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Review Article
Genetic polymorphisms of vein wall remodeling in chronic venous
disease: a narrative and systematic review
Vighnesh Bharath,1 Susan R. Kahn,2 and Alejandro Lazo-Langner3,4
1
Department of Medicine, University of Western Ontario, London, ON, Canada; 2Division of Internal Medicine and Department of Medicine, McGill
University, Montreal, QC, Canada; 3Department of Medicine, Division of Hematology, University of Western Ontario, London, ON, Canada; and
4
Department of Epidemiology and Biostatistics, Western University, London, ON, Canada
Chronic venous disease encompasses a
spectrum of disorders caused by an abnormal venous system. They include
chronic venous insufficiency, varicose
veins, lipodermatosclerosis, postthrombotic syndrome, and venous ulceration.
Some evidence suggests a genetic predisposition to chronic venous disease
from gene polymorphisms associated
mainly with vein wall remodeling. The
literature exploring these polymorphisms
has not been reviewed and compiled thus
far. In this narrative and systematic review,
we present the current evidence available
on the role of polymorphisms in genes
involved in vein wall remodeling and other
pathways as contributors to chronic
venous disease. We searched the EMBASE,
Medline, and PubMed databases from
inception to 2013 for basic science or
clinical studies relating to genetic associations in chronic venous disease and
obtained 38 relevant studies for this
review. Important candidate genes/
proteins include the matrix metalloproteinases (extracellular matrix degradation),
vascular endothelial growth factors (angiogenesis and vessel wall integrity),
FOXC2 (vascular development), hemochromatosis (involved in venous ulceration and iron absorption), and various
types of collagen (contributors to vein
wall strength). The data on associations
between these genes/proteins and the
postthrombotic syndrome are limited
and additional studies are required.
These associations might have future
prognostic and therapeutic implications. (Blood. 2014;124(8):1242-1250)
Introduction
Chronic venous disease (CVD) refers to a spectrum of overlapping
diseases involving abnormalities of the venous system, both structural
and functional. Chronic venous insufficiency (CVI) is a term that
describes functional abnormalities of the venous system, but is often
used to describe the full range of CVD manifestations such as varicose
veins, venous ulceration, lipodermatosclerosis (LDS), and postthrombotic syndrome (PTS) (essentially a secondary form of CVI).1-3
Almost a quarter of the adult population in the Western world has some
form of CVD, but treatment is often delayed or deferred because of an
underestimation of the prevalence and burden of the condition, leading
to significant disability. Treatment is multifactorial, and often includes
mechanical and/or surgical measures such as compression devices, leg
elevation, ablations, and vein stripping.1
CVI is a multifactorial disease, and although most commonly
caused by valvular incompetence and venous hypertension, the exact
pathogenesis remains unclear, although various studies have
suggested a potential genetic contribution.4 This condition may be
primary (abnormalities of vein walls or valves) or secondary (after
venous thrombosis; ie, PTS). Risk factors include age, female
gender, pregnancy, family history, obesity, and prolonged orthostasis. Clinical manifestations include leg pain, lower extremity
edema, skin changes, varicose veins, and venous ulceration.5 Venous
ulcers are a severe complication of CVI, although the underlying
mechanisms are not fully known.
Varicose veins, a form of CVD and the most common
manifestation of CVI, are caused by a loss of vessel wall homeostasis;
venous hypertension leads to vein dilation, distortion, leakage, and
inflammation, causing valve and wall disease and reflux.6-8 Although
sometimes caused by PTS, varicose veins are usually primary
in nature. They are often hereditary and result from extensive
extracellular matrix (ECM) remodeling, leading to vein wall
weakening or dysfunction.9-11
PTS, a type of CVD, is an important and frequent chronic
complication of deep venous thrombosis (DVT) that develops in
20% to 50% of patients (severe in 5% to 10%) after DVT despite
appropriate anticoagulation.12 Risk factors include incomplete DVT
symptom resolution, proximal or previous ipsilateral DVT, obesity,
and increased age.12 Although the pathophysiology of PTS is
not well understood, it involves venous hypertension caused by
persistent venous obstruction and/or valvular reflux from valve
destruction, and recent evidence also supports a role for inflammation.13 Symptoms are similar to CVI and can be debilitating,
often including constant or intermittent limb swelling, aching,
cramps, or numbness/tingling (improved with rest or recumbency).
