On the other hand, it has been demonstrated that endoplasmic reticulum stress from expression of mutant collagen molecules causes a reduction in circadian clock output in tendon fibroblasts (Pickard et al., 2019), raising the possibility that other stressors that perturb ECM homeostasis and contribute to the development of tendinopathy may also be responsible for a diminished circadian clock. The gene discussed is CLOCK; the disease is disease of the tendon.