Aflibercept monotherapy versus aflibercept with targeted retinal laser to peripheral retinal ischemia for diabetic macular oedema (LADAMO)

OBJECTIVE

We tested the hypothesis that targeted retinal laser photocoagulation (TPRP) to peripheral retinal ischaemia reduces the overall burden of aflibercept injections when treating diabetic macular oedema (DMO) over a 24-month period.

METHODS

Prospective, double-masked, multicentre, randomised controlled trial in Australia comparing aflibercept monotherapy, following a treat-and-extend protocol, or combination therapy of aflibercept and TPRP for DMO. The aflibercept monotherapy group received placebo laser. The primary outcome measure was the mean number of intravitreal aflibercept injections for each group at 24 months. Secondary outcome included: mean change in central macular thickness (CMT) and vision at trial completion, the proportion of eyes whose DMO resolved and the mean injection treatment interval. Ocular and systemic adverse events were recorded.

RESULTS

We enrolled 48 eyes of 47 patients; 27 eyes were randomised to combination therapy (aflibercept and TPRP) and 21 to aflibercept monotherapy. Thirty-two eyes (67%) completed the 2-year study. The number of intravitreal treatments given were similar for combination therapy (10.5 (SD 5.8) and monotherapy (11.8 (SD5.6)) (P = 0.44). The mean visual improvement (+4.0 (-1.8, 9.8) and +7.8 (2.6, 12.9) letters, P = 0.32), mean decrease in CMT (-154 (-222,-87) µm and -152 (-218,-86) µm, P = 0.96), proportion of eyes with CMT < 300 µm (48% and 67%; P = 0.50) and safety outcomes were similar in both the combination and monotherapy treatment groups (respectively).

CONCLUSIONS

Laser to areas of ischaemic peripheral retina does not reduce the burden of intravitreal aflibercept injections when treating diabetic macular oedema.

Safety and efficacy of the pipeline embolization device for treatment of small vs. large aneurysms: a systematic review and meta-analysis

Flow diversion with the pipeline embolization device (PED) is increasingly used to treat intracranial aneurysms with high obliteration rates and low morbidity. However, long-term (≥ 1 year) angiographic and clinical outcomes still require further investigation. The aim of this study was to compare the occlusion and complication rates for small (< 10 mm) versus large (10-25 mm) aneurysms at long-term following treatment with PED. A systematic review and meta-analysis were performed in compliance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. We conducted a comprehensive search of English language databases including Ovid MEDLINE and Epub Ahead of Print, In-Process, and Daily, Ovid EMBASE, Ovid Cochrane Central Register of Controlled Trials, Ovid Cochrane Database of Systematic Reviews, and Scopus. Our studies included a minimum of 10 patients treated with PED for small vs. large aneurysms and with at least 12 months of follow-up. The primary safety endpoint was the rate of clinical complications measured by the occurrence of symptomatic stroke (confirmed clinically and radiographically), intracranial hemorrhage, or aneurysmal rupture. The primary efficacy endpoint was the complete aneurysm occlusion rate. Our analysis included 19 studies with 1277 patients and 1493 aneurysms. Of those, 1378 aneurysms met our inclusion criteria. The mean age was 53.9 years, and most aneurysms were small (89.75%; N = 1340) in women (79.1%; N = 1010). The long-term occlusion rate was 73% (95%, CI 65 to 80%) in small compared to 84% (95%, CI 76 to 90%) in large aneurysms (p < 0.01). The symptomatic thromboembolic complication rate was 5% (95%, CI 3 to 9%) in small compared to 7% (95%, CI 4 to 13%) in large aneurysms (p = 0.01). The rupture rate was 2% vs. 4% (p = 0.92), and the rate of intracranial hemorrhage was 2% vs. 4% (p = 0.96) for small vs. large aneurysms, respectively; however, these differences were not statistically significant. The long-term occlusion rate after PED treatment is higher in large vs. small aneurysms. Symptomatic thromboembolic rates with stroke are also higher in large vs. small aneurysms. The difference in the rates of aneurysm rupture and intracranial hemorrhage was insignificant. Although the PED seems a safe and effective treatment for small and large aneurysms, further studies are required to clarify how occlusion rate and morbidity are affected by aneurysm size.

Bone-anchored annular closure device leading to histiocytic-inflammation-induced neuropathy with resolution after removal: a case report

PURPOSE

To determine and report the underlying cause of local inflammation causing recurrent neuropathy and multiple operations in a patient with a Barricaid® device.

METHODS

After removal of this patient's Barricaid® device, we sent local inflammatory tissue to pathology for histochemical analysis. Upon discovery of giant cells formation with polarizable foreign bodies, we performed a literature review regarding the Barricaid® device and its elements.

RESULTS

After two previous operations and three trials of conservative management, the presented patient underwent an L5/S1 TLIF with removal of her previously installed Barricaid® device. There were no signs of device instability/failure nor were there obvious signs of infection. Inflamed tissue proximal to the Barricaid® device was discovered, debrided, and sample sent to pathology. Removal of the Barricaid® device led to subsequent and durable relief of her symptoms. During review of this case, we discovered the polyethylene terephthalate (PET) weave used in the Barricaid® device is known to induce foreign body reactions, and this precise finding was seen in the majority of animal data submitted to the FDA for the device's acceptance.

CONCLUSION

Given the constellation of this patient's symptoms, imaging, intraoperative, and pathology findings, previously published reports, and pre-approval data submitted to the FDA, we conclude that the inflammatory response to the PET weave in this patient's Barricaid® device was the ultimate cause of her continued neuropathy despite multiple prior surgical interventions.

Flow diversion using the Pipeline embolization device for intracranial and extracranial pseudoaneurysms: a systematic review and meta-analysis of the literature

OBJECTIVE

Pseudoaneurysms (PSAs) are complex vascular lesions. Flow diversion has been proposed as an alternative treatment to parent artery occlusion that preserves laminar flow. The authors of the present study investigated the safety and short-term (< 1 year) and long-term (≥ 1 year) aneurysm occlusion rates following the treatment of intracranial and extracranial PSAs using the Pipeline embolization device (PED).

