measures of physical activity (PA) in patients with rheumatoid arthritis (RA). METHOD: Hospital outpatients with RA from central Norway filled in questionnaires about symptoms, psychological factors, and PA. Outcomes were two alternative self-reported measures of PA: (i) fulfilling the aerobic PA recommendations of ≥ 150 min/week at moderate intensity or ≥ 75 min/week at vigorous intensity; or (ii) being in the PA maintenance stage of the Stages of Exercise Behaviour Change framework. Logistic regression was applied to identify factors associated with PA. Step 1 included the independent variables sex, age, and smoking habits. Step 2a added self-reported function, joint pain during the past 6 months, and fatigue to Step 1. Step 2b added Exercise Self-Efficacy and the Relative Autonomy Index (RAI), calculated from the Behavioural Regulation in Exercise Questionnaire-2, to Step 1. Step 3 included all the mentioned independent variables. Steps 1-3 were analysed for each PA measure. RESULTS: In total, 227 patients participated. The RAI had a statistically significant positive association with being physically active according to both PA definitions. Joint pain had a significant negative association with meeting the aerobic PA recommendations but was not associated with being in the PA maintenance stage. CONCLUSION: The degree of self-determined motivation was the most consistent variable associated with self-reported PA behaviour. Joint pain was associated with one of the two PA measures. Motivation and joint pain may be useful targets for intervention in clinical practice to improve PA engagement among patients with RA.

Previous fracture and subsequent fracture risk: a meta-analysis to update FRAX.

A large international meta-analysis using primary data from 64 cohorts has quantified the increased risk of fracture associated with a previous history of fracture for future use in FRAX. INTRODUCTION: The aim of this study was to quantify the fracture risk associated with a prior fracture on an international basis and to explore the relationship of this risk with age, sex, time since baseline and bone mineral density (BMD). METHODS: We studied 665,971 men and 1,438,535 women from 64 cohorts in 32 countries followed for a total of 19.5 million person-years. The effect of a prior history of fracture on the risk of any clinical fracture, any osteoporotic fracture, major osteoporotic fracture, and hip fracture alone was examined using an extended Poisson model in each cohort. Covariates examined were age, sex, BMD, and duration of follow-up. The results of the different studies were merged by using the weighted ß-coefficients. RESULTS: A previous fracture history, compared with individuals without a prior fracture, was associated with a significantly increased risk of any clinical fracture (hazard ratio, HR = 1.88; 95% CI = 1.72-2.07). The risk ratio was similar for the outcome of osteoporotic fracture (HR = 1.87; 95% CI = 1.69-2.07), major osteoporotic fracture (HR = 1.83; 95% CI = 1.63-2.06), or for hip fracture (HR = 1.82; 95% CI = 1.62-2.06). There was no significant difference in risk ratio between men and women. Subsequent fracture risk was marginally downward adjusted when account was taken of BMD. Low BMD explained a minority of the risk for any clinical fracture (14%), osteoporotic fracture (17%), and for hip fracture (33%). The risk ratio for all fracture outcomes related to prior fracture decreased significantly with adjustment for age and time since baseline examination. CONCLUSION: A previous history of fracture confers an increased risk of fracture of substantial importance beyond that explained by BMD. The effect is similar in men and women. Its quantitation on an international basis permits the more accurate use of this risk factor in case finding strategies.

Update of the fracture risk prediction tool FRAX: a systematic review of potential cohorts and analysis plan.

We describe the collection of cohorts together with the analysis plan for an update of the fracture risk prediction tool FRAX with respect to current and novel risk factors. The resource comprises 2,138,428 participants with a follow-up of approximately 20 million person-years and 116,117 documented incident major osteoporotic fractures. INTRODUCTION: The availability of the fracture risk assessment tool FRAX® has substantially enhanced the targeting of treatment to those at high risk of fracture with FRAX now incorporated into more than 100 clinical osteoporosis guidelines worldwide. The aim of this study is to determine whether the current algorithms can be further optimised with respect to current and novel risk factors. METHODS: A computerised literature search was performed in PubMed from inception until May 17, 2019, to identify eligible cohorts for updating the FRAX coefficients. Additionally, we searched the abstracts of conference proceedings of the American Society for Bone and Mineral Research, European Calcified Tissue Society and World Congress of Osteoporosis. Prospective cohort studies with data on baseline clinical risk factors and incident fractures were eligible. RESULTS: Of the 836 records retrieved, 53 were selected for full-text assessment after screening on title and abstract. Twelve cohorts were deemed eligible and of these, 4 novel cohorts were identified. These cohorts, together with 60 previously identified cohorts, will provide the resource for constructing an updated version of FRAX comprising 2,138,428 participants with a follow-up of approximately 20 million person-years and 116,117 documented incident major osteoporotic fractures. For each known and candidate risk factor, multivariate hazard functions for hip fracture, major osteoporotic fracture and death will be tested using extended Poisson regression. Sex- and/or ethnicity-specific differences in the weights of the risk factors will be investigated. After meta-analyses of the cohort-specific beta coefficients for each risk factor, models comprising 10-year probability of hip and major osteoporotic fracture, with or without femoral neck bone mineral density, will be computed. CONCLUSIONS: These assembled cohorts and described models will provide the framework for an updated FRAX tool enabling enhanced assessment of fracture risk (PROSPERO (CRD42021227266)).

