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Home , Abetalipoproteinemia, Combined hyperlipidemia, Hyperlipidemia, Hypoalphalipoproteinemia

Advanced and Genetic Disorders Alan S. Brown, MD, FACC, FNLA Core Curriculum Map for Masters Course Metabolism 5. Lipoprotein metabolism * • 5.1. Intestinal lipid transport and formation, secretion and catabolism * • 5.2. Hepatic lipid transport and VLDL formation, secretion and catabolism * • 5.3. LDL receptor expression, function and catabolism (PCSK9) * • 5.4. HDL synthesis, maturation, catabolism, role in peripheral / reverse transport and non-ASCVD effects * • 5.5. Cholesterol and metabolism * • 5.6. Microbiome • 5.7. Intrahepatic gene regulation via nuclear receptor factors * • 5.7.1. LXR • 5.7.2. FXR • 5.7.3. PPAR • 5.7.4. SREBP) Core Curriculum Map for Genetic

10. Genetic - Masters Course • 10.1. Physical findings

• 10.1.1.

• 10.1.2. (including non-hyperlipidemic causes)

• 10.1.3. Corneal arcus

• 10.1.4. Lipemia retinalis

• 10.1.5. “Test tube” appearance

• 10.2. Hypolipidemias *

• 10.2.1. syndromes (deficiencies in APOA1, apoA1milano, ABCA1 (Tangiers), ABCG1, LCAT (Fish Eye Disease)

• 10.2.2. (MTP deficiency)

• 10.2.3. Hypobetalipoproteinemias

• 10.2.4. PCSK9 loss of function

• 10.2.5. ANGTL 3 loss of function

• 10.3. Major lipid associated genes (GWAS studies) *

• 10.3.1. LDL - LDLR, APOB, PCSK9, APOB, HMGCR, NPC1L1, LDLRAP1, SORT1, ABCG5/ABCG8, CYP27A1

• 10.3.2. - APOCIII, APOCII, APOA5, LPL, ANGPTL4, ANGPTL3, LMF1, GPIHBP1

• 10.3.3. HDL- ABCA1, ABCL1, ABCG1, LCAT, CETP, SR-B1 • 10.3.4. Lp(a) - LPA Core Curriculum Map (cont.) • 10.4. *

• 10.4.1. Polygenic

• 10.4.2. Monogenic hypertriglyceridemia & familial hyperchylomicronemia syndromes (FCS)

• 10.4.2.1. deficiency

• 10.4.2.2. APOCII deficiency

• 10.4.2.3. GPIHBP1 deficiency (glycosylphosphatidylinositol anchored high density lipoprotein binding protein 1)

• 10.4.2.4. LMF1 deficiency (liase maturation factor)

• 10.4.2.5. GPD1 deficiency (glycerol-3-phosphate dehydrogenase 1)

• 10.4.3. Familial dysbetalipoproteinemia (ApoE II/II or other variants)

• 10.5.

• 10.5.1.1. Homozygous familial hypercholesterolemia

• 10.5.1.2. Heterozygous familial hypercholesterolemia

• 10.5.1.3. Polygenic hypercholesterolemia

• 10.5.1.4. Sitosterolemia

• 10.5.1.5. Autosomal recessive hypercholesterolemia

• 10.5.1.6. Lysosomal acid lipase (LAL) deficiency

• 10.6. Combined or mixed dyslipidemia

• 10.6.1. Familial

• 10.6.2. Non-familial combined hyperlipidemia Core Curriculum Map Masters Course- Genetic Dyslipidemias 11. Familial hypercholesterolemia • 11.1. Prevalence • 11.2. Genetics and genetic testing • 11.2.1. LDL receptor • 11.2.2. Defective apo B • 11.2.3. PCSK9 gain of function • 11.3. Diagnostic criteria • 11.4. Relevance of lipoprotein (a) • 11.5. Treatment Overview of Lipid Metabolism • Basics of Lipoprotein particles and their components • Endogenous and Exogenous Lipid Metabolism: “The 30,000 foot view • Focused discussion of each step in lipid metabolism to understand the details • LDL receptor activity and metabolism including role of PCSK9 • HDL metabolism and reverse cholesterol transport including the role of CETP • VLDL and Chylomicron production pathways and role of apoproteins • Summary and review Lipoprotein Structure

TG

CE Polar Surface Coat (Phospholipids, Apoprotein FC, Apoproteins) 3 Lipoprotein Structure

Apoprotein Apoprotein

POLAR SURFACE COAT NONPOLAR Phospholipid LIPID CORE Cholesterol Ester Free cholesterol

Apoprotein

4

Adapted from Treatment of Heart Diseases:1992, Etiologies and Treatment of Hyperlipidemia-Scott Grundy, MD, PhD Lipoprotein Sub-Classes

Chylomicron 0.95 VLDL

VLDL Remnants

1.006 IDL

Chylomicron Remnants 1.02

LDL Density(g/ml)

1.06 HDL2 Atherogenic Lp(a) (found in plaque) 1.10 HDL3DL3 pre-β2 HDL 1.20 pre-β1 HDL 1000 5 10 20 40 60 80 Particle Size (nm) Lipoprotein Composition and Function

Lipoprotein Function

Chylomicrons, B-48 (A-I, C-II, C-III, and E) Delivers TG & Chol (intestinal Chylo-remnants or exog. path)

VLDL, IDL B-100 (C-II, C-III, E) Delivers TG & Chol (endogenous path) LDL B-100 Delivers Chol (endogenous path) Lp(a) B-100, apo (a) Delivers Chol (endogenous path) HDL A-I, A-II (C-II, C-III, E) RCT; Anti-athero; Major Apolipoproteins

Apo Location Function Plasma Levels Athero

A-I HDL (Chyl) Multi anti-athero High ↓↓↓

A-II HDL ?? Moderate ↓?

