GBinsightADVANCED GENETIC TESTING

for Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is an autosomal co-dominant disease, with prevalence of heterozygous FH (HeFH) estimated to be ~1:220 revised from ~1:500 (1-3). Due to founder e�ects, the prevalence is higher in some populations, for example, Lebanon, South Africa and Quebec (4). The prevalence of homozygous FH (HoFH) has been revised to ~1 in 250,000 (5). The relative frequency of FH makes it the most common genetic disorder (6). Untreated FH can increase risk of premature coronary artery disease (CAD) by 20-fold (7,8). Most problematic is that 90% of people with FH are undiagnosed (9). This has led to guidelines published by The Familial Hypercholesterolemia Foundation and others supporting genetic testing for FH for the index patient and cascade screening of biological relatives (10,11).

Risk stra�fica�on

At any strata of LDL cholesterol levels, having a pathogenic FH variant (monogenic FH) confers signi�cantly higher risk of CAD (12). See �gure 1.

This is due to the duration of exposure to high cholesterol in the blood vessels, which is proportional to the risk of CAD.

People with monogenic FH have a greater CAD risk pro�le than people with polygenic FH (13).In general, genetic variants in the following genes confer greater CAD risk (in order of severity): LDLR>PCSK9>APOB (11). Even amongst missense LDLR variants, some variants confer a greater CAD risk pro�le than others. See �gure 2.

Ra�onale of gene�c tes�ng for FH

Figure 1. Impact of FH mutation status on coronary artery disease risk stratified by LDL-cholesterol levels.Adapted from: Khera, A. V. et al. Journal of the American College of Cardiology. 2016;67(22):2578-89

25

20

15

10

5

0Ref

2.2

<130 ≥130-160 ≥ 160-190 ≥190-220 ≥220

1.83.8

2.9

5.6 5.2

17

LDL CHOLESTEROL CATEGORY (mg/dl)

OD

DS

RA

TIO

FO

R C

OR

ON

AR

Y A

RTE

RY

DIS

EASE

7.7

25.8

Figure 2. Enhanced coronary heart disease risk stratification with GBinsight comprehensive genetic analysis

Homozygous LDLR nullHomozygous LDLR defectiveCompound heterozygous

Pathogenic variants

LDLRHeterozygous Homozygous

APOBPCSK9STAP1APOE

Polygenic (multiple LDL-C raising SNPs)

PATIENT WITH DYSLIPIDEMIA OR CHD

CAD Risk Additional Genetic BackgroundLDL-C (mg/dL)

Hypercholesterolemia Genetics

GBinsightCOMPREHENSIVE GENETIC TESTING

High Lp(a)

Reverse cholesterol transport defect

Combined hyperlipidemia

Hypertriglyceridemia

500-1000

130-500

130-200 Risk increasegeneticvariation

Protective genetic

variation

CASCADE SCREENING

LDLRAP1LIPAABCG5ABCG8

Confirma�onGenetic testing for the con�rmation of FH is the gold standard (14).Limitations to diagnosing FH using clinical criteria includes potential “masking” of hypercholesterolemia and CAD due to lipid-lowering therapies and unavailable or unreliable medical histories (11).

Treatment op�onsKnowing one’s FH genotype can inform treatment options.PCSK9 inhibitors are especially e�ective in people with gain-of-function PCSK9 genetic variants (15).PCKS9 inhibitors are not very e�ective in people with loss-of-function LDLR genetic variants (16,17).

Cascade screening90% of people with FH don’t know they have it.O�spring of an a�ected parent have a 50% chance of inheriting the FH variant.US and European public health agencies recommend genetic testing-based cascade screening for FH (18,19). Cascade screening for FH has been shown to be a cost-e�ective means of identifying new FH patients.

By identifying people with FH at an earlier age, treatment can be initiated at an earlier time point and reduce the duration of exposure to hypercholesterolemia (11).

Why use GBinsight for FH gene�c tes�ng screening?

There are many labs that o�er genetic testing for FH. Most of them analyze three core FH genes (LDLR, APOB and PCSK9) that account for the majority of known genetic causes. However, these three genes do not account for the entire spectrum of FH phenotypes, which has implications for risk strati�ca-tion and precision therapies. Autosomal recessive genetic variants in LDLRAP1, LIPA and ABCG5/8 cause an FH-like clinical phenotype. Polygenic FH, caused by the inheritance of a large burden of common, low-to-moderate impact genetic variants, likely explains the majority of FH cases where a pathogenic variant in one of the three prototypical genes is not identi�ed. Other possible causes for a FH-like phenotype in the absence of pathogenic FH mutations in the three genes include: elevated lipoprotein (a) (LP(a)) and autosomal dominant genetic variants in APOE or STAP1. The GBinsight Comprehensive Dyslipidemia Panel o�ers the most comprehensive genetic analysis for FH by sequencing and analyzing all of these paths to clinical FH phenotypes. GBinsight analyzes multiple pathways that work additively to determine CAD risk (see �gure 3).

Figure 3. Heterogeneity of pathways contributing to atherosclerotic cardiovascular disease (ASCVD) and a selection of genes covered by the GBinsight Comprehensive Dyslipidemia panel.