Reducing soft-tissue shrinkage artefacts caused by staining with Lugol's solution.

Diffusible iodine-based contrast-enhanced computed tomography (diceCT) is progressively used in clinical and morphological research to study developmental anatomy. Lugol's solution (Lugol) has gained interest as an effective contrast agent; however, usage is limited due to extensive soft-tissue shrinkage. The mechanism of Lugol-induced shrinkage and how to prevent it is largely unknown, hampering applications of Lugol in clinical or forensic cases where tissue shrinkage can lead to erroneous diagnostic conclusions. Shrinkage was suggested to be due to an osmotic imbalance between tissue and solution. Pilot experiments pointed to acidification of Lugol, but the relation of acidification and tissue shrinkage was not evaluated. In this study, we analyzed the relation between tissue shrinkage, osmolarity and acidification of the solution during staining. Changes in tissue volume were measured on 2D-segmented magnetic resonance and diceCT images using AMIRA software. Partial correlation and stepwise regression analysis showed that acidification of Lugol is the main cause of tissue shrinkage. To prevent acidification, we developed a buffered Lugol's solution (B-Lugol) and showed that stabilizing its pH almost completely prevented shrinkage without affecting staining. Changing from Lugol to B-Lugol is a major improvement for clinical and morphological research and only requires a minor adaptation of the staining protocol.

TDCS effects on pointing task learning in young and old adults.

Skill increase in motor performance can be defined as explicitly measuring task success but also via more implicit measures of movement kinematics. Even though these measures are often related, there is evidence that they represent distinct concepts of learning. In the present study, the effect of multiple tDCS-sessions on both explicit and implicit measures of learning are investigated in a pointing task in 30 young adults (YA) between 27.07 ± 3.8 years and 30 old adults (OA) between 67.97 years ± 5.3 years. We hypothesized, that OA would show slower explicit skill learning indicated by higher movement times/lower accuracy and slower implicit learning indicated by higher spatial variability but profit more from anodal tDCS compared with YA. We found age-related differences in movement time but not in accuracy or spatial variability. TDCS did not skill learning facilitate learning neither in explicit nor implicit parameters. However, contrary to our hypotheses, we found tDCS-associated higher accuracy only in YA but not in spatial variability. Taken together, our data shows limited overlapping of tDCS effects in explicit and implicit skill parameters. Furthermore, it supports the assumption that tDCS is capable of producing a performance-enhancing brain state at least for explicit skill acquisition.

Does treatment with bisphosphonates protect against fractures in real life? The HUNT study, Norway.

Bisphosphonates reduce fractures in randomized controlled trials (RCT); however, there is less information from real life. In our population including 14,990 women and 13,239 men, use of bisphosphonates reduced risk of fractures in hip and forearm in women. The magnitude of the effect was comparable to results from RCT. INTRODUCTION: The objective was to examine if treatment with bisphosphonates (BPs) was associated with reduced risk of fractures in the hip and forearm in women and men in the general population. METHODS: In a cohort study based on data from the third wave of the population-based HUNT Study (HUNT3), the fracture registry in Nord-Trøndelag, and the Norwegian Prescription Database, 14,990 women and 13,239 men 50-85 years were followed from the date of participating in HUNT3 (2006-2008) until the date of first fracture in the hip or forearm, death, or end of study (31 December 2012). Hazard ratios with 95% confidence intervals for hip and forearm fracture according to use of BPs were estimated using Cox proportional hazards models with time-dependent exposure. Adjustment for individual FRAX® fracture risk assessment scores was included. RESULTS: BPs, predominantly alendronate, were used by 9.4% of the women and 1.5% of the men. During a median of 5.2 years of follow-up, 265 women and 133 men had a hip fracture, and 662 women and 127 men had a forearm fracture. Compared with non-users of BPs, the hazard ratios with 95% confidence interval for a fracture among users of BPs adjusted for age and FRAX® were 0.67 (0.52-0.86) for women and 1.13 (0.50-2.57) for men. Among users of glucocorticoids, the corresponding figures were 0.35 (0.19-0.66) and 1.16 (0.33-4.09), respectively. CONCLUSIONS: Use of BPs was associated with reduced risk of fractures in hip and forearm in women, and the magnitude of effect is comparable to results from RCTs.

