Nonconventional Genetic Risk Factors for CVD Tymchuk et al. 185
Figure 1. Steps in the progression of atherosclerosis in the artery wall. I, Low-density lipoprotein (LDL) particles accumulate in the
subendothelial cell layer and become trapped within matrix proteins, where they are oxidized (oxLDL) by cell-derived reactive oxygen
species. II, Chemotactic and growth factors stimulate monocytes to transmigrate across the endothelial cell layer and differentiate into
macrophages. Macrophages begin to engulf the oxLDL, leading to foam cell formation. III, The foam cells produce a variety of mediators
and eventually undergo apoptosis or necrosis, contributing their contents to a growing core of cellular debris and cholesterol. This
process is accompanied by the migration of smooth muscle cells into the intima from the media and the formation of a ﬁbrotic cap.
IV, As the advanced lesion continues to grow, it becomes increasingly unstable and prone to rupture, which can result in a thrombus
or clinical event such as myocardial infarction or stroke.
uting to atherosclerosis, lipoprotein levels, body fat, Family-based Linkage Studies
and other risk factors [3••]. Another level of complex- Since the year 2000, over 10 genome-wide linkage scans
ity involves the interactions between genes themselves have been carried out in families to identify chromosomal
and with environmental factors. Thus, common forms regions segregating with CVD-related traits. Numerous
of CVD result from the interplay between susceptibility loci have been reported, some of which exhibit coincident
genes and lifestyle. linkage with conventional risk factors such as high-den-
Although the role of conventional risk factors in sity lipoprotein (HDL) levels or metabolic syndrome
CVD is generally accepted, it is also likely that there traits. We have summarized these results in Table 1 but
are genetic contributions to CVD that are independent have restricted our discussion to emphasize recent studies
of known risk factors. For example, certain individu- that have identiﬁed loci with major genetic effects and/or
als develop premature heart disease but do not exhibit those not exhibiting coincident linkage with known risk
high cholesterol or hypertension. This may, in part, be factors. Presumably, these regions harbor susceptibility
due to genetic inﬂuences that act at the level of vessel genes that could reﬂect novel pathways for CVD.
wall metabolism, which leads to variations in cellular In the past 2 years, two important genome-wide link-
function or inﬂammatory responses among individu- age analyses for MI and/or CAD have been published.
als. As discussed in the following text, several recent The ﬁrst was by Wang et al. [3••] who studied 428 white
studies support this concept and emphasize the need families in the United States with at least two members
for identifying new genes and pathways for CVD. For affected by premature CAD or MI before the age of 45
the purposes of this review, we refer to CVD as a broad years in men and 55 years in women. Of note, this study
spectrum of disease states including MI, coronary artery used more restrictive criteria for ascertaining families by
disease (CAD), stroke, and surrogate markers of athero- excluding patients with hypercholesterolemia, diabetes,
sclerosis such as carotid intima-media thickness (IMT) or childhood hypertension, and, therefore, speciﬁcally
and coronary artery calciﬁcation (CAC). selected for genetic forms of MI and CAD that are not
Table 1. Chromosomal regions identiﬁed for cardiovascular disease traits that do not exhibit
coincident linkage with conventional risk factors
Study population Chromosomal
(ethnicity) Ascertainment scheme Sample size (n) region (gene) Study
Finnish (white) Angiographically proven 156 families (n = 364) 2q21.1-22; Pajukanta et al. 
premature CAD in proband Xq23-26
German (white) MI or premature CAD before 513 families (n = 1406) 14q32.2 Broeckel et al. 
age of 60 y in proband
Australian MI or unstable angina before 61 sibpairs (n = 122) 2q36-37.3 Harrap et al. 
(not reported) age of 70 y in proband
United States (white) Premature CAD in 2 or 428 families (n = 1163) 1p34-36 Wang et al. [3••]
more family members
United States, British, Premature CAD in proband 438 families (n = 1168) 5q31 Hauser et al. 
Welsh, Swiss, and and 2 siblings
United States (white) Family displaying autosomal 1 family (n = 21) 15q26 Wang et al. 
dominant inheritance of CAD (MEF2A)
US Framingham Prospective cohort study; 311 families (n = 1225) 12q24.3 Fox et al. 
Heart Study (white) linkage analysis with carotid IMT
United States CAD in proband; linkage 91 families (n = 413) 2q35 Wang et al. 