B-48 Chyl Exog. TG & Ch transp Moderate (post-prandial ↑? only) B-100 VLDL, LDL Deliver endog. cholesterol High ↑↑↑

C-II VLDL, HDL ↑LPL activity Low ↓

C-III VLDL, HDL ↓LPL, plq rupt? Low ↑↑

E VLDL, HDL Remn Lp Catab, Chol Low ↑↑↑/↓? Efflux?

(a) Lp(a) Ox FFA scaveng Low ↑↑↑ Overview of Secondary Causes of Dyslipidemia High cholesterol Secondary cause Low HDL-C High LDL-C

Saturated fat caloric excess, Dietary Low-fat diet, high-sugar diet anorexia

Diuretics, cyclosporine, Anabolic steroids, progestins, β- Drugs sirolimus, glucocorticoids, blockers, cigarettes, retinoic acid rosiglitazone,

Disorders of metabolism , pregnancy, DM , type 2 DM

Nephrotic syndrome, biliary Chronic renal failure, dialysis, Diseases obstruction (Lp-X), type 2 DM type 2 DM

Adapted from Stone NJ, Blum CB. Management of in Clinical Practice. 2006. Lipid Metabolism Exogenous Endogenous

B-100 Dietary Fat LDL Receptor E Receptor LDL Remnant (LDLr) (LDLr) Receptor Intestine HTGL HDL LPL B-48 E C II

E C II HDL C II Remnant B-48 LPL TG E Chylomicron ¯ E B-100 FFA LPL TG IDL B-100 ¯ VLDL FFA Apolipoproteins apoA-I HDL structural protein; LCAT( cholesterol acyl transferase) activator;Enhances reverse cholesterol transport apoA-II Hepatic Lipase activation apoA-IV Triglyceride metabolism; LCAT activator; apoB-100 Structural protein of all except HDL Binding to LDL receptor apoB-48 apoC-I Inhibit Lipoprotein binding to LDL Receptor; LCAT activator apoC-II Lipoprotein lipase (LpL) activator apoC-III LpL inhibitor; antagonizes apoE apoE B/E receptor ligand *E2:IDL; *E4: Diet Responsivity Lipid Metabolism Exogenous Endogenous

B-100 Dietary Fat LDL Receptor Liver E Receptor LDL Remnant (LDLr) (LDLr) Receptor Intestine HTGL HDL LPL B-48 E C II

E C II HDL C II Remnant B-48 LPL TG E Chylomicron ¯ E B-100 FFA LPL TG IDL VLDL B-100 ¯ FFA 11 Intestinal Absorption of Cholesterol and Bile Acids Influences Lipoprotein Metabolism

Dietary Cholesterol Bile Liver Chol

BA BA Chol NPC1L1 LDLR

CM CMR Bile acid iBAT sequestrants LDL VLDL BA Blood

Rader DJ, Nature Medicine 2001; 7:1282-1284 Mechanism of Intestinal-Acting Agents Mutations in ABCG5 and ABCG8 Cause Sitosterolemia Hereditary Betasitosterolemia Clinical Summary: ABCG5 and ABCG8

• Mutations in ABCG5 (sterolin-1) and ABCG8 (sterolin-2) cause sitosterolemia • Affected individuals have high levels of plant sterols, but not always cholesterol • Tendon/tuberous xanthomas and accelerated • Must play a key role in regulating dietary sterol absorption and excretion • ? Link between diet and atherosclerosis • Do sterolins prevent the entry of toxic bioactive sterols? FXR and LXR Regulation of Cholesterol Metabolism

FXR activated by bile acids to reduce BA synthesis and increases I-BABP LXR activated by oxysterols to increase BA synthesis and ABCA1 activity http://www.biocarta.com/pathfiles/h_fxrPathway.asp#description FXR and LXR Regulation Pathways

Regulation of transcription of cholesterol and genes by heterodimerisation of RXR and LXR for FXR

A

B

(A)When nuclear receptors RXR and LXR heterodimerize, they bind to a recognition sequence (termed a DR-4 element, in which direct repeats of TGACCT, are separated by four base-pairs) in promoters of target genes (eg ABCA1). Interaction of ligands with binding domains on these receptors stimulated gene transcription, the effect being synergistic if both are bound simultaneously, RNA polymerase complex bound near the transcriptional start site (not shown) is then activated to produce multiple mRNA copies. (B)LXR ligands upregulate ABAC1 in peripheral cells, to increase cholesterol excretion onto lipid-poor apoA-1, and also in intestinal absorptive cells (or, if not ABCA1, another LXR target gene such as ABCG5/ABCG812), to reduce dietary uptake of cholesterol. FXR ligands downregulates 7 α-hydroxylase, to reduce the pool of bile acids and inhibit solubilization and absorption of intestinal cholesterol. RXR ligands activate both FXR and LXR regulated pathways and there is dual suppression of cholesterol absorption. In rodents, though not in human beings, LXR upregulates 7 α-hydroxylase but, since RXR/FXR repression of 7 α-hydroxylase dominates over RXR/LXR stimulation, RXR ligands still completely suppress cholesterol absorption. Wade, et al, Lancet. Volume 357, No. 9251, p161–163, 20 January 2001 SREBP and Cholesterol Homeostasis Pharmacologic Manipulation of ABCA1 and Macrophage Cholesterol Efflux