METHODS

An electronic database search for full-text English-language articles in Ovid MEDLINE and Epub Ahead of Print, Ovid Embase, Ovid Cochrane Central Register of Controlled Trials, Ovid Cochrane Database of Systematic Reviews, and Scopus was conducted following the PRISMA guidelines. Studies of any design including at least 4 patients with intracranial or extracranial PSAs treated using a PED were included in this analysis. The primary outcome of interest was the rate of peri- and postprocedural complications. Secondarily, the authors analyzed the incidence of complete aneurysm occlusion.

RESULTS

A total of 90 patients with 96 PSAs across 9 studies were included. The mean age was 38.2 (SD 15.14) years, and 37.8% of the patients were women. The mean PSA size was 4.9 mm. Most PSAs were unruptured, and the most common etiology was trauma (n = 32, 35.5%), followed by spontaneous formation (n = 21, 23.3%) and iatrogenic injury (n = 19, 21.1%). Among the 51 (53.1%) intracranial and 45 (46.9%) extracranial PSAs were 19 (19.8%) dissecting PSAs. Sixty-six (77.6%) PSAs were in the internal carotid artery and 10 (11.8%) in the vertebral artery. Thirty-three (34.4%) PSAs were treated with ≥ 2 devices, and 8 (8.3%) underwent adjunctive coiling. The mean clinical and angiographic follow-up durations were 10.7 and 12.9 months, respectively. The short-term (< 1 year) and long-term (≥ 1 year) complete occlusion rates were 79% (95% CI 66%-88%, p = 0.82) and 84% (95% CI 70%-92%, p = 0.95), respectively. Complication rates were 8% for iatrogenic dissection (95% CI 3%-16%, p = 0.94), 10% for silent thromboembolism (95% CI 5%-21%, p = 0.77), and 12% for symptomatic thromboembolism (95% CI 6%-23%, p = 0.48). No treatment-related hemorrhage was observed. The overall mortality rate at the last follow-up was 14%.

CONCLUSIONS

The complete occlusion rate for PSAs treated with the PED was high and increased over time. Although postprocedural complications and mortality were not insignificant, flow diversion represents a reasonably safe option for managing these complex lesions.

Novel Use of Time-Resolved Magnetic Resonance Angiography to Evaluate Retrograde Lumbar Vein Flow and Epidural Venous Plexus Enhancement in Chronic Headache Patients With and Without Nutcracker Physiology

OBJECTIVE

Compression of the left renal vein by the superior mesenteric artery, known as nutcracker phenomenon (NCP), can cause retrograde flow and congestion in communicating venous systems. It has recently been speculated that NCP can result in retrograde flow and congestion of the lumbar veins and epidural venous plexus (EVP), thereby affecting the central nervous system. This study describes the novel use of time-resolved magnetic resonance angiography (trMRA) to evaluate for retrograde left second lumbar vein (L2LV) flow and early EVP enhancement in patients with chronic daily headache (CDH) with and without NCP.

METHODS

A retrospective analysis was performed of 31 patients with CDH (27 females and 4 males; median age, 38 years [range, 18-63 years]) who underwent trMRA centered over the L2LV to evaluate the direction of blood flow and presence of early EVP enhancement from May 2020 to March 2022. Descriptive statistics were performed, and anatomic associations were analyzed in patients with and without retrograde L2LV flow and early EVP enhancement. The accuracy of magnetic resonance imaging findings in detecting these flow patterns was also assessed.

RESULTS

Patients with NCP who demonstrated narrowing of the left renal vein, a positive beak sign ( P = 0.052), decreased aortomesenteric distance ( P = 0.038), and decreased SMA angle demonstrated increased rates of retrograde L2LV flow and early EVP enhancement. A positive beak sign was 83% specific, and an aortomesenteric distance of ≤6.5 mm was 61% sensitive and 83% specific for identifying retrograde L2LV flow with early regional EVP enhancement in patients with CDH.

CONCLUSIONS

Retrograde L2LV flow with early EVP enhancement in CDH patients can be effectively evaluated using trMRA and was seen with greater propensity in those patients with NCP.

Daily persistent headache with nutcracker physiology and spinal epidural venous congestion: Treatment with lumbar vein embolization

Nutcracker phenomenon (NCP) can cause various congestion syndromes secondary to the superior mesenteric artery (SMA) compressing the left renal vein (LRV) resulting in venous reflux. It has recently been suggested that reflux into the lumbar vein (LV) and epidural venous plexus (EVP) may cause headaches in some patients with NCP. This report illustrates an example of a patient with refractory headaches and imaging findings suggestive of NCP that underwent treatment with percutaneous LV embolization. The patient is a 60-year-old female with daily persistent headaches for 5 years that failed numerous headache preventative medications. Time-resolved magnetic resonance angiography demonstrated NCP with reflux and congestion of the LV and EVP. Catheter-based venography confirmed these findings and the patient was treated with percutaneous embolization of the LV. This case report demonstrates the use of LV embolization to prevent EVP reflux and treat daily headaches due to NCP. The patient's headache resolved the next day. She has been headache-free for 5 months post-treatment. These findings support prior data suggesting that NCP can cause retrograde LV flow, EVP congestion, and elevated cerebrospinal fluid pressures leading to daily persistent headaches. Percutaneous embolization of the LV may be a minimally invasive treatment option for refractory headaches in patients with NCP, retrograde LV flow, and EVP congestion.

Intracranial Aneurysms in Loeys-Dietz Syndrome: A Multicenter Propensity-Matched Analysis

BACKGROUND

Loeys-Dietz syndrome (LDS) is an autosomal dominant connective tissue disorder characterized by a classic triad of hypertelorism, bifid uvula and/or cleft palate, and generalized arterial tortuosity. There are limited data on the prevalence and rupture risk of intracranial aneurysms (IAs) in the setting of LDS, with no established guidelines.

OBJECTIVE

To analyze the prevalence and rupture risk of IA in LDS.

METHODS

Electronic medical records of patients with a confirmed diagnosis of LDS and available cerebrovascular imaging were reviewed. Patients were divided into 2 groups based on the presence of IA. Unmatched and propensity-matched analyses were used to identify potential risk factors for aneurysm formation.

RESULTS

Records of 1111 patients were screened yielding a total of 60 patients with a diagnosis of LDS. Eighteen (30%) patients had IA, 4 (22.2%) of whom had multiple aneurysms for a total of 24 IAs. Twenty-three (95.8%) aneurysms were located in the anterior circulation; none of them were ruptured. On unmatched analysis, age ( P = .015), smoking history ( P = .034), hypertension ( P = .035), and number of extracranial aneurysms ( P &lt; .001) were significantly higher in patients with IA. After matching for age, sex, race, stroke history, family history, and extracranial aneurysms, smoking history ( P = .009) remained significant.

