Thermoreversible Gels Composed of Colloidal Silica Rods with Short-Range Attractions

Dynamic arrest transitions of colloidal suspensions containing nonspherical particles are of interest for the design and processing of various particle technologies. To better understand the effects of particle shape anisotropy and attraction strength on gel and glass formation, we present a colloidal model system of octadecyl-coated silica rods, termed as adhesive hard rods (AHR), which enables control of rod aspect ratio and temperature-dependent interactions. The aspect ratios of silica rods were controlled by varying the initial TEOS concentration following the work of Kuijk et al. (J. Am. Chem. Soc., 2011, 133, 2346-2349) and temperature-dependent attractions were introduced by coating the calcined silica rods with an octadecyl-brush and suspending in tetradecane. The rod length and aspect ratio were found to increase with TEOS concentration as expected, while other properties such as the rod diameter, coating coverage, density, and surface roughness were nearly independent of the aspect ratio. Ultrasmall angle X-ray scattering measurements revealed temperature-dependent attractions between octadecyl-coated silica rods in tetradecane, as characterized by a low-q upturn in the scattered intensity upon thermal quenching. Lastly, the rheology of a concentrated AHR suspension in tetradecane demonstrated thermoreversible gelation behavior, displaying a nearly 5 orders of magnitude change in the dynamic moduli as the temperature was cycled between 15 and 40 °C. The adhesive hard rod model system serves as a tunable platform to explore the combined influence of particle shape anisotropy and attraction strength on the dynamic arrest transitions in colloidal suspensions with thermoreversible, short-range attractions.

Educating jurors about eyewitness testimony in criminal cases with circumstantial and forensic evidence

We investigated whether the Interview-Identification-Eyewitness factors (I-I-Eye) educational aid could sensitize mock jurors to the quality of eyewitness evidence in criminal cases which also contained circumstantial and forensic evidence. After participants were randomly assigned to read either the I-I-Eye or a control aid, they read a trial transcript containing either strong or weak eyewitness evidence. The police consistently followed scientific interviewing and identification procedures in the strong case, but not in the weak case. In two experiments, the I-I-Eye participants were approximately three times more likely than the control participants to enter guilty verdicts in the strong case than in the weak case. Thus the I-I-Eye educational aid increased participants' sensitivity to the eyewitness evidence. The I-I-Eye method provides a valuable analytical framework for evaluating eyewitness evidence in criminal cases. It may be capable of becoming "a standard feature for criminal cases" with eyewitness evidence.

Increased thrombin generation potential in symptomatic versus asymptomatic moderate or severe carotid stenosis and relationship with cerebral microemboli

INTRODUCTION

The importance of thrombin generation in the pathogenesis of TIA or stroke and its relationship with cerebral microembolic signals (MES) in asymptomatic and symptomatic carotid stenosis has not been comprehensively assessed.

METHODS

Plasma thrombin generation parameters from patients with moderate or severe (≥ 50%) asymptomatic carotid stenosis were compared with those from patients with symptomatic carotid stenosis in the early (≤ 4 weeks) and late phases (≥ 3 months) after TIA or stroke in this prospective, pilot observational study. Thrombin generation profile was longitudinally assessed in symptomatic patients with data at each time point. Bilateral transcranial Doppler ultrasound monitoring of the middle cerebral arteries was performed whenever possible to classify patients as MES-positive or MES-negative.

RESULTS

Data from 31 asymptomatic, 46 'early symptomatic' and 35 'late symptomatic' patients were analysed. Peak thrombin (344.2 nM vs 305.3 nM; p = 0.01) and endogenous thrombin potential (1772.4 vs 1589.7; p = 0.047) were higher in early symptomatic than asymptomatic patients. Peak thrombin production decreased in symptomatic patients followed up from the early to late phase after TIA or stroke (339.7 nM vs 308.6 nM; p = 0.02). Transcranial Doppler ultrasound data were available in 25 asymptomatic, 31 early symptomatic and 27 late symptomatic patients. Early symptomatic MES-positive patients had a shorter 'time-to-peak thrombin' than asymptomatic MES-positive patients (p=0.04), suggesting a more procoagulant state in this early symptomatic subgroup.

