TGFB1 and pulmonary arterial hypertension: Of all the genes found on the Y-chromosome in PAH patients, eight genes showed decreased expression in diseased lung tissues.25 One of these genes is USP9Y, a ubiquitin-associated hydrolase preventing ubiquitin-dependent degradation of proteins including SMAD4, thereby increasing TGFβ signalling (see reference 193 and ENSG00000114374).