CONCLUSION

Patients with LDS have an increased risk of IAs, especially with a history of smoking. The prevalence rate of IAs in our series was 30%. Screening imaging should be considered at diagnosis, and patients should be encouraged to abstain from smoking. Further studies are needed to elucidate the risk of IA rupture and treatment considerations in this unique population.

Through-and-Through Brachio/Radio-Femoral Access Technique for Endovascular Recanalization of the Left Subclavian Artery

The authors illustrate the use of through-and-through brachio/radio-femoral access technique in two patients who presented with subclavian steal syndrome. This is an additional tool in the armamentarium of the endovascular specialist to improve management of complex cases with subclavian steal syndrome. This technique provides several advantages to improve efficiency and precision of the procedure while reserving the open surgical bypass option if needed.

Patents on Endophytic Fungi

BACKGROUND

Endophytic fungi are taxonomically and ecologically heterogeneous group of organisms, mainly belonging to the Ascomycotina and Deuteromycotina. Endophytes usually produce the enzymes necessary for the colonization of plant tissues. Endophytes are able to utilize components of plant cells without disturbing host metabolism, which is confirmed by isozyme analysis and studies on substrate utilization. The patents related to enzymes and metabolites produced by endophytic fungi are associated with their ecological significance. Application of metabolites and growth promoting factors produced from endophytic fungi, in the pharmaceutical and agricultural industries, is now well established. The patents on secretion of extracellular enzymes in vitro by endophytic fungi needed for cell wall degradation, support the hypothesis that fungal endophytes represent a group of organisms specialized to live within plant tissue.

OBJECTIVE

This review presents the patents granted on different aspects of endophytic fungi for the last 11 years. This expresses the scenario and impact of these patents regarding significance in human society.

CONCLUSION

In the last few years, research and inventions regarding the different aspects of endophytic fungi beneficial for host plant as well as for human beings have been carried out, which is supported by the increasing number of patents granted on endophytic fungi.

Change in the collateral and accessory collateral ligament lengths of the proximal interphalangeal joint using cadaveric model three-dimensional laser scanning

The purpose of this study was to assess the lengths of the index and middle finger proximal interphalangeal joint ligaments and determine the relative changes in the collateral and accessory collateral ligament lengths at 0°, 45° and 90° flexion. We generated three-dimensional scans of 16 finger (eight index and eight middle) proximal interphalangeal joints to assess relative changes in ligament length. Significant changes were found between 45°-90° and 0°-90° for the ulnar collateral ligament of the index finger and both collateral ligaments of the middle finger between 45°-90° and 0°-90°. No significant changes in length were found for the radial collateral ligament of the index finger or the accessory collateral ligaments of the index and middle fingers. Overall, it was found that the collateral ligament length changed significantly, but there was no significant change in the accessory collateral ligaments.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Assessment of Bt trait purity in different generations of transgenic cottons

Adequate expression of Bt (Bacillus thuringiensis) toxins and purity of seeds of Bt-transgenic cottons are important for controlling bollworms, and thereby increasing the cotton productivity. Therefore, we examined the variability in expression of Bt toxin proteins in the seeds and in leaves of different cotton (Gossypium hirsutum (L.) hybrids (JKCH 226, JKCH 1947, JKCH Durga, JKCH Ishwar, JKCH Varun KDCHH 441 and KDCHH 621) expressing Bt toxins in F₁ and F₂ generations, using bioassays against the cotton bollworm, Helicoverpa armigera (Hübner), and the lateral flow strip (LFS) test. Toxicity of Bt toxin proteins in the seeds of Bt-transgenic cottons to H. armigera correlated with their toxicity in the leaves in one- toxin Bt cotton hybrids. The Bt-F₁ and Bt-F₂ seeds of JKCH 1947 were more toxic to H. armigera than those of JKCH Varun seeds. The seeds and leaves of F₁s showed greater toxicity than the F2 seeds or leaves of one-toxin (cry1Ac) Bt cotton hybrids. However, no significant differences were observed for the two-toxin (cry1Ac and cry2Ab) hybrid, KDCHH 621. Toxicity of leaves to H. armigera increased with crop age, until 112 days after seedling emergence. The Bt trait purity in F₁ seeds of four two-toxin Bt cotton hybrids ranged from 86.7 to 100%. The present study emphasizes the necessity of 95% Bt trait purity in seeds of transgenic cotton for sustainable crop production.

Recent patents on flavonoids

Flavonoids are substances which are widely distributed in the plant kingdom. They occur in considerable quantities in common food products, spices and beverages. Interest of researchers has been greatly enhanced towards therapeutic potential of flavonoids in last some years. This review summarizes important patents pertaining to recent biotechnological techniques applied for the production, analysis of biosynthetic pathways, effects and applications of different flavonoids. For systematic studies investigations which have been published in the form of patents, are classified in different sectors like biosynthesis, medical application, antimicrobial activity, alteration of flower color, industrial application, cosmetics, food and plant tissue culture. A number of activities have been observed in each sector with vast area of research on flavonoids.

Do topical ophthalmic corticosteroids suppress the hypothalmic-pituitary-adrenal axis in post-penetrating keratoplasty patients?

PURPOSE

To establish whether hypothalmic-pituitary-adrenal axis suppression is possible secondary to long-term topical ophthalmic corticosteroid use in patients who have undergone penetrating keratoplasty (PKP).

METHODS

Patients who had undergone a PKP and had been using corticosteroid-based eye drops continuously for more than 6 months, with no history of concomitant steroid (oral, inhaled, or cutaneous) use, were included within the study. A low-dose short Synacthen (LDSST) test was performed in each patient followed later by a short Synacthen test (SST). The mean SST and LDSST after 30 min were calculated along with their corresponding 95% confidence intervals (CIs). Correlation between both baseline SST and baseline LDSST with duration of treatment was determined using Spearman's correlation.

RESULTS

In all, 20 patients were included within the study. The mean duration treatment was 28.2 months (range 11-96 months). All patients had normal baseline cortisol levels in both SST and LDSST tests. The mean 30 min SST was 753.8 nmol/l (95%CI: 696.6 nmol/l, 811.0 nmol/l) and no patients displayed inadequate adrenal response. The mean 30 min LDSST was 709.8 nmol/l (95%CI: 665.1 nmol/l, 754.5 nmol/l) and only one patient had an inadequate adrenal response. There was no correlation between baseline SST or LDSST and duration of treatment.

