A mild form of Alport syndrome:
Hereditary nephropathy in the
absence of extra-renal features
Yoon H-S, Wilson JC & Eccles MR
Pathology, University of Otago,
Dunedin, New Zealand
Alport syndrome (AS)
• A hereditary disorder resulting from abnormal
type IV collagen
• Nephropathy with considerable genetic and
clinical heterogeneity characterized by
haematuria, proteinuria and progressive renal
failure, first reported by Alport in 1927
• Frequently associated with:
– Eye abnormalities
– High tone sensorineural deafness
• Rarely associated with:
– Mental retardation
– Leiomyomatois
Alport syndrome: genetics
• 85% of AS patients: X-linked inheritance of
mutations in the COL4A5 gene on Xq22 encoding
the a5(IV) collagen chain
– COL4A5 is a large gene comprising 51 exons
– As many as 609 mutations have been described to
date and are spread throughout the gene without any
hot spots (Arup Laboratory 2011)
• 15%: Autosomal inheritance of mutations of the
COL4A3 or COL4A4 gene encoding the a3(IV) or
a4(IV) on 2q36-37:
– 14%: autosomal recessive
– 1%: autosomal dominant
Type IV collagen formation
7S
Collagenous
NC1
a1
a2
a3
a4
a5
a6
a1a1a2
a3a4a5
a5a5a6
a(VI) chain
Protomer
Meshwork formation
Hudson et al, NEJM 348:2543, 2003
Type IV collagen distribution
• a1.a1.a2(IV): Ubiquitously present in basement membrane
(BM) in many tissue
• a3.a4.a5(IV) and a5.a5.a6(IV): Restricted tissue distribution
– In the kidney a1.a1.a2(IV) network predominates during
early nephrogenesis in GBM.
– During the 2nd trimester of foetal development,
a3.a4.a5(IV) network gradually becomes dominant
• a3.a4.a5(IV) is also expressed in the eye, cochlea, lung and
testis while a5.a5.a6(IV) network is present in skin,
oesophagus and smooth muscle.
Initial presentation of the NZ family
• Two sisters (IV6:58 yo and IV8:54 yo) presented to the clinic
to be considered as potential live kidney donors for their
sons (V29:27 yo and V35:33 yo, respectively) who had ESRF.
• Both women were found to have significant proteinuria
(1.8, 1.4g/d, respectively) and hypertension and they
proceeded to a renal biopsy (mild mesangial proliferation
and hypertensive arteriosclerosis).
• Routine questioning revealed a strong familial history of
hypertension and the possibility of a familial form of renal
disease.
• Subsequent clinical review of the family identified a
number of additional family members with renal disease.
• Negative for hearing loss or eye abnormalities in all
individuals tested.
1. Subjects with renal disease identified before DNA tests
Identif- Age (yrs old) Presentation
ication Gender
number
Renal Function
and Blood
Pressure
Biopsy
Inheritance
Identif- Age(yrs old) Presentation
ication Gender
number
III2
F
Died on dialysis
Not done
IV26
IV3
57
M
Not done
Affected/
Carrier
Affected
58
F
Proteinuria
1.8g/24 hr
Hypertension
IV28
54
F
Proteinuria
1.4g/24 hr
Hypertension
Mild mesangial Affected
matrix
expansion
Chronic
Affected
glomerulonephritis
IV5
46
M
ESRF. Dialysis
Renal
Transplant at
41
Proteinuria
Chronic kidney
Hypertension disease
V24
39
M
Proteinuria
Haematuria
Normal renal
function
V29
27
M
ESRF. Dialysis
2nd renal
transplant at 26
V31
36
M
Acute
nephritic
syndrome
Hypertension
Proteinuria
Hypertension
Chronic kidney
disease
BP 136/86
Mesangial cell
proliferation
Affected
V35
33
M
Proteinuria
Haematuria
ESRF and renal
transplant at 28
Chronic
glomerulonephritis
Affected
IV39
72
M
Mild chronic
kidney disease
BP 144/76
Not done
Affected
V42
39
M
Proteinuria
1.6g/24 hr
No
haematuria
Hypertension
Proteinuria
1.1g/24 hr
Normal renal
function
BP 126/80
Mesangial cell
proliferation
Affected
Not done
Dead:1, ESRF:3, Chronic disease:3
Affected
Renal
Function
and Blood
Pressure
BP 152/76
Normal
renal
function
Biopsy
Inheritance
Mesangial cell
proliferation
Hypertensive
arteriosclerosis
Mesangial cell
proliferation
Hypertensive
arteriosclerosis
Carrier
Carrier
Histology of V42
IHC for a3, a4 and a5(IV)
a3
a4
a5
Abs gift from Dr Sado
Diagnostic dilemma
• Is this Alport syndrome?
– No hearing or eye abnormalities
– Mild form of kidney disease and late onset
• 11 Glomerulonephritis
• 4 ESRF (3 males and 1 female)
• Low penetrance!!
