COL11A1 and Stickler syndrome type 2: In the majority of type 2 Stickler Syndrome cases, the pathogenic variant is a missense change or an in-frame deletion [1, 4, 8, 25, 26] and the abnormal COL11A1 pro-alpha chain exerts a dominant negative effect on normal type XI collagen expression in the cochlear extracellular matrix [15].