Hypercholesterolemia

ATHEROSCLEROTICCARDIOVASCULAR

DISEASE(ASCVD)

Lipoprotein remnant clearance defects

Hypertriglyceridemia

Obesity

Thrombosis

Chronic inflammation

Hyperhomocysteinemia

Reverse cholesterol transport defects

High LP(a)

ANGPTL3, ANGPTL4, APOA4, APOA5, APOB, APOC2, APOC3, APOE, CREB3L3,FADS1, FADS2, GCKR, GPIHBP1, LIPC, LIPI, LMF1, LPL, MTTP, MLXIPL, PNPLA3, PPARA, PPARD, PPARG, SREBF1, USF1, ZPR1

ABCA6, ABCA7, ABCG5/8, APOB, APOE, ASGR1,EPHX2, INSIG2, LIPA, LDLR, LDLRAP1, LRP6, PCSK9, SORT1-PSRC1-CELSR2, STAP1, TOMM40

ABCA1, APOA1, CETP, LCAT,LIPC, LIPG, SCARB1

BHMT, CBS, MTHFD1L,MTHFR, MTR, MTRR,PEMT, SHMT1

ADCY3, AGRP, CARTPT,CCKAR, DYRK1B, FTO, GHRL, GNPDA2, KSR2, LEP, LEPR, MC3R, MC4R, NR0B2, NTRK2, POMC, PPARA, PPARD, PPARGC1A, PPARGC1B, RIC3, SDC3, SH2B1, SIM1, TMEM18, TUB, UCP2, UCP3

LPA, APOE

APOE

Polygenic FH

Polygenic FH is found in ~30-40% of patients clinically diagnosed with FH (20,21).GBinsight computes a polygenic score for hypercholesterolemia that employs a weighted score of common and rare genetic variants (22).

These variants are located in coding and non-coding genomic regions.

LP(a)

Elevated LP(a) is an independent risk factor and likely causal factor for premature CAD and aortic valve stenosis.Elevated LP(a) may be a cause of clinical FH in people without a known pathogenic variant (11,23). Elevated LP(a) is largely (estimated around 90%) genetically determined by variants in the LPA and APOE loci (24,25).Elevated LP(a) levels confers a greater CAD risk in those with FH (11,26-28).

The European Atherosclerosis Society recommends screening for LP(a) in those with FH (29).

APOE

Genetic variants in APOE that reduce or completely prevent binding to remnant receptors cause type III hyperlipoproteinemia and premature CAD.Autosomal dominant genetic variants in APOE may clinically manifest similar to FH (30-32).GBinsight sequences and analyzes APOE as part of the comprehensive panel.

GBinsight

References

1. Benn M, Watts GF, Tybjærg-Hansen A, Nordestgaard BG. Corrigendum to “Familial Hypercholesterolemia in the Danish General Population: Prevalence, Coronary Artery Disease, and Cholesterol-Lowering Medication”. J Clin Endocrinol Metab 2014;99:4758–9.

2. Abul-Husn NS, Manickam K, Jones LK, et al. Genetic identi�cation of familial hypercholesterolemia within a single U.S. health care system. Science 2016;354.

3. Wald DS, Bestwick JP, Morris JK, et al. Child-parent familial hypercholesterolemia screening in primary care. N Engl J Med 2016;375:1628–37.

4. www.acc.org/latest-in-cardiology/articles/2015/07/17/08/23/variation-in-the-prevalence-of-familial-hypercholesterolemia-around-the-world accessed on 10/19/2018

5. European Atherosclerosis Society Consensus Panel on Familial Hypercholesterolaemia, Cuchel M, Bruckert E, Ginsberg HN, et al. Homozygous familial hypercholesterolaemia: new insights and guidance for clinicians to improve detection and clinical management. A position paper from the Consensus Panel on Familial Hypercholesterolaemia of the European Atherosclerosis Society. Eur Heart J. 2014 Aug 21;35(32):2146-57.

6. Goldstein JL, Hobbs HH, Brown MS. Familial Hypercholesterolemia. In: Eds Scriver CR, Sly WS, Childs B, et al. The Metabolic and Molecular Bases of Inherited Disease, 8th ed. New York: McGraw-Hill Professional; 2000: 2863–22913.

7. Goldstein J, Brown M. Familial Hypercholesterolaemia In: Scriver C, Beudet A, Sly W, Valle D, eds. The Metabolic Basis of Inherited Disease. New York: McGraw Hill; 1995:1215-45.

8. Williams R, Hamilton-Craig I, Kostner G. MEDPED: An Integrated Genetic Strategy for Preventing Early Deaths. In: Berg K, Boulyjenkov V, Christen Y, eds. Genetic Approaches to Noncommunicable Diseases. Berlin: Springer Verlag; 1996:35-46.

9. Nordestgaard BG, Benn M. Genetic testing for familial hypercholesterolaemia is essential in individuals with high LDL cholesterol: who does it in the world? Eur Heart J 2017;38:1580–3.

