Familial Mediterranean fever, Inflammation and Nephrotic Syndrome: Fibrillary Glomerulopathy and the M680I Missense Mutation

Background Familial Mediterranean fever (FMF) is an autosomal recessive disease characterized by inflammatory serositis (fever, peritonitis, synovitis and pleuritis). The gene locus responsible for FMF was identified in 1992 and localized to the short arm of chromosome 16. In 1997, a specific FMF gene locus, MEFV, was discovered to encode for a protein, pyrin that mediates inflammation. To date, more than forty missense mutations are known to exist. The diversity of mutations identified has provided insight into the variability of clinical presentation and disease progression. Case Report We report an individual heterozygous for the M680I gene mutation with a clinical diagnosis of FMF using the Tel-Hashomer criteria. Subsequently, the patient developed nephrotic syndrome with biopsy-confirmed fibrillary glomerulonephritis (FGN). Further diagnostic studies were unremarkable with clinical workup negative for amyloidosis or other secondary causes of nephrotic syndrome. Discussion Individuals with FMF are at greater risk for developing nephrotic syndrome. The most serious etiology is amyloidosis (AA variant) with renal involvement, ultimately progressing to end-stage renal disease. Other known renal diseases in the FMF population include IgA nephropathy, IgM nephropathy, Henoch-Schönlein purpura as well as polyarteritis nodosa. Conclusion To our knowledge, this is the first association between FMF and the M680I mutation later complicated by nephrotic syndrome and fibrillary glomerulonephritis.


Background
Familial Mediterranean Fever (FMF) is an autosomal recessive disease primarily affecting individuals of Arme-nian, Turkish, Arab, and Jewish origin [1]. The disease is characterized by recurrent episodes of fever, pleuritis, peritonitis, synovitis, and pericarditis [2][3][4]. The most serious complication of FMF is the development of amyloidosis (AA variant), leading to nephrotic syndrome and endstage renal disease [4]. Amyloidosis remains the leading cause of FMF-related mortality in affected individuals not receiving colchicine prophylaxis [5]. Additionally, other non-amyloid renal diseases are reported to occur in the FMF population with variable prevalence; for example, IgA and IgM nephropathy, and vasculitides including both polyarteritis nodosa (PAN) and Henoch-Schonlëin purpura [6]. Differentiation of the underlying renal disease in FMF patients who present with nephrotic syndrome is difficult, often requiring further diagnostic studies to identify the etiology. Moreover, the identification of the etiology of nephrotic syndrome is critical in determining an effective treatment regimen. For example, patients with amyloidosis (AA variant) usually respond to oral colchicine, which is known to prevent the insidious onset of end-stage renal disease [5]. In contrast, patients with PAN or Henoch-Schonlëin purpura usually respond very well to corticosteroids, with some experiencing complete resolution of proteinuria. [6] In 1992, the gene responsible for Familial Mediterranean Fever (FMF), MEFV, was found to reside on the short arm of chromosome 16 [7]. Five-years later, the MEFV gene locus was discovered to encode for a protein, pyrin (marenostrin), a member of the RoRet gene family [8,9]. Pyrin is known to play a role in mitigating an inflammatory response [8,10]. To date, more than forty missense mutations are noted in association with FMF. One specific mutation, M694V, has been implicated as a risk factor for amyloidosis, especially in North African Jews homozygous for the M694V missense mutation [11]. However, individuals with mutations other than M694V are known to develop amyloidosis with renal involvement [11]. For the first time, we report an individual with symptomatic FMF, heterozygous for the M680I missense mutation, who developed progressive proteinuria, hematuria, and subsequent nephrotic syndrome secondary to fibrillary glomerulonephritis.

