Ecological opportunity and the origin of adaptive radiations

Ecological opportunity--through entry into a new environment, the origin of a key innovation or extinction of antagonists--is widely thought to link ecological population dynamics to evolutionary diversification. The population-level processes arising from ecological opportunity are well documented under the concept of ecological release. However, there is little consensus as to how these processes promote phenotypic diversification, rapid speciation and adaptive radiation. We propose that ecological opportunity could promote adaptive radiation by generating specific changes to the selective regimes acting on natural populations, both by relaxing effective stabilizing selection and by creating conditions that ultimately generate diversifying selection. We assess theoretical and empirical evidence for these effects of ecological opportunity and review emerging phylogenetic approaches that attempt to detect the signature of ecological opportunity across geological time. Finally, we evaluate the evidence for the evolutionary effects of ecological opportunity in the diversification of Caribbean Anolis lizards. Some of the processes that could link ecological opportunity to adaptive radiation are well documented, but others remain unsupported. We suggest that more study is required to characterize the form of natural selection acting on natural populations and to better describe the relationship between ecological opportunity and speciation rates.

The placebo effect and its determinants in osteoarthritis: meta-analysis of randomised controlled trials

OBJECTIVE

To examine the placebo effect and its potential determinants in the treatment of osteoarthritis (OA) via a systematic literature search of Medline, EMBASE, Scientific Citation Index, Cumulative Index to Nursing and Allied Health Literature (CINAHL) and Cochrane Library.

METHODS

Randomised placebo controlled trials in OA were included. The placebo effect was defined as the overall change from baseline in the placebo group. It was estimated as the effect size (ES; the standard mean difference between baseline and endpoint) and this was compared with the ES obtained from untreated control. ES for pain was the primary outcome. Statistical pooling was undertaken as appropriate and 95% CIs were used for comparison. Quality of trials was assessed and potential determinants of placebo effect were examined using multiple regression analysis. The partial regression coefficient (beta) was used to present the adjusted size of the association.

RESULTS

We identified 198 trials with 193 placebo groups (16 364 patients) and 14 untreated control groups (1167 patients) that met our inclusion criteria. These included a range of therapies (non-pharmacological, pharmacological and surgical treatments). Placebo was effective at relieving pain (ES 0.51, 95% CI 0.46 to 0.55 for the placebo group and 0.03, 95% CI -0.13 to 0.18 for untreated control). Placebo was also effective at improving function and stiffness. The pain-relieving effect increased when the active treatment effect (beta=0.38, p<0.001), baseline pain (0.006, p=0.014) and sample size (0.001, p=0.004) increased, and when placebo was given through injections/needles (0.144, p=0.020).

CONCLUSION

Placebo is effective in the treatment of OA, especially for pain, stiffness and self-reported function. The size of this effect is influenced by the strength of the active treatment, the baseline disease severity, the route of delivery and the sample size of the study.

Do inhibitors of angiotensin-I-converting enzyme protect against risk of cancer?

BACKGROUND

Previous studies have reported an increased risk of cancer with calcium-channel blockers in man. Other work in animals suggests that inhibitors of angiotensin-I-converting enzyme (ACE) protect against cancer. We aimed to assess the risk of cancer in hypertensive patients receiving ACE inhibitors or other antihypertensive drugs.

METHODS

Our retrospective cohort study was based on the records of 5207 patients who attended the Glasgow Blood Pressure Clinic between Jan 1, 1980, and Dec 31, 1995. The patients' records are linked with the Registrar General Scotland and the West of Scotland Cancer Registry.

FINDINGS

Compared with the West of Scotland controls, the relative risks of incident and fatal cancer among the 1559 patients receiving ACE inhibitors were 0.72 (95% CI 0.55-0.92) and 0.65 (0.44-0.93). Among the 3648 patients receiving antihypertensive drugs other than ACE inhibitors (calcium-channel blockers 1416, diuretics 2099, beta-blockers 2681), the corresponding relative risks were 110 (0.97-1.22) and 1.03 (0.87-1.20). The relative risk of cancer was lowest in women on ACE inhibitors: 0.63 (0.41-0.93) for incident cancer; 0.48 (0.23-0.88) for fatal cancer; and 0.37 (0.12-0.87) for female-specific cancers. The reduced relative risk of cancer in patients on ACE inhibitors was greatest with follow-up of longer than 3 years. Calcium-channel blockers, diuretics, and beta-blockers had no apparent effect on risk of cancer.

