Closing the gap on causal processes of infection risk from cross-sectional data:structural equation models to understand infection and co-infection

BACKGROUND: Epidemiological studies of disease exposure risk are frequently based on observational, cross-sectional data, and use statistical approaches as crucial tools for formalising causal processes and making predictions of exposure risks. However, an acknowledged limitation of traditional models is that the inferred relationships are correlational, cannot easily distinguish direct from indirect determinants of disease risk, and are often considerable simplifications of complex interrelationships. This may be particularly important when attempting to infer causality in patterns of co-infection through pathogen-facilitation. METHODS: We describe analyses of cross-sectional data using structural equation models (SEMs), a contemporary advancement on traditional regression approaches, based on our study system of feline gammaherpesvirus (FcaGHV1) in domestic cats. RESULTS: SEMs strongly supported a latent (host phenotype) variable associated with FcaGHV1 exposure and co-infection risk, suggesting these individuals are simply more likely to become infected with multiple pathogens. However, indications of pathogen-covariance (potential facilitation) were also variably detected: potentially among FcaGHV1, Bartonella spp and Mycoplasma spp. CONCLUSIONS: Our models suggest multiple exposures are primarily driven by host phenotypic traits, such as aggressive male phenotypes, and secondarily by pathogen-pathogen interactions. The results of this study demonstrate the application of SEMs to understanding epidemiological processes using observational data, and could be used more widely as a complementary tool to understand complex cross-sectional information in a wide variety of disciplines

Neurological Signs at the First Psychotic Episode as Correlates of Long-Term Outcome:Results From the AESOP-10 Study

Minor neurological signs are subtle deficits in sensory integration, motor coordination, and sequencing of complex motor acts present in excess in the early stages of psychosis. Still, it remains unclear whether at least some of these signs represent trait or state markers for psychosis and whether they are markers of long-term disease outcome of clinical utility. We examined the relationship between neurological function at illness onset assessed with the Neurological Evaluation Scale and subsequent illness course in 233 patients from AESOP-10 (Aetiology and Ethnicity in Schizophrenia and Other Psychoses), a 10-year follow-up study of a population-based cohort of individuals recruited at the time of their first episode of psychosis in the United Kingdom. In 56 of these patients, we also explored changes in neurological function over time. We included a group of 172 individuals without psychosis as controls. After 10 years, 147 (63%) patients had developed a non-remitting course of illness, and 86 (37%) a remitting course. Already at first presentation, patients who developed a non-remitting course had significantly more primary, motor coordination, and total signs than both remitting patients and healthy controls. While Motor Coordination signs did not change over time, rates of Primary, Sensory Integration, and Total signs increased, independently of illness course type. These findings suggest that motor coordination problems could be a useful early, quick, and easily detectable marker of subsequent clinical outcome. With other motor abnormalities, a measure of motor incoordination could contribute to the identification of the most vulnerable individuals, who could benefit from targeted and more assertive treatment approaches

Symptom remission at 12-weeks strongly predicts long-term recovery from the first episode of psychosis.

BACKGROUND: To determine the baseline individual characteristics that predicted symptom recovery and functional recovery at 10-years following the first episode of psychosis. METHODS: AESOP-10 is a 10-year follow up of an epidemiological, naturalistic population-based cohort of individuals recruited at the time of their first episode of psychosis in two areas in the UK (South East London and Nottingham). Detailed information on demographic, clinical, and social factors was examined to identify which factors predicted symptom and functional remission and recovery over 10-year follow-up. The study included 557 individuals with a first episode psychosis. The main study outcomes were symptom recovery and functional recovery at 10-year follow-up. RESULTS: At 10 years, 46.2% (n = 140 of 303) of patients achieved symptom recovery and 40.9% (n = 117) achieved functional recovery. The strongest predictor of symptom recovery at 10 years was symptom remission at 12 weeks (adj OR 4.47; CI 2.60-7.67); followed by a diagnosis of depression with psychotic symptoms (adj OR 2.68; CI 1.02-7.05). Symptom remission at 12 weeks was also a strong predictor of functional recovery at 10 years (adj OR 2.75; CI 1.23-6.11), together with being from Nottingham study centre (adj OR 3.23; CI 1.25-8.30) and having a diagnosis of mania (adj OR 8.17; CI 1.61-41.42). CONCLUSIONS: Symptom remission at 12 weeks is an important predictor of both symptom and functional recovery at 10 years, with implications for illness management. The concepts of clinical and functional recovery overlap but should be considered separately.This work was supported by UK Medical Research Council (ref: G0500817) and the Department of Health via the National Institute for Health Research (NIHR) Biomedical Research Centre at South London and Maudsley Foundation Trust (SLaM) and King’s College Londo

