Alport_Syndrome[1]

Alport_Syndrome[1] - Alport Syndrome Alport Syndrome...

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Unformatted text preview: Alport Syndrome Alport Syndrome Nephrology Grand Rounds September 22nd, 2009 Aditya Mattoo, MD Objectives Objectives History Background Pathophysiology Inheritance Patterns Clinical Findings Diagnosis Treatment Prognosis History History History History Dr. Leonard Guthrie in 1902, described a family with members who had hematuria that “may vary in extent, liable to paroxysmal exacerbations with influenza­like symptoms, and not marked by edema.” He called the syndrome congenital hereditary family hematuria, none of the affected individuals exhibited evidence of chronic renal damage at the time. Arthur Frederick Hurst in 1923 described the development of uremia in several members of this family. In 1927, Dr. Cecil Alport followed 3 later generations of the same family and he recognized that deafness was a syndromic component and that the disorder tended to be more severe in males than females, that affected males died of uremia, while females lived to old age. Subsequently, many more families were described and the disease was named Alport Syndrome (AS) in 1961. LB Guthrie”Idiopathic,” or congenital, hereditary and familial haematuria.Lancet, London, 1902, 1: 1243­1246. AF Hurst:Hereditary familial congenital haemorrhagic nephritis occurring in sixteen individuals in three generations. Guy’s Hosp Rec, 1923, 3: 368­370 C Alport: Hereditary familial congenital haemorrhagic nephritis. British Medical Journal, London, 1927, I: 504­506. Background Background Background Background The incidence of AS is approximately 1 in 5000 births. In the US, accounts for approximately 3% of children and 0.2% of adults with ESRD. In Europe, the incidence AS is greater and accounts for 0.6% of patients with ESRD. Pathophysiology Pathophysiology Pathophysiology Pathophysiology AS is a primary basement membrane disorder arising from mutations in genes encoding several members of the type IV collagen family. Basement membranes are assembled through an interweaving of type IV collagen with laminins and sulfated proteoglycans. Six genes, COL4A1, COL4A2, COL4A3, COL4A4, COL4A5 and COL4A6 encode the six chains of collagen IV, α1(IV) through α6(IV), respectively. Pathophysiology Pathophysiology Each collagen IV chain has three domains: Short 7S domain at the N­terminal A long, collagenous domain occupying the midsection of the molecule Noncollagenous domain (NC1) positioned at the C terminal Despite the many potential permutations, the six collagen IV chains only form three sets of triple helical molecules called protomers: α1.α1.α2(IV), α3.α4.α5(IV) and α5.α5.α6(IV). Pathophysiology Pathophysiology Two NC1 trimers unite to form a hexamer. Four 7S domains form tetramers with other protomers The three protomers only form three sets of hexamers to form collagenous networks: α1.α1.α2(IV) ­ α1.α1.α2(IV) α3.α4.α5(IV) – α3.α4.α5(IV) α1.α1.α2(IV) – Inheritance Patterns Inheritance Patterns Inheritance Patterns Inheritance Patterns Three genetic forms of AS exist: XLAS, which results from mutations in the COL4A5 gene and accounts for 80­85% of cases. ARAS, which is caused by mutations in either the COL4A3 or the COL4A4 gene and is responsible for approximately 10­15% of cases. Rarely ADAS, which is also caused by a mutation in either the COL4A3 or the COL4A4 gene accounts for the remainder of cases. It is unclear why some heterozygous mutations cause ARAS with progressive renal disease, while others are associated with thin basement nephropathy, which is typically benign. No mutations have been identified solely in the COL4A6 gene. Inheritance Patterns Inheritance Patterns α Chain Genes Chromosome Tissue Distribution α1(IV) COL4A1 13 Ubiquitous Unknown α2(IV) COL4A2 13 Ubiquitous Unknown α3(IV) COL4A3 2 GBM, tubular basement membrane, Descemet membrane, Bruch membrane, anterior lens capsule, lungs, cochlea α4(IV) COL4A4 2 GBM, TBM, Descemet membrane, Bruch membrane, anterior lens capsule, lungs, cochlea α5(IV) COL4A5 X Epidermal basement membrane (EBM), Bowman’s capsule (BC), GBM, distal TBM, Descemet membrane, Bruch membrane, anterior lens capsule, lungs, cochlea α6(IV) COL4A6 X BC, TBM, EBM *Autosomal recessive Alport syndrome, ** Autosomal dominant AS † X­linked AS ‡ ARAS with mutations spanning COL4A5 and COL4A6 genes Mutation ARAS*/ADAS** ARAS/ADAS XLAS† Leiomyomatosis‡ X Linked Mutations X Linked Mutations In the COL4A5 genes from the families with