INTERPRETATION

Long-term use of ACE inhibitors may protect against cancer. The status of this finding is more that of hypothesis generation than of hypothesis testing; randomised controlled trials are needed.

Topical antimicrobial toxicity

Three topical antibiotics and four antiseptics (1% povidone-iodine, 0.25% acetic acid, 3% hydrogen peroxide, and 0.5% sodium hypochlorite) were directly applied to cultured human fibroblasts to quantitatively assess their cytotoxicity. The four antiseptics were found to be cytotoxic; all of the cytotoxic agents except hydrogen peroxide were subsequently found to adversely affect wound healing in an animal model. Comparison of bactericidal and cytotoxic effects of serial dilutions of these four topical agents indicated the cellular toxicity of hydrogen peroxide and acetic acid exceeded their bactericidal potency. Bactericidal noncytotoxic dilutions of povidone-iodine and sodium hypochlorite were identified. These experiments provide evidence that 1% povidone-iodine, 3% hydrogen peroxide, 0.5% sodium hypochlorite, and 0.25% acetic acid are unsuitable for use in wound care. This sequence of experiments could be used to identify bactericidal, noncytotoxic agents prior to their clinical use.

The receptor tyrosine kinase EphB2 regulates NMDA-dependent synaptic function

Members of the Eph family of receptor tyrosine kinases control many aspects of cellular interactions during development, including axon guidance. Here, we demonstrate that EphB2 also regulates postnatal synaptic function in the mammalian CNS. Mice lacking the EphB2 intracellular kinase domain showed wild-type levels of LTP, whereas mice lacking the entire EphB2 receptor had reduced LTP at hippocampal CA1 and dentate gyrus synapses. Synaptic NMDA-mediated current was reduced in dentate granule neurons in EphB2 null mice, as was synaptically localized NR1 as revealed by immunogold localization. Finally, we show that EphB2 is upregulated in hippocampal pyramidal neurons in vitro and in vivo by stimuli known to induce changes in synaptic structure. Together, these data demonstrate that EphB2 plays an important role in regulating synaptic function.

Utah Growth Study: growth standards and the prevalence of growth hormone deficiency

Serial measurements of elementary-school children were conducted for 2 consecutive years to assess height and growth velocity and to determine the prevalence of growth hormone deficiency (GHD) in American children. Trained volunteers measured 114,881 children the first year; 79,495 growth rates were calculated after the second measurements. The height and growth velocity curves generated were very similar to the currently used charts. We examined 555 children with short stature (< 3rd percentile) and poor growth rates (< 5 cm/yr). Five percent had an endocrine disorder. The presence of GHD (peak level, < 10 ng/dl with two provocative tests) was found in 16 previously unrecognized children; 17 children from this school population were already known to have GHD. Boys outnumbered girls 2.7:1 (p = 0.006). Six girls with Turner syndrome also were identified. We conclude that (1) the growth curves generated in the 1960s and 1970s are valid for children of the 1990s; (2) most children growing < 5 cm/yr (a commonly used threshold rate) will not have an endocrine disorder; (3) many children (48% in this study) with GHD and others with Turner syndrome may currently be unrecognized and untreated; (4) GHD appears to be more common in boys; and (5) the prevalence of GHD in the United States is at least 1:3480.