Fibrates, TZDs, dual PPARs, new agents PPARα PPARγ A-I PPARδ

FC LXR/RXR ABCA1 New agents ? New agents Effect of PPAR* α and Υ activation in VLDL, LDL and HDL metabolism PPAR α PPAR Υ Location of action: Liver, kidney, Location of action: Adipose tissue and heart, muscle. intestine. Ligands: fatty acids, fibrates Ligands: arachidonic acid, Glitazones Actions: Stimulate production Actions: increase expression of of apo A I, inhibit apo C III, ABC A-1, increase FFA synthesis Increase lipoprotein lipase, and uptake by adipocytes, increase increase expression of ABC insulin sensitivity (?) A-1, increase FFA uptake and catabolism, decrease FFA and VLDL synthesis. * Peroxisome Proliferator Activated Receptor Lipid Metabolism Exogenous Endogenous

B-100 Dietary Fat LDL Receptor Liver E Receptor LDL Remnant (LDLr) (LDLr) Receptor Intestine HTGL HDL LPL B-48 E C II

E C II HDL C II Remnant B-48 LPL TG E Chylomicron ¯ E B-100 FFA LPL TG IDL B-100 ¯ VLDL FFA Lipoprotein Lipase

• Breaks down triglycerides from TG rich lipoproteins into FFAs • Activated by Apo CII • Inhibited by Apo CIII • Secreted into the interstitium by adiposites and myocytes • Requires transport to the lumen by GPIHBP1 (glycosylphosphatidylinositol anchored high density lipoprotein binding protein 1) The role of GPIHBP1 (glycosylphosphatidylinositol anchored high density lipoprotein binding protein 1) in transporting lipoprotein lipase (LpL) into the capillary lumen

HPSGs= Heparan sulphate Proteoglycans

FA=

LpL= Lipoprotein Lipase

Chylo= Lipoprotein Lipase Movement to the Capillary Lumen Apo C-III Role in Lipid Metabolism

Hepatic Lipoprotein apoC-III Receptors LDL

LPL, HL apoC-III ANGPTL4 ANGPTL3 apoC-III VLDL Atherosclerotic Plaque VLDL Remnant apoA-V LPL

apoC-III apoC-III

Chylomicron Chylomicron Remnant

apoA-V Khetarphal, SA and Rader, DJ. Atheroscler. Thromb. Vas. Biol February 2015 Role of Apo A-V in Lipoprotein Metabolism

J Clin Invest. 2005 Oct 1; 115(10): 2694–2696. Lipid Metabolism Exogenous Endogenous

B-100 Dietary Fat LDL Receptor Liver E Receptor LDL Remnant (LDLr) (LDLr) Receptor Intestine HTGL HDL LPL B-48 E C II

E C II HDL C II Remnant B-48 LPL TG E Chylomicron ¯ E B-100 FFA LPL TG IDL B-100 ¯ VLDL FFA VLDL Packaging in the liver

DGAT=diacylglycerol acyltransferase; PA(P)=phosphatidic acid phosphatase/phosphohydrolase.

Adapted from Bays HE et al. Expert Rev Cardiovasc Ther. 2008;6(3):391-409. HDL Production and Reverse Cholesterol Transport Lipid Metabolism Exogenous Endogenous

B-100 Dietary Fat LDL Receptor Liver E Receptor LDL Remnant (LDLr) (LDLr) Receptor Intestine HTGL HDL LPL B-48 E C II

E C II HDL C II Remnant B-48 LPL TG E Chylomicron ¯ E B-100 FFA LPL TG IDL B-100 ¯ VLDL FFA Production of HDL by Liver and Intestine Liver Intestine

A-I A-I

A-II

HDL HDL HDL and Reverse Cholesterol Transport

Bile

A-I A-I FC CE FC LCAT CE FC CE FC ABCA1 SR-BI Nascent HDL Macrophage Liver Mature HDL HDL Metabolism: Role of CETP (Cholesterol Ester Transfer Protein)

Bile From Liver and Intestine A-I A-I FC LCAT CE CE FC CE FCFC FC SR-BI ABCA1 Macrophage Liver CETP LDLR

B CE TG Kidney

VLDL/LDL HDL and Reverse Cholesterol Transport HDL Metabolism: Role of Hepatic Lipase on TG rich HDL

Liver A-I

PL CE

HL TG

HDL2 A-I

PL CE

HDL 3 Kidney Lipid Metabolism Exogenous Endogenous

B-100 Dietary Fat LDL Receptor Liver E Receptor LDL Remnant (LDLr) (LDLr) Receptor Intestine HTGL HDL LPL B-48 E C II

E C II HDL C II Remnant B-48 LPL TG E Chylomicron ¯ E B-100 FFA LPL TG IDL B-100 ¯ VLDL FFA Upregulation of the LDL Receptor by Inhibition of Cholesterol Synthesis

