Update on Genetics and Molecular Biology

1. Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.
CURRENT
OPINION Update on genetics and molecular biology
Raul D. Santosa,b
and Ana P. Chacraa
Familial hypercholesterolemia is an autosomal
dominant monogenic disorder that overall affects
1/250 individuals in the general population and that
causes early myocardial infarction (MI) [1].
Genome-wide association studies (GWAS) can be
used to develop polygenic scores of common genetic
variants that confer cumulative impact on a given
disease development, and therefore, may help iden-
tify predisposed individuals. Khera et al. [2
&&
] using a
whole genome sequencing approach tested the asso-
ciation of either familial hypercholesterolemia var-
iants or of a previously developed polygenic score
with the presence of early MI (55 years old,
n ¼ 2018, mean age 48 years, 66% women, 75%
whites). Cases were compared with controls from
the Multiethnic Study on Atherosclerosis (MESA).
Familial hypercholesterolemia-causing variants
were encountered in 1.7% (n ¼ 36, all with LDLR
variants, LDL-cholesterol (LDL-C) at presentation
193 mg/dl, estimated untreated LDL-C 202 mg/dl
and only 47% undergoing statin therapy) of the
MI population vs. 0.6% of controls. A high poly-
genic score, defined as the top 5% of distribution on
the population, was encountered in 17% of cases vs.
5% of controls. Individuals with MI did not differ
from controls regarding classical risk factors for
atherosclerosis and had mean LDL-C of 132 mg/dl.
The presence of either was associated with a similar
3.7-fold greater odds of early MI. The authors con-
cluded that a high polygenic score can identify 5%
of the population with a similar cardiovascular
risk as of bearing familial hypercholesterolemia
and where classical risk factors otherwise could
have not identified those individuals. The study is
important and needs to be replicated in other
populations. However, in the majority of individu-
als with an early MI, genetic causes were not
defined. Regarding familial hypercholesterolemia,
the classical aphorism persists: ‘underdiagnosed
and undertreated disease’.
The advent of next generation sequencing
allowed a better characterization of variants associ-
ated with familial hypercholesterolemia. A recent
publication of the Clinical Genome Resource,
through the FH Variant Curation Expert Panel
and global FH community, shows that the number
of familial hypercholesterolemia-related variants
have increased 10-fold in comparison with the last
10 years [3
]. Of 2900 familial hypercholesterolemia-
associated variants, 57.9% were classified by sub-
mitters as pathogenic or likely pathogenic, 15.5 and
10.4% classified, respectively, as a variant of
unknown significance, and as benign or likely
benign. Most difficulties in classification came from
APOB and PCSK9 variants. Unfortunately, most var-
iants were not evaluated by functional tests and
approximately 15% of variants presented conflict-
ing classification by different sources. It is clear
from this study that either co-segregation or
functional tests are important for a better under-
standing molecular causes of familial hypercholes-
terolemia.
Bempedoic acid inhibits ATP-citrate lyase
(ACLY), an enzyme involved in cholesterol biosyn-
thesis in a step above the 3-hydroxy-3-methylglu-
taryl-coenzyme A reductase (HMGCR) in cholesterol
biosynthesis cascade [4]. Bemepdoic acid is being
developed specially as an alternative for patients
that do not tolerate statins. Recently a Mendelian
randomization study compared the impact of loss-
of-function variants of genetic scores of ACLY and
HMGCR on plasma lipids, atherosclerotic cardiovas-
cular disease (ASCVD) and cancer risk in 654 783
participants (16% with previous ASCVD events)
[5
]. For similar LDL-C reductions (10 mg/dl) either
ACLY or HMGCR scores were associated with life-
long reductions in ASCVD risk, respectively, 0.82
[95% confidence interval (CI) 0.78–0.87;
P ¼ 4.0 1014
] and 0.83 [95% CI 0.81–0.87;
P ¼ 3.9 1019
]. Neither scores were associated with
cancer. Of importance, no differences were seen on
ASCVD risk when compared with scores testing
PCSK9 and NPC1L1 (Niemann–Pick C1-like 1) var-
iants. This study suggests that bempedoic acid may
become an alternative for LDL-C lowering in the
future and that its impact will be proportional to
a
Heart Institute (InCor), University of São Paulo Medical School Hospital
and b
Hospital Israelita Albert Einstein, São Paulo, Brazil
Correspondence to Raul D. Santos, Heart Institute (InCor), University of
Sao Paulo Medical School, Sao Paulo, SP 05403-900, Brazil.
E-mail: rauldsf@gmail.com.
Curr Opin Lipidol 2019, 30:414–416
DOI:10.1097/MOL.0000000000000633
www.co-lipidology.com Volume 30 Number 5 October 2019
EDITORIAL COMMENT

2. Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.
