Predicting post-treatment symptom severity for adults receiving psychological therapy in routine care for generalised anxiety disorder: a machine learning approach.

Approximately half of generalised anxiety disorder (GAD) patients do not recover from first-line treatments, and no validated prediction models exist to inform individuals or clinicians of potential treatment benefits. This study aimed to develop and validate an accurate and explainable prediction model of post-treatment GAD symptom severity. Data from adults receiving treatment for GAD in eight Improving Access to Psychological Therapies (IAPT) services (n=15,859) were separated into training, validation and holdout datasets. Thirteen machine learning algorithms were compared using 10-fold cross-validation, against two simple clinically relevant comparison models. The best-performing model was tested on the holdout dataset and model-specific explainability measures identified the most important predictors. A Bayesian Additive Regression Trees model out-performed all comparison models (MSE=16.54 [95 % CI=15.58; 17.51]; MAE=3.19; R²=0.33, including a single predictor linear regression model: MSE=20.70 [95 % CI=19.58; 21.82]; MAE=3.94; R²=0.14). The five most important predictors were: PHQ-9 anhedonia, GAD-7 annoyance/irritability, restlessness and fear items, then the referral-assessment waiting time. The best-performing model accurately predicted post-treatment GAD symptom severity using only pre-treatment data, outperforming comparison models that approximated clinical judgement and remaining within the GAD-7 error of measurement and minimal clinically important differences. This model could inform treatment decision-making and provide desired information to clinicians and patients receiving treatment for GAD.

Examining bi-directional change in sleep and depression symptoms in individuals receiving routine psychological treatment.

BACKGROUND: Sleep disturbance is a common symptom of depression. There is conflicting evidence whether improvements in sleep might impact depressive symptoms, or whether treating the core depressive symptoms might improve sleep disturbance. This study explored the bi-directional impact of sleep and depressive symptom change among individuals receiving psychological treatment. METHODS: Session-by-session change in sleep disturbance and depressive symptom severity scores were explored in patients receiving psychological therapy for depression from Improving Access to Psychological Therapies services in England. Bi-directional change in sleep disturbance and depressive symptoms was modelled using random-intercept cross-lagged panel models with items from the PHQ-9. RESULTS: The sample included 17,732 adults that had received three or more treatment sessions. Both depressive symptoms and sleep disturbance scores decreased. Between initial timepoints, higher sleep disturbance was associated with lower depression scores, but after this point positive cross-lagged effects were observed for both the impact of sleep disturbance on later depressive symptoms, and depressive symptoms on later sleep disturbance scores. The magnitude of effects suggested depressive symptoms may have more impact on sleep than the reverse, and this effect was larger in sensitivity analyses. CONCLUSIONS: Findings provide evidence that psychological therapy for depression results in improvements in core depressive symptoms and sleep disturbance. There was some evidence that depressive symptoms may have more impact on sleep disturbance scores at the next therapy session, than sleep disturbance does on later depressive symptoms. Targeting the core symptoms of depression initially may optimise outcomes, but further research is needed to elucidate these relationships.

Predicting prognosis for adults with depression using individual symptom data: a comparison of modelling approaches.

BACKGROUND: This study aimed to develop, validate and compare the performance of models predicting post-treatment outcomes for depressed adults based on pre-treatment data. METHODS: Individual patient data from all six eligible randomised controlled trials were used to develop (k = 3, n = 1722) and test (k = 3, n = 918) nine models. Predictors included depressive and anxiety symptoms, social support, life events and alcohol use. Weighted sum scores were developed using coefficient weights derived from network centrality statistics (models 1-3) and factor loadings from a confirmatory factor analysis (model 4). Unweighted sum score models were tested using elastic net regularised (ENR) and ordinary least squares (OLS) regression (models 5 and 6). Individual items were then included in ENR and OLS (models 7 and 8). All models were compared to one another and to a null model (mean post-baseline Beck Depression Inventory Second Edition (BDI-II) score in the training data: model 9). Primary outcome: BDI-II scores at 3-4 months. RESULTS: Models 1-7 all outperformed the null model and model 8. Model performance was very similar across models 1-6, meaning that differential weights applied to the baseline sum scores had little impact. CONCLUSIONS: Any of the modelling techniques (models 1-7) could be used to inform prognostic predictions for depressed adults with differences in the proportions of patients reaching remission based on the predicted severity of depressive symptoms post-treatment. However, the majority of variance in prognosis remained unexplained. It may be necessary to include a broader range of biopsychosocial variables to better adjudicate between competing models, and to derive models with greater clinical utility for treatment-seeking adults with depression.