(Mexican-American) analysis with carotid IMT
United States (white) 2 or more siblings with 29 sibships (n = 94) 6p21.3; Lange et al. 
hypertension before age of 60 y; 10q21.3
linkage analysis with CAC
Icelandic (white) Stroke or transient ischemic 179 families (n = 914) 5q13 Gretarsdottir et al. 
attack in proband (PDE4D)
Icelandic (white) MI before age of 75 y in proband 296 families (n = 2454) 13q12-13 Helgadottir et al. [43•]
CAC—coronary artery calciﬁcation; CAD—coronary artery disease; IMT—intima-media thickness; MI—myocardial infarction.
associated with known risk factors. A locus for MI was least one member of a nuclear family. Although several
identiﬁed on chromosome 1p34-36 with a remarkably linked chromosomal regions were identiﬁed in the entire
high logarithm of the odds (LOD) score of 11.7. Such a dataset as well as the stratiﬁed subsets, most of the loci
level of signiﬁcance is very rarely observed for complex overlapped with regions where lipid and metabolic traits
diseases and is more typical of linkage results for single had previously been mapped. However, one locus on
gene disorders. This may be due, in part, to the stringent the distal arm of chromosome 5 exhibited nominal evi-
MI phenotype under study and the exclusion of poten- dence for linkage to CAD (LOD = 1.4), which was derived
tially confounding covariates. Interestingly, no signiﬁcant predominantly from the families excluded for diabetes.
results were obtained for CAD, suggesting that CAD Similar to the results described here previously, this locus
and MI do not necessarily share the same genetic deter- may represent a gene contributing to CVD independent
minants. Connexin 37 (CX37), a potential candidate of known risk factors.
gene that resides in the region, is a gap junction protein As is true for other complex diseases, understanding
expressed in arterial endothelium and has previously mendelian forms of CVD can be a powerful approach for
been associated with MI in a Japanese population . It identifying novel susceptibility genes. Recently, Wang et al.
remains to be determined whether this is the causal gene  conducted a genome scan of a single family with an
for MI in these families. autosomal dominant pattern of CVD consisting of 13
The second genome-wide linkage study was under- individuals affected by CAD or MI. A putative locus was
taken by Hauser et al.  and studied 438 white families mapped to chromosome 15q26 with a signiﬁcant LOD
from the United States and Europe in which at least two score of 4.2 . This region contained 93 genes, including
siblings were affected by premature CAD. The authors the myocyte enhancing factor 2A gene (MEF2A), which
further deﬁned three additional phenotypic stratiﬁca- was evaluated as a possible candidate given its role in vas-
tions of the families, including 1) MI or unstable angina culogenesis. All 10 living affected members of this family
in two or more siblings; 2) the absence of diabetes in were found to carry an in-frame deletion of seven amino
any affected family member; and 3) dyslipidemia in at acids. Functional analysis demonstrated that the mutation
Nonconventional Genetic Risk Factors for CVD Tymchuk et al. 187
acts in a dominant negative fashion and disrupts local- is not entirely clear how PDE4D is involved in stroke,
ization of MEF2A to the nucleus. Although the molecular the enzyme degrades cyclic adenosine monophosphate,
mechanism for increased susceptibility to CAD/MI is and its expression was found to be lower in affected
unknown, the authors speculate that abnormal MEF2A individuals who carried the at-risk alleles compared
activity affects endothelial cell function, rendering the with control subjects.
coronary vessels more susceptible to inﬂammation and In total, genome scans in multiple study popula-
thrombosis . In addition, screening of 207 indepen- tions have mapped over 10 loci for CVD traits. With few
dent CAD/MI cases for mutations in the MEF2A gene by exceptions, there is minimal overlap between these loci,
the same group identiﬁed three rare amino acid substitu- which could be due to differences in the populations,
tions whereas none were identiﬁed in control subjects . the phenotypes measured, or the statistical methods
The signiﬁcance of these ﬁndings has come under debate used for analysis. For example, although MI and CAD
recently from a study by another group that screened for are correlated, these phenotypes could represent distinct
the MEF2A gene in 300 individuals with premature CAD pathophysiologic processes that are controlled by differ-
and 300 elderly control subjects and identiﬁed only one ent genetic factors. Moreover, although these loci do not
amino acid substitution unique to cases . Moreover, exhibit linkage with known risk factors, it is still possible
this latter study did not observe co-segregation of the 7 that the causative genes in these regions could be related
amino acid deletion with CAD/MI in one family where to pathways involving lipid metabolism, blood pressure,
the proband was a carrier of the mutation . Thus, the or obesity. Nonetheless, identiﬁcation of the genes could
contribution of MEF2A mutations to CAD and MI still also provide novel genetic mechanisms leading to CVD.
remains to be conclusively determined.
In addition to MI and CAD, genome scans have also
been conducted for other CVD-related traits such as Candidate Gene and Whole Genome
stroke, CAC, and carotid artery IMT. Carotid IMT is a Association Studies
measure of subclinical atherosclerosis and predictive of Although family-based linkage studies have identiﬁed
subsequent MI and stroke. Two genome-wide linkage numerous loci for CVD and other related traits, the
analyses of carotid IMT have been published, including identity of the underlying genes, with rare exception,
a study by Fox et al.  who found signiﬁcant linkage has remained elusive. Another approach for identifying
of IMT to a locus on chromosome 12 using 311 families genes for CVD has been to conduct association studies
of the Framingham Heart Study Offspring cohort. The with candidate genes or, more recently, through a whole
other genome scan was conducted in 91 Mexican-American genome analysis. Association studies in general provide
families ascertained through a proband with CAD and greater statistical power than linkage analyses for detect-
revealed linkage to chromosome 2q35 . CAC is ing genetic effects, and dozens of studies have examined a
another marker of atherosclerosis that can be measured variety of candidate genes for association with CVD traits.
noninvasively using electron beam computed tomog- Most of these have focused on genes involved in lipid,
raphy. In a genome-wide linkage analysis involving 29 blood pressure, or obesity-related pathways. By compari-
sibships with two or more siblings affected by hyperten- son, fewer studies have examined genes involved in other
sion, Lange et al.  demonstrated signiﬁcant linkage of processes traditionally not considered to be risk factors.