LDL-C lowering not differing from the ones of
approved therapies like statins, ezetimibe or PCSK9
inhibitors. Mendelian randomization is called
nature’s randomization study and that one may
infer the impact of pharmacological treatments
from their results [6]. However, there are some
limitations, data needs to be replicated in different
populations with different genetic backgrounds,
and medications can present pleotropic effects
not totally measured by genes that regulate one
specific function. Actually, absence of pleiotrophins
is a sine qua non condition for a Mendelian random-
ization study. Therefore, the impact on ASCVD and
safety of bempedoic acid needs to be proven in a
properly designed clinical trial like the ongoing
CLEAR-OUTCOMES study (NCT02993406).
Triglyceride-rich lipoproteins (TGRL) have been
independently associated with ASCVD risk. How-
ever, its controversial if triglyceride reduction per se
will prevent cardiovascular events. The concentra-
tion of pro-atherogenic cholesterol-rich remnants of
partially lipolyzed chylomicrons and VLDL can be
estimated by concentrations of APOB. In a Mende-
lian randomization study, Ference et al. [7
] com-
pared the impact of triglyceride-lowering genetic
variants of the lipoprotein lipase LPL and of variants
that reduce LDL-C by acting on the LDL receptor
gene (LDLR). Approximately 655 000 individuals
from 63 cohort case–control studies (mean age,
62.7 years; 51.4% women) were included with
91 129 presenting coronary heart disease. The
impact of variants affecting either lipolysis or the
LDL receptor was measured per 10 mg/dl lowering in
APOB concentrations. For each 10-mg/dl lower level
of ApoB, the LPL score was associated with 69.9 mg/
dl (95% CI 68.1–71.6; P ¼ 7.1 101363
) lower tri-
glyceride levels and 0.7 mg/dl (95% CI 0.03–1.4;
P ¼ 0.04) higher LDL-C levels; whereas the LDLR
score was associated with 14.2 mg/dl (95% CI
13.6–14.8; P ¼ 1.4 10465
) lower LDL-C and
1.9 mg/dl (95% CI 0.1–3.9; P ¼ 0.04) lower triglycer-
ide levels. The LPL and LDLR scores were associated
with similar 23% smaller risks of coronary heart
disease per 10 mg/dl lower levels of APOB. After
multivariable analyses, the associations between tri-
glyceride and LDL-C levels with the risk of coronary
heart disease became null after adjusting for differ-
ences in APOB levels. The authors suggest that the
benefit of triglyceride-lowering therapies will
depend on the reduction of circulating APOB par-
ticles. Despite the elegance of this study, the results
contrast with recent evidence from REDUCE-IT
(Reduction of Cardiovascular Events with Icosapent
Ethyl–Intervention Trial) where no association was
seen between reduction in triglyceride or APOB
levels induced by 4 g day of icosapent ethyl (EPA)
and prevention of cardiovascular events. The study
included high ASCVD risk individuals with moder-
ated elevations of triglycerides undergoing statin
therapy [8
]. Fish oils and selective peroxisome pro-
liferator-activated receptor alpha modulators
(SPPARMa), like pemafibrate, that are being tested
in similar populations to the one from REDUCE-IT
have other possible antiatherosclerotic properties
beyond triglyceride and APOB lowering that may
not be detected in Mendelian randomization
studies [8
,9
].
Acknowledgements
R.D.S. is a recipient of a scholarship from the Conselho
Nacional de Pesquisa e Desenvolvimento Tecnologico
(CNPQ) process # 303734/2018–3.
Financial support and sponsorship
None.
Conflicts of interest
R.D.S. has received honoraria for consulting, speaker
activities and or research from: Astra Zeneca, Amgen,
Akcea, Biolab, Kowa, Esperion, Merck, MSD, Novo-Nor-
disk and Sanofi/Regeneron. A.P.C. – none to declare.
REFERENCES AND RECOMMENDED
READING
Papers of particular interest, published within the annual period of review, have
been highlighted as:
of special interest
of outstanding interest
1. Defesche JC, Gidding SS, Harada-Shiba M, et al. Familial hypercholester-
olaemia. Nat Rev Dis Primers 2017; 3:17093.
2.
Khera AV, Chaffin M, Zekavat SM, et al. Whole-genome sequncing to
characterize monogenic and polygenic contributions in patients hospita-
lized with early-onset myocardial infarction. Circulation 2019; 139:
1593–1602.
This study that enrolled a signficant number of patients with early myocardial
infarction suggests that a polygenic score of SNPs not related to LDL-C implicates
in a similar risk as familial hypercholesterolemia and in the latter, abnormalities are
more frequent than those of familial hypercholesterolemia.
