NIH ImageJ and Slice-O-Matic computed tomography imaging software to quantify soft tissue

Liver transplantation arrests and reverses muscle wasting

Muscle wasting, sarcopenia, is common in advanced cirrhosis and predicts adverse outcomes while awaiting and following liver transplantation. Frequent post-transplant worsening of sarcopenia has attracted recent interest. It is unknown whether this serious problem is an expected metabolic consequence of transplantation or results from confounding conditions such as recurrent allograft liver disease or avoidable post-transplant complications. To clarify this question, we studied pre- and post-transplant muscle mass in a retrospective cohort of 40 patients transplanted for three diseases - alcoholic cirrhosis, non-alcoholic steatohepatitis cirrhosis, and primary sclerosing cholangitis cirrhosis - in whom allograft disease recurrence was monitored and excluded, and who lacked common post-transplant muscle wasting complications such as sepsis, renal failure, ischemia, and cholestasis. We measured skeletal muscle index (SMI) using computed tomography before and 12-48 months after transplant. SMI as a categorical variable significantly improved, from 18 patients above the normal cutoff pre-transplant to 28 post-transplant (p = 0.008). SMI increases were greatest in patients with the lowest pre-transplant SMI (p < 0.01). As a continuous variable, mean SMI remained stable, with a non-significant trend toward improvement. We conclude that after liver transplantation sarcopenia does not progress but is arrested and frequently improves in the absence of confounding conditions.

All-inside meniscal repair devices compared with their matched inside-out vertical mattress suture repair: introducing 10,000 and 100,000 loading cycles

BACKGROUND

All-inside arthroscopic meniscal repairs are favored by most clinicians because of their lower complication rate and decreased morbidity compared with inside-out techniques. Until now, only 1000 cycles have been used for biomechanical testing.

HYPOTHESIS

All-inside meniscal repairs will show inferior biomechanical response to cyclic loading (up to 100,000 cycles) and load-to-failure testing compared with inside-out suture controls.

STUDY DESIGN

Controlled laboratory study.

METHODS

Bucket-handle tears in 72 porcine menisci were repaired using the Omnispan and Fast-Fix 360 (all-inside devices) and Orthocord 2-0 and Ultrabraid 2-0 sutures (matched controls). Initial displacement, displacement after cyclic loading (100, 500, 1000, 2000, 5000, 10,000, and 100,000 cycles) between 5 and 20 N, ultimate load to failure, and mode of failure were recorded, as well as stiffness.

RESULTS

Initial displacement and displacement after cyclic loading were not different between the groups. The Omnispan repair demonstrated the highest load-to-failure force (mean ± SD, 151.3 ± 21.5 N) and was significantly stronger than all the other constructs (Orthocord 2-0, 105.5 ± 20.4 N; Ultrabraid 2-0, 93.4 ± 22.5 N; Fast-Fix 360, 76.6 ± 14.2 N) (P < .0001 for all). The Orthocord vertical inside-out mattress repair was significantly stronger than the Fast-Fix 360 repair (P = .003). The Omnispan (30.8 ± 3.5 N/mm) showed significantly higher stiffness compared with the Ultrabraid 2-0 (22.9 ± 6.9 N/mm, P < .0001) and Fast-Fix 360 (23.7 ± 3.9 N/mm, P = .001). The predominant mode of failure was suture failure.

CONCLUSION

All-inside meniscal devices show comparable biomechanical properties compared with inside-out suture repair in cyclic loading, even after 100,000 cycles.

CLINICAL RELEVANCE

Eight to 10 weeks of rehabilitation might not pose a problem for all repairs in this worst-case scenario.

