Characteristics of patients with cerebral sinus venous thrombosis and JAK2 V617F mutation

OBJECTIVES

Janus kinase 2 (JAK2-V617F) mutations can cause thrombocytosis, polycythemia and hyper viscosity leading to cerebral sinus venous thrombosis (CSVT). However, data regarding the characteristics and prevalence of JAK2-V617F mutation in patients with CSVT are currently lacking. We aimed to evaluate the characteristics of CSVT patients that carry the JAK2 mutation.

MATERIALS AND METHODS

Data of consecutive patients with CSVT, admitted to three large academic medical centers between 2010 and 2020, were retrospectively studied. Demographics, clinical presentations, radiological and clinical outcome parameters were compared between carriers of the JAK2-V617F mutation and controls.

RESULTS

Out of 404 patients diagnosed with CSVT, 26 patients (6.5%) were carriers of the mutation. JAK2 mutation carriers more often had thrombocytosis (54% vs. 1%, p < 0.001). Furthermore, carriers of the JAK2 mutation less often had involvement of the transverse sinus (50% vs. 68%, p = 0.021). Finally, patients with the JAK2 mutation were more prone to have intracerebral hemorrhage (ICH, 31% vs. 17%, p = 0.044), but there was no significant difference between groups in terms of mortality nor functional outcome.

CONCLUSIONS

JAK2 mutation is not uncommon in patients with CSVT and should be routinely screened for in this population. CSVT in JAK2 mutation carriers may have a tendency toward involving specific venous sinuses and is associated with a higher rate of ICH but similar overall prognosis.

Factors influencing real-life use of direct oral anticoagulants in patients with cerebral sinus and venous thrombosis

BACKGROUND

Direct oral anticoagulants (DOAC) are advocated as equally effective to vitamin K antagonists (VKA) for the treatment of patients with cerebral sinus and venous thrombosis (CSVT). However, data concerning the real-life management practices in CSVT patients are is lacking.

METHODS

Prospective CSVT databases from four large academic medical centers were retrospectively studied. Demographics, clinical presentations, risk factors, radiological and outcome parameters were compared between CSVT patients treated with DOAC and VKA.

RESULTS

Out of 504 CSVT patients, 43 (8.5%) were treated with DOAC, and the remaining 461 (91.5%) were treated with VKA. All patients with antiphospholipid syndrome (APLA) were treated with VKA (61 vs. 0, p=0.013). Patients with a history or presence of malignancy were also more often treated with VKA (16% vs. 5%, p=0.046). Other risk factors for thrombosis did not differ between the groups. There were no differences in clot extent or location and no differences in the percentage of favorable outcomes or mortality were observed.

CONCLUSION

Our data suggests that only malignancy and antiphospholipid antibodies significantly influenced physician's decisions towards choosing VKA rather than DOAC. DOAC appear to be as effective and safe as VKA in patients with CSVT.

Clinicoradiologic Criteria for the Diagnosis of Stroke-like Episodes in MELAS

Background and Objectives

Stroke-like episodes (SLEs) in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome are often misdiagnosed as acute ischemic stroke (AIS). We aimed to determine unique clinical and neuroimaging features for SLEs and formulate diagnostic criteria.

Methods

We retrospectively identified patients with MELAS admitted for SLEs between January 2012 and December 2021. Clinical features and imaging findings were compared with a cohort of patients who presented with AIS and similar lesion topography. A set of criteria was formulated and then tested by a blinded rater to evaluate diagnostic performance.

Results

Eleven MELAS patients with 17 SLE and 21 AISs were included. Patients with SLEs were younger (median 45 [37-60] vs 77 [68-82] years, p < 0.01) and had a lower body mass index (18 ± 2.6 vs 29 ± 4, p < 0.01), more commonly reported hearing loss (91% vs 5%, p < 0.01), and more commonly presented with headache and/or seizures (41% vs 0%, p < 0.01). The earliest neuroimaging test performed at presentation was uniformly a noncontrast CT. Two main patterns of lesion topography with a stereotypical spatiotemporal evolution were identified-an anterior pattern (7/21, 41%) starting at the temporal operculum and spreading to the peripheral frontal cortex and a posterior pattern (10/21, 59%) starting at the cuneus/precuneus and spreading to the lateral occipital and parietal cortex. Other distinguishing features for SLEs vs AIS were cerebellar atrophy (91% vs 19%, p < 0.01), previous cortical lesions with typical SLE distribution (46% vs 9%, p = 0.03), acute lesion tissue hyperemia and venous engorgement on CT angiography (CTA) (45% vs 0%, p < 0.01), and no large vessel occlusion on CTA (0% vs 100%, p < 0.01). Based on these clinicoradiologic features, a set of diagnostic criteria were constructed for possible SLE (sensitivity 100%, specificity 81%, AUC 0.905) and probable SLE (sensitivity 88%, specificity 95%, AUC 0.917).