Treatment involves symptomatic relief using graduated elastic
compression stockings or compression devices, leg elevation, or
a trial of horse chestnut seed extract as a last resort.12,14,15
Recently, there has been some research into the genetic contributors and risk factors of CVD, such as varicose veins and venous
ulceration, mainly relating to certain noted polymorphisms in genes
associated with vein wall remodeling. In fact, genetic risk factors are
already known to affect wound progression and healing, and screening
in this regard may aid in the planning of appropriate individualized
treatment and prophylaxis.16 Also, various thrombophilic single
nucleotide polymorphisms (SNPs) may contribute to CVI and ulcers
by increasing the risk of DVT.
More recently, however, other SNPs have been studied in genes
relating specifically to vein wall remodeling and proinflammatory or
angiogenesis-regulating factors and receptors. Although studies in
this area do support a moderate to strong genetic predisposition
Submitted March 3, 2014; accepted July 3, 2014. Prepublished online as
Blood First Edition paper, July 8, 2014; DOI 10.1182/blood-2014-03-558478.
© 2014 by The American Society of Hematology
1242
BLOOD, 21 AUGUST 2014 x VOLUME 124, NUMBER 8
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BLOOD, 21 AUGUST 2014 x VOLUME 124, NUMBER 8
GENETIC POLYMORPHISMS IN CHRONIC VENOUS DISEASE
1243
toward CVI and varicose veins,16 the exact genes are still unknown—
though they likely involve quantitative or qualitative defects in
proteins associated with the vein wall, ECM, and cell organization/
regulation.16 These polymorphisms, in turn, could plausibly increase
the likelihood of CVD, including PTS after DVT, but evidence in this
area is lacking.
Though various candidate genes have been identified as
contributors to CVD, the evidence has not previously been compiled
and critically reviewed. In this review, we use a systematic approach
to explore the current evidence regarding genetic polymorphisms in
vein wall structure and healing/remodeling as potential contributors
to CVD, including PTS. Understanding these genetic associations
may help clarify the underlying pathophysiology, identify patients at
risk, and suggest novel therapeutic options.
Methods
To identify potential genes associated with CVD, we conducted a broad
computerized literature search. We considered for inclusion any studies,
either basic or clinical, describing or potentially describing an association
between any gene, gene mutation, or genetic polymorphism and any of the
following conditions: varicose veins, chronic leg ulcers, CVI, lipodermatosclerosis, PTS, or any combination of these. The search was conducted in
September 2013 from the inception of each of the following databases:
EMBASE, Medline (through the OVID interface), and PubMed. The search
strategy used was: [“varicose veins” OR “chronic venous insufficiency” OR
“leg ulcer” OR “post-thrombotic syndrome” OR “post thrombotic syndrome”
OR “post-phlebitic syndrome” OR “post phlebitic syndrome”] AND
[“genetics” OR “gene” OR “genes” OR “mutation” OR “polymorphism”].
We restricted the search to studies published in English. The retrieved
references were initially screened for eligibility based on titles by 1 author and
confirmed by another author. A preliminary list of potentially relevant studies
was then independently screened by 2 authors based on titles and abstracts and
a final list of studies to review in full was generated by consensus. Any studies
whose relevance was unclear were reviewed in full.
Quality of the studies was not assessed because of the lack of validated
scales for the type of studies included. We did not plan a meta-analysis
because we anticipated substantial heterogeneity among studies. Our results
are presented descriptively by CVI subtype. Finally, although no standards
exist for reporting systematic reviews of basic science studies, whenever
possible we attempted to adhere to the available reporting standards.17,18
Results
Search results
The search process is summarized in Figure 1. The initial search
generated 682 results. The initial screening by title alone resulted in
142 potentially relevant studies. The final selection for review in full
included 41 studies, of which 3 were excluded and 38 articles were
included in the final review.
Genetic polymorphisms and CVD
Our literature search yielded various candidate genes that have
evidence-based associations with a spectrum of CVD including CVI,
varicose veins, LDS, venous ulceration, and PTS (Table 1). There
was significant overlap in that these genes were often associated with
more than 1 CVD manifestation (Figure 2), but they are presented
here according to their most significant associations with a given
subtype. The matrix metalloproteinases (MMPs) are discussed
Figure 1. Flow diagram of the systematic review
separately, given their consistent strong associations with various
forms of CVD.