TG B CE Chol VLDL

HMG CoA reductase CE B LDLR LDL X PCSK9 (proprotein convertase subtilisin/kexin type 9) and LDL Receptor Recycling Genetic Dyslipidemias

• Disorders affecting LDL • Disorders affecting Triglycerides • Low HDL disorders • Low LDL disorders • Lp(a) Classification of Lipoprotein Disorders (Frederickson / Levy / Lees)

I IIa IIb III IV V

Lipoprotein CM LDL LDL+ Remnants VLDL CM+ VLDL VLDL

TG N Xanthomas eruptive tendon none palmar none eruptive tubero- eruptive Clinical CHD CHD CHD none pancreatitis

Etiology LPL LDLR unknown apoE2 unknown unknown apoC-II

Name FCS FH ± FCH FD FEHTG MHTG Genetic Disorders Defect

Hyperchylomicronemia Lipoprotein Lipase, CII

Familial Hypercholesterolemia LDL-Receptors Defective Apo B Apo B Combined Hyperlipidemia Apo B Overproduction Dysbetalipoproteinemia Apo E2:E2 + FCH Hypertriglyceridemia Enlarged VLDL Hypoalphalipoproteinemia Apo AI, HDL

Lp (a) Lp (a) Genetic Disorders of LDL

• Familial hypercholesterolemia (FH) • Heterozygous • Homozygous • Familial defective Apo B-100 • PCSK9 abnormality • Hereditary Sitosterolemia (Can mimic physical findings of FH) • Physical findings of • Corneal arcus • Extensor tendon xanthomas • Achilles xanthomas Prevalence of Familial Hypercholesterolemia (FH)

1. Heterozygotes occur with a frequency of about 1 in 300 to 500 patients. 2. Heterozygous FH is one of the most commonly occurring congenital metabolic disorders. Serum total cholesterol is elevated in the range of 300- 550 mg/dL. 3. There are approximately 620,000 patients in the U.S. with FH. 4. As many as 1 in 100 French Canadians and Dutch Afrikaners have FH. Prevalence of Homozygous FH

1. Homozygotes occur with a frequency of approximately 1 in 1 million. 2. Serum cholesterol ranges from 650-1000 mg/dL. Homozygotes have near total or total loss of LDL-R functionality. 3. Homozygotes can inherit two copies of the same mutant allele, or may be classified as compound homozygotes due to the inheritance of two different mutant alleles. Genetics 1. Defined as an autosomal dominant trait with complete penetrance causing congenitally elevated levels of LDL cholesterol. 2. There is a gene dosage effect with homozygotes having significantly greater elevations of LDL-C and earlier onset than subjects who are heterozygotes. Genetics

1. Affected subjects are at increased risk for all forms of atherosclerotic disease and premature death secondary to lifelong pathogenic elevations in serum LDL-C. There is a 20 fold increased risk for CHD events in untreated patients. 2. The gene for LDLR resides on the short arm of chromosome 19 (19p13.1- 13.3). 3. The Human Gene Mutation Database at the Institute of Medical Genetics in Cardiff lists 1614 mutations in the LDL receptor gene. Other Etiologies for FH Phenotype Other etiologies for the FH phenotype include: 1. Autosomal dominant hypercholesterolemia attributable to gain of function mutations in PCSK9 2. Deficiency of 7-alpha hydroxylase 3. Autosomal recessive hypercholesterolemia (due to reduced expression of an adaptor protein that facilitates the association of LDLR with clathrin in cell surface coated pits). 4. Mutations in the gene for apo B can also give rise to FH (familial defective apo B). 5. Lysosomal Acid Lipase Deficiency Disorders Affecting LDLR Activity • Familial Hypercholesterolemia (FH): Deficient or defective LDL receptors (chromosome #19); impaired LDL removal from plasma

• Familial Defective Apo B100: Mutant Apo B100 poorly recognized by LDL receptor – impaired LDL removal from plasma

• PCSK9 Increase of function mutation

• Autosomal Recessive Hypercholesterolemia: Very rare due to a mutation in the LDL receptor adaptor protein - markedly elevated LDL-C levels

Adapted from Kwiterovich PO, ed. The Johns Hopkins textbook of dyslipidemia. 1st ed. Kwiterovich PO, ed. The Johns Hopkins textbook of dyslipidemia. 1st ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2009. ARIC: PCSK9 Loss-of-Function Mutations, LDL-C, and CHD Risk

PCSK9 Mutation LDL-C CHD Risk Hazard Ratio, Population Mutation Incidence Reduction Reduction 95% CI

ARIC Study 3363 black subjects Y142X or 28% 88% 2.6% 0.11 (0.02-0.81) screened C679X

Patients with loss-of-function mutations in PCSK9 or total lack of PCSK9 • Have naturally low levels of LDL-C and reduced CHD • Are not associated with other detectable abnormalities

Adapted from Cohen JC, et al.[2] Physical Findings

• Yellow-orange cutaneous xanthomas • Tendon xanthomas • Xanthalasma • Corneal arcus • Heart murmur stemming from aortic valve stenosis • Can develop aortic outflow tract stenosis • Arterial bruits (carotid, femoral) arising from diffuse, systemic atherosclerosis • Polyarthritis • Tendinitis Screening

