Fibronectin Glomerulopathy
A primary glomerular disease characterized by proteinuria, type IV renal tubular acidosis, microscopic hematuria and hypertension that may lead to end-stage renal failure in the second to sixth decade of life.
Epidemiology
Fibronectin glomerulopathy exact prevalence is unknown. Only 20 families and 25 sporadic cases have been described in the literature so far.
Clinical description
Fibronectin glomerulopathy may present at different ages, although mostly in adolescence or early adulthood, with typical features of a nephrotic syndrome including hypertension, which can be severe, and edema, which initially develops around the eyes and legs but with time may become generalized. Patients may also present with varying degrees of renal failure that progressively worsen over several years, reaching end stage renal disease in the second to sixth decade of life.
Etiology
Clustering of the disease within families indicates a genetic origin. In 40% of families, the disease is caused by heterozygous mutations in the FN1 gene (2q34) encoding fibronectin. Whole-genome linkage analysis in a large pedigree showed another disease locus on 1q32, however no specific candidate genes has been identified so far.
Diagnostic methods
Diagnosis rests on renal biopsy. Typical findings at light microscopy are enlarged glomeruli with deposits in the mesangium and subendothelial space, usually with scant immunoreactivity for immunoglobulins or complement factors. Electron microscopy reveals deposits mainly located in the subendothelial space but also in the subepithelial and intramembranous spaces. Homogeneous granular deposits dominate in most cases; in some an admixture of fibrils is observed. The most striking finding is the immunoreactivity of the glomerular deposits to fibronectin. Family history is supportive of the diagnosis.
Differential diagnosis
Differential diagnosis includes other chronic non-amyloid glomerulopathies with organized deposits including mixed cryoglobulinemia, fibrillary glomerulonephritis, immunotactoid glomerulopathy, collagen type III glomerulopathy, systemic lupus erythematosus, diabetes glomerulopathy and other non-specific collagen deposition diseases. It is difficult to discriminate fibronectin glomerulopathy from membranoproliferative glomerulonephritis at light microscopy examination.
Genetic counseling
Segregation with disease appearance in successive generations is consistent with an autosomal dominant pattern of inheritance with age-related penetrance. Genetic counseling should be proposed to individuals having the disease-causing mutation informing them that there is 50% risk of passing the mutation to offspring.
Management and treatment
There is no specific treatment for fibronectin glomerulopathy. Treatment of symptoms can include corticosteroids, diuretics and treatment for hypertension. Antiproteinuric and renoprotective treatment with ACE inhibitors or anti-AT1R antagonists could be of help to slow renal disease progression. More advanced cases of renal failure require renal dialysis or transplantation.
Prognosis
Prognosis is uncertain, in some cases the disease follows an indolent course and in others it leads to end stage renal disease and chronic renal failure in the second to sixth decade of life.