CONCLUSIONS

This study found no evidence that patients using continuous long-term corticosteroid eye drops after PKP experienced inadequate adrenal response. We did not find any evidence of a negative correlation between length of treatment and SST or LDSST measurements at baseline.

Iron regulation in tuberculosis research: promise and challenges

Tuberculosis is a major global health challenge and is far from being controlled. Development of resistance to currently available drugs due to the successful adaptation of the pathogen has been a major contributing factor for its control failure. Presently, there is an immense interest in identification of pathways, unique to the intracellular environment that could be utilized for the development of new and better drugs. In this sequence, targeting essential functions of Mycobacterium tuberculosis has emerged as a reliable strategy for containing the spread of the disease by this organism. The fact that iron has been known to be the key player required for its survival and ability to spread infection, the organism must carefully balance iron acquisition with iron uptake for its infectivity. Conversely, this iron homeostatic process could be disrupted to interfere with the survival and replication of this bacterium in host. Urgency to develop such an approach has been further strengthened with the worldwide recrudescence of tuberculosis especially in the developing nations of the world. In the current review, we have focused on the recent developments in targeting the essential functions of mycobacterium especially interfering in its iron homeostatic process. The relevance of iron for mycobacterial virulence, the intracellular survival and the immense potential of targeting iron-sulfur (Fe-S) cluster containing proteins in tuberculosis drug discovery has been discussed.

Correlation of optical coherence tomography and fundus fluorescein angiography following photodynamic therapy for choroidal neovascular membranes

AIMS

To assess the correlation between optical coherence tomography (OCT) and leakage on fundus fluorescein angiography (FFA) following photodynamic therapy (PDT) with verteporfin for choroidal neovascularisation (CNV).

METHODS

Retrospective comparative observational case series of patients who were treated with PDT for CNV from one centre. All patients had 3 monthly FFA and OCT following initial PDT to assess if further treatment was required. A pair of FFA and OCT images from the same visit at a random follow up date were taken from each patient's series and assessed separately by different observers. The presence of pigment epithelial detachment, subretinal fluid, vitreomacular traction, intraretinal fluid, absence of foveal depression, and the retinal thickness on OCT were correlated with presence of leaks on FFA.

RESULTS

A total of 121 eyes of 121 patients were included. The presence of subretinal fluid, gross cystoid macular oedema, sponge-like retinal thickening and retinal thickness of more than 350 mum on OCT correlated well with leak on FFA (p value <0.01). The likelihood ratios were 3.0, 5.7, 2.7, and 3.6, respectively. The presence of a solitary foveal cyst did not correlate well with leaks on FFA.

CONCLUSIONS

The presence of subretinal fluid, intraretinal fluid in the form of gross cystoid macular oedema, or sponge-like retinal thickening, or a retinal thickness more than 350 mum correlates with leaks on FFA and so suggests the need for repeat PDT.

Correlation of optical coherence tomography, with or without additional colour fundus photography, with stereo fundus fluorescein angiography in diagnosing choroidal neovascular membranes

AIMS

To assess the diagnostic accuracy of optical coherence tomography (OCT), with/without colour fundus photographs, in predicting fundus fluorescein angiography (FFA) findings in patients suspected of having choroidal neovascularisation (CNV).

METHODS

A consecutive series of patients suspected of having CNV underwent OCT and stereo FFA images, which were assigned a diagnosis by two masked observers, one examining OCT alone and then OCT plus stereo colour photographs, and one examining FFA alone. The main outcome measures were the diagnostic accuracy of OCT (with/without colour photos) in predicting the presence of CNV and secondly the characteristics of the CNV compared to the FFA findings.

RESULTS

131 eyes of 118 patients were analysed. The sensitivity and specificity of OCT for detecting new potentially treatable CNV lesions compared to FFA was 96.4%, and 66.0%, respectively. For OCT with stereo images the sensitivity was 94.0% and specificity 89.4%. For detecting CNV with a classic component the sensitivity and specificity of OCT alone was 78.6% and 82.7%. With stereo colour images the sensitivity was 82.1% and specificity 89.3%.

CONCLUSION

OCT is good at detecting the presence of CNV in patients suspected of having new CNV. However, it is less accurate at identifying the exact components of CNV. OCT cannot at present replace FFA in accurately diagnosing CNV components. However, this imaging method may have a role as a screening tool to help prioritise FFA requests.

RAPD analysis of herbicide-resistant Brasilian rice lines produced via mutagenesis

Over the last two decades, mutational techniques have become one of the most important tools available to progressive rice- breeding programs. In a mutation-breeding program initiated in 1999 at the Instituto Agronômico of Campinas, SP, Brazil, a rice line, IAC103, was selected for mutational studies with gamma radiation and ethyl methyl sulfonate mutagenesis, with the aim of developing a herbicide-resistant crop. After mutagenesis, surviving plants were exposed to glufosinate to check for herbicide resistance, which was examined up to the second generation. A detailed RAPD analysis was made of the resistant plants. Eighty Operon technology primers were tested and 10 were selected for a detailed study of RAPD markers that could tag herbicide resistance genes. Resistant and susceptible lines produced variation in the RAPD patterns and certain bands were found only in certain lines. These results suggest genetic ligation that will be confirmed through a genetic segregation study.

Transformation system of Beauveria bassiana and Metarhizium anisopliae using nitrate reductase gene of Aspergillus nidulans

An heterologous transformation system for entomopathogenic fungi B. bassiana and M. anisopliae was developed based on the use of A. nidulans nitrate reductase gene (niaD). B. bassiana and M. anisopliae niaD stable mutants were selected by treatment of protoplast with ethane methane sulphonate (EMS) and regenerated on chlorate medium. The cloned gene was capable of transforming B. bassiana and M. anisopliae at a frequency of 5.8 to 20 transformants per microg of DNA. Most of them were mitotically stable.