Varicose veins
The ECM is a complex and dynamic framework of collagen,
proteoglycans, elastin, glycoproteins, and cellular components.
Degradation or destruction of the ECM disrupts the homeostasis of
the vein (much of which is maintained by the MMPs, discussed
later), thereby leading to varicosity. Vein wall weakness is a key
player in the pathophysiology of varicose veins, and collagen is an
important matrix component that provides strength; however,
collagen dysregulation leads to vein wall abnormalities.4 In varicose
veins, the total elastin content is decreased, type I collagen is
upregulated, and type III collagen is downregulated.7,19 Jin et al4
conducted a recent study that examined a 7-base pair insertion/
deletion polymorphism (rs3917) in the COL1A2 (a-2 type I
collagen) gene. They found that this polymorphism upregulated
COL1A2 expression and produced a 1.6-fold increase in CVI risk
and speculated that genetic variations in this gene alter transcriptional activity, affect messenger RNA (mRNA) structure, and
ultimately allow expressional upregulation.4
Kowalewski et al20 demonstrated increased expression of the
cytokine vascular endothelial growth factor A (VEGF-A) and
receptor VEGF R2 in the walls of varicose veins as compared with
normal saphenous veins, particularly if complicated by thrombophlebitis. Similarly, Hollingsworth et al21 observed increased
transcription of VEGF and its receptors in varicose veins, reflecting
a potential early role in varicogenesis. Of note, VEGF-A is involved
in the maintenance of vessel wall integrity. Increased expression of
VEGF-A or its receptor R2 leads to increased activation of nitric
oxide synthase, which then leads to vessel wall damage mediated by
oxygen free radicals as well as decreased vessel tone that predisposes
to venous stasis.20 VEGF also plays a key role in angiogenesis, so
SNPs in the VEGF gene (C936T and 21780 T/C have been
described) can be considered risk factors for impaired wound healing
and venous ulceration.22
Chang et al6 conducted a study using microarray bioinformatics
that systematically explored various genes involved in biological
expression
Basic science/gene
ECM integrity
case-control study
Basic science
BAT1
TNF-a
Oct-1
MGP
with TNFa
Apoptosis; linkage
Inflammation
Intron 10 [–/C]
patients vs 16.3% in controls
Presence of allele: 28.8% in ulcer
patients vs 22.6% in controls
Presence of allele: 43.1% in ulcer
veins vs normal vein tissue
Significantly higher mRNA levels and
(1.74 vs 1.1)
varicose vs nonvaricose vein tissue
Higher relative MGP expression in
collagen 2.33, type III collagen 1.70
vs nonvaricose vein tissue: type I
Relative mRNA expression in varicose
type I collagen and mRNA expression
muscle cells, n 5 8); no difference in
(control vs varicose vein smooth
gene expression
2308G → A
–SNP 3: 1/24 (4.2%)
Type III collagen dpm/106: ;290 vs ;40
protein expression of Oct-1 in varicose
Upregulation
Overexpression
Overexpression
deposition decreased
Type III collagen
stress/regulation of
Cellular response to
Vein wall remodelling
ER, estrogen receptor; HFE, hemochromatosis; NA, not available; NS, not significant; VV, varicose veins.