Skeletal muscle adiposity is associated with physical activity, exercise capacity and fibre shift in COPD

Quadriceps muscle phenotype varies widely between patients with chronic obstructive pulmonary disease (COPD) and cannot be determined without muscle biopsy. We hypothesised that measures of skeletal muscle adiposity could provide noninvasive biomarkers of muscle quality in this population. In 101 patients and 10 age-matched healthy controls, mid-thigh cross-sectional area, percentage intramuscular fat and skeletal muscle attenuation were calculated using computed tomography images and standard tissue attenuation ranges: fat -190- -30 HU; skeletal muscle -29-150 HU. Mean±sd percentage intramuscular fat was higher in the patient group (6.7±3.5% versus 4.3±1.2%, p = 0.03). Both percentage intramuscular fat and skeletal muscle attenuation were associated with physical activity level, exercise capacity and type I fibre proportion, independent of age, mid-thigh cross-sectional area and quadriceps strength. Combined with transfer factor of the lung for carbon monoxide, these variables could identify >80% of patients with fibre type shift with >65% specificity (area under the curve 0.83, 95% CI 0.72-0.95). Skeletal muscle adiposity assessed by computed tomography reflects multiple aspects of COPD related muscle dysfunction and may help to identify patients for trials of interventions targeted at specific muscle phenotypes.

Hypovitaminosis D is associated with increased whole body fat mass and greater severity of non-alcoholic fatty liver disease

BACKGROUND & AIMS

Hypovitaminosis D is common in obesity and insulin-resistant states. Increased fat mass in patients with non-alcoholic fatty liver disease (NAFLD) may contribute to hypovitaminosis D. To determine the relation among plasma vitamin D concentration, severity of disease and body composition in NAFLD.

METHODS

Plasma vitamin D concentration was quantified in 148 consecutive biopsy-proven patients with NAFLD (non-alcoholic steatohepatitis - NASH: n = 81; and hepatic steatosis: n = 67) and healthy controls (n = 39). NAFLD was scored using the NASH CRN criteria. Body composition was quantified by bioelectrical impedance analysis and abdominal CT image analysis.

RESULTS

Plasma vitamin D concentration was significantly lower in NAFLD (21.2 ± 10.4 ng/ml) compared with healthy controls (35.7 ± 6.0 ng/ml). Higher NAFLD activity scores were associated with lower plasma concentration of vitamin D (r(2)  = 0.29; P < 0.001). Subgroup analysis among patients with NAFLD showed that patients with NASH had significantly lower (P < 0.01) vitamin D levels than those with steatosis alone (18.1 ± 8.4 vs. 25.0 ± 11.3 ng/ml). Low concentrations of vitamin D were associated with greater severity of steatosis, hepatocyte ballooning and fibrosis (P < 0.05).On multivariate regression analysis, only severity of hepatocyte ballooning was independently associated (P = 0.02) with low vitamin D concentrations. Plasma vitamin D (P = 0.004) and insulin concentrations (P = 0.03) were independent predictors of the NAFLD activity score on biopsy. Patients with NAFLD had higher fat mass that correlated with low vitamin D (r(2)  = 0.26; P = 0.008).

CONCLUSIONS

Low plasma vitamin D concentration is an independent predictor of the severity of NAFLD. Further prospective studies demonstrating the impact of vitamin D replacement in NAFLD patients are required.

Adipose depots, not disease-related factors, account for skeletal muscle insulin sensitivity in established and treated rheumatoid arthritis

OBJECTIVE

In prior reports, individuals with rheumatoid arthritis (RA) exhibited increased insulin resistance. However, those studies were limited by either suboptimal assessment methods for insulin sensitivity or a failure to account for important determinants such as adiposity and lack of physical activity. Our objectives were to carefully assess, compare, and determine predictors of skeletal muscle insulin sensitivity in RA, accounting for adiposity and physical activity.

METHODS

Thirty-nine individuals with established (seropositive or erosions) and treated RA and 39 controls matched for age, sex, race, body mass index, and physical activity underwent a frequently sampled intravenous glucose tolerance test to determine insulin sensitivity. Inflammation, body composition, and physical activity were assessed with systemic cytokine measurements, computed tomography scans, and accelerometry, respectively. Exclusions were diabetes, cardiovascular disease, medication changes within 3 months, and prednisone use over 5 mg/day. This investigation was powered to detect a clinically significant, moderate effect size for insulin sensitivity difference.