Response to a specific antioestrogen (ICI 182780) in tamoxifen-resistant breast cancer

We treated 19 patients with advanced breast cancer resistant to tamoxifen with a new specific antioestrogen (ICI 182780) which, in animal studies, has no agonist activity. 13 (69%) patients responded (7 had partial responses and 6 showed no change) to monthly intramuscular injections of ICI 182780 after progression on tamoxifen, for a median duration of 18 months with minimum side effects. Preliminary evidence suggests that the agent is without effects on the liver or the hypothalamic-pituitary axis. ICI 182780 appears to be a promising new agent for treatment of advanced and early breast cancer.

Kohn anomalies and electron-phonon interactions in graphite

We demonstrate that graphite phonon dispersions have two Kohn anomalies at the Gamma-E(2g) and K-A'1 modes. The anomalies are revealed by two sharp kinks. By an exact analytic derivation, we show that the slope of these kinks is proportional to the square of the electron-phonon coupling (EPC). Thus, we can directly measure the EPC from the experimental dispersions. The Gamma-E(2g) and K-A'1 EPCs are particularly large, while they are negligible for all the other modes at Gamma and K.

Efficacy of tricyclic drugs in treating child and adolescent depression: a meta-analysis

OBJECTIVE

To examine whether tricyclic antidepressants are superior to placebo in the treatment of child and adolescent depression.

DESIGN

Meta-analysis of 12 randomised controlled trials comparing the efficacy of tricyclic antidepressants with placebo in depressed subjects aged 6-18 years.

MAIN OUTCOME MEASURES

Most studies employed several depression rating scales. For each study the "best available" measure was chosen by using objective criteria, and individual and pooled effect sizes were calculated as the number of standard deviations by which the change scores for the treatment groups exceeded those for the control groups. Where authors had reported numbers "responding" to treatment we calculated individual and pooled ratios for the odds of improvement in treated compared with control subjects.

RESULTS

From the six studies presenting data which enabled an estimation of effect size the pooled effect size was 0.35 standard deviations (95% confidence interval of -0.16 to 0.86) indicating no significant benefit of treatment. From the five studies presenting data on the number of "responders" in each group, the ratio of the odds of a response in the treated compared with the control subjects was calculated and the pooled odds ratio was 1.08 (95% confidence interval of 0.53 to 2.17); again indicating no significant benefit of treatment. The pooled sample had more than an 80% chance of detecting a treatment effect of 0.5 standard deviations or greater. There was an inverse relation between study quality and estimated treatment effect.

CONCLUSIONS

Tricyclic antidepressants appear to be no more effective than placebo in the treatment of depression in children and adolescents.

Autoantibodies in breast cancer: their use as an aid to early diagnosis

BACKGROUND

There is increasing evidence that the immune system produces a humoral response to cancer-derived antigens. This study assessed the diagnostic potential of autoantibodies to multiple known tumour-associated proteins.

PATIENTS AND METHODS

Sera from normal controls (n = 94), primary breast cancer patients (n = 97) and patients with ductal carcinoma in situ (DCIS) (n = 40) were investigated for the presence of autoantibodies to p53, c-myc, HER2, NY-ESO-1, BRCA1, BRCA2 and MUC1 antigens by enzyme-linked immunosorbent assay.

RESULTS

Reproducibly elevated levels of autoantibodies were seen in at least one of the six antigens in 64% of primary breast cancer patient sera and 45% of patients with DCIS at a specificity of 85%. No significant differences were seen when patients were subdivided by age, tumour size, histological grade, lymph node status or detection methodology.

CONCLUSIONS

Autoantibodies against one or more of these tumour-associated antigens appears to indicate the presence of early-stage breast cancers. Autoantibody assays against a panel of antigens could be used as an aid to mammography in the detection and diagnosis of early primary breast cancer, especially in younger women at increased risk of breast cancer where mammography is known to have reduced sensitivity and specificity.

