Alport Syndrome
Nephrology Grand Rounds
September 22nd, 2009
Aditya Mattoo, MD
Objectives
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History
Background
Pathophysiology
Inheritance Patterns
Clinical Findings
Diagnosis
Treatment
Prognosis
History
History
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Dr. Leonard Guthrie in 1902, described a family with members who had
hematuria that “may vary in extent, liable to paroxysmal exacerbations with
influenza-like symptoms, and not marked by edema.”
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He called the syndrome congenital hereditary family hematuria, none of the
affected individuals exhibited evidence of chronic renal damage at the time.
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Arthur Frederick Hurst in 1923 described the development of uremia in
several members of this family.
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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.
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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: 1243-1246.
AF Hurst:Hereditary familial congenital haemorrhagic nephritis occurring in sixteen individuals in three generations. Guy’s Hosp Rec, 1923, 3: 368-370
C Alport: Hereditary familial congenital haemorrhagic nephritis. British Medical Journal, London, 1927, I: 504-506.
Background
Background
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The incidence of AS is approximately 1 in 5000
births.
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In the US, accounts for approximately 3% of
children and 0.2% of adults with ESRD.
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In Europe, the incidence AS is greater and
accounts for 0.6% of patients with ESRD.
Pathophysiology
Pathophysiology
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AS is a primary basement membrane disorder arising
from mutations in genes encoding several members of
the type IV collagen family.
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Basement membranes are assembled through an
interweaving of type IV collagen with laminins and
sulfated proteoglycans.
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Six genes, COL4A1, COL4A2, COL4A3, COL4A4,
COL4A5 and COL4A6 encode the six chains of
collagen IV, α1(IV) through α6(IV), respectively.
Pathophysiology
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Each collagen IV chain has three domains:
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Short 7S domain at the N-terminal
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
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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:
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α1.α1.α2(IV) - α1.α1.α2(IV)
α3.α4.α5(IV) – α3.α4.α5(IV)
α1.α1.α2(IV) – α5.α5.α6(IV)
Inheritance Patterns
Inheritance Patterns
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Three genetic forms of AS exist:
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XLAS, which results from mutations in the COL4A5 gene
and accounts for 80-85% of cases.
ARAS, which is caused by mutations in either the COL4A3
or the COL4A4 gene and is responsible for approximately
10-15% 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
α Chain
Genes
Chromosome
α1(IV)
COL4A1
13
Ubiquitous
Unknown
α2(IV)
COL4A2
13
Ubiquitous
Unknown
Tissue Distribution
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
† X-linked AS
‡ ARAS with mutations spanning COL4A5 and COL4A6 genes
Mutation
ARAS*/ADAS**
ARAS/ADAS
XLAS†
Leiomyomatosis‡
X Linked Mutations
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In the COL4A5 genes from the families with XLAS, more than
300 gene mutations have been reported.
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Most COL4A5 mutations are small and include missense
mutations, splice-site mutations, and small deletions where renal
failure and deafness occur after 30 years of age (adult form).
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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).
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A rare of deletion spanning COL4A5 and COL4A6 genes is
associated with a combination of XLAS and diffuse
leiomyomatosis.
Autosomal Mutations
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To date, only 6 mutations in the COL4A3 gene and 12
mutations in the COL4A4 gene have been identified in
patients with ARAS.
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ARAS patients are either homozygous or compound
heterozygous for their mutations, and their parents are
usually asymptomatic carriers.
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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 wild-type allele.
Embryonic Development
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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 cysteine-rich 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
Clinical Findings
Clinical Findings
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In patients with XLAS, the disease is consistently
severe in males and female carriers are generally less
symptomatic.
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The female carrier variable phenotype is due to
lyonization by which only one X chromosome is active
per cell.
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In patients with ARAS, the disease is equally severe in
male and female homozygotes and the course is similar
to that of XLAS.
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In ADAS, the renal manifestations are typically milder
and present later than XLAS and ARAS.
Renal Manifestations - Hematuria
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Gross or microscopic hematuria is the most common
and earliest manifestation.
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Microscopic hematuria is observed usually in the first
few years of life in all males and in 95% of females.
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Hematuria is usually persistent in males, whereas it can
be intermittent in females.
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Like IgA nephropathy, approximately 60-70% of
patients experience episodes of gross hematuria, often
precipitated by upper respiratory infection, during the
first 2 decades of life.
Renal Manifestations - Proteinuria
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Proteinuria is usually absent in childhood but
eventually develops in males with XLAS and in
both males and females with ARAS.
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Significant proteinuria is infrequent in female
carriers with XLAS, but it may occur.
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Proteinuria usually progresses with age and can
be in the nephrotic range in as many as 30% of
patients.
Renal Manifestations - ESRD
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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 (50-70%).
ESRD – Female Carriers
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The prognosis in females carriers with XLAS is usually
benign, and they develop ESRD at much lower rates.
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The reported probability of developing ESRD in female
carriers is 12% by age 40 years and 30% by age 60
years.
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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
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Bilateral sensorineural hearing loss is a characteristic
feature observed frequently, but not universally.
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May reflect impaired adhesion of the Organ of Corti
(which contain auditory sensory cells) to the basilar
membrane of the inner ear.
