In a mixed cohort of patients with Group 1 PAH, a total of 12 cases harbouring KLK1 variants (10 IPAH, 2 APAH) and 28 cases carried GGCX variants (17 IPAH, 9 APAH, 1 FPAH, 1 unknown subclass) were found. This evidence concerns the gene KLK1 and pulmonary arterial hypertension.