28
Venous ulcers/wound healing
27
expression
Basic science/gene
immunostaining
Basic science/vein
–SNP 2: 2/24 (8%)
3. 241G → T
(not in controls)
–SNP 1: 5/24 (20.8%)
2. 241G → A
P 5 .012
OR: 2.00
P 5 .000155
OR: 2.48
P , .001
P , .0001
Type III: P , .01
Type I: P , .001
P , .005
NA
P , .0001
P 5 2.2E-6
increase in intensity
VV:CV (control veins) $2-fold
P , .001
Strength of association
BHARATH et al
8
19
vein reflux: 14/18) vs 1/12 in referents
SNPs in proximal upstream region of
sequencing
1. 291C → G
with various FOXC2 mutations (deep
Great saphenous vein reflux in 18/18
(VV: 67% vs 45%)
monozygotic vs dizygotic
Concordance rates significantly higher for
with control
32/74 genes upregulated in VV compared
VEGF-R2: 57.47 vs 28.92 ng/g
VEGF-A: 41.76 vs 25.79 ng/g
in VV vs normal wall tissue
Increased VEGF-A and VEGF-R2 content
Results
FOXC2 in VV/hemorrhoid patients
Basic science/genomic
25
(varied)
FOXC2 mutations
Functional variants
Upregulated
expression
Increased mRNA/protein
Polymorphisms/abnormality
analysis and
Basic science
Type I/III collagen
development
D16S520
using marker gene
Lymphatic and
apoptosis
Cell proliferation and
apoptosis
Cell signaling,
Protein degradation
angiogenesis
Vessel wall integrity,
Proposed function
vascular/venous
FOXC2
TGF-b1
ILK
HSP-90
VEGF-A/VEGF-R2
Gene
linkage analysis
Basic science/twin
26
24
Basic science/genetic
6
microarrays
Basic science
Study details
20
VV
Reference
1244
Table 1. Candidate gene polymorphisms/abnormalities and their proposed evidence-based associations in chronic venous disease
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BLOOD, 21 AUGUST 2014 x VOLUME 124, NUMBER 8
Study details
Gene
genotyping
gene expression
(COL1A1)
Proposed function
Results
ECM integrity
ECM integrity
metabolism
Homocysteine
Iron export
absorption
Regulation of iron
3. 13% vs 7%
4. 47% vs 38%
3. 210808G → T
4. 21569C → A
Overexpression
in 39UTR)
indel polymorphism
rs3917 (7-base pair
677C → T
28C → G
282G → A
2. 34% vs 25%
50 000 mm2)
(LDS vs control: 180 vs 97 per
mesenchymal cells/fibroblasts
groups from increased
(COL1A1) in LDS vs other patient
Increased procollagen type I mRNA
of CVI cases vs 8% controls
Indel polymorphism present in 12.2%
vs 5% in healthy population
Overall, 15% homozygous for C677T
C4-6: 20%
C2-3: 10% homozygous for C677T
Based on CEAP classification:
Homozygotes: 8.6% vs 2.3%
vs 30.8% in controls
Heterozygotes: 34% in ulcer patients
Homozygotes: 0.6% vs 0%
vs 1.8% in controls
Heterozygotes: 9.9% in ulcer patients
associated with venous ulceration
T-T-T-A haplotype significantly
1. 58% vs 49%
2. 213850T → C
exon and promoter
repair processes
1. 216849C → T
regions, including 0N
Upstream regulatory
Cases vs controls
Homozygotes: 23.17% vs 13.42%
(rs7895676)
(rs2981578)
patients vs 45.12% in controls
inflammatory and
Estrogen receptor;
expression
Heterozygotes: 53.66% in leg ulcer
(Grzela et al)
FGF-R2: 2451A → G
normal veins
No significant difference in FGF-R
aFGF mRNA
wound healing,
ECM metabolism
protein in VV vs 24.68 pg/g in
Vein wall aFGF content: 32.21 pg/g of
aFGF and increased
Overexpression of
Polymorphisms/abnormality
regeneration,
Connective tissue
ER, estrogen receptor; HFE, hemochromatosis; NA, not available; NS, not significant; VV, varicose veins.
33
Procollagen
(COL1A2)
extraction and
Basic science/pathology 1
collagen
Basic science/DNA
4
LDS
a-2 Type I
Basic science/genetics
MTHFR
FPN1
HFE
ERb
a-FGF/FGF-R2
32
array study
Basic science/DNA
control study
Basic science case
analysis
Basic science/genetic
expression
Basic science/gene
P , .001
P 5 .008
OR: 1.60
P , .001
P 5 .005
OR: 5.2
P 5 .001
OR: 4.5
T-T-T-A haplotype OR: 2.9
4. P 5 .013
3. P 5 .002
2. P 5 .010
1. P 5 .025
P 5 .0103
P , .001
Strength of association
BLOOD, 21 AUGUST 2014 x VOLUME 124, NUMBER 8
CVI
31
30
29
9
Reference
Table 1. (continued)
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GENETIC POLYMORPHISMS IN CHRONIC VENOUS DISEASE
1245
Study details
Basic science/gene
23
Basic science (mice)
IL-6
TIMPs
Inflammation
Inhibitors of MMP
ECM degradation
ER, estrogen receptor; HFE, hemochromatosis; NA, not available; NS, not significant; VV, varicose veins.