An improved cementing technique for revision hip surgery after peri-prosthetic fractures

Replacement of the femoral component by a long-stemmed implant is one possible solution to the management of periprosthetic femoral shaft fractures. A problem often encountered, due to the extensive disruption of the femoral canal, is difficulty in achieving adequate cement pressurisation. We have overcome this by applying a split 60 ml syringe sleeve around the femoral shaft and holding it in position with clamps. This method has been used on five patients of mean age 87.7 (range 82-94) years with fractures that occurred at an average of 7.2 (range 4-17) years after the primary hip surgery. Two of the five patients achieved independent mobility and all of the patients were sufficiently independent to be discharged from the acute orthopaedic unit. We hope this cheap, effective method of supporting the bone fragments, maintaining alignment and achieving an acceptable level of pressurisation will lead to a decrease in the inevitable morbidity and mortality associated with a problem which as a result of an ageing population is likely to become increasingly common.

Pure small cell carcinoma of the prostate

Pure small cell carcinoma of the prostate is a rare anaplastic tumour. This report presents the clinicopathological findings of two patients presenting with this disease. Immunohistochemistry was positive for protein gene product 9.5, neurone specific enolase and calcitonin. Staining was negative for prostate specific antigen and prostate acid phosphatase. androgen ablation has no place in the management of this lesion and patients with this disease should be managed as if they have a neuroendocrine tumour.

A prospective randomized study comparing a catheter-valve with a standard drainage system

OBJECTIVE

To determine if the use of a catheter-valve rather than a standard drainage system decreases the morbidity associated with the use of a long-term catheter.

PATIENTS AND METHODS

One hundred patients undergoing long-term catheterization were recruited into a prospective randomized study to investigate the acceptability and determine any increase in infection associated with the use of a catheter-valve, compared with the standard drainage system. Each patient participated in the study protocol for 3 months, during which the frequency of urinary tract infection was assessed, and the patients' views obtained using a standard questionnaire and by interview.

RESULTS

Ninety-four patients completed the study; most (92%) were happy or satisfied with the valve, as opposed to only 35% of those using a standard drainage bag. There was no significant difference between the groups in the incidence of urinary tract infections.

CONCLUSION

The patients who used the standard drainage system felt their level of activity was impaired, whereas the group who were using the valve did not. In the long-term the valve was cheaper and caused less morbidity, but because it is constructed to allow one-way flow, this was not associated with an increase in the incidence of urinary tract infections.

Localised carcinoma of the prostate: a paradigm of uncertainty

The incidence and prevalence of prostate cancer is increasing. A number of aetiological factors including age, race, family history and diet have been implicated. The majority of patients present with disease which is amenable only to palliation. Digital rectal examination, serum prostate-specific antigen and transrectal ultrasound can lead to a prostatic biopsy. Transrectal ultrasound, magnetic resonance imaging, bone scan and a chest X-ray are used for staging. The management of localised cancer is shrouded in uncertainty. Three options exist, watchful waiting, radiotherapy, and radical total prostatectomy. The published data are inadequate for a valid comparison of these, and none has been shown to offer an advantage. Surgery, and to a lesser degree radiotherapy, have a significant morbidity. It is hoped that through better understanding our management of this disease will improve.

Subpectoral breast reconstruction using the biodimensional system

Increasing awareness among the general public has fuelled a demand for post-mastectomy breast reconstruction. However, owing to the limited number of plastic surgical centres this need is unlikely to be fulfilled in the near future. We report our early experience with a modified technique using a new subpectoral implant--the Biodimensional System. Seventeen consecutive patients underwent reconstruction (16 immediately) after mastectomy. In the group of patients having immediate reconstruction, the surgery was undertaken by the breast surgeon performing the primary procedure. This study demonstrates that an acceptable result can be obtained in the majority of patients and that it is possible for a breast surgeon to undertake primary reconstruction on selected patients using the Biodimensional System. It is hoped that this may aid patients in their physical and mental rehabilitation.

Who decides on the need for antibiotic prophylaxis in patients with major arthroplasties requiring dental treatment: is it a joint responsibility?

The role of antibiotic prophylaxis in patients with prosthetic joints who require dental treatment is controversial. A Working Party of the British Society for Antimicrobial Chemotherapy (BSAC) recently suggested that there was no evidence to support the use of antibiotic prophylaxis in these patients. The purpose of this study was to determine how closely these recommendations were being followed by maxillofacial surgeons (MFS), and to see if there was any consensus on the management of these patients between MFS and orthopaedic surgeons (OPS). With the aid of a postal questionnaire, the opinions of 250 consultant MFS and OPS were sought, response rates were 148 (59.2%) and 113 (41.2%), respectively. Of the OPS, 77.7% always recommended the use of antibiotic prophylaxis as opposed to only 29% of MFS. There were also wide differences in opinion with regard to the antibiotic that should be used in these patients, with the majority of OPS suggesting a cephalosporin, although this may not be the most efficacious antibiotic for oral streptococci. We conclude that this important matter seems to be far from satisfactorily resolved and that further cooperation between the specialties is required to produce guidelines for the safe and effective management of this increasing group of patients.

The impact of the accessibility of cranial CT scans on patient evaluation and management decisions

OBJECTIVES

Cranial CT scans are amongst the most frequently performed radiological investigations performed in most developed countries. However, these tests are relatively expensive and economic realities should compel physicians to re-evaluate the utilization of this technology. The aim of this study was to review the utilization pattern and effect on management decisions of cranial CT scanning.

DESIGN

Retrospective chart review.

SETTING

University-affiliated community teaching hospital.

SUBJECTS

The clinical data on 451 consecutive patients undergoing cranial CT scanning in our radiology department were reviewed. Eighty-five patients were referred from outside the hospital and were subsequently excluded from further analysis.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

The following data was abstracted from each patient's chart: the presenting clinical syndrome, the physician ordering the scan, details of the neurological examination performed prior to scanning, the CT scan findings and the impact the CT scan findings had on management decisions.

RESULTS

The largest percentage of patients were referred from the emergency department (61%). Chronic intracranial lesions were present in 77 (21%) patients. New pathological findings were found in 91 (25%) patients. The commonest new lesions were ischaemic infarcts (43%), followed by intracerebral haemorrhage (13%) and space occupying lesions (11%). Ninety-seven per cent of patients presenting with new focal neurological signs had new findings on the CT scan, compared to 28% of patients with severe headache and 27% with a history of loss of consciousness. Head trauma was the presenting problem in 139 patients. New pathological findings were diagnosed in 24 of these patients. Fifty-four patients had no signs or symptoms referable to the central nervous system. None of these patients had new findings on CT scan. In the vast majority of patients the neurological examination performed prior to CT scanning was incomplete. CT scanning was considered to have altered the management or provided a new diagnosis in 162 (44%) patients; of these patients 61 (67%) were in the group with new findings on CT scanning and 101 (37%) in the group with no new findings.