CAC to two regions on chromosomes 6p21 and 10q21. Studies in the past few years, however, have reported
Similar to the results obtained with more formal measures and conﬁrmed genes that are part of pathways, such as
of CVD, these latter loci also lacked coincident linkage inﬂammation, endothelial cell function, and plaque sta-
with known risk factors. Interestingly, the chromosome bility that are associated with CVD traits. Although not
10 locus for CAC contains the 5-lipoxygenase (5-LO) an exhaustive list, several genes and pathways for which
gene, which as discussed in more detail in the following there is consistent evidence of association with CVD are
text, has recently been associated with atherosclerosis in highlighted in Table 2 and discussed here.
mice and humans.
Strokes can be caused by hemorrhage of an intra- Inﬂammatory processes
cranial blood vessel, occlusion of large or small arteries Using a whole-genome association study design, Ozaki
in the brain, or emboli of cardiac origin as a result of et al. [14••] reported association of the lymphotoxin
atherosclerosis. A genome-wide linkage analysis of 179 alpha LTA gene (LTA) with MI in a Japanese population.
Icelandic families with one affected member mapped a Speciﬁcally, the frequencies of an intronic SNP and an
major locus for stroke on chromosome 5q12 . In a amino acid–altering substitution were signiﬁcantly
follow-up study, the same group further examined this higher in cases compared with control subjects, even
region using ﬁne mapping and a case-control dataset and after adjustment for diabetes, hypertension, and hyper-
obtained evidence for association of stroke with haplo- lipidemia. Both SNPs occur on the same haplotype and
types of single nucleotide polymorphisms (SNPs) in the individually result in either increased expression of LTA
phosphodiesterase 4D (PDE4D) gene . Although it or its activity. Given its role as a cytokine, these results
Table 2. Nonconventional risk factor genes with consistent evidence of association with
cardiovascular disease traits
Gene Type of study (phenotype) Potential mechanism
Myocyte enhancer factor 2A (MEF2A) Family-based, case-control (MI, CAD) Vascular endothelium function (?)
Phosphodiesterase 4D (PDE4D) Family-based, case-control (stroke) cAMP degradation,
cell proliferation (?)
Lymphotoxin alpha (LTA) Case-control, cohort study Inﬂammatory response
(MI, coronary atherosclerosis)
Galectin 2 (LGALS2) Case-control (MI) Regulation of LTA secretion
and inﬂammatory response
Toll-like receptor 4 (TLR4) Cohort study, case-control Receptor signaling
(carotid IMT, MI) and innate immunity
Thrombospondin gene family Case-control (MI) Endothelial cell function
Connexin 37 (CX37) Case-control (CAD, MI) Endothelial cell function
Matrix metalloproteinase gene family (MMP) Case-control, cohort study (coronary Proteolysis and plaque rupture
artery aneurysm, MI, carotid IMT)
Arachidonate 5-lipoxygenase (ALOX5) Cohort study (carotid IMT) LT biosynthesis and
Arachidonate 5-lipoxygenase activating protein Family-based, case-control LT biosynthesis and
(ALOX5AP) (MI and stroke) inﬂammatory response
Leukotriene A4 hydrolase (LTA4H) Case-control (MI and CAD) LTB 4 synthesis and
CAD—coronary artery disease; IMT—intima-media thickness; LT—leukotriene; MI—myocardial infarction.
provide a functional mechanism by which common such as MI [21–23]. Taken together, these studies provide
SNPs of the LTA gene in the human population could convincing evidence for the genetic contribution of the
lead to increased inﬂammation in the artery wall, and LTA and TLR4 genes to CVD and are consistent with the
subsequently MI. Other studies have replicated the hypothesis that immune responses are an important part
association of LTA with CVD traits, including another of atherogenesis.
