The Clinical Utility of Repeating Magnetic Resonance Imaging (MRI) Scans Within 12 Months in the Management of Lumbosacral Degenerative Disc Disease

PURPOSE

Magnetic resonance imaging (MRI) is the gold standard investigation for lumbosacral degenerative disc disease. However, there is controversy regarding the clinical value of repeating an MRI scan within 12 months when a patient presents with recurring or changing symptoms. This study measures rates of radiological change in a real-world cohort to guide clinicians when deciding to repeat a scan.

METHODS

All patients over a 10-year window in one general hospital who underwent two lumbosacral MRI scans for degenerative disc disease within 12 months of each other were included in the study. All MRI reports were manually reviewed. The level of main vertebral pathology was recorded, along with the location of a disc prolapse. Time intervals between the two scans were calculated, and these were collated into 30-day intervals for analysis. The repeat scans were categorized into three groups: no change, radiological improvement, and radiological deterioration. Patients who had clinically significant deterioration in the form of cauda equina compression on MRI scans were recorded.

FINDINGS

Four hundred and eighty-one patients were included for analysis. Three hundred and ninety (81%) showed no change in MRI findings, 18 (3.7%) had improvements in their repeat scans, and 73 (15.3%) demonstrated deterioration in their repeat scans. Of the 73 patients with radiological deterioration, three patients (0.62% of the total) required urgent surgical intervention for cauda equina syndrome (CES).

CONCLUSIONS

Though there is no alternative to detailed clinical assessment in determining whether a repeat MRI scan is indicated, the findings demonstrate that repeating MRI within 12 months for patients with lumbosacral degenerative disc disease has a low chance of altering the management plan. Over the 10-year period, only three patients required an urgent change to their clinical management. We believe this data can help guide clinical decision-making when considering a repeat scan.

Open Minimally Invasive Parathyroidectomy Versus Minimally Invasive Video-Assisted Parathyroidectomy: A Systematic Review and Meta-Analysis

Various minimally invasive techniques exist for surgical parathyroidectomy. The aim of this study was to conduct a meta-analysis comparing two popular minimally invasive techniques: minimally invasive video-assisted parathyroidectomy (MIVAP) and open minimally invasive parathyroidectomy (OMIP). An extensive search was conducted of online databases to identify all previous studies that had compared MIVAP and OMIP. The primary outcome measures considered were visual analog scale (VAS) score 24 hours postoperatively, conversion of operation (to open), failure rate and analgesic consumption. The data from these studies was extracted and compiled into a meta-analysis. The literature search yielded 104 studies of which four were included, enrolling 903 patients in this analysis. A significant difference was found regarding rates of conversion to open parathyroidectomy between the two groups, with the OMIP group demonstrating fewer conversions (MD = 3.52, CI = (2.04-6.08), P< 0.00001). No statistically significant differences were found between the two groups when comparing postoperative VAS scores at 24 hours (MD = -1.75, CI = (-9.8-6.3), P = 0.67), consumption of analgesia (OR = 0.49, CI = 0.07-3.54, P = 0.48) or failure rates (OR = 1.81, CI = 0.58-5.72, P = 0.31). OMIP was seen to require less need to convert to open parathyroidectomy with shorter operative times, while similar complication rates and scar lengths to MIVAP. More studies are required to evaluate the superior technique for parathyroidectomy.

Full-Thickness Skin Graft Versus Split-Thickness Skin Graft for Radial Forearm Free Flap Transfer in Oral Cavity Reconstruction: A Systematic Review and Meta-Analysis

The radial forearm free flap (RFFF) is a surgical technique for addressing intraoral reconstruction. However, with the limitation of an unavoidable defect at the RFFF donor site, split-thickness skin grafts (STSGs) have been a solution for repairing these defects, but they are not without challenges. This study aimed to evaluate an approach using full-thickness skin grafts (FTSGs), comparing their effectiveness in terms of aesthetics, pain, complications, and scarring. A systematic review and meta-analysis were conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Studies comparing FTSG with STSG for RFFF donor site repair in head and neck cancer patients were included. Primary outcomes measured were appearance and pain at the RFFF site, and secondary outcomes were infection, tendon exposure, graft loss, and scar assessment. A meta-analysis and systematic review of eight studies demonstrated that FTSG provided a superior aesthetic appearance at the RFFF donor site compared to STSG (p = 0.001), with low heterogeneity among the studies. The analysis found no significant difference in donor site pain between techniques. There were no significant differences in infection, tendon exposure, or skin graft loss between the two graft methods. This study suggests that FTSG is comparable to STSG in terms of donor site pain, scarring, and infection while offering superior aesthetic outcomes.

