Symptomatic patients with P369S-R408Q mutations: familial Mediterranean fever or mixed auto-inflammatory syndrome?

A 51-year-old South African female of Ashkenazi Jewish descent was admitted with acute pleuritic chest pain, shortness of breath, fatigue and fever. She experienced vague abdominal and calf pains for 30 years. Her monozygotic twin was investigated independently for recurrent abdominal pain. Despite initially responding to antibiotics, treating suspected pneumonia, she developed recurrent fevers and pleuritic chest pain. After thorough investigation without significant findings, she re-attended days after discharge with similar symptoms. Familial Mediterranean fever (FMF) was suggested as she met diagnostic criteria and responded to colchicine, though FMF normally presents before 20 years old. Genetic testing showed no pathogenic mutations but heterozygous P369S and R408Q mutations. The significance of these mutations remains unclear, as they are found in asymptomatic patients, suggesting incomplete penetrance. She remains well, with full symptom resolution, but mixed auto-inflammatory syndrome may be a more appropriate diagnosis in symptomatic patients with both P369S and R408Q mutations.