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      Systematic Review and Meta-Analysis of Neuropsychiatric Symptoms and Executive Functioning in Adults With Phenylketonuria

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          This systematic review and meta-analysis (MA) investigates the impact of elevated blood phenylalanine (Phe) on neuropsychiatric symptoms in adults with phenylketonuria (PKU). The meta-analysis of PKU is challenging because high-quality evidence is lacking due to the limited number of affected individuals and few placebo-controlled, double-blind studies of adults with high and low blood Phe. Neuropsychiatric symptoms associated with PKU exceed general population estimates for inattention, hyperactivity, depression, and anxiety. High Phe is associated with an increased prevalence of neuropsychiatric symptoms and executive functioning deficits whereas low Phe is associated with improved neurological performance. Findings support lifelong maintenance of low blood Phe.

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          Systematic reviews: synthesis of best evidence for clinical decisions.

          Systematic reviews can help practitioners keep abreast of the medical literature by summarizing large bodies of evidence and helping to explain differences among studies on the same question. A systematic review involves the application of scientific strategies, in ways that limit bias, to the assembly, critical appraisal, and synthesis of all relevant studies that address a specific clinical question. A meta-analysis is a type of systematic review that uses statistical methods to combine and summarize the results of several primary studies. Because the review process itself (like any other type of research) is subject to bias, a useful review requires clear reporting of information obtained using rigorous methods. Used increasingly to inform medical decision making, plan future research agendas, and establish clinical policy, systematic reviews may strengthen the link between best research evidence and optimal health care.
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            Phenylalanine blood levels and clinical outcomes in phenylketonuria: a systematic literature review and meta-analysis.

            Blood phenylalanine (Phe) levels provide a practical and reliable method for the diagnosis and monitoring of metabolic status in patients with phenylketonuria (PKU). To assess the reliability of blood Phe levels as a predictive biomarker of clinical outcomes in the development of treatments for PKU, a systematic literature review and meta-analysis of published trials of PKU, which included Phe level and neurological and dietary compliance outcome measures, was conducted. Within-study correlations between Phe level and intelligence quotient (IQ) were extracted from 40 studies. Significant, proportional correlations were found during critical periods (from 0 to 12 years of age) for early-treated patients with PKU (r=-0.35; 95% confidence interval [CI]: -0.44 to -0.27), where each 100 micromol/l increase in Phe predicted a 1.3- to 3.1-point reduction in IQ. Similar significant correlations were observed between IQ and mean lifetime Phe level for early-treated patients (r=0.34; 95% CI: -0.42 to -0.25), where each 100 micromol/l increase in Phe predicted a 1.9- to 4.1-point reduction in IQ. Moderate correlations were found between concurrent Phe level and IQ for early-treated patients. In conclusion, these results confirm a significant correlation between blood Phe level and IQ in patients with PKU, and support the use of Phe as a predictive biomarker for IQ in clinical trials.
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              Single-center trials show larger treatment effects than multicenter trials: evidence from a meta-epidemiologic study.

              A recent study suggested that results of single-center trials are frequently contradicted when similar trials are performed in multicenter settings. To perform a meta-epidemiologic study to evaluate whether estimates of treatment effect differ between single-center and multicenter randomized, controlled trials (RCTs). MEDLINE was searched via PubMed for meta-analyses of RCTs with binary outcomes that were published between August 2008 and January 2009 and in the first 6 months of 2010 in the 10 leading journals of each medical specialty. One issue of the Cochrane Database of Systematic Reviews was also searched. All individual RCTs included in the meta-analyses were selected. Data were extracted and their quality was assessed by use of the risk of bias tool of the Cochrane Collaboration. The primary outcome was the ratio of odds ratios (ROR), used to quantify the difference in estimated intervention effect between single-center and multicenter RCTs. An ROR less than 1 would indicate larger estimates of the intervention effect in single-center trials. Sensitivity analyses were performed with adjustment for sample size, risk of bias within RCTs, and variance of the log odds ratio to take publication bias into account. Forty-eight meta-analyses were selected, including 421 RCTs (223 were single-center and 198 were multicenter). Single-center RCTs showed a larger intervention effect than did multicenter RCTs (combined ROR, 0.73 [95% CI, 0.64 to 0.83]), with low heterogeneity across individual meta-analyses (I(2) = 12.0%; P = 0.24). Adjustment for sample size yielded consistent results (ROR, 0.85 [CI, 0.74 to 0.97]), as did adjustment for risk of bias within RCTs, such as allocation concealment (ROR, 0.76 [CI, 0.67 to 0.86]), and variance of log odds ratio (ROR, 0.83 [CI, 0.72 to 0.96]). Despite sensitivity analyses, meta-confounding cannot be fully excluded. Single-center RCTs showed larger treatment effects than did multicenter RCTs, a finding that was consistent in all sensitivity analyses. These results suggest that this item should be considered when the results of RCTs and meta-analyses are interpreted. Academic grant Recherche sur la Recherche from the Délégation Interrégionale à la Recherche Clinique (DIRC), Ile de France, Assistance Publique-Hôpitaux de Paris (APHP).

                Author and article information

                Dev Neuropsychol
                Dev Neuropsychol
                Developmental Neuropsychology
                Psychology Press
                18 May 2016
                2 November 2016
                : 41
                : 4
                : 245-260
                [ a ]Department of Psychiatry, University of Utah , Salt Lake City, Utah
                [ b ]CTI Clinical Trial and Consulting Services Inc ., Cincinnati, Ohio
                [ c ]BioMarin Pharmaceutical Inc ., Novato, California
                [ d ]Audentes Therapeutics , San Francisco, California
                Author notes
                CONTACT Deborah A. Bilder deborah.bilder@ Department of Psychiatry, University of Utah , 650 South Komas Drive, Suite 200, Salt Lake City, UT 84108.
                Published with license by Taylor & Francis© 2016 Deborah A. Bilder, J. Kay Noel, Erin R. Baker, William Irish, Yinpu Chen, Markus J. Merilainen, Suyash Prasad, and Barbara J. Winslow

                This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (, which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.

                Page count
                Tables: 3, References: 86, Pages: 16
                Funded by: BioMarin Pharmaceutical 10.13039/100008484
                Award ID: not applicable



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