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.
Manzardo AM and Butler MG