Textbook outcome following oesophagectomy for cancer: international cohort study

Background

Textbook outcome has been proposed as a tool for the assessment of oncological surgical care. However, an international assessment in patients undergoing oesophagectomy for oesophageal cancer has not been reported. This study aimed to assess textbook outcome in an international setting.

Methods

Patients undergoing curative resection for oesophageal cancer were identified from the international Oesophagogastric Anastomosis Audit (OGAA) from April 2018 to December 2018. Textbook outcome was defined as the percentage of patients who underwent a complete tumour resection with at least 15 lymph nodes in the resected specimen and an uneventful postoperative course, without hospital readmission. A multivariable binary logistic regression model was used to identify factors independently associated with textbook outcome, and results are presented as odds ratio (OR) and 95 per cent confidence intervals (95 per cent c.i.).

Results

Of 2159 patients with oesophageal cancer, 39.7 per cent achieved a textbook outcome. The outcome parameter ‘no major postoperative complication’ had the greatest negative impact on a textbook outcome for patients with oesophageal cancer, compared to other textbook outcome parameters. Multivariable analysis identified male gender and increasing Charlson comorbidity index with a significantly lower likelihood of textbook outcome. Presence of 24-hour on-call rota for oesophageal surgeons (OR 2.05, 95 per cent c.i. 1.30 to 3.22; P = 0.002) and radiology (OR 1.54, 95 per cent c.i. 1.05 to 2.24; P = 0.027), total minimally invasive oesophagectomies (OR 1.63, 95 per cent c.i. 1.27 to 2.08; P &lt; 0.001), and chest anastomosis above azygous (OR 2.17, 95 per cent c.i. 1.58 to 2.98; P &lt; 0.001) were independently associated with a significantly increased likelihood of textbook outcome.

Conclusion

Textbook outcome is achieved in less than 40 per cent of patients having oesophagectomy for cancer. Improvements in centralization, hospital resources, access to minimal access surgery, and adoption of newer techniques for improving lymph node yield could improve textbook outcome.

Textbook outcome following oesophagectomy for cancer: international cohort study

BACKGROUND

Textbook outcome has been proposed as a tool for the assessment of oncological surgical care. However, an international assessment in patients undergoing oesophagectomy for oesophageal cancer has not been reported. This study aimed to assess textbook outcome in an international setting.

METHODS

Patients undergoing curative resection for oesophageal cancer were identified from the international Oesophagogastric Anastomosis Audit (OGAA) from April 2018 to December 2018. Textbook outcome was defined as the percentage of patients who underwent a complete tumour resection with at least 15 lymph nodes in the resected specimen and an uneventful postoperative course, without hospital readmission. A multivariable binary logistic regression model was used to identify factors independently associated with textbook outcome, and results are presented as odds ratio (OR) and 95 per cent confidence intervals (95 per cent c.i.).

RESULTS

Of 2159 patients with oesophageal cancer, 39.7 per cent achieved a textbook outcome. The outcome parameter 'no major postoperative complication' had the greatest negative impact on a textbook outcome for patients with oesophageal cancer, compared to other textbook outcome parameters. Multivariable analysis identified male gender and increasing Charlson comorbidity index with a significantly lower likelihood of textbook outcome. Presence of 24-hour on-call rota for oesophageal surgeons (OR 2.05, 95 per cent c.i. 1.30 to 3.22; P = 0.002) and radiology (OR 1.54, 95 per cent c.i. 1.05 to 2.24; P = 0.027), total minimally invasive oesophagectomies (OR 1.63, 95 per cent c.i. 1.27 to 2.08; P < 0.001), and chest anastomosis above azygous (OR 2.17, 95 per cent c.i. 1.58 to 2.98; P < 0.001) were independently associated with a significantly increased likelihood of textbook outcome.

CONCLUSION

Textbook outcome is achieved in less than 40 per cent of patients having oesophagectomy for cancer. Improvements in centralization, hospital resources, access to minimal access surgery, and adoption of newer techniques for improving lymph node yield could improve textbook outcome.

Postoperative outcomes in oesophagectomy with trainee involvement

BACKGROUND

The complexity of oesophageal surgery and the significant risk of morbidity necessitates that oesophagectomy is predominantly performed by a consultant surgeon, or a senior trainee under their supervision. The aim of this study was to determine the impact of trainee involvement in oesophagectomy on postoperative outcomes in an international multicentre setting.