37
PTS
Basic science/gene
34
expression
Basic science/genotyping
40
expression
Basic science/gene
expression (mice)
Basic science/gene
expression
Basic science/gene
expression
Basic science/gene
MMPs
Proposed function
IL-6 as therapeutic target
Diminished TIMP-1,2
TIMP-2: 2418G -→ C
of TIMP-1
Overexpression
generated) vs controls; MMP-14 mRNA
(MT1-MMP)
rat IgG
44%) vs those treated with control
fibrosis (intimal thickness reduced by
anti-IL-6 had decreased vein wall
Mice with IVC thrombus treated with
dermatitis vs controls
immunoreactivity of TIMP-1,2 in stasis
Low gene expression and
14.2% in controls
Allele frequency: 23.3% in VV group vs
(2.06 6 0.26)
in varicose vs nonvaricose veins
Higher relative TIMP-1 mRNA expression
controls
upregulated 2.5-fold compared with
MMP-2 activity in ligated cavae (DVT
During resolution of DVT: 71% increase in
least an 80-fold increase
controls; MMP-1, -9, -8, and -13 had at
levels elevated in ulcer tissue vs
MMP-1, -2, -3, -8, -9, -12, and -13 protein
dermatitis) vs controls
-13 mRNA in lesional skin (stasis
Increased expression of MMP-1, -2, and
and TIMP-1
class 4-5 patients relative to MMP-1
Active component of MMP-2 increased in
TIMP-1: 2.56 (control) vs 23.45 (class 6)
(class 4) vs 31.2 (class 6)
MMP-1 mRNA: 0.002 (control) vs 4.15
CVI patients, class 1-6
injury
at 8 and 21 d after stasis thrombosis
less collagen content/fibrosis vs controls
Vein walls of MMP92/2 mice had 45%
group vs 48.3% in controls
21562C allele frequency: 81.7% in VV
282AA 1 AG: 11.1 6 17.1 cm2
282GG: 5.4 6 2 cm2
282GG genotype
Smaller ulcer size in patients with
Results
MMP-2 and MMP-14
Overexpression of
MMP-1,2,3,8,9,12,13
Overexpression of
of MMP-1,2,13
Overexpression
protein
mRNA and MMP-2
Overexpression of MMP-1
MMP-92/2
MMP-9: 21562C/C
MMP-12: 282A → G
Polymorphisms/abnormality
P , .05
NS
Unclear significance
OR: 2.213
P 5 .038
P , .01
P , .05
P , .005 (majority)
P , .05
TIMP-1: P , .05
MMP-1 mRNA: P , .01
P , .01
OR: 6.102
P 5 .000
P 5 .001
Strength of association
BHARATH et al
8
36
42
41
Basic science (mice)
38
expression
Basic science/genotyping
array study
Basic science/DNA
40
31
Gene
1246
MMPs: VV, CVI, venous ulcers
Reference
Table 1. (continued)
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BLOOD, 21 AUGUST 2014 x VOLUME 124, NUMBER 8
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BLOOD, 21 AUGUST 2014 x VOLUME 124, NUMBER 8
pathways that may contribute to varicosity. The results showed that
32 genes were upregulated and 74 genes were downregulated in
varicose veins, most of which were related to apoptosis and
angiogenesis. Important examples of upregulated genes included:
HSP90, ILK, and TGF-b1.6 In fact, Saito et al23 earlier noted that
TGF-b1 stimulates collagen synthesis and alters levels of MMPs
(discussed later).
Mutations in the FOXC2 gene have also been associated with
varicose veins. FOXC2 encodes a transcription factor involved
in lymphatic and vascular development, and mutations in FOXC2
are seen in lymphoedema distichiasis, which is characterized by
lymphoedema and varicose veins.7,24 Ng et al24 conducted an early
twin linkage study that strongly implicated FOXC2 in the development of varicose veins as a heritable condition. Similarly,
knowing that FOXC2 had previously been implicated in primary
venous valve failure, Al-Batayneh et al25 identified 3 specific SNPs
in the FOXC2 gene that may contribute to varicose vein and
hemorrhoid development. More recently, Mellor et al26 conducted
a small study of 18 patients and noted a strong association between
FOXC2 and primary venous valve failure in both superficial and
deep veins of the lower limb.
Other, lesser-known genes have also been examined in preliminary studies and must be mentioned. Jeong et al27 performed
large scale mRNA screens among normal varicose veins and found
the greatest differential expression in the octamer-binding transcription factor-1 gene (Oct-1), which was upregulated in primary
varicose veins. Cario-Toumaniantz et al8 found overexpressed
vitamin K–dependent matrix gla protein (MGP) in varicose veins,
and speculated that its role in wall remodeling involved smooth
muscle proliferation and mineralization processes.