RESULTS

Despite elevated systemic inflammation [interleukin (IL)-6, IL-18, tumor necrosis factor-α; p < 0.05 for all], persons with RA were not less insulin sensitive [SI geometric mean (SD): RA 4.0 (2.4) vs control 4.9 (2.1)*10(-5) min(-1)/(pmol/l); p = 0.39]. Except for visceral adiposity being slightly greater in controls (p = 0.03), there were no differences in body composition or physical activity. Lower insulin sensitivity was independently associated with increased abdominal and thigh adiposity, but not with cytokines, disease activity, duration, disability, or disease-modifying medication use.

CONCLUSION

In established and treated RA, traditional risk factors, specifically excess adiposity, play more of a role in predicting skeletal muscle insulin sensitivity than do systemic inflammation or other disease-related factors.

Cancer Cachexia in the Age of Obesity: Skeletal Muscle Depletion Is a Powerful Prognostic Factor, Independent of Body Mass Index

Purpose

Emerging evidence suggests muscle depletion predicts survival of patients with cancer.

Patients and Methods

At a cancer center in Alberta, Canada, consecutive patients with cancer (lung or GI; N = 1,473) were assessed at presentation for weight loss history, lumbar skeletal muscle index, and mean muscle attenuation (Hounsfield units) by computed tomography (CT). Univariate and multivariate analyses were conducted. Concordance (c) statistics were used to test predictive accuracy of survival models.

Results

Body mass index (BMI) distribution was 17% obese, 35% overweight, 36% normal weight, and 12% underweight. Patients in all BMI categories varied widely in weight loss, muscle index, and muscle attenuation. Thresholds defining associations between these three variables and survival were determined using optimal stratification. High weight loss, low muscle index, and low muscle attenuation were independently prognostic of survival. A survival model containing conventional covariates (cancer diagnosis, stage, age, performance status) gave a c statistic of 0.73 (95% CI, 0.67 to 0.79), whereas a model ignoring conventional variables and including only BMI, weight loss, muscle index, and muscle attenuation gave a c statistic of 0.92 (95% CI, 0.88 to 0.95; P < .001). Patients who possessed all three of these poor prognostic variables survived 8.4 months (95% CI, 6.5 to 10.3), regardless of whether they presented as obese, overweight, normal weight, or underweight, in contrast to patients who had none of these features, who survived 28.4 months (95% CI, 24.2 to 32.6; P < .001).

Conclusion

CT images reveal otherwise occult muscle depletion. Patients with cancer who are cachexic by the conventional criterion (involuntary weight loss) and by two additional criteria (muscle depletion and low muscle attenuation) share a poor prognosis, regardless of overall body weight.

Echoic features of lymph nodes with sarcoidosis determined by endobronchial ultrasound

OBJECTIVE

Endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) is a minimally invasive technique with a high diagnostic yield used in the investigation of mediastinal diseases including sarcoidosis. Although previous reports have discussed the echoic features of metastatic mediastinal lymph nodes in lung cancer, few have addressed those features of mediastinal lymph nodes with sarcoidosis. We therefore investigated whether the echoic features of lymph nodes with sarcoidosis are distinct when compared to those of metastatic lymph nodes in lung cancer.

METHODS

This retrospective analysis was held in one university hospital between April 2007 and June 2011. EBUS-guided biopsies were performed on 219 patients, and thus resulting in sarcoidosis diagnoses in 53 patients. We quantitatively analyzed the echoic morphologic features of 42 lymph nodes from 34 sarcoidosis patients and 59 lymph nodes from 44 patients with lung cancer using digital image analyzing software.

RESULTS

In patients with sarcoidosis, 64.3% of the lymph nodes had a round shape, 71.4% had a distinct margin, and 88.1% exhibited homogeneous echogenicity. A germinal center structure was observed in 71.4% of the cases. In the context of shape and margin, no significant difference could be observed between sarcoidosis and lung cancer metastasis. However, homogeneous low echogenicity and the presence of a germinal center structure were observed in sarcoidosis more frequently than in lung cancer.

CONCLUSION

Homogeneous low echogenicity and the presence of a germinal central structure may be distinctive echoic features of lymph nodes with sarcoidosis. Analyzing the echogenicity of the mediastinal lymph nodes may help to distinguish sarcoidosis from lung cancer.