Japanese population [15–17]. Interestingly, the effect
of LTA was not observed in a third Japanese popula- Vascular endothelium function
tion . Such discrepancies are commonly observed As described previously, endothelial cells can play
in the genetics of complex diseases and demonstrate the an important part in the atherogenic process. Recent
difﬁculties in carrying out these studies. More recently, studies support this concept and suggest that variation
the same investigators who ﬁrst identiﬁed LTA used an in endothelial cell function can be under genetic con-
Escherichia coli two-hybrid system to identify galectin 2 as trol. For example, Topol et al.  carried out a large
a protein that interacts with LTA and potentially regulates case-control study with 62 vascular biology candidate
its secretion from macrophages and smooth muscle cells. genes and obtained the strongest evidence of asso-
In a case-control analysis, the T allele of an intronic SNP ciation of familial premature CAD or MI with three
(C3279T) in the LGALS2 gene was shown to occur at higher members of the thrombospondin (THBS) gene family
frequency in the control group, and thus was protective (THBS-1, THBS-2, and THBS-4). The association between
against MI. Additionally, the T allele had 50% decreased THBS-2 and THBS-4 variants with CAD/MI has since
transcriptional activity in vitro, which would presumably been replicated in several studies [25,26]. Interest-
lead to less LTA secretion and inﬂammation [19•]. ingly, variation in the THBS-2 gene confers protection
Another immune response gene recently associated against CVD whereas SNPs in the THBS-1 and THBS-4
with CVD is toll-like receptor 4 (TLR4). Using a cohort of genes lead to increased risk. Although the exact mech-
810 individuals, Kiechl et al. [20•] demonstrated that car- anism by which the THBS proteins modulate artery
riers of an Asp299Gly substitution in TLR4 had decreased wall metabolism remains to be elucidated, there is
carotid atherosclerosis and plasma biomarkers of inﬂam- functional evidence to suggest that they are involved
mation but they were more susceptible to severe bacterial in endothelial cell function .
infections. Similarly, other investigators have replicated Given the role of CX37 as a gap junction protein
these results with more clinically relevant phenotypes involved in the growth, regeneration after injury, and
Nonconventional Genetic Risk Factors for CVD Tymchuk et al. 189
aging of endothelial cells, several association studies have A Combined Approach Identiﬁes a Novel
examined the CX37 gene in humans. In a large Japanese Pathway for Cardiovascular Disease
case-control study with 112 SNPs in 71 candidate genes, With our ability to perform ﬁne mapping, the power
a C1019T substitution in CX37 was one of only three vari- to map their genes for complex traits, and our ability
ants associated with MI. This association has also been to genetically manipulate their genome, mice provide
observed in an Italian population from Sicily , but a number of advantages for gene discovery. In this
the mechanism by which this variant alters CX37 func- regard, numerous knockout and transgenic mice have
tional is still unknown. been generated with varying effects on atherosclerosis
. Although common forms of CVD in humans are
Plaque instability and rupture not due to the complete inactivation of a single gene,
Plaque instability and rupture is very important from a the ability to genetically modify genes in mice, either
clinical standpoint because it can lead to MI or stroke. through overexpression or inactivation, has provided an
The matrix metalloproteinases (MMPs) are a family invaluable tool for undertaking experiments that would
of over 25 enzymes that degrade extracellular matrix simply not be feasible or ethical in humans. In addition,
proteins such as collagen, elastin, and proteoglycans. linkage mapping studies in mice have identiﬁed over 20
Several of these enzymes, such as MMP-1, are expressed unique loci for atherosclerosis, a subset of which show
in the vulnerable shoulder regions of atherosclerotic conserved synteny with regions of the human genome
lesions where they could contribute to plaque rupture. where CVD traits have also been mapped [34,35].
Accordingly, the genes for these enzymes have also been Importantly, many of the loci identiﬁed in mice do
examined in association studies . In particular, poly- not exhibit linkage with traits such as lipid levels and
morphisms of the MMP-1, MMP-3, and MMP-9 genes have metabolic phenotypes, which is consistent with the
shown associations across several studies with various observations in humans. This further supports the exis-
CVD traits, including coronary artery aneurysms and MI tence of genetic factors that may act at the cellular level,
[29–31]. Interestingly, certain variants of the MMP-1 and perhaps inﬂuencing the function of vascular endothe-
MMP-3 genes increase transcription of the enzymes but lium or leukocytes that inﬁltrate the vessel wall. Thus,
are associated with smaller lesions. A plausible explana- it is possible that the genes segregating with atheroscle-
tion for this apparent paradox is that these alleles lead to rosis in mouse crosses represent unknown pathways for
less extracellular matrix accumulation and thus, smaller atherosclerosis that can be examined in human popula-
plaques, but these plaques are more prone to rupture. tions once the genes have been identiﬁed in mice.
Although other MMPs have also been investigated in Recent studies have elegantly illustrated this com-
genetic studies, the evidence for their contribution is not bined approach and led to the identiﬁcation of a novel
as consistent. Nonetheless, the results are in agreement pathway for CVD with important therapeutic implica-
with the notion that genetic-mediated increased proteolysis tions. Initially, an atherosclerosis-susceptibility locus,
in the arterial wall may act as a susceptibility factor for Artles, was mapped in an F2 intercross between two
CVD, and MI in particular. inbred mouse strains, C57BL/6 and CAST/Ei, and sub-
Based on the association studies, there is convincing sequently conﬁrmed in a congenic strain . Among
evidence for genetic factors that affect atherosclerosis the candidate genes in the linkage interval was the gene
development at the level of the artery wall. As a recent encoding 5-LO (Alox5), the rate-limiting enzyme in the
study suggests, CVD can also be associated with com- production of leukotrienes (LTs), which are a class of
pletely novel mechanisms for which a pathophysiologic inﬂammatory molecules derived from arachidonic acid.