GENETIC POLYMORPHISMS IN CHRONIC VENOUS DISEASE
1247
ulcers; as mentioned previously, this likely led to abnormal
reepithelialization and angiogenesis.
Estrogen is a known contributor to ECM metabolism; in fact,
hormone replacement therapy prevents CVI and topical estrogen
promotes wound healing in the elderly by decreasing the inflammatory
response.30 Although convincing associations have not been elucidated, several SNPs in the ER-b receptor have been associated
with venous ulcers in the elderly.22,30 Ashworth et al30 found that
polymorphisms in the upstream regulatory regions of the ER-b gene
were significantly associated with venous ulceration, but did not
conduct further functional studies to determine the precise mechanism.
Hemochromatosis is an inherited iron-overload disease caused by
mutations in the HFE gene (most commonly allele C282Y), a major
histocompatibility complex class 1-type membrane protein associated with b2-microglobulin. The mutated gene results in abnormalities in the regulation of iron absorption related to interactions
between transferrin and its receptor. In patients with CVI, the HFE
C282Y allele increases the risk of ulceration by almost 7-fold, likely
because of accumulation of iron in tissues surrounding blood vessels, increased free radicals and oxidative stress, and upregulation of
the inflammatory response that finally leads to tissue destruction.22
Moreover, Gemmati et al31 found that the 28CG polymorphism in
the FPN1 gene (ferroportin; involved in exporting iron out of the cell)
increases susceptibility to leg ulcers.
Finally, Sam et al32 suggested from preliminary data that mild to
moderate hyperhomocysteinemia is common in patients with CVI
(approximately 65%, especially with ulceration), and is associated in
one-third of patients with an underlying methylenetetrahydrofolate
reductase C677T homozygous polymorphism.
LDS
Venous ulceration
22
Grzela et al reviewed 4 genes that may play a role in venous
ulceration: tumor necrosis factor (TNF), fibroblast growth factor-R
(FGF-R), estrogen receptor, and HFE. Levels of TNF-a and
interleukin-1 (IL-1) are higher in venous leg ulcers compared with
normal acute wounds, with certain SNPs (such as the 2308A variant
in TNF-a) conferring a higher risk of venous ulceration compared
with wild-type.5,22,28 Along with demonstrating the previously
mentioned association with TNF-a, Wallace et al28 also identified
a polymorphism in intron 10 of the BAT1 gene (human leukocyte
antigen B–associated transcript-1) as being a significant risk factor
for venous ulceration.
Similarly, FGFs and their receptors (FGF-R) are cytokines that
are imperative for the control of connective tissue regeneration in
wound healing. Kowalewski et al9 found increased acidic fibroblast
growth factor (a-FGF) expression in the walls of varicose veins. They
noted that these walls contained extensive ECM remodeling and
altered collagen and glycosaminoglycan differentiation; a-FGF
likely influences the expression of certain enzymes through various
pathways (eg, mitogen-activated protein kinase pathway) involved
in ECM metabolism and varicosity. Furthermore, a-FGF synthesis is
enhanced by hypoxia, which may be a consequence of venous
stasis.9 Previous studies indicate that certain SNPs in FGF-R2, most
frequently the polymorphism A2451G, are more commonly
observed in CVI or ulceration. Though the mechanism is unclear,
these SNPs likely result in lower expression of FGF-R2, causing
impaired regeneration of connective tissue, longer vein wall
reepithelialization, and eventually CVI or ulceration. 22 Nagy
et al29 conducted an association study and identified an SNP in the
FGF-R2 gene that was more prevalent CVI patients with nonhealing
LDS is a consequence of CVI and is characterized by severe skin
changes including hardening, atrophy, dark pigmentation, and
edema. It often progresses to skin breakdown, venous ulceration,
and delayed healing.33,34 deGiorgio-Miller et al33 analyzed leg skin
biopsies from patients with LDS and found enhanced cell proliferation and procollagen gene expression as well as significant
fibrotic changes which correlated directly with ulcer formation and
healing time. Furthermore, imbalances in the MMPs and their
inhibitors (discussed later) have also been implicated in LDS through
the generation of epidermal and dermal skin defects.34
PTS
PTS is a frequent yet poorly understood complication of DVT.
