Abstract
Familial Blau syndrome and sporadic early-onset sarcoidosis (EOS) are both systemic granulomatous diseases evoked by the spontaneous activation of mutated NOD2. In Japan, the R334W amino acid substitution is more frequently identified, whereas the R334Q mutation is rare and, in contrast to western countries where disease causing mutations are typically hereditary, most Japanese cases derive from sporadic mutations. Recently, a case with a six-base deletion in the NOD2 gene was reported. This Blau syndrome/EOS patient presented with the unpainful soft swelling of the dorsal side of the wrist and ankles, as well as flexion contracture at the proximal interphalangeal joint that gradually appeared during their clinical course. These features are useful for the differential diagnosis of Blau syndrome/EOS from juvenile idiopathic arthritis. Owing to their characteristic clinical symptoms, Blau and EOS patients can be identified earlier if medical experts become more acquainted with these distinctions. Even though specific treatment based on pathophysiologic mechanism has not been explored yet, early diagnosis will prevent the progression to severe impairment, which can severely affect patients' lives.
