Late-onset disease is associated with a mild phenotype in children with familial Mediterranean fever.

Familial Mediterranean fever (FMF) is an autosomal recessive disease, characterised by recurrent, self-limited attacks of fever with serositis. Recently, it was shown that patients with early disease onset during childhood period had more severe disease. The aim of this study was to describe the demographic, clinical and genetic features of FMF patients who had late-onset disease during childhood period and to compare them to those with earlier onset patients. Files of patients who had been seen in our department between January 2013 and January 2014 were retrospectively evaluated. Patients were divided into two groups according to age of disease onset (group I, ≤8 years; group II, >8 years), and clinical findings were compared between the two groups. The study group comprised 317 FMF patients. There were 267 patients in group I and 50 patients in Group II. Median attack frequency was 24/year in group I and 12/year in group II (p < 0.05). Fever and M694V homozygosity were less frequently detected in group II (p = 0.003 and p = 0.022). Median delay in diagnosis was 24 months in group I and 12 months in group II (p = 0.002). Disease severity scores and final colchicine dosages were lower in group II (p < 0.001 and p = 0.003). Only a small number of FMF patients had disease onset at older ages in childhood period. It seems that FMF patients with late-onset disease have milder illness. However, more readily expression of their clinical findings in older ages yields earlier diagnosis in this group.