OBJECTIVE: To analyse FN gene polymorphisms in type II mixed cryoglobulinemic syndrome (MCsn), an immune-complex mediated systemic vasculitis linked to hepatitis C virus (HCV) infection and characterized by rheumatoid factor (RF) positive B-cell proliferation at high risk for the progression into non Hogkin's lymphoma (NHL).METHODS: Samples from eighty-one patients, with MCsn (type II serum cryoglobulins and clinical signs of vasculitis were studied. Sixty-five (65/81, 80.3%) patients were HCV-positive. Twenty-one (25.9%) patients had developed a B-cell NHL during the course of MCsn. Seventy-two patients with HCV-negative and MC-unrelated NHL and 110 healthy blood donors (HBDs) were taken as controls. HaeIIIb and MspI FN gene polymorphisms were analysed by ELISA, whenever possible.RESULTS: HaeIIIb and MspI allele and genotypic frequencies did not differ between MCsn patients and HBDs. Of note, the DD-MspI allele and genotype frequencies did not differ between MCsn patients and HBDs. Of note, the DD-MspI (OR = 5.56; DI = 1.67-18.51, p = 0.0046) and the AA-HaeIIIb (OR = 5.54, CI = 1.64- 18.76, p = 0.0066) homozygosis appeared significantly and independently associated with the development of B-cell NHL in MCsn patients, with the HaeIIIbA allele possibly conferring an increased risk of NHL in the general population (OR = 1.72, CI = 1.128-2.635, p = 0.0133). In contrast, the major vasculitic manifestations, such as peripheral neuropathy, skin ulcers and glomerulonephritis tended to be associated with the counterpart MspI C allele. No association between FN plasma levels and FN genotypes was found.CONCLUSION: Genotyping for MspI and HaeIIIb FN gene polymorphisms may be clinically relevant to define the predisposition to the major clinical manifestations in MCsn