Elementary school-aged children's reports of their health: a cognitive interviewing study

There are no standard methods for assessing the quality of young children's perceptions of their health and well-being and their ability to comprehend the tasks involved in reporting their health. This research involved three cross-sectional studies using cognitive interviews of 5-11-year-old children (N = 114) to determine their ability to respond to various presentations of pictorially illustrated questions about their health. The samples had a predominance of children in the 5-7-year-old range and families of lower and middle socio-economic status. The research questions in Study 1 involved children's ability to convert their health experiences into scaled responses and relate them to illustrated items (n = 35); Study 2 focused on the type of response format most effectively used by children (n = 19); and Study 3 involved testing children's understanding of health-related terms and use of a specific recall period (n = 60). The results of Study 1 showed that children identified with the cartoon drawing of a child depicted in the illustrated items, typically responding that the child was at or near their own age and of the same gender, with no differences related to race. Study 2 results indicated that children responded effectively to circles of graduated sizes to indicate their response and preferred them to same-size circles or a visual analogue scale. Tests of three-, four-, and five-point response formats demonstrated that children could use them all without confusion. In Study 3, expected age-related differences in understanding were obtained. In fact, the 5-year-old children were unable to understand a sufficient number of items to adequately describe their health. Virtually all children 8 years of age and older were able to fully understand the key terms and presentation of items, used the full five-point range of response options, and accurately used a 4-week recall period. Six- and seven-year-olds were more likely than older children to use only the extreme and middle responses on a five-point scale. No pattern of gender differences in understanding or in use of response options was found. We conclude that children as young as eight are able to report on all aspects of their health experiences and can use a five-point response format. Children aged 6-7 had difficulty with some health-related terms and tended to use extreme responses, but they understood the basic task requirements and were able to report on their health experiences. These results provide the guidance needed to develop and test a pediatric health status questionnaire for children 6-11 years old.

Mortality in patients of the Glasgow Blood Pressure Clinic

The mortality of 3783 non-malignant hypertensive patients attending the Glasgow Blood Pressure Clinic between 1968 and 1983 and followed for an average of 6.5 years was compared with that in three control groups: the general population of Strathclyde a group of 15 422 subjects aged 45-64 years and screened in Renfrew and Paisley between 1972 and 1976, and a group of hypertensives seen in a blood pressure clinic based on general practice in Renfrew. Average blood pressure for men at entry to the Glasgow Clinic was 181/111 mmHg falling to 158/96 mmHg during treatment. Corresponding values for women were 185/109 mmHg and 161/96 mmHg. Seven hundred and fifty clinic patients (451 males) died during follow-up, the commonest causes of death in both sexes being myocardial infarction and stroke. All-cause age-adjusted mortality (deaths per 1000 patient-years) was 41.4 for men and 22.1 for women. At all ages in both sexes and for all levels of initial blood pressure mortality was less in patients whose blood pressure was reduced most. Without a randomized control group it is not certain that lower mortality in those with well controlled blood pressure was due to treatment, although this is the most likely explanation. Cigarette smoking, a history of myocardial infarction, angina or stroke, retinal arterio-venous nipping, raised blood urea, an abnormal electrocardiogram (ECG) and secondary hypertension were associated with increased risk, but heavy alcohol intake, obesity, haematocrit greater than 45%, hypokalaemia and social class were not. Life table analysis showed that, despite some reduction of mortality by treatment, the relative risk to men and women in the clinic remained two- to five-times that of the general population. The benefits of treatment were not such as to restore normal expectation of life even when blood pressure was well controlled. Excess mortality in the clinic could not be explained by difference of smoking habit or social class. This suggests that there is in the hypertensive patients of the Glasgow Clinic an element of irreducible risk, that treatment may be beneficial in some respects but harmful in others, or that patients at particularly high risk are selectively referred to the clinic.

Management of frozen shoulder: a systematic review and cost-effectiveness analysis

BACKGROUND

Frozen shoulder is condition in which movement of the shoulder becomes restricted. It can be described as either primary (idiopathic) whereby the aetiology is unknown, or secondary, when it can be attributed to another cause. It is commonly a self-limiting condition, of approximately 1 to 3 years' duration, though incomplete resolution can occur.

OBJECTIVES

To evaluate the clinical effectiveness and cost-effectiveness of treatments for primary frozen shoulder, identify the most appropriate intervention by stage of condition and highlight any gaps in the evidence.