METHODS

Data from the multicentre Oesophago-Gastric Anastomosis Study Group (OGAA) cohort study were analysed, which comprised prospectively collected data from patients undergoing oesophagectomy for oesophageal cancer between April 2018 and December 2018. Procedures were grouped by the level of trainee involvement, and univariable and multivariable analyses were performed to compare patient outcomes across groups.

RESULTS

Of 2232 oesophagectomies from 137 centres in 41 countries, trainees were involved in 29.1 per cent of them (n = 650), performing only the abdominal phase in 230, only the chest and/or neck phases in 130, and all phases in 315 procedures. For procedures with a chest anastomosis, those with trainee involvement had similar 90-day mortality, complication and reoperation rates to consultant-performed oesophagectomies (P = 0.451, P = 0.318, and P = 0.382, respectively), while anastomotic leak rates were significantly lower in the trainee groups (P = 0.030). Procedures with a neck anastomosis had equivalent complication, anastomotic leak, and reoperation rates (P = 0.150, P = 0.430, and P = 0.632, respectively) in trainee-involved versus consultant-performed oesophagectomies, with significantly lower 90-day mortality in the trainee groups (P = 0.005).

CONCLUSION

Trainee involvement was not found to be associated with significantly inferior postoperative outcomes for selected patients undergoing oesophagectomy. The results support continued supervised trainee involvement in oesophageal cancer surgery.

Comparison of short-term outcomes from the International Oesophago-Gastric Anastomosis Audit (OGAA), the Esophagectomy Complications Consensus Group (ECCG), and the Dutch Upper Gastrointestinal Cancer Audit (DUCA)

BACKGROUND

The Esophagectomy Complications Consensus Group (ECCG) and the Dutch Upper Gastrointestinal Cancer Audit (DUCA) have set standards in reporting outcomes after oesophagectomy. Reporting outcomes from selected high-volume centres or centralized national cancer programmes may not, however, be reflective of the true global prevalence of complications. This study aimed to compare complication rates after oesophagectomy from these existing sources with those of an unselected international cohort from the Oesophago-Gastric Anastomosis Audit (OGAA).

METHODS

The OGAA was a prospective multicentre cohort study coordinated by the West Midlands Research Collaborative, and included patients undergoing oesophagectomy for oesophageal cancer between April and December 2018, with 90 days of follow-up.

RESULTS

The OGAA study included 2247 oesophagectomies across 137 hospitals in 41 countries. Comparisons with the ECCG and DUCA found differences in baseline demographics between the three cohorts, including age, ASA grade, and rates of chronic pulmonary disease. The OGAA had the lowest rates of neoadjuvant treatment (OGAA 75.1 per cent, ECCG 78.9 per cent, DUCA 93.5 per cent; P < 0.001). DUCA exhibited the highest rates of minimally invasive surgery (OGAA 57.2 per cent, ECCG 47.9 per cent, DUCA 85.8 per cent; P < 0.001). Overall complication rates were similar in the three cohorts (OGAA 63.6 per cent, ECCG 59.0 per cent, DUCA 62.2 per cent), with no statistically significant difference in Clavien-Dindo grades (P = 0.752). However, a significant difference in 30-day mortality was observed, with DUCA reporting the lowest rate (OGAA 3.2 per cent, ECCG 2.4 per cent, DUCA 1.7 per cent; P = 0.013).

CONCLUSION

Despite differences in rates of co-morbidities, oncological treatment strategies, and access to minimal-access surgery, overall complication rates were similar in the three cohorts.

Oral health status among Kenyans in a rural arid setting: dental caries experience and knowledge on its causes

OBJECTIVE

To determine the dental caries experience and knowledge on the causes and preventive measures for dental diseases.

DESIGN

A community based cross-sectional descriptive study.

SETTING

Elwak sub-district hospital, North Eastern Province, Kenya.

SUBJECTS

One hundred and forty one adults who presented themselves during a dental check up at a sub-district hospital and gave written consent.

MAIN OUTCOME MEASURES

Dental caries status and knowledge on its causes and preventive measures. The importance of outreach programmes in obtaining information as well as helping to alleviate the pain and suffering caused by dental diseases among communities living in remote areas is also revealed.