Genetic risk score associations for myocardial infarction are comparable in persons with and without rheumatoid arthritis: the population-based HUNT study.

Persons with rheumatoid arthritis (RA) have increased risk of myocardial infarction (MI). Overlapping associations with MI of weighted genetic risk scores (wGRS) for coronary artery disease (CAD) and RA is unknown in a population-based setting. Data from the prospective Nord-Trøndelag Health Study (HUNT2: 1995-1997 and HUNT3: 2006-2008) were used. wGRS added each participant's carriage of all risk variants weighted by the coefficient from published association studies. Published wGRS for CAD and RA were analysed in Cox regression with MI as outcome, age as analysis time, and censoring at the first MI, death, or 31.12.2017. 2609 of 61,465 participants developed MI during follow-up (mean 17.7 years). The best-fitting wGRS for CAD and RA included 157 and 27 single-nucleotide polymorphisms, respectively. In multivariable analysis including traditional CAD risk factors, the CAD wGRS was associated with MI [hazard ratio = 1.23 (95% CI 1.18-1.27) for each SD increase, p < 0.0001] in RA patients (n = 433) and controls. The RA wGRS was not significant (p = 0.06). Independently from traditional risk factors, a CAD wGRS was significantly associated with the risk for MI in RA patients and controls, whereas an RA wGRS was not. The captured genetic risk for RA contributed little to the risk of MI.

Comparison of methods to construct a genetic risk score for prediction of rheumatoid arthritis in the population-based Nord-Trøndelag Health Study, Norway.

OBJECTIVES: To evaluate selection methods among published single-nucleotide polymorphisms (SNPs) associated with RA to construct predictive genetic risk scores (GRSs) in a population-based setting. METHODS: The Nord-Trøndelag Health (HUNT) Study is a prospective cohort study among the whole adult population of northern Trøndelag, Norway. Participants in HUNT2 (1995-1997) and HUNT3 (2006-2008) were included (489 RA cases, 61 584 controls). The initial SNP selection from relevant genome-wide studies included 269 SNPs from 30 studies. Following different selection criteria, SNPs were weighted by published odds ratios. The sum of each person's carriage of all weighted susceptibility variants was calculated for each GRS. RESULTS: The best-fitting risk score included 27 SNPs [weighted genetic risk score 27 (wGRS27)] and was identified using P-value selection criterion ≤5 × 10-8, the largest possible SNP selection without high linkage disequilibrium (r2 < 0.8), and lasso regression to select for positive coefficients. In a logistic regression model adjusted for gender, age and ever smoking, wGRS27 was associated with RA [odds ratio 1.86 (95% CI 1.71, 2.04) for each s.d. increase, P < 0.001]. The AUC was 0.76 (95% CI 0.74, 0.78). The positive and negative predictive values were 1.6% and 99.7%, respectively, and the positive predictive value was not improved in sensitivity analyses subselecting participants to illustrate settings with increased RA prevalences. Other schemes selected more SNPs but resulted in GRSs with lower predictive ability. CONCLUSION: Constructing a wGRS based on a smaller selection of informative SNPs improved predictive ability. Even with a relatively high AUC, the low PPV illustrates that there was a large overlap in risk variants among RA patients and controls, precluding clinical usefulness.

Proton pump inhibitors and fracture risk. The HUNT study, Norway.

