ACP5 and Spondyloenchondrodysplasia with immune dysregulation: In one representative patient, immunological changes were observed after treatment, including a reduction in CD21<sup>low</sup> B cells and changes in T helper cell subsets.<h4>Conclusion</h4>This study expands the spectrum of <i>ACP5</i> mutations and provides clinical and immunological observations suggesting JAK inhibitor therapy may be considered for immune dysregulation in patients with SPENCD.