CONCLUSION

In this study cranial CT scanning affected clinical management decisions in less than half of the patients. Furthermore, a careful history and neurological examination was performed in the minority of patients undergoing CT scanning. It would therefore appear that the easy accessability of CT scans largely determines the utilization of this diagnostic tool.

Pseudotumour of the bladder

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Liposome fusion and lipid exchange on ultraviolet irradiation of liposomes containing a photochromic phospholipid

A photochromic phospholipid, 1,2-bis[4-4(4-n-butylphenylazo) phenylbutyroyl] phosphatidylcholine (Bis-Azo PC) has been incorporated into liposomes of gel- and liquid-crystalline- phase phospholipids. Liposomes of gel-phase phospholipid are stable in the presence of the trans photostationary state Bis-Azo PC and can encapsulate fluorescent marker dye. On photoisomerization to the cis photostationary state, trapped marker is rapidly released. Liposomes containing Bis-Azo PC can rapidly fuse together after UV isomerization, this process continuing in the dark. Exposure to white light causes reversion of Bis-Azo Pc to the trans form and halts dye leakage and vesicle fusion. Both unilamellar and multilamellar liposomes are able to fuse together on UV exposure. On UV photolysis, liposomes containing Bis-Azo PC do not fuse with a large excess of unlabeled liposomes, but transfer of Bis-Azo PC can be demonstrated spectrophotometrically. Vesicles of pure gel-phase lipid containing trapped marker dye but initially no Bis-Azo PC become leaky as a result of this lipid transfer. Liposomes composed of liquid-crystalline-phase phosphatidylcholine- containing Bis-Azo PC neither leak trapped marker no fuse together on photolysis, nor do liquid-crystalline-phase liposomes fuse with gel-phase liposomes under these conditions. These results are discussed together with some possible applications of liposome photodestabilization.

Environmental monitoring for genotoxicity with plant systems. Results and recommendations

In the first phase of a collaborative study by the International Programme on Chemical Safety (IPCS), four coded chemicals, i.e. azidoglycerol (AG, 3-azido-1,2-propanediol), methyl nitrosourea (MNU), sodium azide (NaN3) and maleic hydrazide (MH), and ethyl methanesulfonate (EMS) as a positive control were tested in four plant bioassays, namely the Arabidopsis embryo and chlorophyll mutation assay, the Tradescantia stamen hair assay (Trad-SH assay), the Tradescantia micronucleus assay (Trad-MCN), and the Vicia faba root tip assay. Seventeen laboratories from diverse regions of the world participated with four to six laboratories each using one plant assay. For the Arabidopsis assay, laboratories were in agreement with MNU and AG giving positive responses and NaN3 giving a negative response. With the exception of one laboratory which reported MH as weakly mutagenic, no mutagenic response was reported for MH by the other laboratories. For the Vicia faba assay, all laboratories reported a positive response for MNU, AG, and MH, whereas two of the six laboratories reported a negative response for NaN3. For the Trad-SH assay, MH was reported as giving a positive response and a positive response was also observed for MNU with the exception of one laboratory. NaN3, which exhibited a relatively high degree of toxicity, elicited a positive response in three of the five laboratories. AG was found positive in only one of the two laboratories which tested this chemical. For the Trad-MCN assay, MNU and MH were reported as positive by all laboratories, while four out of five laboratories reported NaN3 to be positive. Only one of three laboratories reported AG to be positive. The major sources of variability were identified and considered to be in the same range as found in similar studies on other test systems. Recommendations were made for minor changes in methodology and for initiating the second phase of this study.

Arabidopsis assay for mutagenicity

Four laboratories, two in the Czech Republic (Brno and Prague) and two in the CIS (Moscow and Duschanbe), participated in the International Programme on Chemical Safety's (IPCS) collaborative study to evaluate the utility of the most commonly used plant test systems, including the Arabidopsis thaliana assay, for assessing the mutagenic potential of environmental agents. Out of the five compounds evaluated in the Arabidopsis assay, three compounds, i.e., ethyl methanesulfonate, N-methyl-N-nitrosourea, and azidoglycerol, were reported to be mutagenic by all four participating laboratories. Sodium azide (NaN3) demonstrated a negative response in all four laboratories, whereas maleic hydrazide was reported to be weakly mutagenic by one laboratory and nonmutagenic by the other three laboratories.

Environmental monitoring for genotoxicity with plant systems. An introduction and study design

Under the sponsorship of the International Programme on Chemical Safety (IPCS), 17 laboratories from diverse regions of the world participated in evaluating the utility of four plant bioassays for detecting genetic hazards of environmental chemicals. The bioassays included in this collaborative study were: Arabidopsis thaliana embryo and chlorophyll assay and Tradescantia stamen hair assay, Tradescantia paludosa micronucleus assay and Vicia faba root tip assay. Four to six laboratories participated in the performance of each of the bioassays. All laboratories participating in a particular bioassay were supplied with uniform plant material as well as standardized protocol. Five direct acting water soluble test chemicals, i.e. maleic hydrazide, methyl nitrosourea, ethyl methanesulfonate, sodium azide and azidoglycerol, were selected for this study. The study was designed to be completed in three phases. Ethyl methanesulfonate was used as a positive control and has already been reported earlier (Sandhu et al., 1991). The data from the remaining four chemicals used for the evaluation of four plant test systems in the first phase of the collaborative study are reported in this issue.

Tradescantia micronucleus bioassay

Four coded chemicals, azidoglycerol (AG), N-methyl-N-nitrosourea (MNU), sodium azide (NaN3), and maleic hydrazide (MH), were tested with the Tradescantia micronucleus (Trad-MCN) bioassay by five independent laboratories from five different countries. The purpose of this international collaborative study was to evaluate four plant bioassays, of which the Trad-MCN assay was one, for their sensitivity, efficiency and reliability. The study was carried out under the sponsorship of the International Programme on Chemical Safety. All laboratories adhered to a standard Trad-MCN protocol which suggested that three replicate tests be conducted with each chemical. The results reported by all laboratories, although not equal, showed good agreement among the laboratories. In fact, all five laboratories obtained positive results with MH and MNU, while four of the five laboratories achieved positive results with NaN3. AG was tested in only three laboratories. Two reported negative results, while one reported positive results but only at a single high dose. The data from this study suggest that under normal conditions, the Trad-MCN bioassay is an efficient and reliable short-term bioassay for clastogens. It is suitable for the rapid screening of chemicals, and also is specially qualified for in situ monitoring of ambient pollutants.