• Universal screening for elevated serum cholesterol is recommended. • FH should be suspected when untreated fasting LDL-c or non-HDL-C levels are at or above the following: • Adults (≥20 years): LDL-C ≥ 190 mg/dL or non-HDL-C ≥ 220 mg/dL; • Children, adolescents and young adults (<20 years): LDL-C ≥ 160 mg/dL or non-HDL-C ≥ 190 mg/dL. Screening

• For all individuals with these levels, a family history of high cholesterol and heart disease in first-degree relatives should be collected. • The likelihood of FH is higher in individuals with a positive family history of hypercholesterolemia or of premature CHD (onset in men before age 55 years and women before age 65 years). • Cholesterol screening should be considered beginning at age 2 for children with a family history of premature cardiovascular disease or elevated cholesterol. All individuals should be screened by age 20. Screening

• Cascade screening involves testing lipid levels in all first-degree relatives of diagnosed FH patients. • As cascade screening proceeds, newly identified FH cases provide additional relatives who should be considered for screening. • Cascade screening is the most cost-effective means of finding previously undiagnosed FH patients and is also cost-effective in terms of cost per year of life saved. Diagnosis

These LDL cholesterol levels should prompt the clinician to strongly consider a diagnosis of FH and obtain further family information since the likelihood of FH is 80% or more: LDL-C ≥250 mg/dL in a patient aged 30 or more; LDL-C ≥ 220 mg/dL for patients aged 20 to 29; LDL-C ≥ 190 mg/dL in patients under age 20. Treatment Considerations

• Consider initiation of therapy in children at age 8, earlier if homozygous FH • Women of child bearing age should be counseled to stop therapy 4 weeks before stopping contraception. Statins and ezetemibe should not be given during pregnancy and lactation. Bile acid resins can be used when appropriate. LDL apheresis can be used during pregnancy in high risk patients with atherosclerotic disease • Genetic counseling for families with FH regarding risk and followup treatment for their children should be considered. • Homozygous FH patients should be referred to a lipid specialist for treatment and may need LDL apheresis

60 Familial Hypercholesterolemia Exogenous Endogenous LDL

B-100 Dietary Fat LDL Receptor Liver LDL LDL E Receptor LDL Remnant LDL Receptor Intestine HTGL HDL LPL B-48 E C II

E C II HDL C II Remnant B-48 LPL TG E Chylomicron ¯ E B-100 FFA LPL TG IDL B-100 ¯ VLDL FFA The Human LDL Receptor

Domains

1. Ligand Binding (292 Amino Acids)

2. EGF Precursor Homology (~ 400 Amino Acids)

3. O-Linked Sugars (58 Amino Acids) 4. Membrane Spanning (22 Amino Acids) 5. Cytoplasmic (50 Amino Acids) Figure 4 Autosomal Recessive Hypercholesterolemia

Soutar AK and Naoumova RP (2007) Mechanisms of Disease: genetic causes of familial hypercholesterolemia Nat Clin Pract Cardiovasc Med 4: 214–225 doi:10.1038/ncpcardio0836 Cellular Cholesterol Homeostasis (Lysosomal Acid Lipase Deficiency) Schematic view of cellular cholesterol Healthy Individuals LAL D Patients

LDL-C Hepatocyte LDL-C Hepatocyte

LDL-C (CE & TG) LDL-C (CE & TG) Lysosome Lysosome LALLAL LALLAL

LDL-C LDLR LDLR FC & FFA

FA synthesis FA synthesis SREBPs pathway SREBPs pathway Nucleus Nucleus TG TG HMG- ACAT HMG- ACAT CoA r CoA r CE CE FC FC

VLDL-C VLDL-C

ACAT, acyl-CoA:cholesterol acyltransferase; CE, cholesterol ester; FA, fatty acid; FC, free cholesterol; FFA, free fatty acid; HMG-CoA r, 3-hydroxy-3-methyl-glutaryl- CoA reductase; LAL, lysosomal acid lipase; LDL-C, low-density lipoprotein cholesterol; LDLR, low-density lipoprotein remnant; SREBPs, sterol regulatory element- binding proteins; TG, triglyceride; VLDL-C, very-low-density lipoprotein cholesterol. Reiner Ž, et al. Atherosclerosis. 2014;235:211-30. Extensor Tendon Xanthomas in Homozygous FH Achilles Tendon Xanthomas in Heterozygous FH

LDL-C 180 mg/dL HDL-C 51 mg/dL Chol 243 mg/dL TG 90 mg/dL Extensor Tendon Xanthomas in Heterozygous FH Heterozygous Familial Hypercholesterolemia: May be present in FH but not specific for the disorder.

