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A 5 year old child of French and Dutch descent is referred to your pediatric practice for recurrent febrile episodes of unclear etiology. After an uneventful full-term birth to a healthy 30 year old mother, the patient began having febrile episodes in her first year of life. The episodes happen every 4-8 weeks, lasting 4 days to a week, and in between, the child is normal and healthy. The episodes seem to be triggered by vaccinations, minor trauma, and stress, though they also happen at other times. The patient characteristically gets nasal congestion, sore throat, fatigue, headache, or behavioral changes followed by chills, then a rapid onset fever to higher than 38.5. During these episodes, the patient has palpable tender, rubbery lymphadenopathy, mostly cervical. Occasionally, the child complains of abdominal pain, and twice, went to the operating room where a normal appendix (as well as rest of bowel) was found. Splenomegaly was noted, however. During these episodes, she has symmetric arthritis of larger joints which can linger a few days beyond the cessation of fever. The patient also develops an erythematous, macular rash over multiple parts of the body that sometimes become confluent. Acral lesions are more common than truncal ones. ESR, CRP, leukocytes, and ferritin are elevated during attacks. IgA and IgD are elevated both during and in between attacks.

Many other causes have been worked up, including all infectious etiologies, surgical emergencies, pancreatitis, familial Mediterranean fever, and acute intermittent porphyria, which have all been negative.

Challenge: What is this genetic disorder?