3.
Iacocca MA, Chora JR, Carrie A, et al., ClinGen FH Variant Curation Expert
Panel. ClinVar database of global familial hypercholesterolemia-associated
DNA variants. Hum Mutat 2018; 39:1631–1640.
This study shows new information and limitations on the state of the art of genetic
deffects associated with familial hypercholesterolemia.
4. Ray KK, Bays HE, Catapano AL, et al., CLEAR Harmony Trial. Safety and
efficacy of bempedoic acid to reduce LDL cholesterol. New Engl J Med 2019;
380:1022–1032.
5.
Ference BA, Ray KK, Catapano AL, et al. Mendelian randomization study of
ACLY and cardiovascular disease. New Engl J Med 2019; 380:1033–1042.
This study suggests that loss of function variants of ACLY are associated with
lower LDL-C and cardiovascular events and no increment in cancer risk similarly to
what occurs with other genes that affect LDL-C levels.
6. Santos RD. Genetics and molecular biology controversies on Mendelian
randomization and proprotein convertase subtilisin-kexin type 9 inhibitor
clinical trials: more data still necessary. Curr Opin Lipidol 2017; 28:
522–523.
7.
Ference BA, Kastelein JJP, Ray KK, et al. Association of triglyceride-lowering
LPL variants and LDL-C-lowering LDLR variants with risk of coronary heart
disease. JAMA 2019; 321:364–373.
This robust Mendelian randomization study suggests that reduction in cardiovas-
cular risk attributed to variants that either affect the expression of the LDL receptor
or lipolysis of triglyceride-rich lipoproteins is mediated by the concentration of
apolipoprotein B containing lipoproteins.
Bimonthly update Update on genetics and molecular biology
0957-9672 Copyright ß 2019 Wolters Kluwer Health, Inc. All rights reserved. www.co-lipidology.com 415

3. Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.
8.
Bhatt DL, Steg PG, Miller M, et al. Cardiovascular risk reduction with
icosapent ethyl for hypertriglyceridemia. New Engl J Med 2019; 380:11–22.
Study showing that high-dose icosapent ethyl reduces cardiovascular risk.
9.
Fruchart JC, Santos RD, Aguilar-Salinas C, et al. The selective peroxisome
proliferator-activated receptor alpha modulator (SPPARMalpha) paradigm:
conceptual framework and therapeutic potential: a consensus statement from
the International Atherosclerosis Society (IAS) and the Residual Risk Reduc-
tion Initiative (R3i) Foundation. Cardiovasc Diabetol 2019; 18:71.
This review describes the differences between fibrates and SPPARM alpha
medications.
FURTHER RECOMMENDED READING
Benn M, Tybjaerg-Hansen A, Nordestgaard BG. Low LDL cholesterol by PCSK9
variation reduces cardiovascular mortality. J Am Coll Cardiol 2019;
73:3102–3114.
The study confirms previous associations of loss of function variants of PCSK9
with with reduction of cardiovascular disease; however, there was no association
with total mortality in a low cardiovascualr disease risk general population.
Dron JS, Wang J, Cao H, et al. Severe hypertriglyceridemia is primarily polygenic. J
Clin Lipidol 2019; 13:80–88.
Study evalauted genetic causes of severe hipertriglyceridemia in 563 individuals: 1.1%
of patients had biallelic (homozygous or compound heterozygous) rare variants, 14.4%
had heterozygous rare variants, 32% had a high polygenic riskof common variants, and
in 52.6%, no abnormalities were encountered. The study shows that familial chylomi-
cronemia syndrome is indeed a rare cause of severe hypertriglyceridemia.
Ellis KL, Perez de Isla L, Alonso R, et al. Value of measuring lipoprotein(a) during
cascade testing for familial hypercholesterolemia. J Am Coll Cardiol 2019;
73:1029–1039.
This study confirms previous association of familial hypercholesterolemia with
elevated Lp(a) and shows that cascade screening for high Lp(a) in familial
hypercholesterolemia patients will identify higher cardiovascular disease risk
individuals.
Peloso GM, Nomura A, Khera AV, et al. Rare protein-truncating variants in
APOB, lower low-density lipoprotein cholesterol, and protection
against coronary heart disease. Circ Genom Precis Med 2019;
12:e002376.
Study shows association of genetic APOB reduction and less risk of
coronary heart disease risk in 12 case–control studies; interestingly, three
Japanese adult homozygotes had no neurologic deficits or ophthalmologic
disease.
Bimonthly update Update on genetics and molecular biology
416 www.co-lipidology.com Volume 30 Number 5 October 2019