DISCUSSION

Thrombin generation potential is greater in patients with recently symptomatic than asymptomatic carotid stenosis, and decreases over time following TIA or stroke associated with carotid stenosis. These data improve our understanding of the haemostatic/thrombotic biomarker profile in moderate-severe carotid stenosis.

Unlocking Chain Exchange in Highly Amphiphilic Block Polymer Micellar Systems: Influence of Agitation

Chain exchange between block polymer micelles in highly selective solvents, such as water, is well-known to be arrested under quiescent conditions, yet this work demonstrates that simple agitation methods can induce rapid chain exchange in these solvents. Aqueous solutions containing either pure poly(butadiene-b-ethylene oxide) or pure poly(butadiene-b-ethylene oxide-d4) micelles were combined and then subjected to agitation by vortex mixing, concentric cylinder Couette flow, or nitrogen gas sparging. Subsequently, the extent of chain exchange between micelles was quantified using small angle neutron scattering. Rapid vortex mixing induced chain exchange within minutes, as evidenced by a monotonic decrease in scattered intensity, whereas Couette flow and sparging did not lead to measurable chain exchange over the examined time scale of hours. The linear kinetics with respect to agitation time suggested a surface-limited exchange process at the air-water interface. These findings demonstrate the strong influence of processing conditions on block polymer solution assemblies.

PEG-polypeptide block copolymers as pH-responsive endosome-solubilizing drug nanocarriers

Herein we report the potential of click chemistry-modified polypeptide-based block copolymers for the facile fabrication of pH-sensitive nanoscale drug delivery systems. PEG–polypeptide copolymers with pendant amine chains were synthesized by combining N-carboxyanhydride-based ring-opening polymerization with post-functionalization using azide–alkyne cycloaddition. The synthesized block copolymers contain a polypeptide block with amine-functional side groups and were found to self-assemble into stable polymersomes and disassemble in a pH-responsive manner under a range of biologically relevant conditions. The self-assembly of these block copolymers yields nanometer-scale vesicular structures that are able to encapsulate hydrophilic cytotoxic agents like doxorubicin at physiological pH but that fall apart spontaneously at endosomal pH levels after cellular uptake. When drug-encapsulated copolymer assemblies were delivered systemically, significant levels of tumor accumulation were achieved, with efficacy against the triple-negative breast cancer cell line, MDA-MB-468, and suppression of tumor growth in an in vivo mouse model.

Longitudinal assessment of von Willebrand factor antigen and von Willebrand factor propeptide in response to alteration of antiplatelet therapy after TIA or ischaemic stroke

The impact of commencing or changing antiplatelet therapy on von Willebrand factor antigen (VWF:Ag) and von Willebrand factor propeptide (VWF:Ag II) levels has not been comprehensively assessed following TIA or ischaemic stroke. In this pilot, longitudinal, observational analytical study, VWF:Ag and VWF:Ag II levels were simultaneously quantified in platelet poor plasma by ELISA in patients within 4 weeks of TIA or ischaemic stroke (baseline), and then 14 days (14d) and >90 days (90d) after altering antiplatelet therapy. Ninety-one patients were recruited. Eighteen were initially assessed on no antiplatelet therapy, and then after 14d (N = 17) and 90d (N = 8) on aspirin monotherapy; 21 patients were assessed on aspirin and after 14d and 90d on clopidogrel; 52 were assessed on aspirin monotherapy, and after 14d and 90d on aspirin and dipyridamole combination therapy. VWF:Ag, VWF:Ag II levels and VWF:Ag/VWF:Ag II ratio were unchanged at 14d and 90d in the overall study population (p ≥ 0.1). VWF:Ag and VWF:Ag II levels remained stable at 14d and 90d after commencing aspirin (p ≥ 0.054), and after changing from aspirin to clopidogrel (p ≥ 0.2). Following the addition of dipyridamole MR to aspirin, there was a significant reduction in VWF:Ag levels at 14d (p = 0.03) and 90d (p = 0.005), but not in VWF:Ag II levels (p ≥ 0.3). The addition of dipyridamole to aspirin led to a persistent reduction in VWF:Ag but not in VWF:Ag II levels, suggesting that dipyridamole may inhibit release of platelet-derived VWF:Ag following TIA or ischaemic stroke.