Vicia faba chromosomal aberration assay

A collaborative study involving laboratories in six countries was initiated under the sponsorship of the International Programme on Chemical Safety (IPCS) to determine the sensitivity, efficiency and reliability of the Vicia faba root tip meristem chromosomal aberration assay using a standardized protocol. The six laboratories that participated in this study were located in the Slovak Republic, India, Japan, Poland, Sweden and the USA. All laboratories adhered to a standardized protocol for the Vicia faba chromosomal aberration assay. Four coded chemicals, azidoglycerol (AG), N-methyl-N-nitrosourea (MNU), sodium azide (NaN3) and maleic hydrazide (MH) were tested with the Vicia faba chromosomal aberration assay. Of the four chemicals, three (MH, AG and MNU) were found to be clastogenic and gave a concentration related response. However, the results of NaN3 were equivocal which might be explained by the stability of NaN3. The conclusions from this study suggest that the Vicia faba chromosomal aberration bioassay is an efficient and reliable short-term bioassay for the rapid screening of chemicals for clastogenicity.

Application of the Tradescantia micronucleus assay for the genetic evaluation of chemical mixtures in soil and aqueous media

Genotoxic evaluations of arsenic trioxide, dieldrin, lead tetraacetate and their nine binary and one tertiary mixtures were performed using the Tradescantia micronucleus (Trad-MN) assay. The chemicals or their mixtures were either (1) mixed into soil, and chemical exposure to the target cells was through the roots of intact plants grown in the soil or (2) through plant cuttings in which the inflorescences received treatment by absorption through stem of an aqueous solution of the test chemicals. All three chemicals yielded clastogenic responses when tested in soil medium and only two of these i.e. arsenic trioxide and dieldrin were positive when plant cuttings were exposed to the test chemicals in the aqueous medium. The clastogenicity of the chemical mixtures was modified by the ratio of the individual chemical in a particular mixture and also by the medium in which these mixtures were tested.

Synergistic and antagonistic effects on genotoxicity of chemicals commonly found in hazardous waste sites

Synergistic and antagonistic effects on genotoxicity of mixtures of four chemicals; i.e., lead tetraacetate (LTA), arsenic trioxide (ATO), dieldrin (DED), and tetrachloroethylene (TCE), were evaluated by the Tradescantia-micronucleus (Trad-MCN) assay. The chemicals were mixed in ratios of 1:1, 1:2 and 2:1 for mixtures of two chemicals and 1:1:1 each for three chemicals. The concentration of stock solution of these chemicals was around the minimum effective dose (MED) or below the MED for these chemicals as reported by Sandhu et al. (1989). Treatments were applied to plant cuttings by hydroponic uptake of the mixed solutions through the stems of the plant for 30 h followed by fixation of the flower buds in aceto-alcohol (1:3 ratio) without a recovery period. Microslides were prepared for scoring MCN frequencies. Results of two series of repeated experiments indicated that all mixtures of LTA/ATO exhibited antagonistic effects. On the other hand, all mixtures of TCE and DED exhibited synergistic effect. These data indicate that for evaluating biological hazards at chemical waste sites, it is prudent to evaluate the genotoxicity of complex chemical mixtures as these exist in nature because the biological effects based on evaluating individual chemicals may not be true predictors of the interactive effects of the pollutants.

Application of a wheat seedling assay for detecting aneuploidy induced by N-ethyl-N-nitrosourea and 4-nitroquinoline-1-oxide

N-Ethyl-N-nitrosourea (ENU) and 4-nitroquinoline-1-oxide (4NQO) were evaluated in the allohexapolyploid wheat seedling assay developed by Redei and Sandhu (1988), for its ability to induce aneuploidy and/or small chromosome deletions. The wheat strain used (Neatby's virescent) is homozygous for a pair of recessive alleles (v1) present on chromosome 3B and produces virescent seedlings grown at temperatures below 26 degrees C. When the developing embryos are treated with a test chemical, loss of chromosome 3B or its segment bearing the v1 allele in a progenitor cell produces a green sector in the leaf, whereas a gain of this chromosome induces a white sector. ENU and 4NQO induced dose-dependent increases in the frequency of leaf sectors at concentrations ranging from 0.128 to 1.280 mM and 0.052 to 0.263 mM, respectively. The assay is very simple and can be employed for evaluating the genetic potential of chemicals in a laboratory as well as for in situ hazards assessment under natural environmental conditions.

Evaluation of 10 chemicals for aneuploidy induction in the hexaploid wheat assay

This study was a part of an international project sponsored by the Commission of the European Communities to evaluate the utility of certain bioassays including hexaploid wheat assay to identify potential aneugens. Ten suspect spindle poisons, i.e. colchicine (COL), cadmium chloride (CdCl2), chloral hydrate (CH), diazepam (DIZ), econazole (EZ), hydroquinone (HQ), pyrimethamine (PY), thiabendazole (TB), thimerosal (TM), and vinblastin sulphate (VBL) were tested for their ability to induce green and/or white leaf sectors as indicators of loss or gain of a chromosome respectively, in Neatby's strain of Chinese Spring wheat (2n = 6x = 42). All the chemicals tested in this study, with the exception of CH and HQ yielded positive response.

Kinetochore identification in micronuclei in mouse bone-marrow erythrocytes: an assay for the detection of aneuploidy-inducing agents

An in vivo micronucleus assay using mouse bone marrow for identifying the ability of chemicals to induce aneuploidy and/or chromosome breaks is described. Micronucleus formation in bone-marrow erythrocytes of mice is commonly used as an index for evaluating the clastogenicity of environmental agents. However, micronuclei may also originate from intact lagging chromosomes resulting from the effect of aneuploidy-inducing agents. We have used immunofluorescent staining using anti-kinetochore antibodies to classify micronuclei for the presence or absence of kinetochores. Micronuclei positive for kinetochores are assumed to contain intact chromosomes and result from induced aneuploidy; while those negative for kinetochores contain acentric chromosomal fragments and originate from clastogenic events. The assay was evaluated using X-irradiation (a known clastogen) and vincristine sulfate (an aneuploidy-inducing agent). A dose-related response for the induction of micronuclei was observed for both agents. Micronuclei induced by X-irradiation were negative for kinetochores while the majority of the micronuclei resulting from vincristine treatment contained kinetochores. Thus, the micronucleus assay in combination with immunofluorescent staining for kinetochores may provide a useful method to simultaneously assess the ability of chemicals to induce aneuploidy and/or chromosome breaks.