link is unclear or not obvious. In a gene-centric genome 5-LO is expressed primarily in leukocytes and has been
association study, Shiffman et al.  demonstrated that studied mainly in the context of acute, not chronic,
four genes encoding a cytoskeletal protein, a receptor inﬂammation, particularly that associated with asthma
tyrosine kinase, and two G protein–coupled receptors are . Two types of LTs are generated through the 5-LO
associated with MI. These genes would most likely never pathway. The ﬁrst, LTB 4, is generated from LTA4 through
have been selected in candidate gene studies and dem- the enzyme LTA4 hydrolase (LTA4H). Alternatively, LTA4
onstrate the importance of unbiased study designs, such can be shunted into the cysteinyl branch and converted
as whole genome association, to identify genes. Numerous to LTC 4. Although LTB 4 is predominantly involved in
other genes have also been examined but the initial results monocyte chemotaxis and inﬂammatory signaling, the
are very often not replicated in subsequent studies. These cysteinyl LTs promote bronchoconstriction and smooth
discrepancies can be attributed to confounding factors muscle cell contraction.
such as genetic heterogeneity, population stratiﬁcation, To evaluate 5-LO as a positional candidate gene,
the extent of linkage disequilibrium, and varying statisti- Mehrabian et al.  crossed 5-LO knockout mice onto
cal methodologies. Such difﬁculties inherent in human a genetically hyperlipidemic background and observed
studies underscore the need for appropriately designed a profound reduction in aortic lesion formation despite
and sufﬁciently powered studies. cholesterol levels in excess of 500 mg/dL. These studies
were among the ﬁrst to demonstrate the importance of asthma previously led to the development of drugs targeting
5-LO in atherosclerosis. Other studies with 5-LO–deﬁ- different parts of the pathway, such as zileuton, montelukast,
cient mice have suggested the involvement of 5-LO in and zaﬁrlukast. This raises the exciting possibility of admin-
atherosclerosis-related phenotypes as well , and most istering existing drugs, or newly developed ones, to target
recently, 5-LO has been implicated in metabolic traits, the 5-LO pathway for heart disease patients. Indeed, a recent
such as adiposity and bone density . Furthermore, report has demonstrated the efﬁcacy of an ALOX5AP inhibi-
deﬁciency of the LTB 4 receptors (BLTR-1 and BLTR-2) or tor for reducing inﬂammatory biomarkers associated with
their pharmacologic antagonism reduces lipid accumula- atherosclerosis [47••]. Even though the therapeutic appli-
tion and monocyte inﬁltration into the artery wall, and, cations of the 5-LO studies can be considered somewhat
consequently, aortic lesion formation [40,41]. serendipitous, these studies illustrate how identiﬁcation
By extending these ﬁndings to genetic studies in of nonconventional genetic factors for CVD can lead to
humans, an important role for 5-LO pathway genes in potentially new strategies for pharmacologic intervention.
CVD has also been observed (Table 2). For example, in
a cohort study of healthy individuals, Dwyer et al. [42••]
reported that certain alleles of an ALOX5 promoter Conclusions
polymorphism, consisting of a variable number of Sp1 For the more common forms of CVD, a large number of
transcription factor binding sites, were associated with association studies with candidate genes have been per-
signiﬁcantly increased carotid IMT. This study also dem- formed but few have been convincingly conﬁrmed. Those
onstrated a gene-dietary interaction where the effect of that have been conﬁrmed explain only a very small fraction
the proatherogenic alleles was exacerbated in individuals of genetic susceptibility in humans. Over the past few years,
who consumed high levels of arachidonic acid, the sub- new evidence has emerged suggesting that genes that would
strate for 5-LO. However this effect was blunted in those otherwise not be considered good candidates based on their
individuals who consumed high levels of omega-3 fatty roles in pathways unrelated to known risk factors can play
acids, substrates that competitively bind to 5-LO and prevent an important role in the development of CVD as well. Given
the binding of arachidonic acid. the difﬁculty of dissecting complex traits in humans, mouse
In a subsequent study, Helgadottir et al. [43••] per- models can also become increasingly important in the iden-
formed a genome-wide linkage analysis of 296 Icelandic tiﬁcation of novel genes, as exempliﬁed by identiﬁcation of
families and reported linkage of MI to chromosome 13q12- the 5-LO pathway for CVD. Given the genetic complexity
13. Using ﬁne mapping to narrow the locus, a four-SNP of CVD, it is likely that there are important gene-gene inter-
haplotype of the 5-LO activating protein gene (ALOX5AP) actions, particularly between genes in the same pathway,
was found to occur at signiﬁcantly higher frequency in which have yet to be uncovered. The ability to explore such
MI and stroke cases compared with control subjects. hypotheses will require large sample sizes and more sophis-
Stimulated neutrophils from male MI cases carrying this ticated analytic methodology. Newly developed genomic,
“Icelandic” haplotype also produced higher levels of LTB4, statistical, and bioinformatics tools, such as the sequences
consistent with a proatherogenic role for this at-risk allele. of the mouse and human genomes, microarrays, and high-
In contrast, a different haplotype was associated with MI throughput genotyping technologies, should facilitate the
in patients from the United Kingdom, suggesting the exis- search for CVD genes and may lead to more effective diag-
tence of multiple susceptibility alleles in the population. nosis, risk assessment, and treatments.