• A new entity of hereditary kidney disease?
Extended family pedigree
A total of 155 family members for 6 generations examined (81M and 74F).
Black symbols: Biopsy confirmed GN (6M).
Gray symbols: Clinically GN, biopsy not done (4M & 1F).
Black dots: Obligate carriers (21F).
White symbols: No clinical disease (71M & 73F).
Cross: Confirmed by DNA testing.
Predominance of GN in males and lack of male to male transmission
consistent with X-linked inheritance
Family pedigree (simplified)
X-chromosome
microsatellite marker
Two point LOD scores between the GN locus and
markers mapping to chromosome Xq21.33-23
Theta
0
0.01
0.05
0.1
0.2
0.3
0.4
DXS6809
-infinity
-0.31
0.88
1.21
1.25
0.99
0.57
DXS6789
3.14
3.08
2.86
2.58
1.98
1.35
0.69
DXS8096
3.59
3.53
3.28
2.96
2.28
1.56
0.8
DXS1210
3.59
3.53
3.28
2.96
2.28
1.56
0.8
DXS6749
-infinity
-0.61
-0.01
0.16
0.2
0.13
0.05
The linked region encompassing COL4A5
Nucleotide sequence alteration in
COL4A5 in affected family members
G>A substitution at
nucleotide 4913 in Exon 50
(
)
Resulting in Cys1638Tyr
Mae III digest of exon
50 PCR products
A allele
Present in all affected
family members and not
in 192 healthy control
M NC
Affected males Affected & carrier females
1.Renal disease identified before DNA tests
2.Renal disease/carriers identified after DNA tests
Identif- Age (yrs old) Presentation
ication Gender
number
Renal Function
and Blood
Pressure
Biopsy
Inheritance
Identif- Age(yrs old) Presentation
ication Gender
number
III2
F
Died on dialysis
Not done
IV24
IV3
57
M
Not done
Affected/
Carrier
Affected
69
F
Trace
microscopic
haematuria
IV26
58
F
Proteinuria
1.8g/24 hr
Hypertension
Mild mesangial Affected
matrix
expansion
Chronic
Affected
glomerulonephritis
IV28
54
F
Proteinuria
1.4g/24 hr
Hypertension
Normal
renal
function
IV31
69
F
Hypertension
Negative urine
IV34
65
F
Hypertension
Negative urine
IV36
61
F
Microscopic
haematuria
V40
38
F
Haematuria
Normal
renal
function
Normal
renal
function
Normal
renal
function
Normal
renal
function
BP 118/60
IV47
54
F
36
F
Negative urine
BP 148/70
Not done
Carrier
Intermittent
microscopic
haematuria
Not done
Carrier
V49
43
F
Negative urine
Not done
Carrier
V37
39
F
Negative urine
Normal
renal
function
BP 120/76
Normal
renal
function
BP 120/70
Normal
renal
function
Not done
Carrier
IV5
46
M
ESRF. Dialysis
Renal
Transplant at
41
Proteinuria
Chronic kidney
Hypertension disease
V24
39
M
Proteinuria
Haematuria
Normal renal
function
V29
27
M
ESRF. Dialysis
2nd renal
transplant at 26
V31
36
M
Acute
nephritic
syndrome
Hypertension
Proteinuria
Hypertension
V35
IV39
V42
Not done
Chronic kidney
disease
BP 136/86
Mesangial cell
proliferation
Affected
Affected
33
M
Proteinuria
Haematuria
ESRF and renal
transplant at 28
Chronic
glomerulonephritis
Affected
72
M
Proteinuria
1.6g/24 hr
No
haematuria
Hypertension
Proteinuria
1.1g/24 hr
Mild chronic
kidney disease
BP 144/76
Not done
Affected
Normal renal
function
BP 126/80
Mesangial cell
proliferation
39
M
V44
Affected
Renal
Function
and Blood
Pressure
Normal
renal
function
BP 168/86
BP 152/76
Biopsy
Inheritance
Not done
Carrier
Mesangial cell
proliferation
Hypertensive
arteriosclerosis
Mesangial cell
proliferation
Hypertensive
arteriosclerosis
Not done
Carrier
Not done
Carrier
Not done
Carrier
Carrier
Carrier
Mild mesangial Carrier
cell
proliferation
Depiction of NC1 domain showing locations of
cysteine sequence alterations and clinical details
of patients
Summary
We report a unique cysteine to tyrosine
substitution in the NC1 domain of COL4A5 in a
New Zealand family who presented with a
phenotypically mild form of Alport syndrome,
suggesting that in this family substitution of
Cys1638Tyr led to late onset renal failure
without hearing loss or eye abnormalities.
Histology of female carriers (IV26)
6A
6B
EM (carrier IV26)
150nm
EM (carriers IV26)
Summary
• Thin basement membrane nephropathy could
be seen in some carrier women containing
COL4A5 mutations.