Lipid disorders

Lipid disorders encompass a spectrum of metabolic conditions that affect blood lipid levels. They are generally characterized by elevated levels of cholesterol, triglycerides, and/or lipoproteins in the blood, which are often associated with atherosclerotic cardiovascular disease (ASCVD). Hyperlipidemia is most commonly a result of genetic predisposition in combination with lifestyle factors (e.g., diet, lack of activity, alcohol consumption). Hyperlipidemia resulting from single-gene disorders, e.g., familial hypercholesterolemia, can cause severe elevations in lipoprotein levels and early atherosclerotic complications. Lipid disorders are usually detected during laboratory testing as part of an ASCVD risk assessment. A serum lipid panel includes total cholesterol, LDL, HDL, and triglyceride levels. Lipid-lowering therapy is indicated to reduce the risk of cardiovascular disease in adults with LDL > 190 mg/dL, diabetes mellitus, and established ASCVD, and should be considered for other patients based on individual ASCVD risk. The main treatment modalities are lifestyle modifications and lipid-lowering agents such as statins. For individuals < 20 years, see “Pediatric dyslipidemia” for information on screening, diagnostic cut-offs, and management.

Abetalipoproteinemia is a congenital lipid disorder in which a deficiency of apolipoproteins (hypolipoproteinemia) leads to impaired intestinal absorption of fats and fat-soluble vitamins. Symptoms usually appear during childhood and mainly consist of failure to thrive, steatorrhea, and signs of vitamin E deficiency. Treatment includes vitamin E supplementation.

• Dyslipidemia: an abnormal concentration of lipids in the blood (e.g., high or low LDL cholesterol)
• Hyperlipidemia: elevated blood lipid levels (e.g., total cholesterol, LDL cholesterol, and/or triglycerides)
  • Hypercholesterolemia: elevated cholesterol levels (most commonly measured with LDL) based on age and ASCVD risk factors
  • Hyperlipoproteinemia: elevated levels of serum lipoproteins (e.g., high VLDL)
  • Hypertriglyceridemia: elevated triglyceride levels (e.g., > 150 mg/dL in adults)

• Prevalence of hypercholesterolemia
  • Elevated total cholesterol levels: ∼ 38% ^[1]
  • Elevated LDL cholesterol levels: ∼ 29% ^[1]
• Prevalence of hypertriglyceridemia: ∼ 26% ^[1]

Epidemiological data refers to the US, unless otherwise specified.

• Usually multifactorial ^[2]
  • Secondary causes of dyslipidemia
  • Genetic causes
    • Polygenic disease is common, e.g., polygenic type II dyslipidemia. ^[3]
    • Monogenic disease is less common, e.g., heterozygous familial type IIa dyslipidemia (1:200–500 people). ^[3]
    • See also “Frederickson classification of monogenic hyperlipidemias.”

Severe dyslipidemia (e.g., LDL > 190 mg/dL) suggests an underlying monogenic disorder and/or a strong polygenic predisposition. ^[2]

• Elevated LDL cholesterol and reduced HDL cholesterol promote atherosclerosis → increased risk of cardiovascular events
• See “Pathogenesis of atherosclerosis.”

Dyslipidemia is a major risk factor for ASCVD.

• Dyslipidemia is usually asymptomatic.
• Severe and/or persistent elevation can cause:
  • Benign skin and/or eye manifestations, e.g., xanthelasma, lipemia retinalis
  • Complications, e.g., atherosclerosis, hepatic steatosis
• In genetic lipid disorders, symptoms generally occur at an earlier age and are more severe than in acquired lipid disorders.

Skin manifestations

Xanthomas

• Description: nodular lipid deposits in the skin and tendons
• Pathophysiology: : Extremely high levels of triglycerides and/or LDL cholesterol result in extravasation of plasma lipoproteins and their deposition in tissue.
• Histology: large perivascular infiltrates with foam cells (lipid-laden macrophages) and multinucleated histiocytes called Touton giant cells

:

Xanthelasmas

• Description: typically bilateral, yellow, flat plaques on the upper eyelids (nasal side)
• Etiology
  • Idiopathic
  • Increased incidence in:
    • Patients with diabetes mellitus
    • Patients with increased lipoproteins in plasma
    • Usually affects postmenopausal women
• Associated conditions: hypercholesterolemia (e.g., primary biliary cholangitis), hyperapobetalipoproteinemia, ↑ LDL cholesterol levels

