Anti-TNF therapy was given to 48 patients (42.1%) after a median disease duration of 5.4 years (IC95 = [4.6–8.0], Additional file 3: Figure S2A) Thirty-three patients (69%) presented axial disease before instauration of the first biotherapy, with a median axial disease duration of 0.6 years. Here, TNF is linked to glycogen storage disease VI.