Discussion

Clinicoradiologic criteria based on simple anamnesis and a CT scan at presentation can accurately diagnose SLE and lead to early administration of appropriate therapy.

Classification of Evidence

This study provides Class III evidence that an algorithm using clinical and imaging features can differentiate stroke-like episodes due to MELAS from acute ischemic strokes.

Clinical score for early diagnosis and treatment of stroke-like episodes in MELAS syndrome

BACKGROUND AND OBJECTIVES

Stroke-like episodes (SLEs) in patients with MELAS syndrome are often initially misdiagnosed as acute ischemic stroke (AIS), resulting in treatment delay. We aimed to determine clinical features that may distinguish SLEs from AISs and explore the benefit of early L-arginine treatment on patient outcomes.

METHODS

We looked retrospectively for MELAS patients admitted between January 2005 and January 2022 and compared them to an AIS cohort with similar lesion topography. MELAS patients who received L-arginine within 40 days of their first SLE were defined as the early treatment group and the remaining as late or no treatment group.

RESULTS

Twenty-three SLEs in 10 MELAS patients and 21 AISs were included. SLE patients had significantly different features: they were younger, more commonly reported hearing loss, lower body mass index, had more commonly a combination of headache and/or seizures at presentation, serum lactate was higher, and hemiparesis was less common. An SLE Early Clinical Score (SLEECS) was constructed by designating one point to each above features. SLEECS ≥ 4 had 80% sensitivity and 100% specificity for SLE diagnosis. Compared to late or no treatment, early treatment group patients (n = 5) had less recurrent SLEs (total 2 vs. 11), less seizures (14% vs. 25%, p = 0.048), lower degree of disability at first and last follow-up (modified ranking scale, mRS 2 ± 0.7 vs. 4.2 ± 1, p = 0.005; 2 ± 0.7 vs. 5.8 ± 0.5, p < 0.001, respectively), and a lower mortality (0% vs. 80% p = 0.048).

CONCLUSIONS

The SLEECS model may aid in the early diagnosis and treatment of SLEs and lead to improved clinical outcomes.

Delayed CTP-Derived Deep Venous Outflow: A Novel Predictor of Striatocapsular Infarction after M1 Thrombectomy

BACKGROUND AND PURPOSE

Isolated striatocapsular infarction occurs commonly in patients with ischemic stroke following M1 thrombectomy. We aimed to explore the correlation between CTP-derived parameters of deep venous outflow at presentation and subsequent striatocapsular infarction in a retrospective cohort of such patients.

MATERIALS AND METHODS

TTP and peak enhancement were measured on CTP-derived time-attenuation curves of the internal cerebral and thalamostriate veins bilaterally. The difference in TTP (ΔTTP) and the relative decrease in venous enhancement between the ischemic and normal sides were calculated. NCCT performed 24 (SD, 12) hours postthrombectomy was used to determine tissue fate in the caudate head, caudate body, lentiform nucleus, and internal capsule. Striatocapsular ischemia (striatocapsular infarction-positive) was defined as infarction and striatocapsular injury as either infarction, contrast enhancement, or hemorrhagic transformation in ≥1 of these regions. A striatocapsular ischemia score was calculated (0 = no ischemic region, 1 = 1 ischemic region, 2 = ≥2 ischemic regions).

RESULTS

One hundred sixteen patients were included in the analysis. Sixty-one patients had striatocapsular infarction (striatocapsular infarction-positive). The mean thalamostriate ΔTTP was 1.95 (SD, 1.9) seconds for patients positive for striatocapsular infarction and 0.79 (SD, 2.1) for patients negative for it (P = .010). Results were similar for striatocapsular injury. The mean thalamostriate ΔTTP was 0.79 (SD, 2.1), 1.68 (SD, 1.4), and 2.05 (SD, 2) for striatocapsular infarction scores of 0, 1, and 2, respectively (P = .030).