Increased endothelial activation in recently symptomatic versus asymptomatic carotid artery stenosis and in cerebral microembolic-signal-negative patient subgroups

BACKGROUND AND PURPOSE

von Willebrand factor propeptide (VWF:Ag II) is potentially a more sensitive marker of acute endothelial activation than von Willebrand factor antigen (VWF:Ag). These biomarkers have not been simultaneously assessed in asymptomatic versus symptomatic carotid stenosis patients. The relationship between endothelial activation and cerebral microembolic signals (MESs) detected on transcranial Doppler ultrasound is unknown.

METHODS

In this multicentre observational analytical study, plasma VWF:Ag and VWF:Ag II levels in patients with ≥50% asymptomatic carotid stenosis were compared with those from patients with ≥50% symptomatic carotid stenosis in the 'early' (≤4 weeks) and 'late' (≥3 months) phases after transient ischaemic attack or ischaemic stroke. Endothelial activation was also longitudinally assessed in symptomatic patients during follow-up. Transcranial Doppler ultrasound monitoring classified patients as MES-positive or MES-negative.

RESULTS

Data from 31 asymptomatic patients were compared with those from 46 early symptomatic and 35 late phase symptomatic carotid stenosis patients, 23 of whom had undergone carotid intervention. VWF:Ag II levels were higher in early (12.8 μg/ml; P < 0.001), late (10.6 μg/ml; P = 0.01) and late post-intervention (10.6 μg/ml; P = 0.038) symptomatic patients than asymptomatic patients (8.9 μg/ml). VWF:Ag levels decreased in symptomatic patients followed up from the early to late phase after symptom onset (P = 0.048). Early symptomatic MES-negative patients had higher VWF: Ag II levels (13.3 vs. 9.0 μg/ml; P < 0.001) than asymptomatic MES-negative patients.

CONCLUSIONS

Endothelial activation is enhanced in symptomatic versus asymptomatic carotid stenosis patients, in early symptomatic versus asymptomatic MES-negative patients, and decreases over time in symptomatic patients. VWF:Ag II levels are a more sensitive marker of endothelial activation than VWF:Ag levels in carotid stenosis. The potential value of endothelial biomarkers and concurrent cerebral MES detection at predicting stroke risk in carotid stenosis warrants further study.

Size evolution of highly amphiphilic macromolecular solution assemblies via a distinct bimodal pathway

The solution self-assembly of macromolecular amphiphiles offers an efficient, bottom-up strategy for producing well-defined nanocarriers, with applications ranging from drug delivery to nanoreactors. Typically, the generation of uniform nanocarrier architectures is controlled by processing methods that rely on cosolvent mixtures. These preparation strategies hinge on the assumption that macromolecular solution nanostructures are kinetically stable following transfer from an organic/aqueous cosolvent into aqueous solution. Herein we demonstrate that unequivocal step-change shifts in micelle populations occur over several weeks following transfer into a highly selective solvent. The unexpected micelle growth evolves through a distinct bimodal distribution separated by multiple fusion events and critically depends on solution agitation. Notably, these results underscore fundamental similarities between assembly processes in amphiphilic polymer, small molecule and protein systems. Moreover, the non-equilibrium micelle size increase can have a major impact on the assumed stability of solution assemblies, for which performance is dictated by nanocarrier size and structure.

Structural characterization of amphiphilic homopolymer micelles using light scattering, SANS, and cryo-TEM

We report the aqueous solution self-assembly of a series of poly(N-isopropylacrylamide) (PNIPAM) polymers end-functionalized with a hydrophobic sulfur-carbon-sulfur (SCS) pincer ligand. Although the hydrophobic ligand accounted for <5 wt% of the overall homopolymer mass, the polymers self-assembled into well-defined spherical micelles in aqueous solution, and these micelles are potential precursors to solution-assembled nanoreactors for small molecule catalysis applications. The micelle structural details were investigated using light scattering, cryogenic transmission electron microscopy (cryo-TEM), and small angle neutron scattering (SANS). Radial density profiles extracted from the cryo-TEM micrographs suggested that the PNIPAM chains formed a diffuse corona with a radially decreasing corona density profile and provided valuable a priori information about the micelle structure for SANS data modeling. SANS analysis indicated a similar profile in which the corona surrounded a small hydrophobic core containing the pincer ligand. The similarity between the SANS and cryo-TEM results demonstrated that detailed information about the micelle density profile can be obtained directly from cryo-TEM and highlighted the complementary use of scattering and cryo-TEM in the structural characterization of solution-assemblies, such as the SCS pincer-functionalized homopolymers described here.