Abnormal P300 in people with high risk of developing psychosis

Background Individuals with an “at-risk mental state” (or “prodromal” symptoms) have a 20–40% chance of developing psychosis; however it is difficult to predict which of them will become ill on the basis of their clinical symptoms alone. We examined whether neurophysiological markers could help to identify those who are particularly vulnerable. Method 35 cases meeting PACE criteria for the at-risk mental state (ARMS) and 57 controls performed an auditory oddball task whilst their electroencephalogram was recorded. The latency and amplitude of the P300 and N100 waves were compared between groups using linear regression. Results The P300 amplitude was significantly reduced in the ARMS group [8.6 ± 6.4 microvolt] compared to controls [12.7 ± 5.8 microvolt] (p < 0.01). There were no group differences in P300 latency or in the amplitude and latency of the N100. Of the at-risk subjects that were followed up, seven (21%) developed psychosis. Conclusion Reduction in the amplitude of the P300 is associated with an increased vulnerability to psychosis. Neurophysiological and other biological markers may be of use to predict clinical outcomes in populations at high risk

Right and left prefrontal transcranial magnetic stimulation at 1 Hz does not affect mood in healthy volunteers

BACKGROUND: Prefrontal repetitive transcranial magnetic stimulation (rTMS) has been used to induce side-specific mood changes in volunteers and patients. To clarify inconsistencies between reports that used different stimulation frequencies, we conducted a controlled study with a low (1 Hz) frequency, comparing left with right-sided stimulation METHODS: Nineteen healthy volunteers received randomised left or right prefrontal rTMS at a frequency of 1 Hz and 100% of motor threshold in two sessions two weeks apart. RESULTS: There were significant improvements with TMS for performance in the digit symbol substitution and verbal fluency tests, but no change of mood on a number of measures. There was also a reduction of pulse rate after TMS. The only side-specific TMS-effect was on mean arterial pressure, which decreased pressure after left, but not after right prefrontal TMS. CONCLUSIONS: Apart from the unexpected and so far unreplicated effect on mean arterial pressure, there were no side-specific effects on mood in volunteers. It is unlikely that a simple laterality model of mood together with the assumed activating effect of higher and 'quenching' effect of lower stimulation frequency can account for the effects of TMS on mood

Dopamine release in the human striatum: motor and cognitive tasks revisited

Striatal dopamine (DA) release has been shown during behavioural tasks, but the relative contribution of motor, reward, and cognitive components is unclear. Dopamine release was quantified using [11C]-raclopride in two studies using a triple-scan approach, comprising active task, motor control, and rest. In the first, bolus radiotracer was delivered during a sequential motor learning paradigm; in the second, a spatial planning task, bolus plus constant infusion was applied. [11C]-raclopride binding potentials (BPNDs) in striatal functional subdivisions were compared across conditions. [11C]-raclopride BPND was significantly reduced in active task compared with rest in both the sensorimotor and associative striatum in both studies, because of differences between rest and motor control conditions. In both regions, the motor control BPND fell between the rest and active task in the planning study, but the difference between motor control and active task conditions was not significant. No such changes were observed in the limbic striatum. Using rigorous methodology, this study validates earlier evidence that striatal DA release occurs during behavioural challenges. Increased DA release during movement was reliably detected in the sensorimotor and associative striatum, supporting use of the functional subdivision model in humans. No additional DA release was observed specific to the cognitive component of either task

Limbic striatal dopamine D2/3 receptor availability is associated with non-planning impulsivity in healthy adults after exclusion of potential dissimulators

Positron emission tomography (PET) studies have reported an association between reduced striatal dopamine D2/3 receptor availability and higher scores on self-report measures of trait impulsivity in healthy adults. However, impulsivity is a multi-faceted construct, and it is unclear which aspect(s) of impulsivity might be driving these associations. The current study aimed to investigate the relationship between limbic (ventral) striatal D2/3 receptor availability and individual components of impulsivity (attentional, motor and non-planning) using the Barratt Impulsiveness Scale (BIS-11) and [(11)C]raclopride PET in 23 healthy volunteers. A partial correlational analysis showed a significant association between non-planning impulsiveness (lack of forethought or 'futuring') and limbic D2/3 receptor availability, which was only apparent after the exclusion of potential dissimulators (indexed by high scores on impression management). Our findings suggest that non-planning impulsiveness is associated with individual variation in limbic striatal D2/3 receptor availability and that different facets of impulsivity may have specific neurochemical correlates. Future studies that combine D2/3 receptor imaging with behavioral measures of impulsivity are required to further elucidate the precise relationship between individual components of trait impulsivity and brain dopaminergic function