B P4 C27 Lipoprotein Disorders and Cardiovascular Disease Flashcards
A young patient with eruptive xanthomas and a plasma triglyceride level of 22 mmol/L (2000 mg/dL) probably has _____ as a result of LPL deficiency or other monogenic defects
Familial hyperchylomicronemia
A 38-year-old woman with a strong family history of ASCVD, tendinous xanthomas, and an untreated LDL-C of 240 mg/dL (6.4 mmol/L) likely has _____.
Heterozygous familial hypercholesterolemia (HeFH)
An obese,hypertensive middle-aged man with a cholesterol level of 6.4 mmol/L (245 mg/dL), a triglyceride level of 3.1 mmol/L (274 mg/dL), an HDL-C level of 0.8 mmol/L (31 mg/dL), and a calculated LDL-C level of 4.2 mmol/L (162 mg/dL) probably has _____.
Metabolic syndrome
Affected subjects with FH have an elevated LDL-C level greater than the 95th percentile for age and sex, approximately ____ mg/dL (5.0 mmol/L) in adults.
In adulthood, clinical manifestations include tendinous xanthomas over the _____; corneal arcus and xanthelasma are less specific signs of FH.
190 mg/dL
Extensor tendons (MCP joints, patellar, triceps, and Achilles tendons)
- Transmission: Autosomal codominant
- High risk for the development of CAD by the third to fourth decade in men and approximately 8 to 10 years later in women
- Remarkably, prompt recognition in childhood or early adulthood and treatment (statins) can normalize life expectancy.
Gain-of- function mutations in the _____ gene decrease surface availability of the LDL-R protein and cause accumulation of LDL-C in plasma
PCSK9
- A loss-of-function mutation in PCSK9 confers lower LDL-C than in individuals without the mutation
- Black Americans had a higher prevalence of this protective mutation than did whites in the ARIC (Athero- sclerosis Risk in Communities) study, and subjects with life-long low LDL-C because of a mutation at the PCSK9 gene locus had a marked reduction in coronary events, thus confirming that genetically low LDL-C states lower cardiovascular risk.
A rare condition of increased intestinal absorption and decreased excretion of plant sterols (sitosterol and campesterol) can mimic severe FH with extensive xanthoma formation.
Sitosterolemia
- Premature atherosclerosis, often apparent clinically well before adulthood, occurs in patients with sitosterolemia.
- Diagnosis requires specialized analysis of plasma sterols documenting an elevation in sitosterol, campesterol, cholestanol, sitostanol, and campestanol.
- Patients with sitosterolemia have normal or reduced plasma cholesterol levels, and normal triglyceride concentrations.
- Patients with sitosterolemia have rare homozygous (or compound heterozygous) mutations in the ABCG5 and ABCG8 genes.
Conversely, an obese middle- aged man with a plasma triglyceride level of 7 mmol/L (620 mg/dL) probably has mutations in several genes associated with _____ levels.
Plasma triglyceride levels
Disorders of LDL
Familial hypercholesterolemia
LDLR gene defect
Familial defective ApoB
G-O-F of PCSK9
Polygenic hypercholesterolemia
Nonfasting triglycerides are higher than fasting levels (by approximately 0.3 mmol/L or 27 mg/dL), and guidelines consider nonfasting triglycerides _____ mmol/L (_____ mg/dL) as abnormal, while for fasting triglycerides the corresponding level is _____ mmol/L (_____ mg/dL).
Nonfasting:
> 2 mmol/L
> 175 mg/dL
Fasting:
> 1.7 mmol/L
>150 mg/dL
The 2018 American Heart Association/American College of Cardiology (AHA/ACC) cholesterol guideline and the 2019 AHA/ACC prevention guideline consider fasting or nonfasting triglycerides greater than ____ mg/dL as a risk enhancing factor that could prompt consideration for initiating or intensifying statin therapy.
