It was reported that bi-allelic variants in LGI4, a member of the LGI family proteins, cause arthrogryposis multiplex congenita (AMC) with peripheral nerve hypomyelination,20,21 and Lgi4 knockout mice exhibit an AMC-like forelimb defect.22-24 Given that ADAM22 serves also as a receptor for LGI4 in the peripheral nerve system, the symptom of ‘idiopathic arthritis’ observed in the patient may be related to loss of function of ADAM22 in the peripheral nerve system. The gene discussed is LGI4; the disease is arthrogryposis multiplex congenita.