10. Migliara G, Baccolini V, Rosso A, et al. Familial Hypercholesterolemia: A Systematic Review of Guidelines on Genetic Testing and Patient Management. Front Public Health. 2017;5:252.

11. Sturm AC, Knowles JW, Gidding SS, et al. Clinical Genetic Testing for Familial Hypercholesterolemia: JACC Scienti�c Expert Panel. J Am Coll Cardiol. 2018 Aug 7;72(6):662-680.

12. Khera AV, Won HH, Peloso GM, et al. Diagnostic Yield and Clinical Utility of Sequencing Familial Hypercholesterolemia Genes in Patients With Severe Hypercholesterolemia. J Am Coll Cardiol. 2016 Jun 7;67(22):2578-89.

13. Shari� M, Higginson E, Bos S, et al. Greater preclinical atherosclerosis in treated monogenic familial hypercholesterolemia vs. polygenic hypercholesterolemia. Atherosclerosis 2017;263:405–11.

14. Humphries SE, Norbury G, Leigh S, et al. What is the clinical utility of DNA testing in patients with familial hypercholesterolaemia? Curr Opin Lipidol 2008;19: 362–8.

15. Hopkins PN, Defesche J, Fouchier SW, et al. Characterization of autosomal dominant hypercholesterolemia caused by PCSK9 gain of function mutations and its speci�c treatment with alirocumab, a PCSK9 monoclonal antibody. Circ Cardiovasc Genet 2015;8:823–31.

16. International Atherosclerosis Society Severe Familial Hypercholesterolemia Panel. Santos RD, Gidding SS, Hegele RA, et al. De�ning severe familial hypercholesterolaemia and the implications for clinical management: a consensus statement from the International Atherosclerosis Society Severe Familial Hypercholesterolemia Panel. Lancet Diabetes Endocrinol. 2016 Oct;4(10):850-61.

17. Orringer CE, Jacobson TA, Saseen JJ, et al. Update on the use of PCSK9 inhibitors in adults: Recommendations from an Expert Panel of the National Lipid Association. J Clin Lipidol. 2017 Jul - Aug;11(4):880-890.

18. www.cdc.gov/genomics/implementation/toolkit/fh_1.htm

19. www.ncbi.nlm.nih.gov/books/NBK11822/

20. Talmud PJ, Shah S, Whittall R, et al. Use of low-density lipoprotein cholesterol gene score to distinguish patients with polygenic and monogenic familial hypercholesterolaemia: a case-control study. Lancet 2013;381:1293–301.

21. Futema M, Shah S, Cooper JA, et al. Re�nement of variant selection for the LDL cholesterol genetic risk score in the diagnosis of the polygenic form of clinical familial hypercholesterolemia and replication in samples from 6 countries. Clin Chem 2015;61:231–8.

22. Teslovich TM, Musunuru K, Smith AV, et al. Biological, clinical and population relevance of 95 loci for blood lipids. Nature 2010;466:707–13.

23. Langsted A, Kamstrup PR, Benn M, et al. High lipoprotein(a) as a possible cause of clinical familial hypercholesterolaemia: a prospective cohort study. Lancet Diabetes Endocrinol. 2016 Jul;4(7):577-87.

24. Schmidt K, Noureen A, Kronenberg F, Utermann G. Structure, function, and genetics of lipoprotein (a). J Lipid Res. 2016;57(8):1339-59.

25. Moriarty PM, Varvel SA, Gordts PL, et al. Lipoprotein(a) Mass Levels Increase Signi�cantly According to APOE Genotype: An Analysis of 431 239 Patients. Arterioscler Thromb Vasc Biol. 2017 Mar;37(3):580-588.

26. Seed M, Hoppichler F, Reaveley D, et al. Relation of serum lipoprotein(a) concentration and apolipoprotein(a) phenotype to coronary heart disease in patients with familial hypercholesterolemia. N Engl J Med. 1990 May 24;322(21):1494-9.

27. Allard MD, Saeedi R, Youse� M, Frohlich J. Risk strati�cation of patients with familial hypercholesterolemia in a multi-ethnic cohort. Lipids Health Dis. 2014;13:65.

28. Holmes DT, Schick BA, Humphries KH, Frohlich J. Lipoprotein(a) is an independent risk factor for cardiovascular disease in heterozygous familial hypercholesterolemia. Clin Chem. 2005 Nov;51(11):2067-73.

29. European Atherosclerosis Society Consensus Panel, Nordestgaard BG, Chapman MJ, Ray K, et al. Lipoprotein(a) as a cardiovascular risk factor: current status. Eur Heart J. 2010 Dec;31(23):2844-53.

30. Awan Z, Choi HY, Stitziel N, et al. APOE p.Leu167del mutation in familial hypercholesterolemia. Atherosclerosis. 2013 Dec;231(2):218-22.

31. Wintjens R, Bozon D, Belabbas K, et al. Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France. J Lipid Res. 2016;57(3):482-91.

32. Calandra S, Tarugi P, Bertolini S. Impact of rare variants in autosomal dominant hypercholesterolemia causing genes. Curr Opin Lipidol. 2017 Jun;28(3):267-272.

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