XLAS, more than 300 gene mutations have been reported. Most COL4A5 mutations are small and include missense mutations, splice­site mutations, and small deletions where renal failure and deafness occur after 30 years of age (adult form). Approximately 20% of the mutations are major rearrangements at the COL4A5 locus (i.e., large deletions, reading frame shifts, etc) in which patients are symptomatic before the age of 30 (juvenile form). A rare of deletion spanning COL4A5 and COL4A6 genes is associated with a combination of XLAS and diffuse Autosomal Mutations Autosomal Mutations To date, only 6 mutations in the COL4A3 gene and 12 mutations in the COL4A4 gene have been identified in patients with ARAS. ARAS patients are either homozygous or compound heterozygous for their mutations, and their parents are usually asymptomatic carriers. ADAS is more rare than XLAS or ARAS and is a result of a dominant negative mutation of the COL4A3 or COL4A4 genes whose gene product acts antagonistically to the wild­type allele. Embryonic Development Embryonic Development Recent evidence demonstrates that isoform switching of type IV collagen becomes developmentally arrested in patients with AS. In normal embryogenesis, oxidative and physical stress stimulates the replacement of α1.α1.α2(IV) with α3.α4.α5(IV) network. The cysteine­rich α3.α4.α5(IV) chains are thought to enhance the resistance of GBM to proteolytic degradation at the site of glomerular filtration. Thus, anomalous persistence of α1.α1.α2(IV) isoforms confers an unexpected increase in susceptibility to proteolytic enzymes, leading to basement membrane splitting and damage. Embryonic Development Embryonic Development Clinical Findings Clinical Findings Clinical Findings Clinical Findings In patients with XLAS, the disease is consistently severe in males and female carriers are generally less symptomatic. The female carrier variable phenotype is due to lyonization by which only one X chromosome is active per cell. In patients with ARAS, the disease is equally severe in male and female homozygotes and the course is similar to that of XLAS. In ADAS, the renal manifestations are typically milder and present later than XLAS and ARAS. Renal Manifestations ­ Hematuria Renal Manifestations ­ Hematuria Gross or microscopic hematuria is the most common and earliest manifestation. Microscopic hematuria is observed usually in the first few years of life in all males and in 95% of females. Hematuria is usually persistent in males, whereas it can be intermittent in females. Like IgA nephropathy, approximately 60­70% of patients experience episodes of gross hematuria, often precipitated by upper respiratory infection, during the first 2 decades of life. Renal Manifestations ­ Proteinuria Renal Manifestations ­ Proteinuria Proteinuria is usually absent in childhood but eventually develops in males with XLAS and in both males and females with ARAS. Significant proteinuria is infrequent in female carriers with XLAS, but it may occur. Proteinuria usually progresses with age and can be in the nephrotic range in as many as 30% of patients. Renal Manifestations ­ ESRD Renal Manifestations ­ ESRD The risk of progression of renal failure is highest among males with XLAS and in both males and females with ARAS. ESRD develops in virtually all males with XLAS, usually between the ages of 16 and 35 years. Some evidence suggests that ESRD may occur even earlier in ARAS, whereas renal failure has a slower progression in ADAS. Approximately 90% of patients develop ESRD by age 40 years. The probability of ESRD in people younger than 30 years is significantly higher (90%) in patients with large rearrangements of the COL4A5 gene compared to those with minor mutations (50­70%). ESRD – Female Carriers ESRD – Female Carriers The prognosis in females carriers with XLAS is usually benign, and they develop ESRD at much lower rates. The reported probability of developing ESRD in female carriers is 12% by age 40 years and 30% by age 60 years. Risk factors for progression to ESRD are episodes of gross hematuria in childhood, hearing loss, nephrotic range proteinuria, and diffuse GBM lamellations seen on electron microscopy (EM). Hearing Deficits Hearing Deficits Bilateral sensorineural hearing loss is a characteristic feature observed frequently, but not universally. May reflect impaired adhesion of the Organ of Corti (which contain auditory sensory cells) to the basilar membrane of the inner ear. About 50% of male patients with XLAS show sensorineural deafness by age 