A decline in weight and attrition of muscle in colorectal cancer patients receiving chemotherapy with bevacizumab

Weight loss and muscle wasting are of critical importance to cancer patients because of their negative effects on survival, functional status, and tolerability of chemotherapy. Because previous data suggest vascular endothelial growth factor receptor inhibitors disrupt skeletal muscle pathways, such as PI3K and AKT, the current study explored weight loss and muscle wasting in colorectal cancer patients treated with bevacizumab. Patients were assessed for serial weight and radiographic changes in skeletal muscle at baseline and again within 3 months of starting cancer therapy. Computed tomography scans were used to assess muscle. Fifty-seven patients are the focus on this report. These patients manifested a decline in mean weight from 85 to 83 kilograms (P = 0.002). Mean skeletal muscle area at the L3 vertebral level dropped from 148 cm(2) to 145 cm(2) (P = 0.02). This drop in weight and skeletal muscle occurred independently of cancer progression. No statistically significant differences in survival were observed based on loss of weight or skeletal muscle. Colorectal cancer patients prescribed bevacizumab appear to lose weight and muscle over a few months even in the absence of cancer progression.

The advantages and limitations of cross-sectional body composition analysis

PURPOSE OF REVIEW

Cross-sectional (C-S) imaging is now commonly used to measure body composition in clinical studies. This review highlights the advantages, limitations and suggested future directions for this technique.

RECENT FINDINGS

Current understanding of C-S imaging reproducibility, tissue identification and segmentation methods, comparison between imaging techniques and estimates of whole body composition using a single image are described.

SUMMARY

C-S imaging can reliably measure muscle and fat distribution and uniquely discriminate between intra-abdominal organ and muscle component of fat-free mass. It precisely tracks changes within an individual, but is less able to distinguish true differences in whole body estimates between individuals.

Comparison of all-inside meniscal repair devices with matched inside-out suture repair

BACKGROUND

All-inside meniscal repairs are performed with increasing frequency because of the availability of newly developed devices. A comparison of their biomechanical characteristics may aid physicians in selecting a method of meniscal repair.

HYPOTHESIS

All-inside meniscal repairs will be superior to their inside-out controls in response to cyclic loading and load-to-failure testing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixty-six bucket-handle tears in matched porcine menisci were repaired using the Ultra FasT-Fix, Meniscal Cinch, Ultrabraid No. 0, and FiberWire 2-0 sutures. Initial displacement, cyclic loading (100, 300, and 500 cycles), and load-to-failure testing were performed. The displacement, response to cyclic loading, and mode of failure were recorded. The stiffness was calculated.

RESULTS

The Meniscal Cinch demonstrated a significantly higher initial displacement than the other methods tested (P = .04). No significant difference was found among the methods in response to cyclic loading. The inside-out FiberWire repair demonstrated the highest load to failure (120.8 ± 23.5 N) and was significantly higher than both the Meniscal Cinch (64.8 ± 24.1 N, P < .001) and the Ultra FasT-Fix (88.3 ± 14.3 N, P = .002). It was not significantly higher than the inside-out Ultrabraid suture repair (98.8 ± 29.2 N). The inside-out FiberWire repair had the highest stiffness (28.7 ± 7.8 N/mm). It was significantly higher than the Meniscal Cinch (18.0 ± 8.8 N/mm, P = .01). The most common mode of failure in all methods was suture failure.

CONCLUSION

An inside-out suture repair affords surgeons the best overall biomechanical characteristics of the devices tested (initial displacement, response to cyclic loading, and load to failure). For an all-inside repair, the Ultra FasT-Fix reproduces the characteristics of its matched inside-out suture repair more closely than the Meniscal Cinch.

CLINICAL RELEVANCE

Inside-out sutures and all-inside devices have similar responses to cyclic loading.

Reliability of computed tomography measurements in assessment of thigh muscle cross-sectional area and attenuation

Background

Advancement in technology of computer tomography (CT) and introduction of new medical imaging softwares enables easy and rapid assessment of muscle cross-sectional area (CSA) and attenuation. Before using these techniques in clinical studies there is a need for evaluation of the reliability of the measurements. The purpose of the study was to evaluate the inter- and intra-observer reliability of ImageJ in measuring thigh muscles CSA and attenuation in patients with anterior cruciate ligament (ACL) injury by computer tomography.

