A total of 10 studies [10,12,13,24,25,26,27,28,29,31] contained statistics of the number of anti-U1 RNP antibody-positive patients in the CTD-PAH group and the connective tissue disease without pulmonary arterial hypertension (CTD-no PAH) group, respectively. This evidence concerns the gene U1 and pulmonary arterial hypertension.