Increased platelet activation in early symptomatic vs. asymptomatic carotid stenosis and relationship with microembolic status: results from the Platelets and Carotid Stenosis Study

BACKGROUND

Cerebral microembolic signals (MES) may predict increased stroke risk in carotid stenosis. However, the relationship between platelet counts or platelet activation status and MES in symptomatic vs. asymptomatic carotid stenosis has not been comprehensively assessed.

SETTING

University teaching hospitals.

METHODS

This prospective, pilot observational study assessed platelet counts and platelet activation status, and the relationship between platelet activation and MES in asymptomatic vs. early (≤ 4 weeks after TIA/stroke) and late phase (≥ 3 months) symptomatic moderate or severe (≥ 50%) carotid stenosis patients. Full blood count measurements were performed, and whole blood flow cytometry was used to quantify platelet surface activation marker expression (CD62P and CD63) and circulating leucocyte-platelet complexes. Bilateral simultaneous transcranial Doppler ultrasound monitoring of the middle cerebral arteries was performed for 1 h to classify patients as MES positive or MES negative.

RESULTS

Data from 31 asymptomatic patients were compared with 46 symptomatic patients in the early phase, and 35 of these patients were followed up to the late phase after symptom onset. The median platelet count (211 vs. 200 × 10(9)  L(-1) ; P = 0.03) and the median percentage of lymphocyte-platelet complexes was higher in early symptomatic than asymptomatic patients (2.8 vs. 2.4%; P = 0.001). The percentage of lymphocyte-platelet complexes was higher in early symptomatic than in asymptomatic patients with ≥ 70% carotid stenosis (P = 0.0005) and symptomatic patients recruited within 7 days of symptom onset (P = 0.028). Complete TCD data were available in 25 asymptomatic, 31 early phase symptomatic and 27 late phase symptomatic patients. Twelve per cent of asymptomatic vs. 32% of early phase symptomatic (P = 0.02) and 19% of late phase symptomatic patients (P = 0.2) were MES positive. Early symptomatic MES-negative patients had a higher percentage of lymphocyte-platelet complexes than asymptomatic MES-negative patients (2.8 vs. 2.3%; P = 0.0085).

DISCUSSION

Recently, symptomatic carotid stenosis patients have had higher platelet counts (potentially reflecting increased platelet production, mobilization or reduced clearance) and platelet activation status than asymptomatic patients. MES were more frequently detected in early symptomatic than asymptomatic patients, but the differences between late symptomatic and asymptomatic groups were not significant. Increased lymphocyte-platelet complex formation in recently symptomatic vs. asymptomatic MES-negative patients indicates enhanced platelet activation in this early symptomatic subgroup. Platelet biomarkers, in combination with TCD, have the potential to aid risk-stratification in asymptomatic and symptomatic carotid stenosis patients.

Acute Cerebrovascular Disease in the Young

Background and Purpose—

Strokes have especially devastating implications if they occur early in life; however, only limited information exists on the characteristics of acute cerebrovascular disease in young adults. Although risk factors and manifestation of atherosclerosis are commonly associated with stroke in the elderly, recent data suggests different causes for stroke in the young. We initiated the prospective, multinational European study Stroke in Young Fabry Patients (sifap) to characterize a cohort of young stroke patients.

Methods—

Overall, 5023 patients aged 18 to 55 years with the diagnosis of ischemic stroke (3396), hemorrhagic stroke (271), transient ischemic attack (1071) were enrolled in 15 European countries and 47 centers between April 2007 and January 2010 undergoing a detailed, standardized, clinical, laboratory, and radiological protocol.

Results—

Median age in the overall cohort was 46 years. Definite Fabry disease was diagnosed in 0.5% (95% confidence interval, 0.4%–0.8%; n=27) of all patients; and probable Fabry disease in additional 18 patients. Males dominated the study population (2962/59%) whereas females outnumbered men (65.3%) among the youngest patients (18–24 years). About 80.5% of the patients had a first stroke. Silent infarcts on magnetic resonance imaging were seen in 20% of patients with a first-ever stroke, and in 11.4% of patients with transient ischemic attack and no history of a previous cerebrovascular event. The most common causes of ischemic stroke were large artery atherosclerosis (18.6%) and dissection (9.9%).