Methods

31 patients from an ongoing study of rehabilitation and muscle atrophy after ACL reconstruction were included in the study. Axial CT images with slice thickness of 10 mm at the level of 150 mm above the knee joint were analyzed by two investigators independently at two times with a minimum of 3 weeks between the two readings using NIH ImageJ. CSA and the mean attenuation of individual thigh muscles were analyzed for both legs.

Results

Mean CSA and mean attenuation values were in good agreement both when comparing the two observers and the two replicates. The inter- and intraclass correlation (ICC) was generally very high with values from 0.98 to 1.00 for all comparisons except for the area of semimembranosus. All the ICC values were significant (p < 0,001). Pearson correlation coefficients were also generally very high with values from 0.98 to 1.00 for all comparisons except for the area of semimembranosus (0.95 for intraobserver and 0.92 for interobserver).

Conclusion

This study has presented ImageJ as a method to monitor and evaluate CSA and attenuation of different muscles in the thigh using CT-imaging. The method shows an overall excellent reliability with respect to both observer and replicate.

HIFU Lesion Volume as a Function of Sonication Time, as Determined by MRI, Histology, and Computations

Characterization of high-intensity focused ultrasound (HIFU) systems using ex vivo tissues is an important part of the preclinical testing for new HIFU devices. In ex vivo characterization, the lesion volume produced by the absorption of HIFU energy is quantified as operational parameters are varied. This paper examines the three methods used for lesion-volume quantification: histology, magnetic resonance (MR) imaging, and numerical calculations. The methods were studied in the context of a clinically relevant problem for HIFU procedures—that of quantifying the change in the lesion volume with changing sonication time. The lesion volumes of sonicated samples of porcine liver were determined using the three methods, at focal intensities ranging from 800 W/cm2 to 1700 W/cm2 and sonication times between 20 s and 40 s. It was found that histology consistently yielded lower lesion volumes than the other two methods, and the calculated values were below magnetic resonance imaging (MRI) at high applied energies. Still, the three methods agreed with each other to within a ±10% difference for all of the experiments. Increasing the sonication time produced much larger changes in the lesion volume than increasing the acoustic intensity, for the same total energy expenditure, at lower energy (less than 1000 J) levels. At higher energy levels, (around 1500 J), increasing the sonication time and increasing the intensity produced roughly the same change in the lesion volume for the same total energy expenditure.

Loss of synaptotagmin IV results in a reduction in synaptic vesicles and a distortion of the Golgi structure in cultured hippocampal neurons

Fusion of synaptic vesicles with the plasma membrane is mediated by the SNARE (soluble NSF attachment receptor) proteins and is regulated by synaptotagmin (syt). There are at least 17 syt isoforms that have the potential to act as modulators of membrane fusion events. Synaptotagmin IV (syt IV) is particularly interesting; it is an immediate early gene that is regulated by seizures and certain classes of drugs, and, in humans, syt IV maps to a region of chromosome 18 associated with schizophrenia and bipolar disease. Syt IV has recently been found to localize to dense core vesicles in hippocampal neurons, where it regulates neurotrophin release. Here we have examined the ultrastructure of cultured hippocampal neurons from wild-type and syt IV -/- mice using electron tomography. Perhaps surprisingly, we observed a potential synaptic vesicle transport defect in syt IV -/- neurons, with the accumulation of large numbers of small clear vesicles (putative axonal transport vesicles) near the trans-Golgi network. We also found an interaction between syt IV and KIF1A, a kinesin known to be involved in vesicle trafficking to the synapse. Finally, we found that syt IV -/- synapses exhibited reduced numbers of synaptic vesicles and a twofold reduction in the proportion of docked vesicles compared to wild-type. The proportion of docked vesicles in syt IV -/- boutons was further reduced, 5-fold, following depolarization.