Case Report
A forty-nine year-old American man of Armenian ancestry was diagnosed clinically with Familial Mediterranean Fever (FMF) at age 39. At that time, he presented with recurrent, episodic fevers, peritonitis, synovitis, and pleuritis. Since the initial diagnosis, his treatment consisted of oral colchicine (1.2 mg/day), resulting in a decrease in the frequency, duration, and intensity of his inflammatory episodes. However, over the subsequent decade, his inflammatory episodes became more frequent, occurring every 7-10 days, with an average duration of approximately 3 days. His symptoms consisted of diffuse abdominal pain, sharp, non-radiating chest pain, and fevers as high as 103 degrees F. An extensive workup for other etiologies responsible for febrile illness was unremarkable (e.g. infection, malignancy, connective tissue disorders). Upon further examination, the previous diagnosis of FMF was confirmed using the Tel-Hashomer criteria [12].
Despite an increase in the oral colchicine dose to 1.8 mg/ day, his symptoms persisted, prompting further diagnostic studies to correlate the clinical diagnosis with genotype. A serum sample was sent to the UCLA Medical Center for genetic analysis. Polymerase chain reaction, testing for the nine most common mutations [ Table 1], was performed by methods previously described [13]. The results demonstrated the presence of an MEFV missense mutation (M680I) on one allele. Several months later, he presented with complaints of lower extremity edema without associated symptoms of cough, shortness of breath, dyspnea on exertion, orthopnea, paroxysmal nocturnal dyspnea, or chest pain. Upon further questioning, the patient admitted to gradual development of lower extremity edema over the past 2 to 3 months. He denied complaints of dysuria, polyuria, hematuria, or any discoloration of his urine. The remainder of the review of systems was unremarkable. A 2-dimensional echocardiogram revealed a normal size heart, normal valvular structure and function, and preserved left ventricular systolic function with a left ventricular ejection fraction of 55-60 percent. Relevant serological studies were conducted to evaluate the etiology of nephrosis. In addition to a urinalysis, the urine protein and creatinine were measured. Results from the urinalysis were positive for proteinuria (3+) and red blood cells (50-100 RBC's/ HPF). The spot urine protein/creatinine ratio was 4.0. The patient's blood urea nitrogen (BUN) and serum creatinine were 17 mg/dl and 0.9 mg/dl, respectively. Erythrocyte sedimentation rate was 72 mm/hr with a normal complete blood count and differential. Serological tests for HIV (types I and II), HIV p24 antigen, Hepatitis A, B, and C titers were negative. Furthermore, tests for ANA, RPR, rheumatoid factor, c-ANCA, p-ANCA, cryoglobulin, lupus anticoagulant and anticardiolipin antibodies were negative. Both C3 and C4 complement levels were within nor-

Discussion
Once regarded simply as an inflammatory, autosomal recessive disease of unknown etiology, the spectrum of FMF has evolved as a complex genetic puzzle during the genomic era. More than forty missense mutations resulting in abnormal pyrin proteins have led to a new para-Renal biopsy (Light Microscopy) Figure 1 Renal biopsy (Light Microscopy). Light microscopy image of a glomerulus demonstrating negative staining for both Congored and thioflavin-T. Expansion of the mesangium with increased hyalinization of the basement membrane (arrow) and thickening capillary loops is present.
digm for FMF as an inherited state of dysregulated inflammation. The altered gene products -the so-called pyrins -are fundamental to understanding FMF. Pyrincontaining proteins play a pivotal role in the immune response by serving as key inflammatory mediators. Unsurprisingly, pyrin is found in large quantities in neutrophils and released in response to inflammatory stimuli. Additionally, a recently discovered pyrin-like domain was found to exist at the amino-terminal of several proteins involved in cell-signaling pathways inherent to inflammation. One pyrin protein, belonging to a larger class of the pyrin domain family, is involved in the Nuclear Factorkappa B (NF-kB) cell-signaling pathway. Nuclear Factorkappa B is an important transcription factor involved in inflammation via its induction of pro-inflammatory gene products. In individuals with the "wild-type" MEFV gene, pyrin serves a key role in regulating the intensity of the inflammatory response. In contrast, individuals with one or more missense mutations at the MEFV locus produce a pyrin protein with altered or absent function. Consequently, the response to inflammation is altered. The resultant dysregulated inflammatory response often times exceeds physiologic parameters and is disproportionate to the insult. [18][19][20][21][22] The inflammation of FMF may not only be characterized as dysregulated, but is also chronic and recurrent. Its severity and duration have been associated with the secondary development of amyloidosis (AA variety). The amyloid fibrils that lead to nephrotic syndrome in FMF are derived from a serum precursor, serum amyloid A (SAA), itself the result of chronic inflammation. Amyloidosis, with renal involvement and nephrotic syndrome, has become the expected complication of longterm FMF. [14][15][16][17] The novel association between FMF and fibrillary glomerulopathy in this patient raises two contingent questions. First, is the association itself a chance one, but if it is not, is fibrillary glomerulopathy like amyloidosis the result of material deposition that reflects chronic, dysregulated inflammatory activity? The present state of knowledge regarding fibrillary glomerular diseases strongly suggests that the presence of fibrils in the glomeruli of affected individuals represents fibrillar derivation from circulating immunologic molecules, fragments, or immune complexes [14]. Since their etiology, deposition and structure are analogous to that of amyloid in FMF, it is highly intriguing to postulate that this patient's renal involvement is more than a chance occurrence. Prior disease associations with the fibrillary glomerulopathies involve the presence of immune response-associated products [14,15]. Future reports of individuals or kindred with FMF, nephrotic syndrome and fibrillary glomerulopathy will be required to substantiate our theory.

Conclusions
Although the association between chronic inflammation and amyloidosis (AA) is well known, the present description of fibrillary glomerulopathy in FMF requires further elucidation. Nevertheless, the new association among FMF, nephrotic syndrome, fibrillary glomerulopathy, and an M680I (Figure 3) heterozygous genotype may represent a novel renal complication of FMF. Furthermore, it is suggested that symptomatic heterozygous individuals may actually be compound heterozygotes for a mutation not yet identified [22]. As the number of MEFV mutations discovered continues to increase, more data will become available revealing further relationships among the many different MEFV missense mutations and their phenotypic expression in various ethnic groups.