Transdiagnostic symptom dynamics during psychotherapy.

Psychotherapy is an effective treatment for many common mental health problems, but the mechanisms of action and processes of change are unclear, perhaps driven by the focus on a single diagnosis which does not reflect the heterogeneous symptom experiences of many patients. The objective of this study was to better understand therapeutic change, by illustrating how symptoms evolve and interact during psychotherapy. Data from 113,608 patients from psychological therapy services who completed depression and anxiety symptom measures across three to six therapy sessions were analysed. A panel graphical vector-autoregression model was estimated in a model development sample (N = 68,165) and generalizability was tested in a confirmatory model, fitted to a separate (hold-out) sample of patients (N = 45,443). The model displayed an excellent fit and replicated in the confirmatory holdout sample. First, we found that nearly all symptoms were statistically related to each other (i.e. dense connectivity), indicating that no one symptom or association drives change. Second, the structure of symptom interrelations which emerged did not change across sessions. These findings provide a dynamic view of the process of symptom change during psychotherapy and give rise to several causal hypotheses relating to structure, mechanism, and process.

Role of age, gender and marital status in prognosis for adults with depression: An individual patient data meta-analysis.

AIMS: To determine whether age, gender and marital status are associated with prognosis for adults with depression who sought treatment in primary care. METHODS: Medline, Embase, PsycINFO and Cochrane Central were searched from inception to 1st December 2020 for randomised controlled trials (RCTs) of adults seeking treatment for depression from their general practitioners, that used the Revised Clinical Interview Schedule so that there was uniformity in the measurement of clinical prognostic factors, and that reported on age, gender and marital status. Individual participant data were gathered from all nine eligible RCTs (N = 4864). Two-stage random-effects meta-analyses were conducted to ascertain the independent association between: (i) age, (ii) gender and (iii) marital status, and depressive symptoms at 3-4, 6-8, and 9-12 months post-baseline and remission at 3-4 months. Risk of bias was evaluated using QUIPS and quality was assessed using GRADE. PROSPERO registration: CRD42019129512. Pre-registered protocol https://osf.io/e5zup/. RESULTS: There was no evidence of an association between age and prognosis before or after adjusting for depressive 'disorder characteristics' that are associated with prognosis (symptom severity, durations of depression and anxiety, comorbid panic disorderand a history of antidepressant treatment). Difference in mean depressive symptom score at 3-4 months post-baseline per-5-year increase in age = 0(95% CI: -0.02 to 0.02). There was no evidence for a difference in prognoses for men and women at 3-4 months or 9-12 months post-baseline, but men had worse prognoses at 6-8 months (percentage difference in depressive symptoms for men compared to women: 15.08% (95% CI: 4.82 to 26.35)). However, this was largely driven by a single study that contributed data at 6-8 months and not the other time points. Further, there was little evidence for an association after adjusting for depressive 'disorder characteristics' and employment status (12.23% (-1.69 to 28.12)). Participants that were either single (percentage difference in depressive symptoms for single participants: 9.25% (95% CI: 2.78 to 16.13) or no longer married (8.02% (95% CI: 1.31 to 15.18)) had worse prognoses than those that were married, even after adjusting for depressive 'disorder characteristics' and all available confounders. CONCLUSION: Clinicians and researchers will continue to routinely record age and gender, but despite their importance for incidence and prevalence of depression, they appear to offer little information regarding prognosis. Patients that are single or no longer married may be expected to have slightly worse prognoses than those that are married. Ensuring this is recorded routinely alongside depressive 'disorder characteristics' in clinic may be important.

The importance of transdiagnostic symptom level assessment to understanding prognosis for depressed adults: analysis of data from six randomised control trials.