Impaired voluntary neuromuscular activation limits muscle power in mobility-limited older adults

BACKGROUND

Age-related alterations of neuromuscular activation may contribute to deficits in muscle power and mobility function. This study assesses whether impaired activation of the agonist quadriceps and antagonist hamstrings, including amplitude- and velocity-dependent characteristics of activation, may explain differences in leg extension torque and power between healthy middle-aged, healthy older, and mobility-limited older adults.

METHODS

Torque, power, and electromyography were recorded during maximal voluntary leg extension trials across a range of velocities on an isokinetic dynamometer.

RESULTS

Neuromuscular activation was similar between middle-aged and older healthy groups, with differences in torque and power explained predominantly by muscle size. However, the older mobility-limited group demonstrated marked impairment of torque, power, and agonist muscle activation, with the greatest deficits occurring at the fastest movement velocities. Agonist muscle activation was found to be strongly associated with torque output.

CONCLUSIONS

Similar neuromuscular activation between the middle-aged and older healthy groups indicates that impaired voluntary activation is not an obligatory consequence of aging. However, the finding that the mobility-limited group exhibited impaired activation of the agonist quadriceps and concomitant deficits in torque and power output suggests that neuromuscular activation deficits may contribute to compromised mobility function in older adults.

Effects of exercise training intensity on nocturnal growth hormone secretion in obese adults with the metabolic syndrome

CONTEXT

Abdominal adiposity is associated with reduced spontaneous GH secretion, and an increased incidence of the metabolic syndrome, type 2 diabetes, and cardiovascular disease. Exercise training increases GH secretion, induces abdominal visceral fat loss, and has been shown to improve the cardiometabolic risk factor profile. However, little is known about the effects of endurance training intensity on spontaneous GH release in obese individuals.

OBJECTIVE

Our objective was to examine the effects of 16 wk endurance training on spontaneous 12-h overnight GH secretion in adults with the metabolic syndrome.

DESIGN AND SETTING

This randomized, controlled exercise intervention was conducted at the University of Virginia.

PARTICIPANTS

A total of 34 adults with the metabolic syndrome (mean +/- sem: age: 49.1 +/- 1.8 yr) participated.

INTERVENTION

Participants were randomized to one of three groups for 16 wk: no exercise training (control), low-intensity exercise training, or high-intensity training.

MAIN OUTCOME MEASURE

Change in nocturnal integrated GH area under the curve (AUC) was calculated.

RESULTS

Both exercise training conditions augmented within-group nocturnal GH AUC pretrain to post-training (low-intensity exercise training approximately (upward arrow) 49%, P < 0.05; and high-intensity training approximately (upward arrow) 65%, P < 0.01), and these changes were also greater than the changes in the control group (P < 0.01). The change in nocturnal GH AUC was inversely associated with the change in fat mass across the entire sample (r = -0.34; P = 0.051; n=34) but was not significantly associated with the change in abdominal visceral fat (r = 0.02; P = 0.920; n = 34).

CONCLUSIONS

Sixteen wk of supervised exercise training in adults with the metabolic syndrome increases spontaneous nocturnal GH secretion independent of exercise training intensity.

Effect of exercise training intensity on abdominal visceral fat and body composition

The metabolic syndrome is a complex clustering of metabolic defects associated with physical inactivity, abdominal adiposity, and aging.

PURPOSE

To examine the effects of exercise training intensity on abdominal visceral fat (AVF) and body composition in obese women with the metabolic syndrome.

METHODS

Twenty-seven middle-aged obese women (mean +/- SD; age = 51 +/- 9 yr and body mass index = 34 +/- 6 kg x m(-2)) with the metabolic syndrome completed one of three 16-wk aerobic exercise interventions: (i) no-exercise training (Control): seven participants maintained their existing levels of physical activity; (ii) low-intensity exercise training (LIET): 11 participants exercised 5 d x wk(-1) at an intensity < or = lactate threshold (LT); and (iii) high-intensity exercise training (HIET): nine participants exercised 3 d x wk(-1) at an intensity > LT and 2 d x wk(-1) < or = LT. Exercise time was adjusted to maintain caloric expenditure (400 kcal per session). Single-slice computed tomography scans obtained at the L4-L5 disc space and midthigh were used to determine abdominal fat and thigh muscle cross-sectional areas. Percent body fat was assessed by air displacement plethysmography.

