Abstract Chondroitin sulfate (CS)/dermatan sulfate (DS) proteoglycans that play indispensable roles in multiple physiological processes, including cell proliferation, cell adhesion, development, neuronal guidance, and cartilage formation. Depletion of CS/DS caused by biosynthetic enzyme loss of function impairs these processes and results in embryonic lethality. However, some individuals with mutant enzymes survive and exhibit severe phenotypes.