Conclusions—

Definite Fabry disease occurs in 0.5% and probable Fabry disease in further 0.4% of young stroke patients. Silent infarcts, white matter intensities, and classical risk factors were highly prevalent, emphasizing the need for new early preventive strategies.

Clinical Trial Registration Information—

URL: http://www.clinicaltrials.gov .Unique identifier: NCT00414583

Longitudinal assessment of thrombin generation potential in response to alteration of antiplatelet therapy after TIA or ischaemic stroke

The impact of changing antiplatelet therapy on thrombin generation potential in patients with ischaemic cerebrovascular disease (CVD) is unclear. We assessed patients within 4 weeks of TIA or ischaemic stroke (baseline), and then 14 days (14d) and >90 days (90d) after altering antiplatelet therapy. Thrombin generation was assessed in platelet poor plasma. Ninety-one patients were recruited. Twenty-four were initially assessed on no antiplatelet therapy, and then after 14d (N = 23) and 90d (N = 8) on aspirin monotherapy; 52 were assessed on aspirin monotherapy, and after 14 and 90 days on aspirin and dipyridamole combination therapy; 21 patients were assessed on aspirin and after 14 days (N = 21) and 90 days (N = 19) on clopidogrel. Peak thrombin generation and endogenous thrombin potential were reduced at 14 and 90 days (p ≤ 0.04) in the overall cohort. We assessed the impact of individual antiplatelet regimens on thrombin generation parameters to investigate the cause of this effect. Lag time and time-to-peak thrombin generation were unchanged at 14 days, but reduced 90 days after commencing aspirin (p ≤ 0.009). Lag time, peak thrombin generation and endogenous thrombin potential were reduced at both 14 and 90 days after adding dipyridamole to aspirin (p ≤ 0.01). Lag time was reduced 14 days after changing from aspirin to clopidogrel (p = 0.045), but this effect was not maintained at 90 days (p = 0.2). This pilot study did not show any consistent effects of commencing aspirin, or of changing from aspirin to clopidogrel on thrombin generation potential during follow-up. The addition of dipyridamole to aspirin led to a persistent reduction in peak and total thrombin generation ex vivo, and illustrates the diverse, potentially beneficial, newly recognised 'anti-coagulant' effects of dipyridamole in ischaemic CVD.

Retrospective comparison of the original and revised McDonald criteria in a general neurology practice in Ireland

BACKGROUND

The McDonald criteria were introduced in 2001 as guidelines to facilitate early and accurate diagnosis of multiple sclerosis (MS). They were revised in 2005. Although validated in a number of research-focused clinical centres, their adequacy and utility in the general neurology setting is less certain.

OBJECTIVE

In this study, we assessed new diagnoses of MS in our practice for compliance with both the original and the revised criteria.

METHODS

We retrospectively identified new diagnoses of MS from 2001. Clinical notes and imaging were evaluated for compliance with McDonald criteria.

RESULTS

Sixty-two patients were included: 53 with ;practice-definite' and nine with ;practice-possible' diagnoses of MS. At the time of diagnosis, 47% of the ;practice-definite' group fulfilled the 2001 criteria and 49% the revised criteria. Among patients not satisfying the criteria at time of diagnosis, 21% went on to fulfil the McDonald criteria over the 23-month follow-up.

CONCLUSIONS

There is a considerable gap between the clinical diagnosis of MS in a general neurology setting and compliance with the McDonald criteria. Failure to perform follow-up MRI on patients with clinically isolated syndromes is a sizeable factor in this diagnostic-gap and needs to be improved. In this setting, practical differences between the original and revised criteria appear to be small.

Cost of disorders of the brain in Ireland

The "Cost of Disorders of the Brain in Europe" (CBDE) study was conducted by the European Brain Council (EBC) to estimate prevalence and cost of the twelve leading disorders encountered in Neurology, Neurosurgery, and Psychiatry. The data for Ireland are presented here. Prevalence and costing information was obtained by structured review of published literature for each country. Where such information was lacking, figures were estimated from European data. Costs included direct medical, direct non-medical, and indirect costs. None of the costs presented here are directly from Irish data and the prevalence figures are mostly estimated from known European rates. In 2004, 1.1 million people in Ireland were affected by a disorder of the brain. Total cost of included disorders in Ireland was 3.0 billion Euro, representing 3% of gross national product, and costing each Irish citizen Euro 775 per year. Brain disorders are prevalent and pose significant economic burden in Ireland.