BACKGROUND: Depression is commonly perceived as a single underlying disease with a number of potential treatment options. However, patients with major depression differ dramatically in their symptom presentation and comorbidities, e.g. with anxiety disorders. There are also large variations in treatment outcomes and associations of some anxiety comorbidities with poorer prognoses, but limited understanding as to why, and little information to inform the clinical management of depression. There is a need to improve our understanding of depression, incorporating anxiety comorbidity, and consider the association of a wide range of symptoms with treatment outcomes. METHOD: Individual patient data from six RCTs of depressed patients (total n = 2858) were used to estimate the differential impact symptoms have on outcomes at three post intervention time points using individual items and sum scores. Symptom networks (graphical Gaussian model) were estimated to explore the functional relations among symptoms of depression and anxiety and compare networks for treatment remitters and those with persistent symptoms to identify potential prognostic indicators. RESULTS: Item-level prediction performed similarly to sum scores when predicting outcomes at 3 to 4 months and 6 to 8 months, but outperformed sum scores for 9 to 12 months. Pessimism emerged as the most important predictive symptom (relative to all other symptoms), across these time points. In the network structure at study entry, symptoms clustered into physical symptoms, cognitive symptoms, and anxiety symptoms. Sadness, pessimism, and indecision acted as bridges between communities, with sadness and failure/worthlessness being the most central (i.e. interconnected) symptoms. Connectivity of networks at study entry did not differ for future remitters vs. those with persistent symptoms. CONCLUSION: The relative importance of specific symptoms in association with outcomes and the interactions within the network highlight the value of transdiagnostic assessment and formulation of symptoms to both treatment and prognosis. We discuss the potential for complementary statistical approaches to improve our understanding of psychopathology.

Contributory factors in surgical incidents as delineated by a confidential reporting system.

Background Confidential reporting systems play a key role in capturing information about adverse surgical events. However, the value of these systems is limited if the reports that are generated are not subjected to systematic analysis. The aim of this study was to provide the first systematic analysis of data from a novel surgical confidential reporting system to delineate contributory factors in surgical incidents and document lessons that can be learned. Methods One-hundred and forty-five patient safety incidents submitted to the UK Confidential Reporting System for Surgery over a 10-year period were analysed using an adapted version of the empirically-grounded Yorkshire Contributory Factors Framework. Results The most common factors identified as contributing to reported surgical incidents were cognitive limitations (30.09%), communication failures (16.11%) and a lack of adherence to established policies and procedures (8.81%). The analysis also revealed that adverse events were only rarely related to an isolated, single factor (20.71%) - with the majority of cases involving multiple contributory factors (79.29% of all cases had more than one contributory factor). Examination of active failures - those closest in time and space to the adverse event - pointed to frequent coupling with latent, systems-related contributory factors. Conclusions Specific patterns of errors often underlie surgical adverse events and may therefore be amenable to targeted intervention, including particular forms of training. The findings in this paper confirm the view that surgical errors tend to be multi-factorial in nature, which also necessitates a multi-disciplinary and system-wide approach to bringing about improvements.

Application of audio fingerprinting to neonatal EEG.

A clinical neurophysiologist must recognize patterns in EEG signals to evaluate the health of a patient's brain activity. Rare or unusual patterns may take time to correctly identify. The ability to automatically assist this recall would be beneficial in ensuring that appropriate measures could be taken in a timely fashion. Audio fingerprinting is a method used to identify songs using only a snippet of the song. Fingerprints are extracted from a sub-section of the song and matched against a database of previously computed fingerprints. In this paper, a fingerprint quantization technique is implemented on neonatal EEG data to attempt to identify sections of EEG data when only seeing a sub-section of the data. The impact of signal distortions is investigated and results from a database of one hour recordings from 40 newborns are presented.

Molecular epidemiology of Mycobacterium abscessus complex isolates in Ireland.

BACKGROUND: The Mycobacterium abscessus complex are the rapidly growing mycobacteria (RGM) most commonly causing lung disease, especially in cystic fibrosis (CF) patients. Ireland has the world's highest CF incidence. The molecular epidemiology of M. abscessus complex in Ireland is unreported. METHODS: We performed rpoB gene sequencing and multi-locus sequence typing (MLST) on M. abscessus complex strains isolated from thirty-six patients in 2006-2012 (eighteen known CF patients). RESULTS: Twenty-eight strains (78%) were M. abscessus subsp. abscessus, eight M. abscessus subsp. massiliense, none were M. abscessus subsp. bolletii. Sequence type 1 (ST1) and ST26 (M. abscessus subsp. abscessus) were commonest. Seven M. abscessus subsp. abscessus STs (25%) were novel (two with novel alleles). Seven M. abscessus subsp. massiliense STs were previously reported (88%), including two ST23, the globally successful clone. In 2012, of 552 CF patients screened, eleven were infected with M. abscessus complex strains (2%). CONCLUSIONS: The most prevalent M. abscessus subsp. abscessus and M. abscessus subsp. massiliense strains in Ireland belong to widely-distributed STs, but there is evidence of high M. abscessus subsp. abscessus diversity.