CONCLUSIONS

CTP-derived thalamostriate ΔTTP is an excellent surrogate marker for striatocapsular infarction in patients post-M1 thrombectomy. The novel approach of extracting venous outflow parameters from CTP has numerous potential applications and should be further explored.

Clinical improvement of a toddler with COVID-19 focal cerebral arteriopathy possibly due to intra-arterial nimodipine

Pediatric stroke is considered an infrequent complication of COVID-19. Focal cerebral arteriopathy (FCA) is one of the most common causes of arterial ischemic stroke in a previously healthy child. The present report describes a toddler with FCA most likely induced by SARS-CoV-2 infection who showed significant clinical improvement that may be related to injection of intra-arterial nimodipine. To our knowledge, this is the first reported use of nimodipine in this setting.

Cardiac CT for intra-cardiac thrombus detection in embolic stroke of undetermined source (ESUS)

INTRODUCTION

Embolic stroke of undetermined source (ESUS) is a common medical challenge regarding secondary prevention strategy. Cardiac imaging is the cornerstone of embolic stroke workup, in an effort to diagnose high risk cardio-embolic sources. Cardiac computed tomography angiography (CCTA) is an emerging imaging modality with high diagnostic performance for intra-cardiac thrombus detection. The yield of CCTA implementation in addition to standard care in ESUS workup is unknown. Thus, the aim of this study was to assess the utility of CCTA in detecting intra-cardiac thrombi in the routine ESUS workup.

PATIENTS AND METHODS

This is a retrospective observational analysis of ESUS cases managed in vascular neurology unit between 2019 and 2021. Within this ESUS registry, consecutive patients undergoing CCTA were included and carefully analyzed.

RESULTS

During the study period 1066 Ischemic stroke (IS) cases were treated and evaluated. 266/1066 (25%) met ESUS criteria and 129/266 (48%) underwent CCTA. Intra-cardiac thrombus was detected by CCTA in 22/129 (17%; 95% CI, 11.5%-23.5%) patients: left ventricular thrombus (LVT) in 13 (10.1%) patients, left atrial appendage (LAA) thrombus in 8 (6.2%) patients, and left atrial (LA) thrombus in 1 (0.8%) patient. Only 5/22 (23%) of these thrombi were suspected, but could not be confirmed, in trans-thoracic echocardiogram (TTE). Among CCTA-undergoing patients, 27/129 (21%; 95% CI, 14%-28%) were found to have an indication (including pulmonary embolism) for commencing anticoagulation (AC) treatment, rather than anti-platelets. In favor of CCTA implementation, 22/266 (8.2%; 95% CI, 4.9%-11.5%) patients within the entire ESUS cohort were diagnosed with intra-cardiac thrombus, otherwise missed.

CONCLUSION

CCTA improves the detection of intra-cardiac thrombi in addition to standard care in ESUS patients. The implementation of CCTA in routine ESUS workup can change secondary prevention strategy in a considerable proportion of patients.

Janus Kinase-2 V617F Mutation and Antiphospholipid Syndrome in Cerebral Sinus Venous Thrombosis: Natural History and Retrospective Bicenter Analysis

Background

Cerebral sinus venous thrombosis (CSVT) is a rare neurovascular entity, usually associated with acquired or genetic hypercoagulable states. In up to 30% of the cases it remains idiopathic. Bone marrow proliferation disorders that are associated with Janus Kinase 2 V617F mutation (JAK-2) are known causes of the systemic and cerebral thrombosis—at times despite normal blood counts—for which hematologic treatment exists. However, JAK-2 prevalence in the CSVT cases is not clear.

Methods

In this retrospective analysis, data of 236 patients with CSVT admitted to two tertiary centers between 2010 and 2020 were analyzed, with emphasis on laboratory and imaging data and clinical and interventional outcomes.

Results

A total of 236 patients were included in the analysis. The patients' median age was 42 years and the average age was 44 years (±19 years), with 59% female patients. JAK-2 positivity rate was 18% (among 77 patients tested for the mutation). Patients with normal blood counts on presentation comprised 36% of the JAK-2 positive cases. Other hypercoagulability states were also investigated, with the antiphospholipid syndrome (APLA) showing the highest prevalence (11%) followed by other etiologies including oral contraceptive use, Factor V Leiden, prothrombin mutation, and malignancy. Selected JAK-2, APLA, and prothrombin mutation cases showed a more severe clinical course.