Surgical management of macular holes: a report by the American Academy of Ophthalmology

OBJECTIVE

The document describes macular hole surgery and examines the available evidence to address questions about the efficacy of the procedure for different stages of macular hole, complications during and after surgery, and modifications to the technique.

METHODS

A literature search conducted for the years 1968 to 2000 retrieved over 400 citations that matched the search criteria. This information was reviewed by panel members and a methodologist, and it was evaluated for the quality of the evidence presented.

RESULTS

There are three multicenter, controlled, randomized trials that constitute Level I evidence and compare the value of surgery versus observation for macular hole. There are three multicenter, controlled, randomized trials studying the use of adjuvant therapy in macular hole repair. Postoperative vision of 20/40 or better has been reported in 22% to 49% of patients in randomized trials. The risks of surgical complications include retinal detachment (3%), endophthalmitis (<1%), cataract (>75%), and late reopening the hole (2% to 10%).

CONCLUSIONS

The evidence does not support surgery for patients with stage 1 holes. Level I evidence supports surgery for stage 2 holes to prevent progression to later stages of the disease and further visual loss. Level I evidence shows that surgery improves the vision in a majority of patients with stage 3 and stage 4 holes. There is no strong evidence that adjuvant therapy used at the time of surgery results in improved surgical outcomes. Patient inconvenience, patient preference, and quality of life issues have not been studied.

Scleral outfolding for macular translocation

PURPOSE

To report experimental study and clinical observation of scleral outfolding for macular translocation.

METHODS

In six human cadaver eyes, circumferential mattress sutures to create sclera infoldings were compared with radial-interrupted mattress sutures to create scleral outfoldings. In a 75-year-old man with macular degeneration and choroidal neovascular membrane, radial-interrupted mattress sutures were used for macular translocation.

RESULTS

In the human cadaver eyes, circumferential mattress sutures for scleral infolding created an average decrease in corresponding internal anteroposterior retinal contour of 0.36 mm. Radial-interrupted mattress sutures for scleral outfoldings created an average decrease in the corresponding internal anteroposterior retinal contour of 4. 61 mm. The statistical significance of the difference between infoldings of the sclera versus outfoldings of the sclera had a P value of.0001.

CONCLUSIONS

Initial experimental and clinical study suggests that radial-interrupted mattress sutures may generate more shortening of the internal scleral surface and greater macular translocation than circumferential mattress sutures. Additional studies are needed to evaluate the long-term effects of radial-interrupted mattress sutures and macular translocation for treatment of subfoveal choroidal neovascularization secondary to age-related macular degeneration.

Typical Friedreich's ataxia without GAA expansions and GAA expansion without typical Friedreich's ataxia

We clinically assessed and performed polymerase chain reaction analysis for the GAA trinucleotide repeat expansion in 103 patients from 73 families in Ireland, with a prior clinical diagnosis of Friedreich's ataxia (FA) or an unclassified progressive ataxic syndrome. The patients were classified as "typical" or "atypical" FA according to Harding's mandatory clinical diagnostic criteria. All patients underwent blood glucose analysis, and electrocardiography and echocardiography was performed in 99 and 101 patients, respectively. Mutation screening for expanded CAG trinucleotide repeats, associated with spinocerebellar ataxia (SCA) 1, 2, 3 and 6 was performed in 86 patients overall, including all GAA negative patients. Forty-nine of 56 typical patients and 13 of 47 atypical patients were either homozygous or heterozygous for the GAA expansion. Seven patients with a typical FA phenotype were negative for the GAA expansion. Although one of these patients had vitamin E deficiency, and two had raised alpha-fetoprotein levels, three other GAA negative patients with a typical FA phenotype had no other identifiable cause for their ataxia, once again raising the possibility of locus heterogeneity in FA. It is also possible that these patients have two point mutations in the X25 gene, or that they have another ataxic syndrome mimicking the FA phenotype. Two families who were homozygous for the GAA expansion exhibited intrafamilial phenotypic variability. Only one GAA negative patient had the SCA 3 mutation, and this was the only patient in the study with a possible autosomal dominant inheritance pattern. In the homozygous GAA population typical patients had significantly more repeats on the smaller allele than atypical patients, and there was an inverse relationship between the number of repeats on the smaller allele and the age at presentation. There was also an inverse relationship between the repeat size on both the larger and the smaller of the two alleles and the age at becoming wheelchair bound. There was no significant relationship between repeat size and the other indices of disease severity, including the presence or absence of diabetes or cardiomyopathy. This is the first large study of an Irish population with progressive ataxia that has shown a similar phenotype/genotype relationship to studies of FA in other European and non-European populations. The relatively low sensitivity and specificity of Harding's clinical diagnostic criteria must be appreciated when clinically assessing patients with a progressive ataxic syndrome. Although molecular genetic analysis now plays an essential role in diagnosis and classification, patients with a typical FA phenotype without any identifiable cause for their ataxia exist.

