Manzardo AM and Butler MG
Context: Methylation changes observed in Prader-Willi syndrome (PWS) may impact global methylation as well as regional methylation status of imprinted genes on chromosome 15 (in cis) or other imprinted obesity-related genes on other chromosomes (in trans) leading to differential effects on gene expression impacting obesity phenotype unique to PWS. Objective: Characterize the global methylation profiles and methylation status for select imprinted genes associated with obesity phenotype in a well-characterized imprinted, obesity-related syndrome PWS relative to a cohort of obese and non-obese individuals. Design: Global methylation was assayed using two methodologies: 1) enriched LINE-1 repeat sequences by Epigen Dx and 2) ELISA-based immunoassay method sensitive to genomic 5-methylcytosine by Epigentek. Target gene methylation patterns at selected candidate obesity gene loci were determined using methylation-specific PCR. Setting: Study participants were recruited as part of an ongoing research program on obesity-related genomics and Prader-Willi syndrome. Participants: Individuals with non-syndromic obesity (N=26), leanness (N=26) and PWS (N=39). Results: A detailed characterization of the imprinting status of select target genes within the critical PWS 15q11-q13 genomic region showed enhanced cis but not trans methylation of imprinted genes. No significant differences in global methylation were found between non-syndromic obese, PWS or non-obese controls. Intervention: None. Main outcome measures: Percentage methylation and the methylation index. Conclusion: The methylation abnormality in PWS due to errors of genomic imprinting effects both upstream and downstream effectors in the 15q11-q13 region showing enhanced cis but not Trans methylation of imprinted genes. Obesity in our subject cohorts did not appear to impact global methylation levels using the described methodology.