RESULTS

Of the one hundred and forty one individuals, who were included in the study, 63.1% were women and 36.9% were men. Their ages ranged between 18 and over 65 years. 41.1% were in the 18-24-year age bracket. Regarding the oral health knowledge, 43% did not know any causes of dental diseases while 36%, 17% and 12% knew that diet, "dirt" on teeth and bacteria were possible causes, respectively. Fifty percent did not know any preventive measures for dental diseases while the rest indicated abstention from the consumption of sugary foods; and only 0.8% mentioned use of fluoridated toothpaste as a preventive measure for dental caries. 56.7% of the subjects were caries free. The mean DMFT for all ages was 3.4. Of those with caries 72.1% were women.

CONCLUSION

There is a low level of oral health awareness and a moderately high level of dental caries experience in this community with women apparently carrying the biggest burden of dental caries.

The effect of intracalyceal distribution on the clearance of renal stones of ≥ 20 mm in children after extracorporeal lithotripsy

OBJECTIVES

To determine the effect of the intracalyceal distribution of renal stones on clearance rates after treating paediatric nephrolithiasis with extracorporeal shock wave lithotripsy (ESWL).

PATIENTS AND METHODS

We assessed a retrospective case series of children (aged < or = 14 years) undergoing lithotripsy on an MPL 9000 (Dornier GmbH, Germany) echo-guided lithotripter. Patients were identified using an international coding and indexing system and ESWL registry. In all, 125 children were treated during 1990-2003, but 21 had stones of > or = 20 mm. Stone clearance was assessed at 1 and 3 months, the stone-free state being defined as no radiological evidence of stone or fragments of < or = 3 mm. Failed treatments were analysed to identify any correlation with stone site.

RESULTS

The overall stone-free rate was 81%; in four children the treatment failed (all girls) and subsequently they required ancillary procedures. Nineteen patients (90%) received up to three sessions of ESWL; two required four or more sessions. Of the four children in whom treatment failed, two had JJ stents; the stones were in the lower pole calyx in two, and the renal pelvis and lower pole calyx in two. The mean stone size in those where treatment failed was 25 mm, vs 21 mm in the stone-free group. The complication rate was 19%, but only one child required admission to hospital.

CONCLUSIONS

ESWL is very effective for renal stones in children, with minimal morbidity. Lower pole and partial staghorn stones with a major component in the lower pole calyx should preferably be treated by a percutaneous approach.

Chromosomal inversions and the reproductive isolation of species

Recent genetic studies have suggested that many genes contribute to differences between closely related species that prevent gene exchange, particularly hybrid male sterility and female species preferences. We have examined the genetic basis of hybrid sterility and female species preferences in Drosophila pseudoobscura and Drosophila persimilis, two occasionally hybridizing North American species. Contrary to findings in other species groups, very few regions of the genome were associated with these characters, and these regions are associated also with fixed arrangement differences (inversions) between these species. From our results, we propose a preliminary genic model whereby inversions may contribute to the speciation process, thereby explaining the abundance of arrangement differences between closely related species that co-occur geographically. We suggest that inversions create linkage groups that cause sterility to persist between hybridizing taxa. The maintenance of this sterility allows the species to persist in the face of gene flow longer than without such inversions, and natural selection will have a greater opportunity to decrease the frequency of interspecies matings.

Consequences of recombination rate variation on quantitative trait locus mapping studies. Simulations based on the Drosophila melanogaster genome

We examine the effect of variation in gene density per centimorgan on quantitative trait locus (QTL) mapping studies using data from the Drosophila melanogaster genome project and documented regional rates of recombination. There is tremendous variation in gene density per centimorgan across this genome, and we observe that this variation can cause systematic biases in QTL mapping studies. Specifically, in our simulated mapping experiments of 50 equal-effect QTL distributed randomly across the physical genome, very strong QTL are consistently detected near the centromeres of the two major autosomes, and few or no QTL are often detected on the X chromosome. This pattern persisted with varying heritability, marker density, QTL effect sizes, and transgressive segregation. Our results are consistent with empirical data collected from QTL mapping studies of this species and its close relatives, and they explain the "small X-effect" that has been documented in genetic studies of sexual isolation in the D. melanogaster group. Because of the biases resulting from recombination rate variation, results of QTL mapping studies should be taken as hypotheses to be tested by additional genetic methods, particularly in species for which detailed genetic and physical genome maps are not available.