Importantly, association of the ALOX5AP gene and CVD
has been observed in other cohorts as well, replicating the
initial results and lending further support for the role of Acknowledgments
the 5-LO pathway in CVD [44••,45••]. This work is supported by NIH grant HL079353 (H.A. and
Very recently, SNP variants of LTA4H have also been M.M), American Heart Association grant 0435223N (H.A.),
associated with MI in case-control cohorts from Iceland the Robert E. and Mary R. Wright Foundation (H.A.), and
and the United States [46••]. Interestingly, the increased the James H. Zumberge Innovation Fund (H.A.).
risk of MI in blacks was threefold higher than that in
whites, suggesting the existence of interactions with other
genes in individuals of African ancestry. Although this References and Recommended Reading
latter study implicates the LTB 4 branch of the pathway Papers of particular interest, published recently,
in atherogenesis, it is still not clear whether the cysteinyl have been highlighted as:
LTs are also involved. Thus, additional studies with the • Of importance
other 5-LO pathway genes will be required to genetically •• Of major importance
dissect the mechanism by which LTs contribute to CVD.
1. Lusis AJ: Atherosclerosis. Nature 2000, 407:233–241.
From a clinical standpoint, these ﬁndings may have a 2. Lusis AJ, Weinreb A, Drake TA, Allayee H: Genetics of Athero-
major impact on the development of novel treatments for sclerosis. In Textbook of Cardiovascular Disease. Edited by Topol
CVD. Knowledge that 5-LO and leukotrienes are involved in EJ. Philadelphia: Lippincott-Raven; 2002:Chapter 98.
Nonconventional Genetic Risk Factors for CVD Tymchuk et al. 191
3.•• Wang Q, Rao S, Shen GQ, et al.: Premature myocardial 20.• Kiechl S, Lorenz E, Reindl M, et al.: Toll-like receptor 4
infarction novel susceptibility locus on chromosome polymorphisms and atherogenesis. N Engl J Med 2002,
1P34-36 identiﬁed by genomewide linkage analysis. 347:185–192.
Am J Hum Genet 2004, 74:262–271. This study examined genetic variants of the TLR4 gene that had pre-
This genome scan study identiﬁed a highly signiﬁcant LOD score viously been shown to confer a diminished inﬂammatory response
for MI in a large set of families with premature CAD. The impor- to bacterial endotoxin in carriers. These authors found that the same
tance of this study was the exclusion of families with diabetes and SNPs were also protective against increased carotid atherosclerosis,
hyperlipidemia to enrich for forms of CAD that are not associated supporting the role of inﬂammation in atherogenesis.
with known risk factors. 21. Ameziane N, Beillat T, Verpillat P, et al.: Association of the
4. Yamada Y, Izawa H, Ichihara S, et al.: Prediction of the Toll-like receptor 4 gene Asp299Gly polymorphism with
risk of myocardial infarction from polymorphisms in acute coronary events. Arterioscler Thromb Vasc Biol 2003,
candidate genes. N Engl J Med 2002, 347:1916–1923. 23:e61–e64.
5. Hauser ER, Crossman DC, Granger CB, et al.: A genome- 22. Holloway JW, Yang IA, Ye S: Variation in the toll-like recep-
wide scan for early-onset coronary artery disease in 438 tor 4 gene and susceptibility to myocardial infarction.
families: the GENECARD Study. Am J Hum Genet 2004, Pharmacogenet Genom 2005, 15:15–21.
75:436–447. 23. Balistreri CR, Candore G, Colonna-Romano G, et al.: Role
6. Wang L, Fan C, Topol SE, et al.: Mutation of MEF2A in of Toll-like receptor 4 in acute myocardial infarction and
an inherited disorder with features of coronary artery longevity. JAMA 2004, 292:2339–2340.
disease. Science 2003, 302:1578–1581. 24. Topol EJ, McCarthy J, Gabriel S, et al.: Single nucleotide
7. Bhagavatula MR, Fan C, Shen GQ, et al.: Transcription polymorphisms in multiple novel thrombospondin genes
factor MEF2A mutations in patients with coronary artery may be associated with familial premature myocardial
disease. Hum Mol Genet 2004, 13:3181–3188. infarction. Circulation 2001, 104:2641–2644.
