COL9A3 and Stickler syndrome: Whilst these two subtypes make up the majority of cases of Stickler Syndrome, several studies have identified cases of recessive SS, associated with both homozygous and compound heterozygous inheritance most commonly those encoding Type IX collagen, namely COL9A1, (ref. [17]) COL9A2 (ref. [18]) and COL9A3 (ref. [19]).