Background Although some patients with familial Mediterranean (FMF) have heterozygous mutations for MEFV gene, there is a debate about whether heterozygosity for MEFV mutations in FMF might be responsible for disease symptoms or not.

Objectives To evaluate differences between the patients with FMF having homozygos (Hom) or heterozygos (Het) MEFV mutations in terms of clinical features and severity of the disease as well as concomitant disorders.

Methods We included 259 unrelated patients (female: 143, male: 116; mean age: 33.5±12 years) who were clinically diagnosed as having FMF and who met the Tell-Hashomer’s diagnostic criteria. The presence of MEFV mutations was investigated in exon 2,3,5 and 10 by multiplex-PCR reverse hybridization method. All clinical manifestations and their features were revised. All the patients were questioned for the presence of concurrent disorders, and the medical records of these patients were revised retrospectively. A previous diagnosis of a concomitant disease was taken into consideration if it met the relevant criteria.

Results In 12 of 259 patient, MEFV mutation analysis was not performed. No mutation was not determined in 8 FMF patients (3.2%). Hom mutation was found in 79 patients with FMF (31.9%), Het plus compound heterozygotes (cHet) in 160 FMF patients (64.7%). Early onset and early diagnosis of FMF were found in Hom group compared to Het plus cHet group (8.4 years vs 13.6 years; 23.3 years vs 28.6 years, p<0.0001, respectively). The number of patients with a higher severity score was significantly higher in hom group than Het plus cHet group (p<0.001). No significant difference was found between Hom and Het plus cHet group in terms of clinical features except for erysipelas like erythema (ELE) (p<0.0001). Concomitant disorders were as follows: ankylosing spondylitis (AS) 24 (9.3%), amyloidosis 13 (5%), Behcet’s disease 8 (3%). Amyloidosis (9 vs 4) was significantly higher in Hom group than Het plus cHet group (p<0.01).

Conclusions The presence of homozygous MEFV mutations in contrast to Het mutations creates a tendency for early onset of the disease, early diagnosis, frequent ELE and amyloidosis and severe disease phenotype.

Acknowledgements None

Disclosure of Interest None declared