CTSD and type 2 diabetes mellitus: Our findings that (1) type 2 diabetic patients have higher plasma CTSD activity compared to healthy controls and (2) plasma CTSD activity positively correlates with indicators of type 2 diabetes (HbA1c, HOMA-IR and glucose) point toward the link between plasma CTSD activity and disturbed glucose metabolism (or insulin resistance) in type 2 diabetes.