The effects of recombinant human growth hormone on body composition and glucose metabolism in HIV-infected patients with fat accumulation

GH has been proposed as a therapy for patients with HIV-associated fat accumulation, but the pharmacological doses (6 mg/d) used have been associated with impaired fasting glucose and hyperglycemia. In contrast, physiologic doses of GH ( approximately 1 mg/d) in HIV-negative men reduced visceral adiposity and eventually improved insulin sensitivity, despite initially causing insulin resistance. We conducted an open-label study to evaluate the effects of a lower pharmacologic dose of GH (3 mg/d) in eight men with HIV-associated fat accumulation. Oral glucose tolerance, insulin sensitivity, and body composition were measured at baseline, and 1 and 6 months. Six patients completed 1 month and 5, 6 months of GH therapy. IGF-I levels increased 4-fold within 1 month of GH treatment. Over 6 months, GH reduced buffalo hump size and excess visceral adipose tissue. Total body fat decreased (17.9 +/- 10.9 to 13.5 +/- 8.4 kg, P = 0.05), primarily in the trunk region. Lean body mass increased (62.9 +/- 6.4 to 68.3 +/- 9.1 kg, P = 0.03). Insulin-mediated glucose disposal, measured by a euglycemic hyperinsulinemic clamp, declined at month 1 (49.7 +/- 27.5 to 25.6 +/- 6.6 nmol/kg(LBM).min/pmol(INSULIN)/liter, P = 0.04); values improved at month 6 (49.2 +/- 22.6, P = 0.03, compared with month 1) and did not differ significantly from baseline. Similarly, the integrated response to an oral glucose load worsened at month 1 (glucose area under the curve 20.1 +/- 2.3 to 24.6 +/- 3.7 mmol.h/liter, P < 0.01), whereas values improved at month 6 (22.1 +/- 1.5, P = 0.02, compared with month 1) and did not differ significantly from baseline. One patient developed symptomatic hyperglycemia within 2 wk of GH initiation; baseline oral glucose tolerance testing revealed preexisting diabetes despite normal fasting glucose. In conclusion, GH at 3 mg/d resulted in a decrease in total body fat and an increase in lean body mass in this open-label trial. While insulin sensitivity and glucose tolerance initially worsened, they subsequently improved toward baseline. However, the dose of GH used in this trial was supraphysiologic and led to an increase in IGF-I levels up to three times the upper normal range. Because there are known adverse effects of long-term GH excess, the effectiveness of lower doses of GH should be studied. We also recommend a screening oral glucose tolerance test be performed to exclude subjects at risk for GH-induced hyperglycemia.

Metabolic effects of indinavir in healthy HIV-seronegative men

BACKGROUND

Therapy with HIV protease inhibitors (PI) has been associated with hyperglycemia, hyperlipidemia and changes in body composition. It is unclear whether these adverse effects are drug related, involve an interaction with the host response to HIV or reflect changes in body composition.

METHODS

Indinavir 800 mg twice daily was given to 10 HIV-seronegative healthy men to distinguish direct metabolic effects of a PI from those related to HIV infection. Fasting glucose and insulin, lipid and lipoprotein profiles, oral glucose tolerance (OGTT), insulin sensitivity by hyperinsulinemic euglycemic clamp, and body composition were measured prior to and after 4 weeks of indinavir therapy.

RESULTS

Fasting glucose (4.9 +/- 0.1 versus 5.2 +/- 0.2 mmol/l; P = 0.05) insulin concentrations (61.7 +/- 12.2 versus 83.9 +/- 12.2 pmol/l; P < 0.05), insulin : glucose ratio (12.6 +/- 1.7 versus 15.9 +/- 1.9 pmol/mmol; P < 0.05) and insulin resistance index by homeostasis model assessment (1.9 +/- 0.3 versus 2.8 +/- 0.5;P < 0.05) all increased significantly. During OGTT, 2 h glucose (5.1 +/- 0.4 versus 6.5 +/- 0.6 mmol/l; P < 0.05) and insulin levels (223.1 +/- 48.8 versus 390.3 +/- 108.8 pmol/l;P =0.05) also increased significantly. Insulin-mediated glucose disposal decreased significantly (10.4 +/- 1.4 versus 8.6 +/- 1.2 mg/kg x min per microU/ml insulin; 95% confidence interval 0.6--.0;P < 0.01). There was no significant change in lipoprotein, triglycerides or free fatty acid levels. There was a small loss of total body fat (15.8 +/- 1.4 versus 15.2 +/- 1.4 kg;P = 0.01) by X-ray absorptiometry without significant changes in weight, waist : hip ratio, and visceral or subcutaneous adipose tissue by computed tomography.

CONCLUSIONS

In the absence of HIV infection, treatment with indinavir for 4 weeks causes insulin resistance independent of increases in visceral adipose tissue or lipid and lipoprotein levels.

