Indeed, local \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$r_g$$\end{document}rg s have been observed between neuropsychiatric traits18 and between AD and PD (specifically in the HLA19 and MAPT loci20). Here, MAPT is linked to Parkinson disease.