8. Weng L, Kavaslar N, Ustaszewska A, et al.: Lack of MEF2A 25. McCarthy JJ, Parker A, Salem R, et al.: Large scale association
mutations in coronary artery disease. J Clin Invest 2005, analysis for identiﬁcation of genes underlying premature
115:1016–1020. coronary heart disease: cumulative perspective from analy-
9. Fox CS, Cupples LA, Chazaro I, et al.: Genomewide link- sis of 111 candidate genes. J Med Genet 2004, 41:334–341.
age analysis for internal carotid artery intimal medial 26. Wessel J, Topol EJ, Ji M, et al.: Replication of the association
thickness: evidence for linkage to chromosome 12. between the thrombospondin-4 A387P polymorphism and
Am J Hum Genet 2004, 74:253–261. myocardial infarction. Am Heart J 2004, 147:905–909.
10. Wang D, Yang H, Quinones MJ, et al.: A genome-wide scan 27. Yamada Y, Ichihara S, Izawa H, et al.: Genetic risk for coro-
for carotid artery intima-media thickness: the Mexican- nary artery disease in individuals with or without type 2
American Coronary Artery Disease family study. Stroke diabetes. Mol Genet Metab 2004, 81:282–290.
2005, 36:540–545. 28. Listi F, Candore G, Lio D, et al.: Association between
11. Lange LA, Lange EM, Bielak LF, et al.: Autosomal genome- C1019T polymorphism of connexin37 and acute myocar-
wide scan for coronary artery calciﬁcation loci in sibships dial infarction: a study in patients from Sicily.
at high risk for hypertension. Arterioscler Thromb Vasc Biol Int J Cardiol 2005, 102:269–271.
2002, 22:418–423. 29. Newby AC, Johnson JL: Genetic strategies to elucidate the
12. Gretarsdottir S, Sveinbjornsdottir S, Jonsson HH, et al.: roles of matrix metalloproteinases in atherosclerotic plaque
Localization of a susceptibility gene for common forms growth and stability. Circ Res 2005, 97:958–960.
of stroke to 5q12. Am J Hum Genet 2002, 70:593–603. 30. Pollanen PJ, Lehtimaki T, Mikkelsson J, et al.: Matrix
13. Gretarsdottir S, Thorleifsson G, Reynisdottir ST, et al.: The metalloproteinase3 and 9 gene promoter polymorphisms:
gene encoding phosphodiesterase 4D confers risk of joint action of two loci as a risk factor for coronary artery
ischemic stroke. Nat Genet 2003, 35:131–138. complicated plaques. Atherosclerosis 2005, 180:73–78.
14.•• Ozaki K, Ohnishi Y, Iida A, et al.: Functional SNPs in 31. Pearce E, Tregouet DA, Samnegard A, et al.: Haplotype
the lymphotoxin-alpha gene that are associated with effect of the matrix metalloproteinase-1 gene on risk of
susceptibility to myocardial infarction. Nat Genet 2002, myocardial infarction. Circ Res 2005, 97:1070–1076.
32:650–654. 32. Shiffman D, Ellis SG, Rowland CM, et al.: Identiﬁcation of
This was one of the ﬁrst whole-genome association studies carried four gene variants associated with myocardial infarction.
out for complex diseases. The paper identiﬁes functional SNPs in Am J Hum Genet 2005, 77:596–605.
the lymphotoxin alpha (LTA) gene that increase the risk of MI. 33. Ohashi R, Mu H, Yao Q, Chen C: Cellular and molecular
15. Iwanaga Y, Ono K, Takagi S, et al.: Association analysis mechanisms of atherosclerosis with mouse models.
between polymorphisms of the lymphotoxin-alpha gene Trends Cardiovasc Med 2004, 14:187–190.
and myocardial infarction in a Japanese population. 34. Allayee H, Ghazalpour A, Lusis AJ: Using mice to dissect
Atherosclerosis 2004, 172:197–198. genetic factors in atherosclerosis. Arterioscler Thromb Vasc Biol
16. Laxton R, Pearce E, Kyriakou T, Ye S: Association of the 2003, 23:1501–1509.
lymphotoxin-alpha gene Thr26Asn polymorphism with 35. Wang X, Ishimori N, Korstanje R, et al.: Identifying novel
severity of coronary atherosclerosis. Genes Immunol 2005, genes for atherosclerosis through mouse-human compara-
6:539–541. tive genetics. Am J Hum Genet 2005, 77:1–15.
17. Szolnoki Z, Havasi V, Talian G, et al.: Lymphotoxin-alpha 36. Mehrabian M, Allayee H: 5-lipoxygenase and athero-
gene 252G allelic variant is a risk factor for large-ves- sclerosis. Curr Opin Lipidol 2003, 14:447–457.
sel-associated ischemic stroke. J Mol Neurosci 2005, 37. Mehrabian M, Allayee H, Wong J, et al.: Identiﬁcation of 5-
27:205–211. lipoxygenase as a major gene contributing to atherosclerosis
18. Yamada A, Ichihara S, Murase Y, et al.: Lack of association of susceptibility in mice. Circ Res 2002, 91:120–126.
polymorphisms of the lymphotoxin alpha gene with myo- 38. Zhao L, Moos MP, Grabner R, et al.: The 5-lipoxygenase
cardial infarction in Japanese. J Mol Med 2004, 82:477–483. pathway promotes pathogenesis of hyperlipidemia-
19.• Ozaki K, Inoue K, Sato H, et al.: Functional variation dependent aortic aneurysm. Nat Med 2004, 10:966–973.