Environmental Exposures-The Missing Link in Immune Responses After Transplantation.

In transplantation, immunosuppression has been directed at controlling acute responses, but treatment of chronic rejection has been ineffective. It is possible that factors that have previously been unaccounted for, such as exposure to inhaled pollution, ultraviolet light, or loss of the normal equilibrium between the gut immune system and the outside environment may be responsible for shifting immune responses to an effector/inflammatory phenotype, which leads to loss of self-tolerance and graft acceptance, and a shift towards autoimmunity and chronic rejection. Cells of the immune system are in a constant balance of effector response, regulation, and quiescence. Endogenous and exogenous signals can shift this balance through the aryl hydrocarbon receptor, which serves as a thermostat to modulate the response one way or the other, both at mucosal surfaces of interface organs to the outside environment, and in the internal milieu. Better understanding of this balance will identify a target for maintenance of self-tolerance and continued graft acceptance in patients who have achieved a "steady state" after transplantation.

First outbreak of linezolid-resistant vancomycin-resistant Enterococcus faecium in an Irish hospital, February to September 2014.

An outbreak of linezolid-resistant vancomycin-resistant Enterococcus faecium (LRVREfm) occurred in the hepatology ward of a tertiary referral hospital in Ireland between February and September 2014. LRVREfm was isolated from 15 patients; pulsed-field gel electrophoresis confirmed spread of a single clone. This is the first report of an outbreak of linezolid-resistant vancomycin-resistant enterococcus in Ireland.

Cyclodextrin mediated delivery of NF-κB and SRF siRNA reduces the invasion potential of prostate cancer cells in vitro.

Prostate cancer is the most common cancer in men of the western world. To date, no effective treatment exists for metastatic prostate cancer and consequently, there is an urgent need to develop new and improved therapeutics. In recent years, the therapeutic potential of RNA interference (RNAi) has been extensively explored in a wide range of diseases including prostate cancer using numerous gene delivery vectors. The aims of this study were to investigate the ability of a non-viral modified cyclodextrin (CD) vector to deliver siRNA to the highly metastatic PC-3 prostate cancer cell line, to quantify the resulting knockdown of the two target genes (RelA and SRF) and to study the effects of the silencing on metastasis. Data from a Matrigel in vitro invasion assay indicated that the silencing of the target genes achieved by the CD vector resulted in significant reductions (P=0.0001) in the metastatic potential of these cells. As the silencing of these target genes was shown not to have a negative impact on cell viability, we hypothesise that the mechanism of invasion inhibition is due, in part, to the significant reduction observed (P⩽0.0001) in the level of pro-inflammatory cytokine, MMP9, which is known to be implicated in the metastasis of prostate cancer.

Stream computing for biomedical signal processing: A QRS complex detection case-study.

Recent developments in "Big Data" have brought significant gains in the ability to process large amounts of data on commodity server hardware. Stream computing is a relatively new paradigm in this area, addressing the need to process data in real time with very low latency. While this approach has been developed for dealing with large scale data from the world of business, security and finance, there is a natural overlap with clinical needs for physiological signal processing. In this work we present a case study of streams processing applied to a typical physiological signal processing problem: QRS detection from ECG data.

Early-stage development of novel cyclodextrin-siRNA nanocomplexes allows for successful postnebulization transfection of bronchial epithelial cells.