Corneal arcus Xanthelasma

Courtesy of Dr. Jean Davignon, University of Montreal Homozygous Familial Hypercholesterolemia:

5-year old 17-year old 21-year old DAVIGNON 2006 Homozygous Familial Hypercholesterolemia:

12-year old girl with left main coronary 21-year old woman with stenosis supravalvular Genetic Disorders of Triglycerides

• Chylomicronemia • Lipoprotein lipase deficiency • Apo CII deficiency • Familial combined dyslipidemia • Overproduction of Apo B-100 • Familial hypertriglyceridemia • Large VLDL particles • Minimal  CAD risk • Type III dyslipidemia Clues to Lipid Abnormalities by Serum Examination Tuberoeruptive Xanthomas in Hypertriglyceridemia Tuberoeruptive Xanthomas in Chylomicronemia Lipemia Retinalis

TG = 8000 mg/dL Chylomicronemia Exogenous Endogenous

B-100 Dietary Fat LDL Receptor Liver E Receptor LDL Remnant Receptor Intestine HTGL HDL LPL B-48 E C II

E C II HDL C II Remnant B-48 LPL TG E Chylomicron ¯ E B-100 FFA LPL TG IDL B-100 ¯ Chylomicrons VLDL FFA Chylomicronemia syndromes

• Monogenic: Familial Chylomicronemia Syndrome ( Null mutation for Lipoprotein Lipase) • Polygenic: More subtle for chylomicrons with superimposed other disorders such as or insulin resistance Genetics: Known mutations responsible for FCS

% of Monogenic Gene Gene product function Molecular features mutations

Hydrolysis of TGs Severely reduced or absent LPL 95% and peripheral uptake of FFA LPL enzyme activity Absent or nonfunctional APOC2 Required cofactor of LPL 2.0% ApoC-II Stabilizes the binding of Absent or defective GPIHBP1 2.0% chylomicrons near LPL GPI-HBP1

APOA5 Enhancer of LPL activity Absent or defective apoA-V 0.6%

Chaperone molecule required LMF1 Absent or defective LMF1 0.4% for proper LPL folding

Adapted from Brahm, Nat Rev Endocrinol, 2015. Abbreviations: FFA, free fatty acid; LPL, lipoprotein lipase; TG, triglyceride. 1. Brahm AJ, Hegele RA. Chylomicronaemia—current diagnosis and future therapies. Nat Rev Endocrinol. 2015;11:352-362. doi:10.1038/nrendo.2015.26. 2. 2. Rodrigues R, Artieda M, Tejedor D, et al. Pathogenic classification of LPL gene variants reported to be associated with LPL deficiency. J Clin Lipidol. 2016;10(2):394-409. doi:10.1016/j.jacl.2015.12.015. Apo C-III Role in Lipid Metabolism

Hepatic Lipoprotein apoC-III Receptors LDL

LPL, HL apoC-III ANGPTL4 ANGPTL3 apoC-III VLDL Atherosclerotic Plaque VLDL Remnant apoA-V LPL

apoC-III apoC-III

Chylomicron Chylomicron Remnant

apoA-V Khetarphal, SA and Rader, DJ. Atheroscler. Thromb. Vas. Biol February 2015 Familial Combined Dyslipidemia Exogenous Endogenous

B-100 Dietary Fat LDL Receptor Liver E Receptor LDL Remnant Receptor Intestine HTGL HDL LPL B-48 E C II B-100 E C II HDL C II Remnant B-100 B-48 LPL TG E Chylomicron ¯ E B-100 FFA LPL TG IDL VLDL B-100 ¯ B-100 FFA VLDL B-100 Familial Combined Hyperlipidemia

• Use Non-HDL cholesterol or Apo B rather than LDL • Apo B/LDL > 1.0 • Autosomal Dominant/Family Screening/Valuable • Evaluate Lp (a), homocysteine Familial Hypertriglyceridemia Exogenous Endogenous

B-100 Dietary Fat LDL Receptor Liver E Receptor LDL Remnant Receptor Intestine HTGL HDL LPL B-48 E C II

E C II HDL C II Remnant B-48 LPL TG VLDL E Chylomicron ¯ E B-100 FFA VLDL LPL TG IDL B-100 ¯ VLDL FFA Familial Hypertriglyceridemia

• Family member has hypertriglyceridemia only • Apo B/LDL < 1.0 • HDL usually low • CHD risk only slightly above average Type III Dyslipidemia

• Extremely rare (1:10,000) • Combination of familial combined dyslipidemia and Apo E2/E2 phenotype •  risk for CAD • Extremely diet sensitive • Orange palmar creases • Palmar xanthomas Type III Dyslipidemia Exogenous Endogenous

B-100 Dietary Fat LDL Receptor Liver E Receptor LDL Remnant Receptor Intestine HTGL HDL LPL B-48 E C II B-100 E C II HDL C II Remnant B-100 B-48 LPL TG E Chylomicron ¯ E B-100 FFA LPL TG IDL VLDL B-100 ¯ B-100 FFA VLDL B-100 Orange Palmar Creases in Type III Tubero-Eruptive Xanthomata- Dysbetalipoprotenemia Palmar xanthomas in Type III Palmar Xanthomas in Type III (Dysbetalipoproteinemia) Primary (Genetic) Causes of Hypoalphalipoproteinemia (low HDL)

• ApoA-I (FHA, Milano) • ABCA1 (Tangier’s) • LCAT (Fish eye)

These are rare causes of low HDL-C Low HDL Cholesterol is Usually Found in Patients with Increased Cardiovascular Risk

Low HDL cholesterol levels are commonly found in patients who:

• Smoke • Are sedentary • Are obese • Are insulin resistant or diabetic • Have hypertriglyceridemia • Have chronic inflammatory disorders Low HDL Syndromes

• Familial hypoalphalipoproteinemia • Underproduction of HDL • High risk for CAD • Autosomal dominant • A1 Milano Gene • High HDL turnover • Low risk for CAD Low HDL Syndromes (cont)

