Final answer:
Crusted hyperkeratosis in Zn-responsive dermatosis is caused by a zinc deficiency.
Step-by-step explanation:
Crusted hyperkeratosis in Zn-responsive dermatosis is caused by a deficiency in zinc. Zinc is an essential mineral that plays a role in many biological processes, including skin health. When there is a lack of zinc in the body, it can lead to a condition called Zn-responsive dermatosis, which is characterized by crusted hyperkeratosis.