BACKGROUND: Successful delivery of small interfering RNA (siRNA) to the lungs remains hampered by poor intracellular delivery, vector-mediated cytotoxicity, and an inability to withstand nebulization. Recently, a novel cyclodextrin (CD), SC12CDClickpropylamine, consisting of distinct lipophilic and cationic subunits, has been shown to transfect a number of cell types. However, the suitability of this vector for pulmonary siRNA delivery has not been assessed to date. To address this, a series of high-content analysis (HCA) and postnebulization assays were devised to determine the potential for CD-siRNA delivery to the lungs. METHODS: SC12CDClickpropylamine-siRNA mass ratios (MRs) were examined for size and zeta potential. In-depth analysis of nanocomplex uptake and toxicity in Calu-3 bronchial epithelial cells was examined using IN Cell(®) HCA assays. Nebulized SC12CDClickpropylamine nanocomplexes were assessed for volumetric median diameter (VMD) and fine particle fraction (FPF) and compared with saline controls. Finally, postnebulization stability was determined by comparing luciferase knockdown elicited by SC12CDClickpropylamine nanocomplexes before and after nebulization. RESULTS: SC12CDClickpropylamine-siRNA complexation formed cationic nanocomplexes of ≤200 nm in size depending on the medium and led to significantly higher levels of siRNA associated with Calu-3 cells compared with RNAiFect-siRNA-treated cells at all MRs (p<0.001, n=3×4), with evidence of toxicity only at MRs 50-100. Nebulization of SC12CDClickpropylamine nanocomplexes using the Aeroneb(®) Pro resulted in VMDs of ∼4 µm and FPFs of ∼57% at all MRs. SC12CDClickpropylamine-siRNA-mediated luciferase knockdown was found to be 39.8±3.6% at MR=20 before and 35.6±4.55% after nebulization, comparable to results observed using unnebulized commercial transfection reagent, RNAiFect. CONCLUSIONS: SC12CDClickpropylamine nanocomplexes can be effectively nebulized for pulmonary delivery of siRNA using Aeroneb technology to mediate knockdown in airway cells. To the best of our knowledge, this is the first study examining the suitability of SC12CDClickpropylamine-siRNA nanocomplexes for pulmonary delivery. Furthermore, this work provides an integrated nanomedicine-device combination for future in vitro and in vivo preclinical and clinical studies of inhaled siRNA therapeutics.

Gene silencing of TNF-alpha in a murine model of acute colitis using a modified cyclodextrin delivery system.

Inflammatory bowel disease (IBD) is a chronic relapsing inflammation of the gastrointestinal tract. The cytokine TNF-alpha (TNF-α) plays a pivotal role in mediating this inflammatory response. RNA interference (RNAi) holds great promise for the specific and selective silencing of aberrantly expressed genes, such as TNF-α in IBD. The aim of this study was to investigate the efficacy of an amphiphilic cationic cyclodextrin (CD) vector for effective TNF-α siRNA delivery to macrophage cells and to mice with induced acute-colitis. The stability of CD.siRNA was examined by gel electrophoresis in biorelevant media reflecting colonic fluids. RAW264.7 cells were transfected with CD.TNF-α siRNA, stimulated with lipopolysaccharide (LPS) and TNF-α and IL-6 responses were measured by PCR and ELISA. Female C57BL/6 mice were exposed to dextran sodium sulphate (DSS) and treated by intrarectal administration with either CD.siRNA TNF-α or a control solution. In vitro, siRNA in CD nanocomplexes remained intact and stable in both fed and fasted simulated colonic fluids. RAW264.7 cells transfected with CD.TNF-α siRNA and stimulated with LPS displayed a significant reduction in both gene and protein levels of TNF-α and IL-6. CD.TNF-α siRNA-treated mice revealed a mild amelioration in clinical signs of colitis, but significant reductions in total colon weight and colonic mRNA expression of TNF-α and IL-6 compared to DSS-control mice were detected. This data indicates the clinical potential of a local CD-based TNF-α siRNA delivery system for the treatment of IBD.

Characterisation of cationic amphiphilic cyclodextrins for neuronal delivery of siRNA: effect of reversing primary and secondary face modifications.

Significant research is focused on the development of non-viral vectors for delivery of siRNA to neurons and the central nervous system. Cyclodextrins (CDs) have shown great promise as efficient and low toxicity gene delivery vectors in various cell types. Here, we investigate two CDs for siRNA delivery in a neuronal cell model. These CDs were substituted on opposite faces (primary and secondary) with amphiphilic and cationic groups. Physical properties of CD.siRNA complexes, including size, charge and stability were measured. In vitro investigations were carried out in immortalised hypothalamic neurons. Neuronal cell uptake was measured by flow cytometry and cytotoxicity was assessed by MTT assay. Knockdown of a luciferase reporter gene was used as a measure of gene silencing efficiency. Both CDs interacted with siRNA, yielding nanosized cationic complexes which exhibited good stability on storage. A favourable toxicity profile was demonstrated for the CD.siRNA complexes. However, only one of the two CDs mediated high levels of neuronal uptake and efficient gene silencing, equivalent to those achieved with a commercial lipid-based vector. Despite the suitability of both CDs as siRNA delivery vectors in terms of their ability to complex siRNA and the properties of the complexes yielded, only one CD achieved good transfection efficiency. This was likely due to the differences in their chemical structures. The effective CD offers great potential as a novel non-toxic vector for neuronal siRNA delivery.

Click-modified cyclodextrins as nonviral vectors for neuronal siRNA delivery.