Evolutionary history of microsatellites in the obscura group of Drosophila

The evolutionary origins of microsatellites are not well understood. Some investigators have suggested that point mutations that expand repeat arrays beyond a threshold size trigger microsatellites to become variable. However, little empirical data has been brought forth on this and related issues. In this study, we examine the evolutionary history of microsatellites in six species within the obscura group of Drosophila, tracing changes in microsatellite alleles using both PCR product size and sequence data. We found little evidence supporting a general role of point mutations triggering initial microsatellite expansion, and no consistent threshold size for expansion was observed. Flanking region length variation was extensive when alleles were sequenced in distantly related species, and some species possessed altogether different repeat arrays between the same primer binding sites. Our results suggest extreme caution in using microsatellite allele sizes for phylogenetic analyses or to infer divergences between populations.

Differences in (G+C) content between species: a commentary on Forsdyke's "chromosomal viewpoint" of speciation

Forsdyke (1999) has recently argued that differences in (G+C)%, or G+C content, may trigger new species formation. He further argues that the genic model has shortcomings that can be overcome by his "chromosomal" (hereafter, "G+C") model. We disagree on several counts. First, we do not accept that the genic model has the shortcomings suggested by Forsdyke. There is an abundance of empirical support for the contribution of individual genes, as well as of mapped chromosomal regions, to post-zygotic reproductive isolation (and Haldane's rule). Further, we argue that the G+C model suffers from the same theoretical difficulties as other speciation models based on underdominance. We also question the evidence Forsdyke uses to support his model. Finally, we describe analyses of G+C content in a well-studied model system of speciation (the Drosophila melanogaster species complex), the results of which are incompatible with the G+C model. Thus, while Forsdyke's G+C model cannot be explicitly ruled out, it is not directly supported by empirical data. In contrast, the genic model is well supported by empirical data, holds up on theoretical grounds, and does not require any assistance from the G+C model.

The genetics of reproductive isolation and the potential for gene exchange between Drosophila pseudoobscura and D. persimilis via backcross hybrid males

Hybrid male sterility, hybrid inviability, sexual isolation, and a hybrid male courtship dysfunction reproductively isolate Drosophila pseudoobscura and D. persimilis. Previous studies of the genetic bases of these isolating mechanisms have yielded only limited information about how much and what areas of the genome are susceptible to interspecies introgression. We have examined the genetic basis of these barriers to gene exchange in several thousand backcross hybrid male progeny of these species using 14 codominant molecular genetic markers spanning the five chromosomes of these species, focusing particularly on the autosomes. Hybrid male sterility, hybrid inviability, and the hybrid male courtship dysfunction were all associated with X-autosome interactions involving primarily the inverted regions on the left arm of the X-chromosome and the center of the second chromosome. Sexual isolation from D. pseudoobscura females was primarily associated with the left arm of the X-chromosome, although both the right arm and the center of the second chromosome also contributed to it. Sexual isolation from D. persimilis females was primarily associated with the second chromosome. The absence of isolating mechanisms being associated with many autosomal regions, including some large inverted regions that separate the strains, suggests that these phenotypes may not be caused by genes spread throughout the genome. We suggest that gene flow between these species via hybrid males may be possible at loci spread across much of the autosomes.

Courtship songs of Drosophila pseudoobscura and D. persimilis. II. Genetics of species differences

Although male courtship songs have been repeatedly implicated in sexual isolation between numerous Drosophila species, no genetic studies have evaluated the genetic basis of differences between species beyond using quantitative genetic analyses of hybrids or surveying associations of song characters to five or fewer genetic markers. Here, we dissect the genetic basis of the difference between D. pseudoobscura and D. persimilis in two courtship song elements (interpulse interval and intrapulse frequency) using 15 molecular markers. We also evaluate the association between song elements and sexual isolation in these backcross hybrid males of these species. We find that song differences between these species are associated with at least two or three genomic regions, and the species difference in interpulse interval may be oligogenic. Courtship song differences are especially strongly associated with two inversions that differentiate these species. Further, we found that interpulse interval is strongly associated with mating success to D. pseudoobscura females, while intrapulse frequency is associated with mating success to D. persimilis females. Implications of these findings are discussed.

