SOX9 and polygenic risk score: Rare loss of function mutations in the SOX9 gene on chromosome 17 are established risk factors for PRS, along with mutations in other genes including; COL11A1, COL11A2, COL2A1, which cause a syndromic form of PRS -Stickler’s syndrome [7, 8], mutations in SATB2, which have been shown to cause another syndromic form of PRS [9] and 22q11.2 chromosomal deletions [10].