RNA interference (RNAi) holds great promise as a strategy to further our understanding of gene function in the central nervous system (CNS) and as a therapeutic approach for neurological and neurodegenerative diseases. However, the potential for its use is hampered by the lack of siRNA delivery vectors which are both safe and highly efficient. Cyclodextrins have been shown to be efficient and low toxicity gene delivery vectors in various cell types in vitro. However, to date, they have not been exploited for delivery of oligonucleotides to neurons. To this end, a modified ß-cyclodextrin (CD) vector was synthesized, which complexed siRNA to form cationic nanoparticles of less than 200 nm in size. Furthermore, it conferred stability in serum to the siRNA cargo. The in vitro performance of the CD in both immortalized hypothalamic neurons and primary hippocampal neurons was evaluated. The CD facilitated high levels of intracellular delivery of labeled siRNA, while maintaining at least 80% cell viability. Significant gene knockdown was achieved, with a reduction in luciferase expression of up to 68% and a reduction in endogenous glyceraldehyde phosphate dehydrogenase (GAPDH) expression of up to 40%. To our knowledge, this is the first time that a modified CD has been used as a safe and efficacious vector for siRNA delivery into neuronal cells.

Opportunities and challenges for oral delivery of hydrophobic versus hydrophilic peptide and protein-like drugs using lipid-based technologies.

Peptide and protein-like drugs are macromolecules currently produced in increasing numbers by the pharmaceutical biotechnology industry. The physicochemical properties of these molecules posebarriers to oral administration. Lipid-based drug-delivery systems have the potential to overcome these barriers and may be utilized to formulate safe, stable and efficacious oral medicines. This review outlines the design of such lipid-based technologies. The mechanisms whereby these formulations enhance the absorption of lipophilic versus hydrophilic peptide and protein-like drugs are discussed. In the case of lipophilic compounds, the advantages of lipid-based drug-delivery systems including increased solubilization, decreased intestinal efflux, decreased intracellular metabolism and possible lymphatic transport are well established as is evident from the success of Neoral and other drug products on the market. In contrast, with respect to hydrophilic compounds, the situation is more complex and, while promising formulation approaches have been studied, issues including reproducibility of response, intersubject variability and duration of response require further optimization before commercially viable products are possible.

Meeting breast cancer patients' information needs during radiotherapy: what can we do to improve the information and support that is currently provided?

Previous research has reported that patients require specific information relating to radiotherapy; however, these studies fail to describe patients' specific information needs over time. The aims of this study were to determine the specific information needs of breast cancer patients who are receiving radiotherapy and identify when patients prefer to receive specific information. Semi-structured interviews were conducted with 34 early breast cancer patients and 14 health professionals. Seventeen patients were interviewed after treatment completion, and 17 patients were interviewed on at least two occasions during their radiotherapy. Grounded theory and the constant comparative method were used to analyse the data. Three main categories emerged from the data: 'repertoire of information', 'amount of information relating specifically to radiotherapy' and'tailoring information to match patients' radiotherapy journeys'. Patients' information needs were identified, and key messages and strategies to inform patients were described. This paper identifies breast cancer patient's specific information needs during radiotherapy and shows that patients' information needs are highest during their first appointment with their radiation oncologist and at the time of their planning appointment. The findings presented will enable health professionals to develop and refine their approaches to patient education in radiotherapy.

Linkage validation of RP25 Using the 10K genechip array and further refinement of the locus by new linked families.

Retinitis pigmentosa (RP) is a clinically and genetically heterogeneous group of retinal dystrophies, characterised by rod photoreceptor cell degeneration with autosomal recessive RP (arRP) as the commonest form worldwide. To date, a total of 26 loci have been reported for arRP, each having a prevalence of 1-5%, except for the RP25 locus which was identified as the genetic cause of 14% of arRP cases in Spain. In order to validate the original linkage of RP25, we undertook a total genome scan using the 10K GeneChip mapping array on three of the previously linked families. The data obtained supported the initial findings of linkage. Additionally, linkage analysis in 18 newly ascertained arRP families was performed using microsatellite markers spanning the chromosome 6p12.1-q15 interval. Five out of the 18 families showed suggestive evidence of linkage to RP25, hence supporting the high prevalence of this locus in the Spanish population. Furthermore, the finding of a crossover in one of these families is likely to have refined the disease interval from the original 16 cM to only a 2.67 cM region between D6S257 and D6S1557.