A re-evaluation of 12S ribosomal RNA variability in Drosophila pseudoobscura

Two recent studies have presented conflicting views on variation present within the 294 base third domain of the 12S rRNA gene in the genus Drosophila, and in D. pseudoobscura in particular. One study suggested that this gene is highly invariant across the genus, while another recovered 22 distinct haplotypes from 22 strains of D. pseudoobscura. We have sequenced this gene in numerous lines of D. pseudoobscura and its relatives, noting only two haplotypes in the third domain, and we failed to confirm any of the published sequences. Second, we note that the published sequence divergence between strains of D. pseudoobscura was as great as that documented between distantly related Drosophila species. Third, we show that the published polymorphisms of this region within D. pseudoobscura would disrupt the secondary structure of the resulting molecule. We conclude that the published 12S rRNA sequences of D. pseudoobscura do not accurately reflect variability of the functional gene, and that this gene is relatively invariant in D. pseudoobscura and D. persimilis.

High frequency of microsatellites in Drosophila pseudoobscura

Using 30,000 bp of anonymous sequence data, we note that dinucleotide repeat arrays appear to be much more common in Drosophila pseudoobscura than in D. melanogaster or D. simulans. Repeat arrays bearing five or more units are situated on average once every 3000 bp in D. pseudoobscura, and repeat arrays bearing ten or more units are situated on average once every 7500 bp. We did not detect an association between microsatellite presence and GC-content of flanking regions.

Genetic variation in the spread of Drosophila subobscura from a nonequilibrium population

Drosophila subobscura was first identified in North America in the early 1980s, and a newer D. subobscura population in Utah appears to have been established more than 10 years later. In this study, we use nuclear microsatellite allele frequencies, mitochondrial restriction fragment length polymorphism (RFLP) allele frequencies, and computer simulations to investigate possible scenarios of how this species has spread across North America. Our method develops a 95% confidence interval for the maximum and minimum number of founders that could have colonized the new population given various scenarios for spread. Unlike many other methods, it may be applied to nonequilibrium source populations given certain conditions. We find that observed allele frequency differences between newer and older D. subobscura populations are consistent with very few inseminated females being transported east from the coast in a single step or with larger numbers of colonizers invading after several intermediate steps. They are not consistent with a large, panmictic population of D. subobscura colonizing Utah in a single step.

Recombination, statistical power, and genetic studies of sexual isolation in Drosophila

Genetic studies of sexual isolation in Drosophila have generally failed to fully evaluate the effects of their sample size and recombination between markers on their conclusions. In this study we evaluate recombinational distances between markers in Drosophila pseudoobscura and D. persimilis, a species pair in which numerous genetic mapping studies have been performed. We conclude that, contrary to assertions, the inversions that distinguish these two species still allow for much recombination within most of their chromosome arms in F1 hybrid females. Such recombination may have caused previous mapping studies in these species to miss (or grossly underestimate) the effects of several genomic regions. We also evaluate the effects of sample size and recombination on genetic studies of sexual isolation in other Drosophila species groups. We conclude that some of these studies may have been heavily biased toward detecting only genes of large effect. Future studies of sexual isolation should be preceded by detailed statistical power analyses that determine the effects of recombination and sample size in the species pair being studied to avoid these complications.

Microsatellite variation in populations of Drosophila pseudoobscura and Drosophila persimilis

We have isolated, characterized and mapped 33 dinucleotide, three trinucleotide and one tetranucleotide repeat loci from the four major chromosomes of Drosophila pseudoobscura. Average inferred repeat unit length of the dinucleotide repeats is 12 repeat units, similar to D. melanogaster. Assays of D. pseudoobscura and populations of its sibling species, D. persimilis, using 10 of these loci show extremely high levels of variation compared with similar studies of dinucleotide repeat variation in D. melanogaster populations. The high levels of variation are consistent with an average mutation rate of approximately 10(-6) per locus per generation and an effective population size of D. pseudoobscura approximately four times larger than that of D. melanogaster. Consistent with allozymes and nucleotide sequence polymorphism, the dinucleotide repeat loci reveal minimal structure across four populations of D. pseudoobscura. Finally, our preliminary recombinational mapping of 24 of these microsatellites suggests that the total recombinational genome size may be larger than previously inferred using morphological mutant markers.

Reinforcement and other consequences of sympatry

The pattern of greater species mating discrimination between sympatric taxa than between allopatric taxa has been attributed to the strengthening of mate discrimination to avoid maladaptive hybridization. This process, termed reinforcement, has been highly contentious, particularly with regard to its role in speciation. Here, I review some recent studies of reinforcement, discuss alternative explanations for the pattern of greater species discrimination in sympatric taxa, and point to some new directions that may help to clarify the evolutionary forces involved. In particular, we need more ecological work on putative cases of reinforcement, more theoretical models that give diagnostic predictions of reinforcement relative to other modes of divergence, and empirical studies to evaluate these diagnostic predictions.

