“…In subsequent studies on the serological level of DKK-1 in patients with AS, some studies ( 17 , 20 , 22 , 24 , 26 – 28 , 44 , 47 , 49 , 51 – 53 , 55 , 56 , 59 , 60 , 62 ) also demonstrated lower serum DKK-1 levels in patients than in controls. In contrast, some studies ( 15 , 16 , 18 , 21 , 23 , 25 , 43 , 45 , 48 – 50 , 57 , 58 , 63 ) have reported that the serum level of DKK-1 in patients was higher than that in controls. Furthermore, there were also some studies ( 19 , 29 , 41 , 42 , 46 , 54 , 61 , 64 , 65 ) showing that there was no significant diversity in DKK-1 serum levels among AS patients and healthy controls.…”