Clinically, patients with SpA and obesity have been reported to demonstrate heightened disease activity (BASDAI, ASDAS), impaired function (BASFI), accelerated radiographic progression (syndesmophytes, enthesophytes), and diminished biologic response rates, potentially attributable to pharmacokinetic alterations (e.g., subtherapeutic TNF inhibitor levels) and pharmacodynamic resistance. Here, TNF is linked to obesity due to melanocortin 4 receptor deficiency.