Mutation and evolution of microsatellites in Drosophila melanogaster

Levels of nucleotide polymorphism in the Drosophila melanogaster genome are correlated with rates of recombination. This relationship may be due to hitchhiking of advantageous mutations (selective sweeps) or to continual removal of deleterious mutations from the genome (background selection). One test of the relative contributions of selective sweeps and background selection to the observed levels of variation in the genome of D. melanogaster is to compare levels of nucleotide variability (with a mutation rate on the order of 10(-9) per nucleotide per generation) with more rapidly evolving DNA loci such as microsatellites. This test depends critically on details of the mutational process of microsatellites. In this paper, we summarize our studies of microsatellite characteristics and mutation rates in D. melanogaster. We find that D. melanogaster microsatellites are short and have a mutation rate (6.5 x 10(-6) per locus per generation) several orders of magnitude lower than mammals studied to date. We further show that genetic variation at 18 dinucleotide repeat microsatellites in a population of D. melanogaster from Maryland is correlated with regional rates of recombination. These and other microsatellite data suggest that both background selection and selective sweeps may contribute to the correlation between DNA sequence variation and recombination in Drosophila.

Synchronous glomus tumors in a distal digit: a case report

Glomus tumors occurring synchronously in the subungual region and the pulp of a fingertip are extremely uncommon. Awareness of this will lead to early diagnosis and treatment.

Genetics of a difference in cuticular hydrocarbons between Drosophila pseudoobscura and D. persimilis

We identify a fixed species difference in the relative concentrations of the cuticular hydrocarbons 2-methyl hexacosane and 5,9-pentacosadiene in Drosophila pseudoobscura and D. persimilis, and determine its genetic basis. In backcross males, this difference is due to genes on both the X and second chromosomes, while the other two major chromosomes have no effect. In backcross females, only the second chromosome has a significant effect on hydrocarbon phenotype, but dominant genes on the X chromosome could also be involved. These results differ in two respects from previous studies of Drosophila cuticular hydrocarbons: strong epistasis is observed between the chromosomes that produce the hydrocarbon difference in males, and the difference is apparently unrelated to the strong sexual isolation observed between these species.

Speciation by reinforcement: a model derived from studies of Drosophila

Reinforcement is an increase in premating reproductive isolation between taxa resulting from selection against hybrids. We present a model of reinforcement with a novel type of selection on female mating behavior. Previous models of reinforcement have focused on the divergence of female mating preferences between nascent species. We suggest that an increase in the level of female mating discrimination can yield reinforcement without further divergence of either male characters or female preferences. This model indicates that selection on mating discrimination is a viable mechanism for reinforcement and may allow speciation under less stringent conditions than selection on female preference. This model also incorporates empirical results from genetic studies of hybrid fitness determination in Drosophila species. We find that the details of inheritance, which include sex-linked transmission, sex-limited fertility reduction, and X-autosome epistasis, have important effects on the likelihood of reinforcement. In particular, X-autosome epistasis for hybrid fitness determination facilitates reinforcement when hybrid fertility reduction occurs in males, but hinders the process when it occurs in females. HALDANE's rule indicates that hybrid sterility will generally evolve in males prior to females within nascent species. Thus, HALDANE's rule and X-autosome epistasis provide conditions that are surprisingly favorable for reinforcement in Drosophila.

Speciation driven by natural selection in Drosophila

Reinforcement is the process by which natural selection strengthens sexual isolation between incipient species, reducing the frequency of maladaptive hybridization and hence completing reproductive isolation. Although this model of speciation was once widely accepted, its plausibility and experimental support have been recently attacked. Here we provide an example of speciation by reinforcement, in the North American fruitfly Drosophila pseudoobscura. The results suggest that females of D. pseudoobscura evolved increased sexual isolation from their sibling species, D. persimilis, by natural selection against maladaptive hybridization.

Ipsilateral fracture dislocation of the radial shaft head associated with elbow dislocation: case report

A severe form of an extremely unusual injury, ipsilateral fracture dislocation of the radial shaft head associated with elbow dislocation, is described. Radial shaft fracture was irreducible even after the radial head and the elbow were reduced. Open reduction and internal fixation are viable options.

A simple and inexpensive external fixator

A simple and inexpensive external fixator has been designed. It is constructed of galvanized iron pipe and mild steel bolts and nuts. It can easily be manufactured in a hospital workshop with a minimum of tools.