They validated the link between 2PY and 4PY levels and inflammation in large-ish cohorts (US and EU) that were not screened for the genetic defect. They also found inflammation from 4PY in some in vitro studies as well as in vivo mouse studies. The genetic defect is what lead them down this line of inquiry, but it's not the only evidence of an issue with high levels of niacin metabolites. From what I understand, anyway.
