SMN1 and systemic sclerosis: A significant between-group difference for PI (p for trend = 0.004) and RI (p for trend = 0.032) was observed for patients with different SSc subsets; patients with sine scleroderma and lcSSc showed lower SMA RI and PI median values (0.84 and 0.87, and 2.4 and 2.7, respectively) in comparison with dcSSc (0.88 and 3.1) (Table 3).