Microsatellite instability in sporadic colorectal carcinoma is not an indicator of prognosis

Fifty sporadic colorectal carcinomas diagnosed in 1991 were analysed for microsatellite instability at four loci. Five of 50 (10 per cent) tumours showed replication errors (RERs) at two or more loci and were classed as RER-positive (RER+). A further five showed RERs at one locus only. A significant association (Fisher exact test) was found between RER+ tumours and location in the proximal colon, exophytic shape, size >5 cm, histological margin, lymphoid reaction, and near-diploid DNA content. There was no significant difference for age, sex, grade, mucin production, p53 protein overexpression or Duke's stage. There was no significant difference in survival as measured over a 60-month follow-up period. The findings, though limited by the small case numbers involved, show an association between RER positivity in sporadic colorectal tumours and certain clinico-pathological features. They do not suggest a better clinical outcome for sporadic RER+ tumours.

An automated heteroduplex assay for the Pi(A) polymorphism of glycoprotein IIb/IIIa, multiplexed with two prothrombotic genetic markers

Screening for the PIA polymorphism has been made faster and simpler with the advent of heteroduplex technology. Simultaneous screening for three common prothrombotic polymorphisms pl(A), factor V Leiden, and MTHFR(C677T) has been achieved with multiplex heteroduplex analysis. We describe a quick and simple method for PlA heteroduplex probe production. The probe was multiplexed with heteroduplex probes for MTHFR(C677T) and factor V Leiden polymorphisms in a one tube assay, allowing rapid automated genotyping of all three. This automated multiplex assay was applied to a cohort of 165 patients and showed excellent correlation with gel-based assays, both PAGE and RFLP. This approach will facilitate the analysis of multiple polymorphisms in complex disease in large populations.

Prospective evaluation of the risk conferred by factor V Leiden and thermolabile methylenetetrahydrofolate reductase polymorphisms in pregnancy

Factor V (FV) Leiden and thermolabile methylenetetrahydrofolate reductase (MTHFR) are 2 common polymorphisms that have been implicated in vascular thrombosis. We determined whether these mutations predicted an adverse outcome in pregnancy. Second, we looked for an interaction between these 2 mutations in patients with recurrent fetal loss or thrombosis in pregnancy. Primigravid subjects at their booking visit to the National Maternity Hospital (Holles Street, Dublin, Ireland) were screened for the polymorphisms. Thermolabile MTHFR and FV Leiden genotypes were detected by either restriction fragment length polymorphism or heteroduplex capillary chromatography. The carrier frequency of FV Leiden in the screened primigravid population was 2.7% (allele frequency 1.36%), all being heterozygous for the mutation. This value was lower than expected from previous studies in European populations. Forty-nine percent of the screened population (289 of 584) were heterozygous for thermolabile MTHFR, and 10.6% were homozygous (62 of 584). The frequency of the 2 polymorphisms was no higher in those who subsequently developed preeclampsia (n=12) or intrauterine growth retardation (n=9), and none of the screened population developed thrombosis. However, the frequency of FV Leiden was higher in patients who subsequently miscarried after the first trimester of pregnancy (allele frequency of 5.5%, P=0.0356). Among those positive for FV Leiden, 3 of 27 miscarried, compared with 24 of 572 of FV Leiden-negative patients (11% versus 4.2%). No interaction was found between the 2 mutations in the control or patient populations. In patients with a prior history of venous thrombosis, the carrier rate of FV Leiden was increased (4 of 33, allele frequency of 7.6%, P=0. 0115). In contrast, the carrier frequency for thermolabile MTHFR was no higher, and there was no interaction between the 2 mutations. Neither mutation occurred at a significantly higher frequency in patients with a prior history of recurrent fetal loss. In conclusion, FV Leiden is a risk factor for thrombosis in pregnancy and possibly for second-trimester miscarriage independent of thermolabile MTHFR. However, prospective analysis suggests that the risk conferred by FV Leiden is low in a primigravid population. The thermolabile MTHFR genotype was not implicated in any adverse outcome.