RESULTS

HIET significantly reduced total abdominal fat (P < 0.001), abdominal subcutaneous fat (P = 0.034), and AVF (P = 0.010). There were no significant changes observed in any of these parameters within the Control or the LIET conditions.

CONCLUSIONS

The present data indicate that body composition changes are affected by the intensity of exercise training with HIET more effectively for reducing total abdominal fat, subcutaneous abdominal fat, and AVF in obese women with the metabolic syndrome.

Optic nerve axon number in mouse is regulated by PAX2

BACKGROUND

Papillorenal syndrome is an autosomal-dominant disease caused by mutations in the PAX2 transcription factor gene. Patients often exhibit congenital excavation of the optic nerve and a spectrum of congenital kidney abnormalities. Using a novel mouse model of this syndrome (C57BL/6J PAX2(A220G/+)), we investigated the effect of PAX2 haploinsufficiency on optic nerve axon number. Because PAX2 expression and retinal pigment epithelium pigmentation have a mutually exclusive relationship during development and because tyrosinase (Tyr) has been shown to modify the penetrance of other ocular development genes, we also investigated whether tyrosinase modified the mutant PAX2 phenotype.

METHODS

C57BL/6J PAX2(A220G/+)Tyr(+/+) mice were crossed with mice of the same genetic background (C57BL/6J) that are homozygous for an effective null allele of tyrosinase (Tyr(c-2J/c-2J)) over two generations to create mice with four distinct genotypes: PAX2(A220G/+) Tyr(+/c-2J), PAX2(A220G/+) Tyr(c-2J/c-2J), PAX2(+/+) Tyr(c-2J/+), and PAX2(+/+)Tyr(c-2J/c-2J). Mouse optic nerves were examined clinically and histologically. Axon number was assessed in a masked fashion in optic nerves from mice of all four genotypes and compared with parental strains.

RESULTS

Mice heterozygous for a PAX2 mutation show reduced optic nerve axon number compared with age-matched controls. Tyrosinase does not appear to modify this phenotype.

CONCLUSIONS

Our results show that PAX2 is important in determining axon number in mouse optic nerve. The developmental effects of tyrosinase and PAX2 mutation appear to act via different pathways.

Appropriateness of current thresholds for obesity-related measures among Aboriginal people

BACKGROUND

Despite the high prevalence of obesity and diabetes in the Canadian Aboriginal population, it is unknown whether the current thresholds for body mass index and waist circumference derived from white populations are appropriate for Aboriginal people. We compared the risk of cardiovascular disease among Canadian Aboriginal and European populations using the current thresholds for body mass index and waist circumference.

METHODS

Healthy Aboriginal (n = 195) and European (n = 201) participants (matched for sex and body mass index range) were assessed for demographic characteristics, lifestyle factors, total and central adiposity and risk factors for cardiovascular disease. Among Aboriginal and European participants, we compared the relation between body mass index and each of the following 3 factors: percent body fat, central adiposity and cardiovascular disease risk factors. We also compared the relation between waist circumference and the same 3 factors.

RESULTS

The use of body mass index underestimated percent body fat by 1.3% among Aboriginal participants compared with European participants (p = 0.025). The use of waist circumference overestimated abdominal adipose tissue by 26.7 cm2 among Aboriginal participants compared with European participants (p = 0.007). However, there was no difference in how waist circumference estimated subcutaneous abdominal and visceral adipose tissue among the 2 groups. At the same body mass index and waist circumference, we observed no differences in the majority of cardiovascular disease risk factors among Aboriginal and European participants. The prevalence of dyslipidemia, hypertension, impaired fasting glucose and metabolic syndrome was similar among participants in the 2 groups after adjustment for body mass index, waist circumference, age and sex.

INTERPRETATION

We found no difference in the relation between body mass index and risk of cardiovascular disease between men and women of Aboriginal and European descent. We also found no difference between waist circumference and cardiovascular disease risk among these groups. These data support the use of current anthropometric thresholds in the Canadian Aboriginal population.