Instability Of The X-Linked Dystonia-Parkinsonism Hexanucleotide Repeat In Males And Females
Conducted By
Aiden Houck, Dr. Alan Jesus Mejia Maza,
and Dr. Vanessa Wheeler
Massachucetts General Hospital,
Center for Genomic Medicine
Abstract
X-Linked Dystonia-Parkinsonism (XDP) is a Mendelian neurodegenerative disease endemic to the island of Panay, Philippines, and associated with a founder haplotype. XDP is caused by disease-specific SINE-VNTR-Alu (SVA)-type retrotransposon insertion into intron 32 of the TAF1 gene. This SVA region contains a hexameric (CCCTCT)n / (AGAGGG)n repeat tract of variable length, which is inversely associated with age at disease onset. The CCCTCT repeat tract increases in length over time (“somatic expansion”), likely due to faulty DNA repair. Males and females generally inherit similar repeat lengths; however, we have found that females exhibit less somatic expansion than males in blood. The hypothesis informing this study is that repeat expansion is lower in females than in males, as expansion depends on an active chromatin state. We have established experimental conditions for an assay that allows us to digest the active X chromosome using a methylation-sensitive restriction endonuclease (HhaI), inhibiting PCR amplification of the hexameric repeat with primers flanking both the repeat and HhaI site. In silico digests confirm enzymatic digestion when the genome is un-methylated. This sets the stage for future investigation aimed at determining whether a quantitative measure of repeat expansion is altered following HhaI digestion of female XDP blood DNAs.