Photodynamic therapy: a new approach to the treatment of choroidal neovascularization secondary to age-related macular degeneration

Visual loss as a result of choroidal neovascularization secondary to age-related macular degeneration continues to be a major challenge for all ophthalmologists. Photodynamic therapy represents an exciting and novel technique that uses light-activated drugs and nonthermal light to achieve the selective destruction of choroidal neovascularization with minimal effects on the surrounding normal tissues. In Phase I-II clinical trials of photodynamic therapy with both benzoporphyrin derivative and tin ethyl etiopurpurin, closure of choroidal neovascularization was seen 24 hours after the treatment. However, recurrence of choroidal neovascularization can occur 2 to 3 months after treatment. Double-blind, multicenter, randomized Phase III clinical trials with benzoporphyrin derivative and tin ethyl etiopurpurin are currently underway.

Microsatellite instability in sporadic colorectal carcinoma is not an indicator of prognosis

Fifty sporadic colorectal carcinomas diagnosed in 1991 were analysed for microsatellite instability at four loci. Five of 50 (10 per cent) tumours showed replication errors (RERs) at two or more loci and were classed as RER-positive (RER+). A further five showed RERs at one locus only. A significant association (Fisher exact test) was found between RER+ tumours and location in the proximal colon, exophytic shape, size >5 cm, histological margin, lymphoid reaction, and near-diploid DNA content. There was no significant difference for age, sex, grade, mucin production, p53 protein overexpression or Duke's stage. There was no significant difference in survival as measured over a 60-month follow-up period. The findings, though limited by the small case numbers involved, show an association between RER positivity in sporadic colorectal tumours and certain clinico-pathological features. They do not suggest a better clinical outcome for sporadic RER+ tumours.

Disparity between fundus camera and scanning laser ophthalmoscope indocyanine green imaging of retinal pigment epithelium detachments

PURPOSE

Indocyanine green (ICG) angiograms of each of five patients with retinal pigment epithelium (RPE) detachments were made using first a Topcon fundus camera and then a Heidelberg scanning laser ophthalmoscope (SLO); for each patient, both types of angiograms were obtained on the same day. In each case, the serous fluid appeared bright throughout the fundus camera studies and dark throughout the SLO studies. This study sought to explain the disparity in the appearance of the lesions in the two kinds of images and to determine whether there was dye in the serous fluid.

METHODS

Simple model eyes were constructed to demonstrate the effects of Mie light scatter and integrating sphere behavior of the sclera on ICG image formation by the fundus camera and SLO optics. Analysis was made of both the clinical angiograms and model eye images to structure an explanation for the disparate RPE detachment angiographic images.

RESULTS

Indocyanine green fluorescent light from choroidal vessels adjacent to the lesions and scattered by the turbid serous fluid accounted for the lesion brightness seen in the fundus camera images. The models confirmed that SLOs suppress scattered light.

CONCLUSIONS

The apparent fluorescence of serous fluid beneath RPE detachments in fundus camera early-phase ICG angiogram images is not attributable to the presence of dye; rather, it appears to be attributable to serous fluid light scatter of fluorescent light arising from adjacent fluorescent structures. This light scatter is a consequence of the fundus camera illumination and recording optics and is not present in SLO-generated images. The necessity of understanding such phenomena as absorption, diffraction, polarization, and scatter of light and routinely applying them to ICG angiogram interpretation is underscored when it is shown that they offer simple explanations for unusual or unexpected angiographic results, as in the case of the patients with RPE detachment discussed here.