Unless they’re dense they used the inside of the upper arm to avoid sun damage.
The bigger issue is that Steve Horvath calibrated and has successfully marketed a DNA methylation based “epigenetic clock” accurate to within a couple of years, from blood, with hundreds of not thousands of citations and successful replications since 2013. DNA is more stable than RNA, and blood is easier to come by than fibroblasts (skin punches), so this seems like a nonstarter to me.
Horvath’s clock works in arbitrary other tissues; we’ve applied it to pediatric and adult tumors, adjacent normal, and blood samples at diagnosis, remission, and relapse, and it works quite well (unlike the knockoffs that followed). I don’t see the point of a less reliable, less proven clock on less stable molecules (RNA), when I can use a handful of targeted amplicons to run Horvath’s for $30/sample on blood DNA (even dried blood) or other tissues.
The bigger issue is that Steve Horvath calibrated and has successfully marketed a DNA methylation based “epigenetic clock” accurate to within a couple of years, from blood, with hundreds of not thousands of citations and successful replications since 2013. DNA is more stable than RNA, and blood is easier to come by than fibroblasts (skin punches), so this seems like a nonstarter to me.
Horvath’s clock works in arbitrary other tissues; we’ve applied it to pediatric and adult tumors, adjacent normal, and blood samples at diagnosis, remission, and relapse, and it works quite well (unlike the knockoffs that followed). I don’t see the point of a less reliable, less proven clock on less stable molecules (RNA), when I can use a handful of targeted amplicons to run Horvath’s for $30/sample on blood DNA (even dried blood) or other tissues.
Ref: https://genomebiology.biomedcentral.com/articles/10.1186/gb-...