DATA SOURCES

A systematic review was conducted. Nineteen databases and other sources including the Cumulative Index to Nursing and Allied Health (CINAHL), Science Citation Index, BIOSIS Previews and Database of Abstracts of Reviews of Effects (DARE) were searched up to March 2010 and EMBASE and MEDLINE up to January 2011, without language restrictions. MEDLINE, CINAHL and PsycINFO were searched in June 2010 for studies of patients' views about treatment.

REVIEW METHODS

Randomised controlled trials (RCTs) evaluating physical therapies, arthrographic distension, steroid injection, sodium hyaluronate injection, manipulation under anaesthesia, capsular release or watchful waiting, alone or in combination were eligible for inclusion. Patients with primary frozen shoulder (with or without diabetes) were included. Quasi-experimental studies were included in the absence of RCTs and case series for manipulation under anaesthesia (MUA) and capsular release only. Full economic evaluations meeting the intervention and population inclusion criteria of the clinical review were included. Two researchers independently screened studies for relevance based on the inclusion criteria. One reviewer extracted data and assessed study quality; this was checked by a second reviewer. The main outcomes of interest were pain, range of movement, function and disability, quality of life and adverse events. The analysis comprised a narrative synthesis and pair-wise meta-analysis. A mixed-treatment comparison (MTC) was also undertaken. An economic decision model was intended, but was found to be implausible because of a lack of available evidence. Resource use was estimated from clinical advisors and combined with quality-adjusted life-years obtained through mapping to present tentative cost-effectiveness results.

RESULTS

Thirty-one clinical effectiveness studies and one economic evaluation were included. The clinical effectiveness studies evaluated steroid injection, sodium hyaluronate, supervised neglect, physical therapy (mainly physiotherapy), acupuncture, MUA, distension and capsular release. Many of the studies identified were at high risk of bias. Because of variation in the interventions and comparators few studies could be pooled in a meta-analysis. Based on single RCTs, and for some outcomes only, short-wave diathermy may be more effective than home exercise. High-grade mobilisation may be more effective than low-grade mobilisation in a population in which most patients have already had treatment. Data from two RCTs showed that there may be benefit from adding a single intra-articular steroid injection to home exercise in patients with frozen shoulder of < 6 months' duration. The same two trials showed that there may be benefit from adding physiotherapy (including mobilisation) to a single steroid injection. Based on a network of nine studies the MTC found that steroid combined with physiotherapy was the only treatment showing a statistically and clinically significant beneficial treatment effect compared with placebo for short-term pain (standardised mean difference -1.58, 95% credible interval -2.96 to -0.42). This analysis was based on only a subset of the evidence, which may explain why the findings are only partly supportive of the main analysis. No studies of patients' views about the treatments were identified. Average costs ranged from £36.16 for unguided steroid injections to £2204 for capsular release. The findings of the mapping suggest a positive relationship between outcome and European Quality of Life-5 Dimensions (EQ-5D) score: a decreasing visual analogue scale score (less pain) was accompanied by an increasing (better) EQ-5D score. The one published economic evaluation suggested that low-grade mobilisation may be more cost-effective than high-grade mobilisation. Our tentative cost-effectiveness analysis suggested that steroid alone may be more cost-effective than steroid plus physiotherapy or physiotherapy alone. These results are very uncertain.

LIMITATIONS

The key limitation was the lack of data available. It was not possible to undertake the planned synthesis exploring the influence of stage of frozen shoulder or the presence of diabetes on treatment effect. As a result of study diversity and poor reporting of outcome data there were few instances where the planned quantitative synthesis was possible or appropriate. Most of the included studies had a small number of participants and may have been underpowered. The lack of available data made the development of a decision-analytic model implausible. We found little evidence on treatment related to stage of condition, treatment pathways, the impact on quality of life, associated resource use and no information on utilities. Without making a number of questionable assumptions modelling was not possible.