Conclusion

JAK-2 mutation is underdiagnosed and its screening may be warranted in the cases of idiopathic CSVT, even despite normal blood counts, to allow disease-modifying treatment and blood cell count monitoring. JAK-2, APLA, and prothrombin mutation may be associated with a more complicated clinical course.

Detection and prevalence of intra-cardiac thrombus in patients with embolic stroke of undetermined source

Background

Embolic Stroke of Undetermined Source (ESUS) is defined as non-lacunar brain infarct without proximal arterial stenosis or known cardioembolic source (including atrial arrythmias). Little is known about the prevalence of intra-cardiac thrombus as a potential source of embolism in patients presenting with ESUS.

Objectives

To examine the use of contrast-enhanced electrocardiogram-gated computed tomography (CT) to elucidate the prevalence of intra-cardiac thrombus in patients suspected of ESUS.

Methods

We retrospectively investigated 101 consecutive patients who presented to our hospital with ESUS between January 2019 and March 2021 and underwent 2D echocardiography and CT as part of stroke etiology evaluation.

Results

In our study population (73.2±9.98 years, 41% female), CT detected intra-cardiac thrombus in 19 (18.8%) patients. Left ventricular thrombus (LVT) was found in 10 (9.9%) patients and left atrial/left atrial appendage in 8 patients. All of cases of LVT were detected by cardiac CT, while 2D echocardiography was able to detect only four of these cases. All cases of LVT were associated with significant coronary obstructive disease, while in 2 out of 10 patients, a previous history of ischemic heart disease was unknown. Using CT 2 patients after transcatheter aortic valve implantation were diagnosed with hypoattenuated leaflet thickening, and 3 patients with concomitant pulmonary embolism. In total, the finding of CT resulted in change of management, indication for anticoagulation instead of antiplatelets drugs, in 23 (22.7%) patients.

Conclusion

CT may help to improve the detection of intra-cardiac thrombus in patients presenting with ESUS and therefore provide relevant information for anticoagulation therapy and need of further coronary evaluation and intervention. The high prevalence of intra-cardiac thrombus in ESUS patients make the use of complementary 3D imaging important.

Funding Acknowledgement

Type of funding sources: None.

Left appendage morphology as risk factors for cardio-embolism in patients with stroke of undetermined source

Background

Left atrium (LA) volume and function and certain left atrial appendage (LAA) morphologies are known to be strongly associated with the risk of thrombus formation and thromboembolism in patients with atrial fibrillation (AF). Little is known about the role of LA parameters and LAA morphology in patients with Embolic Stroke of Undetermined Source (ESUS).

Purpose

To assess LA volume and function and LAA morphologies in ESUS patients and the potential association with cardioembolic risk.

Methods

Twenty consecutive patients with ESUS who underwent contrast enhanced electrocardiogram-gated computed tomography (CT) as part of stroke etiology evaluation were matched by age and gender to patients with and without history of AF (twenty in each group) who had CT as part of standard evaluation before transcatheter aortic valve implantation. LA maximum (LAVmax) and minimum (LAVmin) volumes and function, measured as total emptying volume (LAEV) and total emptying fraction (LAEF) were assessed, and three- dimensional structures of the LA and LAA were constructed using the volume-rendered post-processing technique.

Results

The mean age of patients was 75.9±8.61, 76.1±8.52, 77.8±7.72) in the ESUS, AF and non-AF groups, respectively, with 11 (55%) females in each group. Compared to patients with ESUS, patients with AF showed significantly greater LAVmax (100.59±31.59 ml vs.155.78±63.15 ml, respectively, p=0.001) and LAVmin (71.38±30.69 ml vs. 140.73±64.60 ml; respectively, p&lt;0.001), while LAV max and LAVmin were similar, in patients with ESUS and non-AF. The distribution of LAA morphologies significantly differed between patients with ESUS and patients with AF and non-AF: 1 (5%) vs. 9 (45%) chicken-wing; 14 (70%) vs. 8 (40%) cauliflower; and 5 (25%) vs. 3 (15%) Cactus; respectively.

Conclusion

LA appendage morphology, but not LA volume, seems to be associated with ESUS. LAA morphologies with multiple lobes, cauliflower and cactus, seems to be associated with ESUS. Larger studies are needed to confirm these associations.