Clastogenicity evaluation of seven chemicals commonly found at hazardous industrial waste sites

7 chemicals commonly found at the industrial waste sites were tested with the Tradescantia-Micronucleus (Trad-MCN) assay to evaluate their clastogenic potential. Chemicals selected from the US EPA Superfund Priority 1 list were: aldrin, arsenic trioxide, 1,2-benz[a, h]anthracene, dieldrin, heptachlor, lead tetraacetate and tetrachloroethylene. Results of repeated tests for clastogenicity yielded the minimum effective dose (MED) for clastogenicity of 0.44 ppm for lead tetraacetate, 1.88 ppm for heptaclor, 3.81 ppm for dieldrin and arsenic trioxide and 1,2-benz[a, h]anthracene yielded positive responses at the MED of 3.96 ppm and 12.50 ppm respectively. Aldrin and tetrachloroethylene were considered to be immiscible with water, and the tests yielded negative responses. Tetrachloroethylene in gaseous state was also used to treat the flower buds. Results of tetrachloroethylene vapor phase treatment yielded a positive response at the MED of 30 ppm/min after a 2-h exposure. 5 chemicals determined to be clastogens by this test were ranked according to their MED in the descending order of potency as follows: lead tetraacetate, heptachlor, dieldrin, arsenic trioxide and 1,2-benz[a, h]anthracene. Results of this study indicate that the Trad-MCN bioassay could be effectively utilized for assessing the potential clastogenicity of the chemicals commonly found at the industrial hazardous waste sites.

A genetic method to quantitate induced chromosome breaks using a mouse/human monochromosomal hybrid cell line: identification of potential clastogenic agents

A genetic assay to detect the clastogenic potential of environmental agents is described. This assay is based on the cloning efficiency of cells in a medium that permits the growth of cells following loss of a specific chromosome segment resulting from a chromosome break. For this purpose a mouse/human hybrid cell line R12-2 containing a dominantly marked chromosome 5 as the only human component has been constructed. This chromosome 5 carries two dominant selectable markers, Ecogpt and the gene for sensitivity to diphtheria toxin (DTs). Ecogpt codes for the enzyme xanthine-guanine phosphoribosyltransferase which allows selection for cells containing chromosome 5 or the segment carrying Ecogpt as judged by growth in medium supplemented with mycophenolic acid and xanthine (MX medium). Human cells are sensitive to 10(-13) M DT, whereas mouse cells are resistant to 10(-7) M DT and DTs is expressed as a dominant phenotype. Cultivation of R12-2 cells in the medium containing 10(-13) M DT permit the selection of cells that have lost chromosome 5 or the segment carrying DTs. The presence of two selectable markers on the same chromosome permits the identification and quantitation of cells for the selective loss of a specific chromosome segment. Growth of R12-2 cells in MX medium containing 10(-13) M DT therefore, provides a convenient method to determine the frequency of clastogen induced breaks in chromosome 5. The utility of the proposed genetic assay is assessed using X-irradiation as a model clastogen. Our results clearly show a dose related response that is consistent with cytogenetic observations.

In situ assessment of genotoxic hazards of environmental pollution

The potential impact of the environmental pollutants on human health can be evaluated by the laboratory analysis of the environmental samples or by the measurement of the biological effects on indigenous populations and/or specific test organisms placed in the environment to be monitored. A canary in a cage, used by 19th century miners as a biological indicator for rising levels of toxic gases, is a classical example of in situ hazard identification. The induced toxic effects are often the result of synergistic and antagonistic interactions among various physical and chemical factors that are difficult to reproduce in the laboratory. Therefore, conceivably the biological effects measured on or near the impacted site have greater relevancy for hazard assessment to man than from the data derived from the environmental samples analyzed in the lab. The organisms most commonly employed for the assessment of mutagenicity under real-world conditions are: (1) flowering plants, (2) wild and captive mammals, and (3) aquatic vertebrates. Plant species such as Tradescantia paludosa, Zea mays, and Osmunda regalis have been used for monitoring ambient air quality around several major industrial cities in the U.S.A., nuclear power plants, and industrial waste sites, and also for the assessment of potential health effects of municipal sewage sludges. Domestic animals such as dogs can be used as sentinels to provide information on the effects of contaminants in the environment and have been used to a limited extent to evaluate the environmental influences on the occurrence of breast cancer and osteosarcoma. Cytogenetic analysis from feral and wild animals has been employed for assessing the health hazards and prioritizing the clean-up efforts at hazardous waste sites. Aquatic animals have been used more often than terrestrial animals or plants to identify and characterize the genotoxic effects of environmental pollution. Since 1970, a number of studies has been reported on the mutagenic and neoplastic effects on aquatic animals from coastal areas and continental rivers, lakes, and ponds. The limitations of in situ environmental assessment are lack of control over the physical environmental components, inherent variability and interactions of test organisms, lack of control of exposure doses, and difficulty of finding concurrent experimental controls. Nevertheless, flowering plants, terrestrial, and aquatic animals may serve as useful sentinels and biomarkers of environmental pollution.

A monochromosomal hybrid cell assay for evaluating the genotoxicity of environmental chemicals

The development and utilization of a monochromosomal hybrid cell assay for detecting aneuploidy and chromosomal aberrations are described. The monochromosomal hybrid cell lines were produced by a two-step process involving transfer of a marker bacterial gene to a human chromosome and then by integration of that human chromosome into a mouse complement of chromosomes through microcell fusion. For chemically induced aneuploidy, the segregation of a single human chromosome among mouse chromosomes is used as a cytogenetic marker. The genetic assay for aneuploidy is based on the ability of the cells to grow in a medium that selects for the loss of the human chromosome. The assay for clastogenicity is based on survival of the cells after treatment with the chemicals in medium that selects for retention of the human chromosome but loss of its segment containing diphtheria toxin locus. The assays greatly simplify the detection of chromosomal aberrations induced by environmental factors at low-dose levels.