• Tangiers Disease( ABC A1 deficiency)

• LCAT deficiency Hypoalphalipoproteinemia

• Very low HDL • HDLC generally < 25 mg/dL risk 3 fold of CHD events • Often does not respond to treatment • 50% of offspring may express it • Normal HDLC (mg/dL) • 40 in males • 55 in females • In Hypoalphalipoproteinemia , HDL £ 25 mg/dL ApoA-I gene deletions and HDL production Liver Intestine

A-I A-I

A-II

HDL HDL Effect of ApoA-I Mutations on HDL Metabolism

A-I Nascent HDL A-I LCAT CE FC FC ABCA1 Macrophage Rapid catabolism Flat Planar - Apo A-1 Gene Defect Limone sul Garda: Home of apoA-I Milano

98 Apo A1 Milano

• University of Milan 1980 • Valerio Dagnoli of lakeside town Limone Sul Garda • Of 1000 inhabitants, 40 had gene and were traced to common ancestors Giovanni Pomaroli and Rosa Giovanelli (1780) • Apo A1 mutation at position 173 arginine to cysteine • Reduced risk of atherosclerosis • IV and po synthetic forms have been tested in clinical trials Tangier’s Disease

• First described in 5 y/o boy from Tangier Island in early 1960’s • Defect in gene for ABC A1 transporter protein • Mutation in chromosome 9q31

HDL Metabolism in

A-I Nascent HDL A-I LCAT CE FC FC ABCA1 Macrophage Rapid catabolism Histologic Findings in Tangier Disease Tangier Disease (Orange Tonsils) Tangier Disease Heterozygotes

Heterozygotes carrying an ABCA1 mutation on one allele have reduced HDL-C levels in the 20-40 mg/dL range Tangier’s Disease Summary

• Defective ABCA1 transporter protein • Autosomal recessive trait • HDL< 5 mg/dl , slight increase TG • Premature atherosclerosis, orange tonsils, splenomegally, hepatomegally, • neuropathy • Increased clearance of apo A1 • Mild increase in TG • Mutation of ABCA1 gene on Chromosome 9q31 • First described by Donald Fredrickson in 5 y/o boy from Tangier Island • Heterozygotes with milder presentation LCAT Deficiency

• Complete : , proteinuria, renal failure due to absence of LCAT toward HDL and LDL • Unesterified chol accumulates in cornea, kidneys, and erythrocytes • Partial : (Fish Eye disease) corneal opacities, Hdl < 10 mg/dl with high/normal TG due to absence of LCAT towards HDL only • Not associated with increased CHD risk Lecithin: Cholesterol Acyltransferase Deficiency (LCAT deficiency (FLD) and Fish Eye Disease (FED))

CLINICAL  Corneal opacification, chronic progressive proteinuria, hemolytic anemia, and renal failure FED has a milder phenotype than FLD ASPECTS

 LCAT mutation results in lack of cholesterol esterification in MECHANISM plasma, impaired RCT, lipoprotein remodeling (LpX) and FC accumulation in tissues,

 HDL-C and apoAI markedly reduced TG  to , TC & LDL  BIOCHEMISTRY or N Plasma CE  to 1-20% vs. 75% of TC in N

 Mutations of LCAT gene on Chr 16q21-22 GENETICS  Autosomal Recessive, rare

DAVIGNON 2006 LCAT Deficiency Heterozygotes

Heterozygotes carrying an LCAT mutation on one allele have relatively normal HDL-C levels HDL Metabolism in LCAT Deficiency

A-I Nascent HDL A-I CE LCAT FC FC ABCA1 Macrophage Rapid catabolism Primary (Genetic) Causes of Hyperalphalipoproteinemia (high HDL)

• CETP deficiency • Other genetic etiologies CETP Deficiency is Associated with Markedly Increased HDL-C Levels Bile A-I A-I FC CE CE FC LCAT FC FC CE ABCA1 SR-BI Liver Macrophage LDLR CETPX

CE B TG

VLDL/LDL Genetic Disorders Causing Low Levels of ApoB-containing Lipoproteins

• (Abnormal apo B) • Abetalipoproteinemia (MTP defect) Hypobetalipoproteinemia

• Total cholesterol generally < 100 mg/dL; LDL-C generally < 60 mg/dL • Autosomal dominant inheritance • No apparent clinical sequelae • Associated with protection from CHD and longevity • Apo B mutation Regulation of Hepatic VLDL Production

B-100 apoB-100 VLDL

TG LDLR B-100 LDL Mutations in apoB Can Impair Secretion and/or Promote Catabolism Causing Hypobetalipoproteinemia

B-100* apoB-100* VLDL

TG LDLR B-100* LDL Abetalipoproteinemia

• Spinocerebellar and retinal degeneration leading to severe disability and blindness • Severe E deficiency • Extremely low total cholesterol, absent plasma VLDL, LDL, and apoB • Autosomal recessive inheritance • Absent MTP Microsomal transfer protein (MTP) is required for VLDL assembly and secretion

B-100 apoB-100 VLDL MTP TG LDLR B-100 LDL Genetic Absence of MTP is the Cause of Abetalipoproteinemia

Degradation B apoB VLDL MTP TG LDLR B LDL Hepatic Secretion of apoB is Required for Efficient Transport of to the CNS

