TOP1 and pulmonary arterial hypertension: Multiple variants in IFN genes linked to mortality and discrete phenotypes of SSc, such as dcSSc, lcSSc, anti-DNA topoisomerase I antibody (ATA), anticentromere antibodies (ACA), and pulmonary arterial hypertension (PAH), point to the importance of the IFN pathway, both in the development and progression of SSc.