in LGALS2 confers risk of myocardial infarction and 39. Mehrabian M, Allayee H, Stockton J, et al.: Integrating geno-
regulates lymphotoxin-alpha secretion in vitro. Nature typic and expression data in a segregating mouse population
2004, 429:72–75. to identify 5-lipoxygenase as a susceptibility gene for obesity
This paper identiﬁes galectin-2 as a protein that interacts with lym- and bone traits. Nat Genet 2005, 37:1224–1233.
photoxin alpha and regulates its secretion. A SNP in the galectin-2 40. Aiello RJ, Bourassa PA, Lindsey S, et al.: Leukotriene B4
gene (LGALS2) was also found to be associated with MI. receptor antagonism reduces monocytic foam cells in
mice. Arterioscler Thromb Vasc Biol 2002, 22:443–449.
41. Subbarao K, Jala VR, Mathis S, et al.: Role of leukotriene B4 46.•• Helgadottir A, Manolescu A, Helgason A, et al.: A variant
leceptors in the development of atherosclerosis: potential of the gene encoding leukotriene A4 hydrolase confers
mechanisms. Arterioscler Thromb Vasc Biol 2004, 24:369–375. ethnicity-speciﬁc risk of myocardial infarction. Nat
42.•• Dwyer JH, Allayee H, Dwyer KM, et al.: Arachidonate Genet 2005, In press.
5-lipoxygenase promoter genotype, dietary arachidonic This study builds on earlier mouse studies and identiﬁes polymor-
acid, and atherosclerosis. N Engl J Med 2004, 350:29–37. phisms in three 5-lipoxygenase pathway genes that are associated
This study builds on earlier mouse studies and identiﬁes polymor- with various CVD traits. A clinical trial further demonstrated that
phisms in three 5-lipoxygenase pathway genes that are associated a 5-LO pathway inhibitor decreases biomarkers of inﬂammation
with various CVD traits. A clinical trial further demonstrated that a that are associated with CVD.
5-LO pathway inhibitor decreases biomarkers of inﬂammation that 47.•• Hakonarson H, Thorvaldsson S, Helgadottir A, et al.:
are associated with CVD. Effects of a 5-lipoxygenase-activating protein inhibitor
43.•• Helgadottir A, Manolescu A, Thorleifsson G, et al.: The on biomarkers associated with risk of myocardial infarc-
gene encoding 5-lipoxygenase activating protein confers tion: a randomized trial. JAMA 2005, 293:2245–2256.
risk of myocardial infarction and stroke. Nat Genet 2004, This study builds on earlier mouse studies and identiﬁes polymor-
36:233–239. phisms in three 5-lipoxygenase pathway genes that are associated
This study builds on earlier mouse studies and identiﬁes polymor- with various CVD traits. A clinical trial further demonstrated that
phisms in three 5-lipoxygenase pathway genes that are associated a 5-LO pathway inhibitor decreases biomarkers of inﬂammation
with various CVD traits. A clinical trial further demonstrated that a that are associated with CVD.
5-LO pathway inhibitor decreases biomarkers of inﬂammation that 48. Pajukanta P, Cargill M, Viitanen L, et al.: Two loci on
are associated with CVD. chromosomes 2 and X for premature coronary heart
44.•• Lohmussaar E, Gschwendtner A, Mueller JC, et al.: ALOX5AP disease identiﬁed in early- and late-settlement popula-
gene and the PDE4D gene in a central European popula- tions of Finland. Am J Hum Genet 2000, 67:1481–1493.
tion of stroke patients. Stroke 2005, 36:731–736. 49. Broeckel U, Hengstenberg C, Mayer B, et al.: A comprehen-
This study builds on earlier mouse studies and identiﬁes polymor- sive linkage analysis for myocardial infarction and its
phisms in three 5-lipoxygenase pathway genes that are associated related risk factors. Nat Genet 2002, 30:210–214.
with various CVD traits. A clinical trial further demonstrated that a 50. Harrap SB, Zammit KS, Wong ZY, et al.: Genome-wide
5-LO pathway inhibitor decreases biomarkers of inﬂammation that linkage analysis of the acute coronary syndrome suggests
are associated with CVD. a locus on chromosome 2. Arterioscler Thromb Vasc Biol
45.•• Helgadottir A, Gretarsdottir S, St Clair D, et al.: Association 2002, 22:874–878.
between the gene encoding 5-lipoxygenase-activating
protein and stroke replicated in a Scottish population.
Am J Hum Genet 2005, 76:505–509.
This study builds on earlier mouse studies and identiﬁes polymor-
phisms in three 5-lipoxygenase pathway genes that are associated
with various CVD traits. A clinical trial further demonstrated that a
5-LO pathway inhibitor decreases biomarkers of inﬂammation that
are associated with CVD.