Urinary glycosaminoglycan levels as a marker of renal amyloidosis in patients with familial Mediterranean fever

Abstract

Introduction and aim: Familial Mediterranean Fever (FMF) is an autosomal recessive disease with a defect in the pyrine gene and is manifested with short attacks of inflammatory serositis, fever, and erysipelas-like skin lesions. Secondary amyloidosis is the most serious complication of the disease, in which extracellular deposits of amyloid (an amorphous and eosinophilic protein) are seen in tissues. Glycosaminoglycans are mucopolysaccharide molecules that take place in amyloid deposits with fibrillar links to amyloid. They form glycoproteins by linking to proteins, and their free forms are excreted in the urine in the form of polysaccharides. The aims of this study were to evaluate if the urinary levels of glycosaminoglycans have a predictive value in the diagnosis of amyloidosis secondary to FMF and if these levels are affected by treatment with colchicine.

Materials and methods: The study included 55 volunteer patients (age range: 18-36 years) with FMF (15 with amyloidosis) of the same socio-economic circumstances without other concomitant inflammatory, malignant, or chronic diseases, along with 20 healthy subjects as control. Urinary glycosaminoglycan levels were determined twice, once when the patients were on medication and once after they have stopped treatment for two weeks.

Results: Initial mean urinary GAG levels were significantly lower in amyloidosis patients. Mean urinary GAG levels determined two weeks after the cessation of colchicine was also significantly lower than controls in both amyloidosis and non-amyloidosis FMF patients. Likewise, in patients with a disease duration longer than ten years, urinary GAG levels were also lower than those with a disease duration of less than three years.

Conclusion: Urinary GAG level can have a predictive value for amyloidosis in patients with FMF, and it can also be used as a non-invasive marker for screening the effects of colchicine on fibrillogenesis as well as for the follow-up of the patients.