Characteristics of patients with familial Mediterranean fever in Denmark: a retrospective nationwide register-based cohort study

Objectives: To investigate epidemiology, demography, and genetic and clinical characteristics of patients with familial Mediterranean fever (FMF) in Denmark. Method: In this population-based, cross-sectional cohort study, we identified FMF patients from discharge diagnoses using ICD-10 codes in the Danish National Patient Register, and linked data from the Danish Civil Registration System and laboratory databases for results of MEFV gene variant screening. Results: We identified 495 FMF patients (prevalence 1:11 680) with a median age of 29 years and a female ratio of 51%. The median age at diagnosis of FMF was 13 (IQR 7-22) years, with an estimated median diagnostic delay of 3 (IQR 0.7-6.9) years. The predominant ethnicities were Turkish (41.8%), Lebanese (15.8%), Syrian (6.5%), South-West Asian (7.9%), and South-East Asian (3.0%). The MEFV genotype distribution was 18.7% homozygous, 21.2% compound heterozygous, 32.0% heterozygous, 11.0% with complex alleles or unresolved zygosity, and 17.1% with no detected variants. M694V was the most prevalent variant in the overall cohort (32.5%). Homozygous or compound heterozygous MEFV exon 10 variants were associated with younger age at diagnosis (p < 0.001) and reduced number of hospital contacts before diagnosis (p = 0.008). The Charlson Comorbidity Index was ≥ 2 in 8.1% of patients. The prevalence of amyloidosis was 1.0%. Conclusions: FMF in Denmark is rare and patients are mainly of Eastern Mediterranean ethnicity. Diagnostic delay was long but patients with exon 10 MEFV variants were diagnosed at a younger age. Prolonged diagnostic delay is probably caused by lack of FMF awareness in the Danish healthcare system.