25 years, and about 90% are deaf by age 40 years. Hearing Deficits Hearing Deficits Hearing loss is never present at birth. Usually, hearing loss becomes apparent by late childhood or early adolescence, generally before the onset of renal failure. Hearing impairment is always associated with renal involvement. Some families with AS have been found to have severe nephropathy without hearing loss. Ocular Findings – Anterior Lenticonus Ocular Findings – Anterior Lenticonus Conical protrusion of the central portion of the lens into the anterior chamber. It is most marked anteriorly because it is the region where the capsule is thinnest, the stresses of accommodation are greatest, and the lens is least supported. Occurs in approximately 15­20% of AS patients. Ocular Findings – Anterior Lenticonus Ocular Findings – Anterior Lenticonus Pathognomonic feature if found. Not present at birth, but it develops and worsens with increasing age leading to a slowly progressive deterioration of vision. Not accompanied by eye pain, redness, night blindness or defect in color vision. Can be complicated by cataract formation. Ocular Findings – Anterior Lenticonus Ocular Findings – Anterior Lenticonus Ocular Findings – Dot and Fleck Ocular Findings Dot and Fleck Retinopathy The most common ocular manifestation of AS. Occurs in approximately 70% of males with XLAS and about 10% female carriers. Small yellow or white granulations scattered around the macula or periphery of the retina. Rarely observed in childhood, and it usually becomes apparent at the onset of renal failure. Usually asymptomatic with no associated visual impairment or night blindness. Ocular Findings – Dot and Fleck Ocular Findings – Dot and Fleck Retinopathy Leiomyomatosis Leiomyomatosis Diffuse leiomyomatosis of the gastrointestinal, respiratory and female genital tracts has been reported in some families with AS (particularly esophagus and tracheobronchial tree). Seen in 2­5% of patients and carriers of XLAS who have deletions that involve COL4A5 and extend to the second intron of the adjacent COL4A6 gene. Symptoms usually appear in late childhood and include dysphagia, postprandial vomiting, substernal or epigastric pain, recurrent bronchitis, dyspnea, cough, and Diagnosis Diagnosis Diagnosis Diagnosis Historical information (family history, hearing loss, visual disturbances, gross hematuria) Tissue biopsy often reveals ultrastructural abnormalities and confirm diagnosis. Skin biopsy is less invasive than renal biopsy and should be obtained first. Molecular genetic testing in equivocal biopsy cases, patients in whom biopsy is contraindicated and prenatal testing. Skin Biopsy Skin Biopsy The absence of α5(IV) chains in the epidermal basement membrane on skin biopsy is diagnostic of XLAS. However, the absence of α5(IV) chains in the epidermal basement membrane is observed in only 80% of males with XLAS. Therefore, the presence of α5(IV) chains in the epidermal basement membrane does not rule out the diagnosis of XLAS. Furthermore, α3(IV) and α4(IV) chains are not found in the epidermal basement membrane so skin biopsy can not be used for the diagnosis of ARAS and ADAS. Skin Biopsy ­ IF Skin Biopsy ­ IF A, ARAS. Normal staining of EBM for α5(IV), indistinguishable from normal controls. B, Female carrier of XLAS. Linear staining for α5(IV) on right side, loss of staining on left. C, Male XLAS. No staining for α5(IV) of EBM. Renal Biopsy ­ Light Microscopy Renal Biopsy ­ Light Microscopy Light microscopy findings are nonspecific. Can see focal and segmental glomerular hypercellularity of the mesangial and endothelial cells. Renal interstitial foam cells can be found and represent lipid­laden macrophages which can be seen in many renal diseases. Renal Biopsy ­ IF Renal Biopsy ­ IF Monoclonal antibodies directed against α3(IV), α4(IV), and α5(IV) chains of type IV collagen can be used to evaluate the GBM for the presence or absence of these chains. The absence of these chains from the GBM is diagnostic of AS and has not been described in any other condition. Renal Biopsy ­ IF Renal Biopsy ­ IF A, TBMN with normal diffuse linear staining for α5(IV), indistinguishable from controls. B, Female carrier of XLAS. Discontinuous staining of GBM and BC. C, ARAS. No GBM staining, but BC and TBM preserved. α3(IV) staining negative (not shown). D, Male XLAS. Staining for α5(IV) completely negative. Renal Biopsy ­ EM Renal Biopsy ­ EM Earliest finding is thinning of GBM. Characteristic finding of longitudinal splitting of lamina densa of