On the optimistic performance evaluation of newly introduced bioinformatic methods

Most research articles presenting new data analysis methods claim that “the new method performs better than existing methods,” but the veracity of such statements is questionable. Our manuscript discusses and illustrates consequences of the optimistic bias occurring during the evaluation of novel data analysis methods, that is, all biases resulting from, for example, selection of datasets or competing methods, better ability to fix bugs in a preferred method, and selective reporting of method variants. We quantitatively investigate this bias using an example from epigenetic analysis: normalization methods for data generated by the Illumina HumanMethylation450K BeadChip microarray.

On the optimistic performance evaluation of newly introduced bioinformatic methods

Most research articles presenting new data analysis methods claim that “the new method performs better than existing methods”, but the veracity of such statements is questionable. Our manuscript discusses and illustrates consequences of the optimistic bias occurring during the evaluation of novel data analysis methods, that is, all biases resulting from, for example, selection of datasets or competing methods; better ability to fix bugs in a preferred method; and selective reporting of method variants. We quantitatively investigate this bias using a topical example from epigenetic analysis: normalization methods for data generated by the Illumina HumanMethylation450K BeadChip microarray.

Genome-wide epigenetic analyses in Japanese immigrant plantation workers with Parkinson’s Disease and exposure to organochlorines reveal possible involvement of glial genes and pathways involved in neurotoxicity

Background: Parkinson’s Disease (PD) is a disease of the central nervous system that progressively affects the motor system. Epidemiological studies have provided evidence that exposure to agriculture-related occupations or agrichemicals elevate a person’s risk for PD. Here, we sought to examine the possible epigenetic changes associated with working on a plantation on Oahu, HI and/or exposure to organochlorines (OGC) in PD cases. Results: We measured genome-wide DNA methylation using the Illumina Infinium HumanMethylation450K BeadChip array in matched peripheral blood and postmortem brain biospecimens in PD cases (n=20) assessed for years of plantation work and presence of organochlorines in brain tissue. The comparison of 10+ to 0 years of plantation work exposure detected 7 and 123 differentially methylated loci (DML) in brain and blood DNA, respectively (P<0.0001). The comparison of cases with 4+ to 0-2 detectable levels of OGC, identified 8 and 18 DML in brain and blood DNA, respectively (P <0.0001). Pathway analyses revealed links to key neurotoxic and neuropathologic pathways related to impaired immune and proinflammatory responses as well as impaired clearance of damaged proteins, as found in the predominantly glial cell population in these environmental exposure-related PD cases.Conclusions: These results suggest that distinct DNA methylation biomarker profiles related to environmental exposures in PD cases with previous exposure can be found in both brain and blood.

Genome-wide epigenetic analyses in Japanese immigrant plantation workers with Parkinson’s Disease and exposure to organochlorines reveal glial genes and pathways involved in neurotoxicity

Background: Parkinson’s Disease (PD) is a disease of the central nervous system that progressively affects the motor system. Epidemiological studies have provided evidence that exposure to agriculture-related occupations or agrichemicals elevate a person’s risk for PD. Here, we sought to examine the possible epigenetic changes associated with working on a plantation on Oahu, HI and/or exposure to organochlorines (OGC) in PD cases. Results: We measured genome-wide DNA methylation using the Illumina Infinium HumanMethylation450K BeadChip array in matched peripheral blood and postmortem brain biospecimens in PD cases (n=21) assessed for years of plantation work and presence of organochlorines in brain tissue. The comparison of 10+ to 0 years of plantation work exposure detected 7 and 123 differentially methylated loci (DML) in brain and blood DNA, respectively ( P <0.0001). The comparison of cases with 4+ to 0-2 detectable levels of OGC, identified 8 and 18 DML in brain and blood DNA, respectively ( P <0.0001). Pathway analyses revealed links to key neurotoxic and neuropathologic pathways related to impaired immune and proinflammatory responses as well as impaired clearance of damaged proteins, as found in the predominantly glial cell population in these environmental exposure-related PD cases. Conclusions : These results suggest that distinct DNA methylation biomarker profiles related to environmental exposures in PD cases with previous exposure can be found in both brain and blood.

The Influence of Metabolic Syndrome and Sex on the DNA Methylome in Schizophrenia

Introduction. The mechanism by which metabolic syndrome occurs in schizophrenia is not completely known; however, previous work suggests that changes in DNA methylation may be involved which is further influenced by sex. Within this study, the DNA methylome was profiled to identify altered methylation associated with metabolic syndrome in a schizophrenia population on atypical antipsychotics.Methods. Peripheral blood from schizophrenia subjects was utilized for DNA methylation analyses. Discovery analyses (n=96) were performed using an epigenome-wide analysis on the Illumina HumanMethylation450K BeadChip based on metabolic syndrome diagnosis. A secondary discovery analysis was conducted based on sex. The top hits from the discovery analyses were assessed in an additional validation set (n=166) using site-specific methylation pyrosequencing.Results. A significant increase inCDH22gene methylation in subjects with metabolic syndrome was identified in the overall sample. Additionally, differential methylation was found within theMAP3K13gene in females and theCCDC8gene within males. Significant differences in methylation were again observed for theCDH22andMAP3K13genes, but notCCDC8, in the validation sample set.Conclusions. This study provides preliminary evidence that DNA methylation may be associated with metabolic syndrome and sex in schizophrenia.