Vit E Degradation B apoB VLDL Vit E MTPX TG Vit E LDLR B LDL

CNS Vit E Lp(a) and Heart Disease Lp(a) Structure

Plasminogen Apoprotein a TG

CE Polar Surface Coat Apo B - Plasmin (Phospholipids, 100 FC, Apoproteins) Lp(a): What is It ? Why is It Dangerous ? • Abnormal protein attached to LDL • Genetic inheritance on Chromosome #6 • One of the best predictors of • Heart attack • Coronary bypass surgery failure • Carotid artery disease • 50% of brothers/sisters and sons/daughters will have it • Particularly bad if another abnormality is also present • Difficult to measure accurately Tsimikas, S. (2017). A Test in Context: Lipoprotein(a) Diagnosis, Prognosis, Controversies, and Emerging Therapies. Journal of the American College of , 69(6), 695. http://dx.doi.org/10.1016/j.jacc.2016.11.042 Conclusions for Lp(a)

• Elevated Lp(a) increases risk of CAD events and increases risk of Aortic stenosis • Lp(a) is an acute phase reactant • Heritable autosomal dominant trait • Treatment is to lower LDL even lower in 2017 though residual risk remains • ? • Apo a antisense therapy Genetic Disorders Defect

Hyperchylomicronemia Lipoprotein Lipase, CII

Familial Hypercholesterolemia LDL-Receptors Defective Apo B Apo B Combined Hyperlipidemia Apo B Overproduction Dysbetalipoproteinemia Apo E2:E2 + FCH Hypertriglyceridemia Enlarged VLDL Hypoalphalipoproteinemia Apo AI, HDL

Lp (a) Lp (a) Low HDL disorders

• Familial Hypoalphalipoproteinemia (defective/low apo A1) • Apo A1 Milano • Tangier’s ( ABC1 transporter protein) • LCAT (Fish eye disease) High HDL disorders

• CETP deficiency Low LDL disorders

• Familial Hypobetalipoproteinemia (Abnormal apo B) • Abetalipoproteinemia ( absent MTP) LIPC mutations affect Hepatic Lypase activity

• At least 10 mutations in the LIPC gene have been found to cause hepatic lipase deficiency. This condition leads to abnormal levels of various fats (lipids) in the bloodstream, although it is unclear whether these changes impact the risk of developing heart disease. The LIPC gene mutations that cause this condition change single protein building blocks (amino acids) in the hepatic lipase enzyme. These mutations prevent the enzyme's release from the liver or decrease its activity in the bloodstream. As a result, VLDLs and IDLs are not efficiently converted into LDLs, and HDLs carrying cholesterol and triglycerides remain in the bloodstream. It is unclear what effect this change in fat levels has on people with hepatic lipase deficiency, as some affected people develop an accumulation of fatty deposits on the artery walls (atherosclerosis) and heart disease in mid- adulthood, while others do not.

NIH US National Library of Medicine, Genetics Home Reference, Jan 2018 Gene variants may predict LDL reduction with Statin Therapy • Variants in SNPs for HMGCR , ABCB1and CYP27A1, among others, may affect responsiveness to statin therapy • Apo A1, CETP and ABCB1 variants were associated with increased risk of MI within 1 year of follow-up in CAD patients

Poduri,et al, DNA Cell Biol. 2010 Oct;29(10):629-37. doi: 10.1089/dna.2009.1008. Sort1 Gene Mutations and MI

• SNP rs599839 on chromosome 1p13.1 is located in the 3′ untranslated region of the PSRC1 gene and is near the SORT1 gene. SNP rs599839 has been reported to be associated with LDL-C levels (Sandhu et al., 2008; Willer et al., 2008; Kleber et al., 2010). The minor allele G was associated with increased expression levels of SORT1 mRNA and that overexpression of SORT1 led to a significant increase in LDL uptake into cells (Linsel-Nitschke et al., 2010). A very recent study further showed that overexpression of SORT1 resulted in a decrease in total plasma cholesterol and LDL-C levels (Musunuru et al., 2010). The study also demonstrated that knockdown of SORT1 expression by siRNA caused a 46% increase in total cholesterol and a more than twofold increase in LDL-C levels (Musunuru et al., 2010). Thus, SORT1appears to be the causal gene for reduced LDL-C levels at the 1p13.3 locus, and may lower the risk of MI by decreasing the LDL-C levels.

Wang, et al, Annals of Human Genetics, Volume 75, Issue 4,July 2011 Pages 475–482 Genotypes and Statin Exposure

3.5

3

2.5

2 SLCO1B1 1.5 ABCG2 ABCB1 1

Figure 1 Effects of SLCO1B1, ABCG2, and ABCB1 genotypes on the systemic exposure of various statins. Data are shown as multiples of increase in plasma area under the plasma concentration–time curve by SLCO1B1 c.521CC, ABCG2 c.421AA, and ABCB1 c.1236TT-c.2677TT-c.3435TT genotype as compared with the reference genotype (c.521TT, c.421CC, and c.1236CC-c.2677GG-c.3435CC, respectively). Weighted mean values from various studies are shown for pitavastatin, , and pravastatin. References are in the text.

Clinical pharmacology & Therapeutics | VOLUME 87 NUMBER 1 | january 2010 Lipid Metabolism Summary

See! Lipid Metabolism isn’t all That Difficult!