Proton pump inhibitors (PPIs) have been linked to increased risk of fracture; the data have, however, been diverging. We did not find any increased risk of fractures among users of PPIs in a Norwegian population of 15,017 women and 13,241 men aged 50-85 years with detailed information about lifestyle and comorbidity. INTRODUCTION: Proton pump inhibitors (PPIs) are widely prescribed and have been linked to increased risk of fracture. METHODS: We used data from the Nord-Trøndelag Health Study (HUNT3), The Fracture registry in Nord-Trøndelag, and the Norwegian Prescription Database, including 15,017 women and 13,241 men aged 50-85 years. The study population was followed from the date of participating in HUNT3 (2006-2008) until the date of first fracture (forearm or hip), death, or end of study (31 December 2012). The Cox proportional hazards model with time-dependent exposure to PPIs was applied, and each individual was considered as unexposed until the first prescriptions was filled. To be included, the prescription of PPIs should minimum be equivalent to 90 defined daily doses (DDD) in the period. Individuals were defined as exposed until 6 months after end of drug supply. RESULTS: The proportion of women and men using PPIs was 17.9% and 15.5%, respectively. During a median of 5.2 years follow-up, 266 women and 134 men had a first hip fracture and 662 women and 127 men, a first forearm fracture. The combined rate/1000 patient-years for forearm and hip fractures in women was 49.2 for users of PPIs compared with 64.1 among non-users; for men 18.6 and 19.8, respectively. The hazard ratios with 95% confidence interval for the first forearm or hip fracture among users of PPIs in the age-adjusted analysis were 0.82 (0.67-1.01) for women and 1.05 (0.72-1.52) for men. Adjusting for age, use of anti-osteoporotic drugs, and FRAX, the HR declined to 0.80 (0.65-0.98) in women and 1.00 (0.69-1.45) in men. CONCLUSIONS: Use of PPIs was not associated with an increased risk of fractures.

The Pronephros; a Fresh Perspective.

Contemporary papers and book chapters on nephrology open with the assumption that human kidney development passes through three morphological stages: pronephros, mesonephros, and metanephros. Current knowledge of the human pronephros, however, appears to be based on only a hand full of human specimens. The ongoing use of variations in the definition of a pronephros hampers the interpretation of study results. Because of the increased interest in the anamniote pronephros as a genetic model for kidney organogenesis we aimed to provide an overview of the literature concerning kidney development and to clarify the existence of a pronephros in human embryos. We performed an extensive literature survey regarding vertebrate renal morphology and we investigated histological sections of human embryos between 2 and 8 weeks of development. To facilitate better understanding of the literature about kidney development, a referenced glossary with short definitions was composed. The most striking difference between pronephros versus meso- and metanephros is found in nephron architecture. The pronephros consists exclusively of non-integrated nephrons with external glomeruli, whereas meso- and metanephros are composed of integrated nephrons with internal glomeruli. Animals whose embryos have comparatively little yolk at their disposal and hence have a free-swimming larval stage do develop a pronephros that is dedicated to survival in aquatic environments. Species in which embryos do not have a free-swimming larval stage have embryos that are supplied with a large amount of yolk or that develop within the body of the parent. In those species the pronephros is usually absent, incompletely developed, and apparently functionless. Non-integrated nephrons were not identified in histological sections of human embryos. Therefore, we conclude that a true pronephros is not detectable in human embryos although the most cranial part of the amniote excretory organ is often confusingly referred to as pronephros. The term pronephros should be avoided in amniotes unless all elements for a functional pronephros are undeniably present.

Anti-osteoporosis drug use: too little, too much, or just right? The HUNT study, Norway.

Use of anti-osteoporotic drugs (AODs) was examined in a Norwegian population 50-85 years. Among them with Fracture Risk Assessment Tool (FRAX) score for major osteoporotic fracture ≥ 20, 25% of the women and 17% of the men received AODs. The strongest predictors for AODs were high age in women and use of glucocorticoids among men. INTRODUCTION: To examine the use of anti-osteoporotic drugs (AODs) and to identify predictors for prescriptions. METHODS: Data were obtained from the Nord-Trøndelag Health Study (HUNT3) performed in 2006-2008 and the Norwegian Prescription Database, including 15,075 women and 13,386 men aged 50-85 years. Bone mineral density (BMD) in the femoral neck was measured in a subgroup of 4538 women and 2322 men. High fracture risk was defined as a FRAX score for major osteoporotic fracture (MOF) ≥ 20%; in the subgroup with BMD, high risk was in addition defined as FRAXMOF ≥ 20% or T-score ≤ - 2.5. Hazard ratios (HRs) for predictors of incident use of AODs within 2 years after HUNT3 were estimated by Cox' proportional hazards model. RESULTS: Among individuals with FRAX MOF ≥ 20%, 25% of the women and 17% of the men were treated with AODs. Among those with FRAX MOF < 20%, 3% and 1% were treated, respectively. In the subgroup with BMD measurement, 24% of the women and 16% of the men at high risk of fractures were treated, compared to 3 and 1% in women and men not fulfilling the criteria. In women, high age was the strongest predictor for treatment (HR 3.84: 95% confidence interval 2.81-5.24), followed by use of glucocorticoids (GCs) (2.68:1.84-3.89). In men, predictors were use of GCs (5.28: 2.70-10.35) followed by multimorbidity (3.16:1.31-7.63). In the subgroup with BMD, T-score ≤ - 2.5 was the strongest predictor (women 3.98:2.67-5.89; men 13.31:6.17-28.74). CONCLUSIONS: This study suggests an undertreatment of AODs in individuals at high risk of fracture.

