Mice harboring a mutation in the Col9a1 gene display progressive IDD characteristics, potentially attributable to compromised synthesis or assembly of the non-fibrillar Col9a1 chain (26); polymorphisms in the COL9A2 and COL9A3 genes have been associated with sciatica and IDD within the Finnish population (27, 28). Here, COL9A2 is linked to intervertebral disk degenerative disorder.