GBM. May not be seen in young AS patients. The proportion of GBM that shows splitting increases from 30% by age 10 to more than 90% by age 30. Rumpelt, HJ. Hereditary nephropathy: Correlation of clinical data with GBM alterations. Clin Nephrol 1980; 13:203. Renal Biopsy ­ EM Renal Biopsy ­ EM EM of patient with AS, arrows are pointing to the splitting and lamellation of the GBM. Renal Biopsy ­ EM Renal Biopsy ­ EM EM reveals GBM with lamellation (left) and another segment with thinning (right) Renal Biopsy ­ EM Renal Biopsy ­ EM A, EM of glomerular basement membrane, showing segments of thickening and thinning with irregular contours. B, Magnification of a thickened segment showing lamellation, electron­lucent areas and electron­dense granules. Treatment Treatment Treatment – Angiotensin Blockade Treatment – Angiotensin Blockade It has been proposed, although unproven, that angiotensin blockade may diminish the rate of proteinuria leading to glomerulosclerosis and thereby disease progression. To date, only small uncontrolled trials have demonstrated the effect of ACE inhibitors on reducing proteinuria in humans. Preemptive therapy with ACE inhibitors in an α3(IV) knockout Alport mouse model prolonged lifespan until death from renal failure by more than 100%. In the absence of more data, the use of ACE inhibitors is reasonable in patients with Alport syndrome. Cohen, EP. In hereditary nephritis ACE inihibition decreases proteinuria and may slow the rate of progression. Am J Kidney Dis, 1996; 27:199. Gross, O et al. Preemptive ramipril therapy delays renal failure and reduces renal fibrosis in COL4A3­knockout mice with Alport syndrome. KI 2003; 63: 438­446. Treatment ­ Cyclosporine Treatment ­ Cyclosporine Cyclosporine has also been studied in small uncontrolled trials as well. One study of eight Alport males who received cyclosporine for a mean duration of 8.4 years suggested a slower progression to ESRD as compared to related effected males. Another study demonstrated reduction in proteinuria, however, 4 of 9 patients exhibited cyclosporine nephrotoxicity. Callis, L et al. Long­term effects of cyclosporine A in Alport’s syndrome, KI 1999; 55: 1051­1056 Charbit, M et al. Cyclosporine therapy in patients with Alport syndrome. Pediatric Nephrology 2007; 22:57­63. Treatment – Stem Cells Treatment – Stem Cells Cell based therapies have shown some curative potential in animal models, however, have yet to be tested in humans. Two research groups have reported that treating mice with wild­type bone marrow derived cells can improve the disease in α3(IV) knockout Alport mice. The bone marrow stem cells differentiated into podocytes which then secreted the missing α3(IV) chains in this mouse model. Prodromidi, EI et al. Bone marrow­derived cells contribute to podocyte regeneration and amelioration of renal disease in a mouse model of Alport syndrome. Stem Cells. 2006; 24: 2448­2455. Sugimoto H et al. Bone marrow–derived stem cells repair basement membrane collagen defects and reverse genetic kidney disease. Proc Natl Acad Sci USA 2006; 103:7321­7326. Treatment – Renal Transplant Treatment – Renal Transplant AS is essentially cured with renal transplantation, and as one would suspect unless the donor has the disease, AS will not occur in the transplanted organ. The most significant and devastating, albeit rare, complication of transplantation is antiglomerular basement membrane nephritis. Approximately 3­5% of patients with Alport syndrome who receive a transplant develop anti­ GBM antibody to the NC1 component of the α3(IV) chain. Post­transplant anti­GBM nephritis usually develops within the first year of the transplant. Treatment – Renal Transplant Treatment – Renal Transplant For unclear reasons, certain patients are at very low risk for developing post­transplant anti­GBM nephritis, including patients with normal hearing, patients with late progression to ESRD, or females with XLAS. Unlike de novo anti­GBM nephritis, pulmonary hemorrhage is never observed because the patient's lung tissue does not contain the antigen. Treatment with plasmapheresis and cyclophosphamide is usually unsuccessful, and most patients lose the allograft. Retransplantation in most patients results in recurrence of anti­ GBM nephritis despite the absence of detectable circulating anti­ GBM antibodies before transplantation. Kashtan CE. Alport syndrome and thin glomerular basement membrane disease. J Am Soc Nephrol. 1998;9:1736. Thank you. Thank you. ...
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