Validation of FRAX and the impact of self-reported falls among elderly in a general population: the HUNT study, Norway.

Fracture Risk Assessment Tool (FRAX) without bone mineral density (BMD) for hip fracture prediction was validated in a Norwegian population 50-90 years. Fracture risk increased with higher FRAX score, and the observed number of hip fractures agreed well with the predicted number, except for the youngest and oldest men. Self-reported fall was an independent risk factor for fracture in women. INTRODUCTION: The primary aim was to validate FRAX without BMD for hip fracture prediction in a Norwegian population of men and women 50-90 years. Secondary, to study whether information of falls could improve prediction of fractures in the subgroup aged 70-90 years. METHODS: Data were obtained from the third survey of the Nord-Trøndelag Health Study (HUNT3), the fracture registry in Nord-Trøndelag, and the Norwegian Prescription Database (NorPD), including 15,432 women and 13,585 men. FRAX hip without BMD was calculated, and hip fractures were registered for a median follow-up of 5.2 years. The number of estimated and observed fractures was assessed, ROC curves with area under the curve (AUC), and Cox regression analyses. For the group aged 70-90 years, self-reported falls the last year before HUNT3 were included in the Cox regression model. RESULTS: The risk of fracture increased with higher FRAX score. When FRAX groups were categorized in a 10-year percentage risk for hip fracture as follows, <4, 4-7.9, 8-11.9, and ≥12%, the hazard ratio (HR) for hip fracture between the lowest and the highest group was 17.80 (95% CI: 12.86-24.65) among women and 23.40 (13.93-39.30) in men. Observed number of hip fractures agreed quite well with the predicted number, except for the youngest and oldest men. AUC was 0.81 (0.78-0.83) for women and 0.79 (0.76-0.83) for men. Self-reported fall was an independent risk factor for fracture in women (HR 1.64, 1.20-2.24), and among men, this was not significant (1.09, 0.65-1.83). CONCLUSIONS: FRAX without BMD predicted hip fracture reasonably well. In the age group 70-90 years, falls seemed to imply an additional risk among women.

The Impact of Patient Demographics, Anatomy, Comorbidities, and Peri-operative Planning on the Primary Functional Maturation of Autogenous Radiocephalic Arteriovenous Fistula.

OBJECTIVES: The aim of this study was to evaluate the collective and/or independent impact of patient demographics, comorbidities, anatomical factors, and peri-operative parameters on the primary functional maturation of RCAVFs. This study also aimed to identify the range and best cut off value for each variable and evaluate the likelihood, significance and percentage of primary functional maturation of RCAVFs. METHODS: This was a prospective consecutive single centre cohort study over a 4 year period; it was conducted on patients with the intention-to-treat using a radiocephalic arteriovenous fistula (RCAVF) (Brescia-Cimino). During this period 548 vascular access procedures, inclusive of RCAVF, were performed. Variables included patient demographics (age, gender), anatomical variance (cephalic vein, radial artery diameter, laterality), comorbidities (diabetes mellitus, ischaemic heart disease, congestive cardiac failure, hypertension), aetiology of renal failure, and anaesthesia type (local versus general anaesthesia). RESULTS: Of the total, 324 patients, cephalic vein diameter > 1.5 mm (OR 4.57, 95% CI, 2.42-8.63, p < .001) (non-augmented) and radial artery diameter > 1.6 mm (OR 12.26, 95% CI, 6.27-23.97, p < .001) were found to be independently associated with the primary functional maturation of 86% in the RCAVF formation. CONCLUSION: Of all the variables, cephalic vein and radial artery diameter are independently associated with the primary functional maturation of RCAVFs.

Psoriasis, fracture risk and bone mineral density: the HUNT Study, Norway.