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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
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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
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Conical protrusion of the central portion of the
lens into the anterior chamber.
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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.
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Occurs in approximately 15-20% of AS patients.
Ocular Findings – Anterior Lenticonus
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Pathognomonic feature if found.
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Not present at birth, but it develops and worsens with
increasing age leading to a slowly progressive
deterioration of vision.
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Not accompanied by eye pain, redness, night blindness
or defect in color vision.
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Can be complicated by cataract formation.
Ocular Findings – Anterior Lenticonus
Ocular Findings – Dot and Fleck
Retinopathy
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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
Retinopathy
Leiomyomatosis
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Diffuse leiomyomatosis of the gastrointestinal, respiratory
and female genital tracts has been reported in some
families with AS (particularly esophagus and
tracheobronchial tree).
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Seen in 2-5% of patients and carriers of XLAS who have
deletions that involve COL4A5 and extend to the second
intron of the adjacent COL4A6 gene.
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Symptoms usually appear in late childhood and include
dysphagia, postprandial vomiting, substernal or epigastric
pain, recurrent bronchitis, dyspnea, cough, and stridor.
Diagnosis
Diagnosis
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Historical information (family history, hearing loss,
visual disturbances, gross hematuria)
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Tissue biopsy often reveals ultrastructural abnormalities
and confirm diagnosis.
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Skin biopsy is less invasive than renal biopsy and
should be obtained first.
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Molecular genetic testing in equivocal biopsy cases,
patients in whom biopsy is contraindicated and
prenatal testing.
Skin Biopsy
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The absence of α5(IV) chains in the epidermal basement membrane
on skin biopsy is diagnostic of XLAS.
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However, the absence of α5(IV) chains in the epidermal basement
membrane is observed in only 80% of males with XLAS.
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Therefore, the presence of α5(IV) chains in the epidermal basement
membrane does not rule out the diagnosis of XLAS.
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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
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
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Light microscopy findings
are nonspecific.
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Can see focal and segmental
glomerular hypercellularity
of the mesangial and
endothelial cells.
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Renal interstitial foam cells
can be found and represent
lipid-laden macrophages
which can be seen in many
renal diseases.
Renal Biopsy - IF
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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.
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The absence of these chains from the GBM is
diagnostic of AS and has not been described in
any other condition.
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
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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
EM of patient with AS, arrows are pointing to the splitting and lamellation of the GBM.
Renal Biopsy - EM
EM reveals GBM with lamellation (left) and another segment with thinning (right)
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, electron-lucent areas and
electron-dense granules.
Treatment
Treatment – Angiotensin Blockade
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It has been proposed, although unproven, that angiotensin
blockade may diminish the rate of proteinuria leading to
glomerulosclerosis and thereby disease progression.
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To date, only small uncontrolled trials have demonstrated the
effect of ACE inhibitors on reducing proteinuria in humans.
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Preemptive therapy with ACE inhibitors in an α3(IV) knockout
Alport mouse model prolonged lifespan until death from renal
failure by more than 100%.
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In the absence of more data, the use of ACE inhibitors is
reasonable in patients with Alport syndrome.
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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 COL4A3-knockout mice with Alport
syndrome. KI 2003; 63: 438-446.
Treatment - Cyclosporine
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Cyclosporine has also been studied in small
uncontrolled trials as well.
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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.
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Another study demonstrated reduction in proteinuria,
however, 4 of 9 patients exhibited cyclosporine
nephrotoxicity.
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Callis, L et al. Long-term effects of cyclosporine A in Alport’s syndrome, KI 1999; 55: 1051-1056
Charbit, M et al. Cyclosporine therapy in patients with Alport syndrome. Pediatric Nephrology 2007; 22:57-63.
Treatment – Stem Cells
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Cell based therapies have shown some curative potential
in animal models, however, have yet to be tested in
humans.
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Two research groups have reported that treating mice
with wild-type bone marrow derived cells can improve
the disease in α3(IV) knockout Alport mice.
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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 marrow-derived cells contribute to podocyte regeneration and amelioration of renal disease in a mouse
model of Alport syndrome. Stem Cells. 2006; 24: 2448-2455.
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; 103:7321-7326.
Treatment – Renal Transplant
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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.
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The most significant and devastating, albeit rare,
complication of transplantation is antiglomerular
basement membrane nephritis.
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Approximately 3-5% of patients with Alport syndrome
who receive a transplant develop anti-GBM antibody to
the NC1 component of the α3(IV) chain.
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Post-transplant anti-GBM nephritis usually develops
within the first year of the transplant.
Treatment – Renal Transplant
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For unclear reasons, certain patients are at very low risk for
developing post-transplant anti-GBM nephritis, including patients
with normal hearing, patients with late progression to ESRD, or
females with XLAS.
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Unlike de novo anti-GBM nephritis, pulmonary hemorrhage is
never observed because the patient's lung tissue does not contain
the antigen.
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Treatment with plasmapheresis and cyclophosphamide is usually
unsuccessful, and most patients lose the allograft.
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Retransplantation in most patients results in recurrence of antiGBM nephritis despite the absence of detectable circulating antiGBM antibodies before transplantation.
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Kashtan CE. Alport syndrome and thin glomerular basement membrane disease. J Am Soc Nephrol. 1998;9:1736.
Thank you.