CONCLUSIONS

There was limited clinical evidence on the effectiveness of treatments for primary frozen shoulder. The economic evidence was so limited that no conclusions can be made about the cost-effectiveness of the different treatments. High-quality primary research is required.

Social class gradients in health during adolescence

STUDY OBJECTIVE

To review existing data on social class gradients in adolescent health and to examine whether such gradients exist in new data concerning US adolescents.

DESIGN

Review of relevant publications and unpublished data; regression analyses using adolescent self reported health status data to determine whether there are gradients by social class, using three classes categorised by adolescent reported parental work status and education.

PARTICIPANTS

Adolescents of ages 11-17.

MAIN RESULTS

Findings from the literature indicate the presence of social class gradients in some but not all aspects of adolescent health. Results from new data showed social class gradients in several domains of health and in profiles of health. The likelihood of being satisfied with one's health, of being more resilient (better family involvement, better problem solving, more physical activity, better home safety), having higher school achievement, and of being in the best health profiles were significantly and progressively greater as social class rose. Moreover, the probability of being in the poorest health profile type group was progressively higher as social class declined.

CONCLUSIONS

The review of existing data and the new findings support the existence of social class gradients in satisfaction with one's health, in resilience to health threats, in school achievement, and in being in the best health overall (as manifested by the health profiles composed of four major domains of health). The study had two especially notable findings: (1) the paucity of studies using the same or similar indicators, and (2) the consistent existence of social class gradients in characteristics related to subsequent health, particularly intake of nutritional foods and physical activity. The sparseness of existing data and the different aspects of health investigated in the relatively few studies underscore the need for (1) the development of conceptual models specifically focused on adolescent health and social class; (2) additional inquiry into the measurement of social class and adolescent perceptions of class; (3) inclusion of contextual variables in study design; and (4) longitudinal cohort studies to better understand the specific determinants of health during adolescence.

Social networks of people with mental retardation in residential settings

Information was collected on the social networks of 500 adults with mental retardation receiving different types of residential supports. Results indicated that (a) the reported median size of participants' social networks (excluding staff) was 2 people; (b) 83% of participants were reported to have a staff member; 72%, a member of their family; 54%, another person with mental retardation; and 30%, a person who did not fit into any of these categories in their social network; (c) variation in the size and composition of participants' social networks was associated with a range of variables, including the personal characteristics of residents (age, autism, ability, and challenging behavior), the type of previous and current accommodation, staffing ratios, institutional climate, and the implementation of "active support."

Lifestyle related risk factors for poor health in residential settings for people with intellectual disabilities

Little information is available on the prevalence and determinants of lifestyle related risk factors for poor health (obesity, poor diet, physical inactivity, smoking and alcohol abuse) among people with intellectual disabilities. This study reports the prevalence of these risk factors for 500 people with intellectual disabilities living in different forms of residential provision in the UK. Variables which predict the presence of these risk factors are also identified. While levels of smoking and alcohol abuse were low, the prevalence of poor diet, obesity in women and physical inactivity was high. Analyses of predictors of risk factors present a mixed pattern with regard to participant and service characteristics, with greater ability and less restrictive residential settings being associated with poor diet, smoking and obesity, but physical inactivity being associated with lower ability and more restrictive settings. It is argued that increasing levels of moderate or vigorous physical activity among people with intellectual disabilities would be the single most effective way of improving the health of people with intellectual disabilities.

Statistical issues in analyzing 24-hour dietary recall and 24-hour urine collection data for sodium and potassium intakes