BACKGROUND: An association between psoriasis and osteoporosis has been reported. OBJECTIVES: To investigate, in a large prospective population-based Norwegian study, whether psoriasis is associated with increased risk of forearm or hip fracture; to investigate the cross-sectional association between psoriasis and bone mineral density (BMD) T-score in a subpopulation. METHODS: Hospital-derived fracture data from Nord-Trøndelag County (1995-2013) were linked to psoriasis information, BMD measurements and lifestyle factors from the third survey of the Nord-Trøndelag Health Study 2006-08 (HUNT3); socioeconomic data from the National Education Database; and use of medication from the Norwegian Prescription Database. RESULTS: Among 48 194 participants in HUNT3, we found no increased risk of forearm or hip fracture in 2804 patients with self-reported psoriasis [overall age- and sex-adjusted hazard ratio 1·03, 95% confidence interval (CI) 0·82-1·31]. No clear association was found between psoriasis and mean BMD T-score; overall age- and sex-adjusted differences in total hip, femoral neck and lumbar spine BMD T-scores were 0·02 (95% CI -0·11 to 0·14), 0·05 (95% CI -0·06 to 0·17) and 0·07 (95% CI -0·09 to 0·24), respectively. No clear association was found between psoriasis and prevalent osteoporosis in either total hip, femoral neck or lumbar spine; overall age- and sex-adjusted odds ratio was 0·77 (95% CI 0·54-1·10). Associations did not change substantially after adjustment for education, smoking, systemic steroid use and body mass index. CONCLUSIONS: We found no association between psoriasis and risk of fracture. The study did not indicate reduced BMD T-score or higher prevalence of osteoporosis among patients with psoriasis.

HPV knowledge gaps and information seeking by oral cancer patients.

OBJECTIVES: The incidence of human papillomavirus (HPV) positive oral squamous cell carcinoma (OSCC) continues to increase over time, challenging healthcare providers to address their patients' HPV-related concerns. MATERIALS AND METHODS: This prospective study assessed health literacy, HPV knowledge, utilization and trust in information sources among patients with incident HPV-positive or HPV-negative OSCC diagnosed at the Ohio State University from 2011 to 2015. Health literacy was assessed with a standardized scale. Additional questions evaluated HPV knowledge (including transmission, prevalence, health consequences and treatment), the frequency and type of information sources sought, and trust in those sources. RESULTS: Surveys were collected from 372 OSCC cases (HPV-positive, n=188; HPV-negative, n=184). Despite high mean health literacy scores, only 45.2% of HPV-related knowledge questions were answered correctly. HPV was known to be a sexually transmitted infection and a cause of cervical and anal cancer by 66.0%, 56.5% and 15.2%, respectively. In all domains, cases with HPV-positive OSCC were significantly more informed than HPV-negative cases (for all, p<0.01). Only 52.7% and 56.2% of patients with HPV-positive OSCC felt they knew enough to be comfortable discussing HPV with their doctor or sexual partner, respectively. The most frequently used information source was the internet (80.9%), which ranked 8th in trust of 15 possible sources. Although most (95.5%) patients trusted information from their doctors, only 37.9% used doctors as an information source. CONCLUSIONS: Doctors are a highly trusted, but infrequent utilized, information source and should facilitate patient access to high-quality HPV information sources.

ICRP Publication 131: Stem cell biology with respect to carcinogenesis aspects of radiological protection.

Current knowledge of stem cell characteristics, maintenance and renewal, evolution with age, location in 'niches', and radiosensitivity to acute and protracted exposures is reviewed regarding haematopoietic tissue, mammary gland, thyroid, digestive tract, lung, skin, and bone. The identity of the target cells for carcinogenesis continues to point to the more primitive and mostly quiescent stem cell population (able to accumulate the protracted sequence of mutations necessary to result in malignancy), and, in a few tissues, to daughter progenitor cells. Several biological processes could contribute to the protection of stem cells from mutation accumulation: (1) accurate DNA repair; (2) rapid induced death of injured stem cells; (3) retention of the intact parental strand during divisions in some tissues so that mutations are passed to the daughter differentiating cells; and (4) stem cell competition, whereby undamaged stem cells outcompete damaged stem cells for residence in the vital niche. DNA repair mainly operates within a few days of irradiation, while stem cell replications and competition require weeks or many months depending on the tissue type. This foundation is used to provide a biological insight to protection issues including the linear-non-threshold and relative risk models, differences in cancer risk between tissues, dose-rate effects, and changes in the risk of radiation carcinogenesis by age at exposure and attained age.