Previous studies have explored genes involved in vein wall
remodeling in relation to CVI and its manifestations (eg, varicose
veins, venous ulcers). These are also manifestations of PTS, and it is
logical to infer that polymorphisms in these very genes may
potentially increase the risk of PTS as well. In fact, Deatrick et al35
noted ongoing vein wall remodeling 6 months after an acute DVT
that was associated with biomarkers such as MMP-9, which directly
correlate with resolution and predict PTS. There is, however, a dearth
of literature that directly associates the above genes with PTS.
An early study by Dahi et al36 demonstrated increased MMP-2
and MT1-MMP activity (potentially mediated by thrombin) during
DVT resolution, which, in turn, increased the risk of PTS. Wojcik
et al37 used a mouse model to conclude that IL-6 is associated with
reduced monocyte recruitment, leading to reduced vein wall
thickness and fibrosis. Given that PTS involves extensive perivenous
and mural fibrosis, IL-6 may serve as a therapeutic target to prevent
these fibrotic complications. Another recent mouse model study by
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1248
BLOOD, 21 AUGUST 2014 x VOLUME 124, NUMBER 8
BHARATH et al
development and severity of PTS. However, their preliminary data
did show increased MMP-9 and decreased Toll-like receptor 9
expression in acute DVT. MMP-9 levels have been shown to be
increased in varicose veins and venous ulcers, and some data suggest
a potential role in DVT resolution, with gene deletions being
associated with less collagen deposition. In fact, Beidler et al42 used
multiplexed protein analysis to show that all MMPs except MMP-7
were highly expressed in venous leg ulcers, especially MMP-8 and
MMP-9. In addition, Singh et al43 analyzed various SNPs associated
with venous leg ulcers and found that MMP-12 gene polymorphisms
may have a role in ulcer progression.
Interestingly, Kurzawski et al44 demonstrated that polymorphisms
in MMP-1 and MMP-3 did not predict susceptibility to varicose veins,
but this study likely did not have the power to uncover the milder
effects of these genes on an otherwise multifactorial disorder.
Discussion
Figure 2. Candidate genes and their overlapping associations with the
spectrum of chronic venous disease.
Deatrick et al38 reveals that MMP-9 modulates vein wall collagen
content and contributes to inflammation and fibrosis, thus implicating it as a potential target to reduce the fibrotic complications of PTS.
To our knowledge, there has been no study to date that has analyzed
polymorphisms in the previously mentioned candidate genes to
uncover a direct association with PTS. Some of the studies presented in
Table 1 involve tissue blocks from veins complicated by thrombophlebitis, and some of the patients were noted to have a history of
venous thrombosis (however, scant patient data were provided), but
none of the studies specifically included PTS as a subset.
MMPs
Perhaps the most studied genes in venous disease are the MMPs and
tissue inhibitors of metalloproteinases (TIMPs). A systematic review
by Lim et al7 revealed that MMP-1, MMP-2, MMP-3, MMP-7,
MMP-9, TIMP-1, and TIMP-3 were all upregulated in varicose
veins. Similarly, Raffetto et al39 noted that MMPs are involved in
ECM degradation, which subsequently leads to venous remodeling,
structural wall changes, and ultimately venous dilation and valve
dysfunction; they are thus heavily involved in the pathogenesis of
CVD. Though the molecular mechanisms of these genetic anomalies
have not been fully elucidated, it appears that MMPs regulate or
degrade the ECM through hydrolysis, whereas TIMPs are tissue
inhibitors of MMPs that influence vascular remodeling. Hence, an
imbalance between these proteins may lead to abnormalities in
the vessel wall and, ultimately, vascular disease such as varicosity
and ulceration.7,35,40 Moreover, misregulation of MMP activity and
TIMP counterregulation contributes to impaired ulcer healing.34 An
early study by Saito et al23 suggested that increased MMP-2 levels
affect tissue remodeling and contribute to a proulcer environment.
Subsequently, Herouy et al41 examined stasis dermatitis, a common
consequence of impaired venous drainage characterized by dermal
neovascularization, and noted elevated MMP-1, 22, and 213 and
diminished TIMP-1 and 22 in the skin lesions. More recently, Xu
et al40 showed that specific polymorphisms in the MMP-9 and TIMP2 genes potentially put patients at a higher risk for developing
varicose veins. Deatrick et al35 examined vein remodeling and
associated gene expressions, but did not correlate results with the
In this review, we examined different candidate genes and their
polymorphisms (mostly SNPs) that have been linked to various
forms of CVD.