Eye manifestations

• Lipemia retinalis
  • Description: opaque, white appearance of the retinal vessels, visible on fundoscopic exam
  • Associated condition: hyperlipoproteinemia type I, III, and IV
• Arcus lipoides corneae
  • Associated with hyperlipoproteinemia type II
  • Not pathological in advanced age

Overview of inherited hyperlipoproteinemia

This table describes monogenic dyslipidemias; polygenic dyslipidemia can also be categorized based on disease phenotype using the Frederickson classification. ^[3]

Abetalipoproteinemia

• Etiology
  • Deficiency of apolipoproteins (ApoB-48, ApoB-100)
  • Due to a mutation in the microsomal triglyceride transfer protein (MTTP) gene
• Pathophysiology
  • Autosomal recessive disease
  • Deficiency of chylomicrons, VLDL, and LDL (hypolipoproteinemia)
• Clinical features
  • Early
    • Steatorrhea
    • Failure to thrive
    • Fat malabsorption → fat-soluble vitamin deficiency
    • Acanthocytosis
  • Late
    • Developmental delay
    • Retinitis pigmentosa
    • Myopathy
    • Progressive ataxia
    • Spinocerebellar degeneration as a result of vitamin E deficiency
• Diagnostics
  • Extremely low levels of plasma cholesterol (< 50 mg/dL)
  • Acanthocytes in the blood
  • Other tests performed include complete blood count with differential, stool studies, and fasting lipid profile.
  • Confirmatory test: genetic testing to detect mutations in the MTTP gene
  • Intestinal biopsy: Histology may reveal lipid-laden enterocytes.
• Treatment
  • Vitamin E supplementation (high doses)
  • Reduced long-chain fatty acids intake

Chylomicronemia syndrome ^[16]

• Definition: a constellation of symptoms resulting from severely elevated serum triglyceride levels (> 1500 mg/dL) ^[16]
• Etiology
  • Genetic causes (e.g., familial hypertriglyceridemia, familial partial lipodystrophy)
  • Multifactorial chylomicronemia syndrome (MFCS)
• Clinical features
  • Abdominal pain
  • Eruptive xanthomas
  • Lipemia retinalis
  • Confusion and memory loss
• Diagnostics: fasting serum triglyceride level
• Management
  • A very low-fat diet until triglyceride levels are < 1000 mg/dL. ^[16]
  • Mitigate secondary causes of hyperlipidemia.
  • If triglyceride levels remain > 500 mg/dL: ^[16]
    • Initiate fibrates.
    • If still elevated after fibrates, add omega-3 fatty acids and/or niacin.
  • Initiate ASCVD prevention once triglyceride levels are < 500 mg/dL. ^[16]
• Complications
  • Acute pancreatitis
  • ASCVD

A very low-fat diet is the mainstay of therapy for patients with familial hyperchylomicronemia, as there is typically minimal response to lipid-lowering medications. ^[16]

General principles ^[17][18]

• Order a lipid panel when evaluating patients with a known secondary cause of dyslipidemia, e.g., diabetes mellitus or nephrotic syndrome.
• Screen for lipid disorders based on age and family history.
• If lipid levels are abnormal:
  • Repeat a lipid panel at least once to confirm the diagnosis. ^[2]
  • Assess for secondary causes of dyslipidemia. ^[1]
  • Calculate ASCVD risk.
  • Consider testing for monogenic disorders based on clinical suspicion. ^[17]

Screening for lipid disorders ^[1]

• Adults age 20–75 years: A nonfasting or fasting lipid panel (FLP) is acceptable. ^[17]
  • Screen at least every 4–6 years. ^[19]
  • See “ASCVD risk assessment" for details.
• Individuals < 20 years: See “Pediatric dyslipidemia screening.”

Diagnostic confirmation ^[5][17][18]

For individuals < 20 years, see “Diagnostics for pediatric dyslipidemia” for different cut-off values.