175 mg/dL
There are some differences in the guideline cutpoints for severe hypertriglyceridemia, defined as fasting triglycerides greater than _____ mmol/L (_____ mg/dL) in European guidelines or _____mg/dL (_____mmol/L) in US guidelines
EU: >10 mmol/L or 885 mg/dL
US: > 5.7 mmol/L or 500mg/dL
Because the triglyceride to cholesterol ratio in TRLs progressively increases as the hypertriglyceridemia becomes more severe, the Friedewald equation (which assumes a fixed triglyceride to cholesterol ratio of triglycerides/5 [mg/dL] or triglycerides/2.2 [mmol/L]) to calculate LDL-C is inaccurate when triglycerides are greater than 4.5 mmol/L (400 mg/dL), as it underestimates the true LDL-C at high triglyceride levels. Instead, it is preferable to use _____ instead of calculated LDL-C for LDL-related treatment decisions in patients with hypertriglyceridemia, as direct LDL-C assays may also be inaccurate
Non-HDL-C or apo B
Primary causes of hypertriglyceridemia: Mild-to-moderate HTG (TG 2.0–9.9mmol/L)
Multifactorial or polygenic HTG (formerly HLP Type 4 or familial HTG)
Complex genetic susceptibility (see above)
Dysbetalipoproteinemia (formerly HLP Type 3 or dysbetalipoproteinemia)
Complex genetic susceptibility (see above), plus
APOE E2/E2 homozygosity or
APOE dominant rare variant heterozygosity
Combined hyperlipoproteinemia (formerly HLP Type 2B or familial combined hyperlipidemia)
Complex genetic susceptibility (see above), plus
Accumulation of common small effect LDL-C-raising polymorphisms
Primary causes of hypertriglyceridemia: Severe HTG (TG >10 mmol/L)
Monogenic chylomicronemia (formerly HLP Type 1 or familial chylomicronemia syndrome)
Lipoprotein lipase deficiency (Bi-allelic LPL gene mutations)
Apo C-II deficiency (Bi-allelic APOC2 gene mutations)
Apo A-V deficiency (Bi-allelic APOA5 gene mutations)
Lipase maturation factor 1 deficiency (Bi-allelic LMF1 gene mutations)
GPIHBP1 deficiency (Bi-allelic GPIHBP1 gene mutations)
Multifactorial or polygenic chylomicronemia (formerly HLP Type 5 or mixed hyperlipidemia)
Complex genetic susceptibility, including
Heterozygous rare large-effect gene variants for monogenic chylomicronemia (see above); and/or
Accumulated common small-effect TG-raising polymorphisms (e.g., numerous GWAS loci including APOA1-C3-A4-A5; TRIB1, LPL, MLXIPL, GCKR, FADS1-2-3, NCAN, APOB, PLTP, ANGPTL3)
Other
Transient infantile HTG (glycerol-3-phosphate dehydrogenase 1 deficiency) from bi-allelic GPD1 gene mutations
______ results from both common and rare genetic variants that result in increased VLDL particles.
Polygenic hypertriglyceridemia (formerly Type IV hyperlipidemia)
- Fasting plasma concentrations of tri- glycerides range between 2.3 to 5.7 mmol/L (200 to 500 mg/dL).
- After a meal, plasma triglycerides may exceed 11.3 mmol/L (1000 mg/dL).
- Polygenic hypertriglyceridemia does not associate with clinical signs such as corneal arcus, xanthoma, and xanthelasmas.
Polygenic hypertriglyceridemia does not associate with clinical signs such as ______.
Corneal arcus, xanthoma, and xanthelasmas
Polygenic hypertriglyceridemia has a weaker relationship with _____ than combined hyperlipoproteinemia (familial combined hyperlipidemia), and not all studies support this association
CAD
Lifestyle modifications should be the first step in treatment of Polygenic hypertriglyceridemia, including:
(1) Weight reduction in overweight individuals
(2) Limiting alcohol intake
(3) Reducing caloric intake
(4) Increasing exercise
(5) Withdrawal of hormones (estrogens and progesterone or anabolic steroids)
An unrelated X–linked genetic disorder,_____, may mimic familial hypertriglyceridemia because most measurement techniques for triglycerides use the measurement of glycerol after enzymatic hydrolysis of triglycerides.
Diagnosis of of this disease requires ultracentrifugation of plasma and analysis of glycerol.
Familial glycerolemia
A less common subset of patients have more severe hypertriglyceridemia which is characterized by a more severe elevation in both VLDL and chylomicrons and are classified as having _____.
Polygenic chylomicronemia (formerly Type V hyperlipidemia)
A rare disorder of HDL deficiency, identified in a proband from Tangier Island in Virginia, Tangier disease and familial HDL deficiency result from mutations in the _____ gene
ABCA1 gene
Reduced plasma levels of _____ consistently correlate with the development or presence of ASCVD
HDL-C
_____ all associate with reduced HDL-C levels.
Monogenic hyperchylomicronemia
Polygenic hypertriglyceridemia
Combined hyperlipoproteinemia
C-H-oMP
Plasma triglyceride and HDL-C levels vary inversely. Several mechanisms contribute to this association:
(1) Decreased lipolysis of TRLs decreases the availability of substrate (phospholipids) for HDL maturation
(2) HDL enriched with triglyceride has an increased catabolic rate and hence reduced plasma concentration
(3) The augmented pool of TRLs saps cholesterol from the HDL compartment by CETP-mediated exchange.