Funding Acknowledgement

Type of funding sources: None.

Reduction in Acute Stroke Admissions during the COVID-19 Pandemic: Data from a National Stroke Registry

Introduction

The COVID-19 pandemic overwhelmed health-care systems worldwide, and medical care for other acute diseases was negatively impacted. We aimed to investigate the effect of the COVID-19 outbreak on admission rates and in-hospital care for acute stroke and transient ischemic attack (TIA) in Israel, shortly after the start of the pandemic.

Methods

We conducted a retrospective observational study, based on data reported to the Israeli National Stroke Registry from 7 tertiary hospitals. All hospital admissions for acute stroke or TIA that occurred between January 1 and April 30, 2020 were included. Data were stratified into 2 periods according to the timing of COVID-19 restrictions as follows: (1) “pre-pandemic” − January 1 to March 7, 2020 and (2) “pandemic” − March 8 to April 30, 2020. We compared the weekly counts of hospitalizations between the 2 periods. We further investigated changes in demographic characteristics and in some key parameters of stroke care, including the percentage of reperfusion therapies performed, time from hospital arrival to brain imaging and to thrombolysis, length of hospital stay, and in-hospital mortality.

Results

2,260 cases were included: 1,469 in the pre-COVID-19 period and 791 in the COVID-19 period. Hospital admissions significantly declined between the 2 periods, by 48% for TIA (rate ratio [RR] = 0.52; 95% CI 0.43–0.64) and by 29% for stroke (RR = 0.71; 95% CI 0.64–0.78). No significant changes were detected in demographic characteristics and in most parameters of stroke management. While the percentage of reperfusion therapies performed remained unchanged, the absolute number of patients treated with reperfusion therapies seemed to decrease. Higher in-hospital mortality was observed only for hemorrhagic stroke.

Conclusion

The marked decrease in admissions for acute stroke and TIA, occurring at a time of a relatively low burden of COVID-19, is of great concern. Public awareness campaigns are needed as patients reluctant to seek urgent stroke care are deprived of lifesaving procedures and secondary prevention treatments.

Incorporation of relative cerebral blood flow into CT perfusion maps reduces false ’at risk' penumbra

Purpose

The region defined as ‘at risk’ penumbra by current CT perfusion (CTP) maps is largely overestimated. We aimed to quantitate the portion of true ‘at risk’ tissue within CTP penumbra and to determine the parameter and threshold that would optimally distinguish it from false ‘at risk’ tissue, that is, benign oligaemia.

Methods

Among acute stroke patients evaluated by multimodal CT (NCCT/CTA/CTP) we identified those that had not undergone endovascular/thrombolytic treatment and had follow-up NCCT. Maps of absolute and relative CBF, CBV, MTT, TTP and Tmax as well as summary maps depicting infarcted and penumbral regions were generated using the Intellispace Portal (Philips Healthcare, Best, Netherlands). Follow-up CT was automatically co-registered to the CTP scan and the final infarct region was manually outlined. Perfusion parameters were systematically analysed – the parameter that resulted in the highest true-negative-rate (ie, proportion of benign oligaemia correctly identified) at a fixed, clinically relevant false-negative-rate (ie, proportion of ‘missed’ infarct) of 15%, was chosen as optimal. It was then re-applied to the CTP data to produce corrected perfusion maps.

Results

Forty seven acute stroke patients met selection criteria. Average portion of infarcted tissue within CTP penumbra was 15%±2.2%. Relative CBF at a threshold of 0.65 yielded the highest average true-negative-rate (48%), enabling reduction of the false ‘at risk’ penumbral region by ~half.

Conclusions

Applying a relative CBF threshold on relative MTT-based CTP maps can significantly reduce false ‘at risk’ penumbra. This step may help to avoid unnecessary endovascular interventions.

Shifting Perceptions of Risk and Reward: Use of Anticoagulation in Patients With Acute Brain Ischemia and Atrial Fibrillation: Nine-Year Data From a National Acute Stroke Registry (National Acute Stroke Israeli Survey [NASIS])

BACKGROUND AND PURPOSE

Despite overwhelming evidence for the benefits of anticoagulation in patients with brain ischemia and atrial fibrillation, vast underuse has been reported.

