TMPRSS2 and pulmonary arterial hypertension: TMPRSS2 belongs to the type II transmembrane serine protease family and is commonly expressed in epithelial tissues such as those lining the upper airways, bronchi and lung.30,31 Influenza viruses and other coronaviruses all critically depend on TMPRSS2 for viral activation and cellular infection.31,32 Viruses such as influenza virus, respiratory syncytial virus (RSV) and parainfluenza virus likely account for most of the respiratory infections in DS,22,33 and those with congenital cardiac conditions or pulmonary hypertension may be particularly vulnerable.