Dietary recalls and urine assays provide different metrics for assessing sodium and potassium intakes. Means, variances, and correlations of data obtained from these two modes of measurement differ. Pooling of these data is not straightforward, and results from studies employing the different modes may not be comparable. To explore differences between these metrics, the authors used data from the Trial of Nonpharmacologic Intervention in the Elderly (TONE), which included repeated standardized 24-hour dietary recalls and 24-hour urine collections administered over 3 years of follow-up, to estimate sodium and potassium intakes. The authors examined data from 341 control participants assigned to usual care that were collected between August 1992 and December 1995. Dietary recalls yielded estimates of sodium intake that averaged 22% less than those from urine assays and estimates of potassium intake that averaged 16% greater than those from urine assays. Sodium intake estimates were less repeatable (r = 0.22 for diet; r = 0.30 for urine) than potassium intake estimates (r = 0.49 for diet; r = 0.50 for urine), making relations with outcomes more difficult to characterize. Overall, the performance of the two measurement modes was fairly similar across demographic subgroups. Errors in separate estimations of long term sodium and potassium intakes using short term data were strongly correlated, more strongly than the underlying long term intakes of these electrolytes. Because of the correlated measurement error, estimated regression coefficients for linear models including both electrolytes as predictors may be confounded such that the separate relations between these nutrients and outcomes such as blood pressure cannot be reliably estimated by common analytical strategies.

Neurofilament immunoreactivity in populations of rat primary afferent neurons: a quantitative study of phosphorylated and non-phosphorylated subunits

Neurofilament subunits in rat dorsal root ganglion (DRG) neurons were examined using five antibodies: NFH, RT97 and NFHP- recognise the 200 kDa subunit (NF200); NFH recognises both phosphorylated and non-phosphorylated forms of NF200 whereas RT97 and NFHP- are specific for the phosphorylated and non-phosphorylated forms respectively; 155 and anti-68 kD recognise the 155 kDa and 68 kDa subunits respectively. All the antibodies apart from NFHP- distinguished between the two populations of neurons corresponding to the light (L) and small dark (SD) cell types as previously shown for RT97. This demonstrates that L and SD neurons contain different levels of neurofilament and that the ability to discriminate between them is not unique to the antibody RT97. It is also evident that DRG neurons contain neurofilament composed of all three subunits. Since NFH and RT97, but not NFHP-, distinguished between the two populations, it appears that it is the presence of the phosphorylated form of NF200 that provides the basis for discrimination between the two cell types. After dephosphorylation of the neurofilament, NFHP- also discriminated between the two populations, indicating that there is more NF200 regardless of phosphorylation state in the L neurons. Observations made from unfixed DRGs indicate that all neurons contain some neurofilament and the neurofilament rich and neurofilament poor populations were also apparent. The use of colchicine apparently caused a small increase in neurofilament levels in at least some perikarya, presumably due to its blocking effect on axoplasmic transport. This caused some SD neurons to become neurofilament rich. We conclude that L neurons contain more neurofilament than SD neurons since both cell types contain non-phosphorylated NF200, but the L neurons also contain a much greater amount of the phosphorylated form.

Alleles of APC modulate the frequency and classes of mutations that lead to colon polyps

Most inherited mutant alleles of the adenomatosis polyposis coli gene (APC) cause the appearance of large numbers of colon polyps, the familial polyposis syndrome. (These mutant alleles are designated APCp alleles.) A subset of APC mutations, the attenuated or APC(AP) alleles, predispose to only a few colon polyps. This leads to the hypothesis that if mutation of the inherited normal allele is rate limiting in polyp development, the increased number of polyps associated with the APCp allele indicates that the frequency of mutations that can lead to polyp formation is higher among APCp carriers than among APC(AP) carriers. We have previously suggested that the APC protein might modulate the frequency of mutations, such as loss of heterozygosity (LOH), necessary for colon polyp formation. We thus reasoned that tumours from patients who carry an APC(AP) allele might show a reduced frequency of LOH compared with tumours from patients who carry an APCp allele. Loss of AAPC mutant alleles is designated as LOH(AP). Screening of tumours from APC(AP) carriers revealed a reduction of LOH compared with that of an unselected group of polyposis patients. In fact, no loss of the inherited APC(N) allele was observed, although sequencing showed that the inherited APC(N) allele had frequently undergone point mutations and small deletions in the tumours. A low frequency loss of the inherited APC(AP) allele was seen. These findings support the suggestion that the APC(AP) allele has residual gene activity and that this activity modulates the spectrum and frequency of mutations that lead to adenoma formation.