METHODS

Use of anticoagulation for secondary stroke prevention was assessed in the National Acute Stroke Israeli Survey registry (NASIS) of hospitalized patients with atrial fibrillation and acute brain ischemia. Logistic regression analysis was performed to evaluate the effects of clinical covariates on anticoagulation therapy at discharge, and anticoagulation use over time was assessed in subgroups of patients with identified barriers to anticoagulation utilization.

RESULTS

There were 1254 survivors of acute brain ischemia with atrial fibrillation (mean age 77.2±10.6 years; 57.7% female). Between 2004 and 2013, the proportion of patients discharged on anticoagulation increased from 55% to 76.2%, and among those without perceived contraindications from 70% to 96% (P<0.0001). Older age, greater stroke severity, earlier registry period, and presence of contraindications were independent predictors of withholding therapy. Increased anticoagulation use over the years was observed even in patients with barriers to anticoagulation use, including patients with potential contraindications (P<0.001).

CONCLUSIONS

In survivors of acute brain ischemia with atrial fibrillation, we observed a substantial increase in anticoagulation utilization within less than a decade. This change was mainly driven by greater utilization of anticoagulation in subgroups with traditional clinical barriers to anticoagulation use, indicating a shift in physicians' perceptions of the risk-benefit ratio of anticoagulation.

[Clinical-pathologic conference (cpc) - pulmonary insufficiency in Myasthenia Gravis patient]

A 64 year old Myasthenia Gravis patient was admitted with pulmonary insufficiency. The autopsy revealed diffuse Strongyloides stercoralis infection.

Genomic instability in cancer

Solid tumours have abnormal, deficient vascular and lymphatic systems. As a result, perfusion within these malignancies is inadequate and chaotic, and the cancers contain regions that are transiently and chronically exposed to low pH, severe hypoxia and nutrient deprivation. These microenvironmental inadequacies are present from the earliest point in the development of solid tumours, and are fully established while the neoplasms are still microscopic. Exposures to acidic and hypoxic environments have been shown to produce a wide range of cytogenetic changes. These include increases in mutation frequencies; deficits in DNA repair; DNA overreplication and gene amplification; the induction of chromosomal fragile sites, triggering genomic rearrangements; and changes in gene expression. Moreover, exposure of cells to adverse microenvironments such as those in solid tumours selects for cells which have defects in the structure or expression of the genes that normally regulate cell proliferation. The genetic changes and selection pressures induced by hypoxia may be critical in causing the development of the genomic instability and genetic heterogeneity which is characteristic of solid tumours and in fostering the evolution of relatively benign cell populations in solid tumours to increasingly malignant, increasingly aggressive phenotypes.

ATM-dependent expression of the insulin-like growth factor-I receptor in a pathway regulating radiation response

The ATM gene is mutated in the syndrome of ataxia telangiectasia (AT), associated with neurologic dysfunction, growth abnormalities, and extreme radiosensitivity. Insulin-like growth factor-I receptor (IGF-IR) is a cell surface receptor with tyrosine kinase activity that can mediate mitogenesis, cell transformation, and inhibition of apoptosis. We report here that AT cells express low levels of IGF-IR and show decreased IGF-IR promoter activity compared with wild-type cells. Complementation of AT cells with the ATM cDNA results in increased IGF-IR promoter activity and elevated IGF-IR levels, whereas expression in wild-type cells of a dominant negative fragment of ATM specifically reduces IGF-IR expression, results consistent with a role for ATM in regulating IGF-IR expression at the level of transcription. When expression of IGF-IR cDNA is forced in AT cells via a heterologous viral promoter, near normal radioresistance is conferred on the cells. Conversely, in ATM cells complemented with the ATM cDNA, specific inhibition of the IGF-IR pathway prevents correction of the radiosensitivity. Taken together, these results establish a fundamental link between ATM function and IGF-IR expression and suggest that reduced expression of IGF-IR contributes to the radiosensitivity of AT cells. In addition, because IGF-I plays a major role in human growth and metabolism and serves as a survival and differentiation factor for developing neuronal tissue, these results may provide a basis for understanding other aspects of the AT syndrome, including the growth abnormalities, insulin resistance, and neurodegeneration.