In assessing these studies, a few candidate genes should be
highlighted as having the strongest link to the development of CVD
(because we could not perform a meta-analysis, these assessments
are qualitative and based on the available evidence). Three studies
agree that SNPs in FOXC2, a transcription factor involved in
lymphatic and vascular development, provide a strong link toward
venous varicosity, valve failure, and hemorrhoids. On the other hand,
a polymorphism in the HFE gene increases the risk of venous
ulceration by almost 7-fold, while also causing the known
dysregulation in iron absorption. The MMPs (and, to a lesser extent,
their inhibitors, TIMPs) are perhaps the best studied in venous
disease. MMPs are involved in ECM degradation and structural vein
wall changes, ultimately contributing to venous remodeling, dilation,
and valve dysfunction. They are thus heavily involved in the
pathogenesis of CVD. The exact mechanisms have yet to be
elucidated and further research is required in this area.
Although genetic markers in CVD have been examined in some
detail, there is a lack of evidence correlating these genes with the
development and severity of PTS. If these polymorphisms are
potentially associated with CVI, LDS, varicose veins, venous ulcers,
and DVT resolution, it is plausible that they could also provide an
underlying substrate for the development of PTS. The MMPs have
once again been implicated in this respect, but data are scarce and
further research is warranted.
In general, a limitation of all of the studies included in this review
relates to the fact that they were conducted either in animal models,
in very limited numbers of patients, or using surgical samples
(eg, saphenectomy). It is difficult to assess the quality of each study
because no standardized tools exist in this regard—in contrast to the
quality assessment scales used for clinical studies. We believe that
the included studies were methodologically sound; however, we
cannot totally rule out the possibility of biased results.
Clearly, the genetic predisposition to CVD, particularly PTS,
is controversial and unclear at best, and more studies are needed
to clarify these associations. Earlier studies have promoted the use
of a genome-wide approach; this allows for the identification of
previously unknown markers, and may be a consideration for the
future. Clinically, this would be a novel way to reexamine a patient’s
propensity toward developing CVD, predict those who go on to
From www.bloodjournal.org by guest on June 15, 2017. For personal use only.
BLOOD, 21 AUGUST 2014 x VOLUME 124, NUMBER 8
GENETIC POLYMORPHISMS IN CHRONIC VENOUS DISEASE
develop it, and provide a better understanding of the underlying
mechanisms to ultimately improve treatment options.
1249
Acknowledgments
The researching, writing, and editing were performed solely
by the authors and no other individuals or organizations were
involved.
Conclusions
Herein, we examine the role of various candidate genes and their
polymorphisms in the development of CVD, including the lesser
studied PTS. Our observations support a genetic predisposition to
CVD related to vein wall remodeling. Genes of significance include
FOXC2, HFE, and the MMPs, all of which show strong associations
with varicose veins, CVI, or venous ulceration. The data surrounding
PTS are more limited, but given that it is a type of CVD with similar
manifestations, we may infer that some of the above genes may be
implicated. Thus, further studies are needed to examine these
associations more directly. Most importantly, given the burden of
this disease worldwide and the paucity of treatment options currently
available, studying these polymorphisms could potentially allow us
to better identify patients at higher risk of developing CVD, and also
provide novel therapeutic targets.
Authorship
Contribution: A.L.L. and S.K. conceived the idea; V.B. and A.L.L.
performed the systematic review; V.B. wrote an initial draft of the
article; V.B., S.K., and A.L.L. reviewed and edited the manuscript;
and all authors reviewed and approved the final manuscript.
Conflict-of-interest disclosure: The authors declare no competing
financial interests.
Correspondence: Alejandro Lazo-Langner, Hematology Division, London Health Sciences Centre, 800 Commissioners
Rd E, Rm E6-216A, London, ON, N6A 5W9, Canada; e-mail:
[email protected].
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2014 124: 1242-1250
doi:10.1182/blood-2014-03-558478 originally published
online July 8, 2014
Genetic polymorphisms of vein wall remodeling in chronic venous
disease: a narrative and systematic review
Vighnesh Bharath, Susan R. Kahn and Alejandro Lazo-Langner
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