Pollen competition in a natural population of Cucurbita foetidissima (Cucurbitaceae)

The pollen competition hypothesis predicts that when the number of pollen grains deposited onto stigmas exceeds the number of ovules, selection can operate in the time frame between deposition and fertilization. Moreover, because of the overlap in gene expression between the two phases of the life cycle, selection on microgametophytes may alter the resulting sporophytic generation. The extent to which pollen competition occurs in nature has been unclear, because tests of the predictions of the pollen competition hypothesis have used cultivars and/or artificial growth conditions and hand-pollination techniques. In this study we used a wild species, Cucurbita foetidissima, in its natural habitat (southern New Mexico) to determine the amount and timing of the arrival of pollen onto stigmas, the relationship between pollen deposition and seed number, and the effects of the intensity of pollen competition on progeny vigor. We found that ∼900 pollen grains are necessary for full seed set and that a single visit by a pollinator results in the deposition of 653.0 ± 101.8 pollen grains. About 29% of the flowers receiving a single pollinator visit had 900 or more pollen grains on its stigma. Moreover, within 2 h of anthesis, >4000 pollen grains were deposited onto a typical stigma, indicating that multiple pollinator visits must have occurred. Fruits produced by multiple visits had greater seed numbers (206 vs. 147) than fruits produced by a single visit. Finally, the progeny produced by multiple pollinator visits were more vigorous than those produced by single visits with respect to five measures of vegetative growth (MANCOVA, Wilks' lambda = 0.96, F(6,370) = 2.54, P < 0.02. These data demonstrate that conditions for pollen competition exist in nature and support the prediction that pollen competition enhances offspring vigor.

Floral plasticity in an iteroparous plant: the interactive effects of genotype, environment, and ontogeny in Campanula rapunculoides (Campanulaceae)

Phenotypic variation in 11 floral and reproductive traits was studied in cloned plants of Campanula rapunculoides replicated in three discrete environments. Using an ANOVA approach, we determined the relative influence of genotype (G), environment (E), G × E interaction, and ontogeny (position on the raceme) on the 11 traits. Two traits, duration of flowering and pollen size, showed no significant variation. All nine remaining traits had significant genotypic variation, accounting for 21-38% of the total phenotypic variation. Correlations among variant traits in seven genotypes were predominantly positive, but several significant correlations in one environment changed sign or were nonsignificant in another environment. Ovule number was negatively correlated with most male function traits: the negative correlation between ovule and pollen number was particularly strong and consistent across environments. Six traits varied significantly across environments, including number of flowers, number of ovules per flower, and duration of the male phase, but pollen traits did not show a significant environmental main effect. The G × E interaction was significant for flower number, corolla size, nectar quality, duration of the male phase, pollen viability, and ovule number. The contribution of interaction variance to the total phenotypic variation (5-14%) was comparable to that of the environment alone (7-21%). Ovule number decreased in flowers on the upper part of the raceme by nearly 25%, but other traits did not vary significantly by floral position. These results suggest that (1) pollen traits are buffered against environmental change more than ovule number or other floral characters, (2) a male-female trade-off exists and is complicated by ontogenic factors, (3) G × E interactions are common but may have small effects, and (4) specific correlation patterns among floral traits can be dependent upon the environment under which they develop.

Cloning, expression, and chromosomal assignment of the human mitochondrial intermediate peptidase gene (MIPEP)

The mitochondrial intermediate peptidase of Saccharomyces cerevisiae (YMIP) is a component of the yeast mitochondrial protein import machinery critically involved in the biogenesis of the oxidative phosphorylation (OXPHOS) system. This leader peptidase removes specific octapeptides from the amino terminus of nuclear-encoded OXPHOS subunits and components of the mitochondrial genetic apparatus. To address the biologic role of the human peptidase [MIPEP gene, HMIP polypeptide], we have initiated its molecular and functional characterization. A full-length cDNA was isolated by screening a human liver library using a rat MIP (RMIP) cDNA as a probe. The encoded protein contained a typical mitochondrial leader peptide and showed 92 and 54% homology to RMIP and YMIP, respectively. A survey of human mitochondrial protein precursors revealed that, similar to YMIP, HMIP is primarily involved in the maturation of OXPHOS-related proteins. Northern analysis showed that the MIPEP gene is differentially expressed in human tissues, with the highest levels of expression in the heart, skeletal muscle, and pancreas, three organ systems that are frequently affected in OXPHOS disorders. Using fluorescence in situ hybridization, the MIPEP locus was assigned to 13q12. This information offers the possibility of testing the potential involvement of HMIP in the pathophysiology of nuclear-driven OXPHOS disorders.