• Lipid panel: includes total cholesterol, HDL, LDL, and triglycerides
  • Nonfasting is appropriate for most situations.
  • Fasting lipid panel is indicated if initial triglycerides are ≥ 400 mg/dL.
• Other tests
  • Direct measurement of LDL cholesterol: indicated if the estimated level is < 70/mg/dL ^[17][20]
  • Lipoprotein(a) and apolipoprotein B: Consider as part of ASCVD risk assessment. ^[17][18]

Normal lipid levels

For individuals < 20 years, see “Diagnostics for pediatric dyslipidemia” for different cut-off values.

• Total cholesterol: < 200 mg/dL
• HDL cholesterol: ≥ 40 mg/dL for men; ≥ 50 mg/dL for women ^[21]
• Non-HDL cholesterol < 130 mg/dL ^[22]
• LDL cholesterol: depends on ASCVD risk ^[18]
  • < 100 mg/dL in adults at average risk
  • < 70 mg/dL in patients with ASCVD or at high risk
• Triglycerides: < 150 mg/dL
• Lipoprotein(a): < 50 mg/dL
• Apolipoprotein B: < 130 mg/dL

Assays for apolipoprotein B and lipoprotein(a) are not formally standardized and results may therefore be unreliable.

Additional evaluation ^[1][2][18]

Secondary causes ^[1][2][18]

• Obtain the following studies based on clinical suspicion.
  • Fasting blood glucose or HbA1c ^[23][24]
  • TSH
  • Liver chemistries to screen for cholestatic liver disease ^[1]
  • Urinalysis and serum creatinine to screen for renal disease, e.g., nephrotic syndrome
  • HIV testing ^[18]
  • Testing for autoimmune diseases, e.g., SLE diagnostics
• Consider other secondary causes based on patient history, e.g., antipsychotic use or lifestyle factors

Monogenic causes ^{[2][5][25][26]}

• Clinical scoring systems (e.g., Dutch Lipid Clinic Network criteria) may be used to diagnose familial hypercholesterolemia.
• Refer for targeted gene sequencing if results will influence management decisions. ^[2]
• Factors that increase suspicion for a monogenic disorder include: ^[2][25]
  • Persistent and/or severe dyslipidemia, e.g., LDL cholesterol > 190 mg/dL
  • Premature ASCVD ^[26]
  • Family history of premature ASCVD or dyslipidemia
  • Concerning clinical features, e.g., achilles tendon xanthoma ^[2]

This section focuses on the treatment of severe LDL cholesterol and triglyceride elevations in adults. For adults with nonsevere hyperlipidemia, the calculated ASCVD risk determines treatment. . For children, see “Management of pediatric dyslipidemia.”

Approach ^[1][17]

• Encourage lifestyle modifications for ASCVD prevention for all patients, including:
  • Physical activity
  • Dietary modifications
• Mitigate secondary causes of hyperlipidemia.
  • Limit alcohol use.
  • Manage associated medical conditions (e.g., diabetes mellitus).
  • Avoid medications that increase triglyceride or cholesterol levels.
• Initiate pharmacotherapy based on the type and severity of dyslipidemia.
• Consult a lipid specialist for patients with:
  • Inherited hyperlipoproteinemias
  • Statin intolerance
  • Persistent hypercholesterolemia (e.g., for treatment with LDL apheresis) ^[17]

Unaddressed secondary causes of dyslipidemia can prevent patients from responding to treatment for monogenic disease (e.g., familial hyperlipidemia). ^[2]

Pharmacotherapy

Very high LDL cholesterol ^[17][26][27]

• Indication: LDL cholesterol ≥ 190 mg/dL in adults 20–75 years of age ^[17]
• Goals
  • ≥ 50% reduction in LDL cholesterol levels from baseline (with maximally tolerated statin therapy)
  • LDL cholesterol targets vary, e.g.:
    • 20–75 years of age (regardless of etiology or ASCVD risk): < 100 mg/dL ^[17]
    • 30–75 years of age with heterozygous familial hypercholesterolemia and established ASCVD: < 70 mg/dL ^[28][29]
• First-line treatment: high-intensity statin therapy, e.g., atorvastatin or rosuvastatin ^[17]
• Subsequent treatment
  • Repeat lipid panel 6–12 weeks after treatment initiation or dose adjustment. ^[2][5]
  • If treatment goals are not met, consider adding nonstatin lipid-lowering agents sequentially, e.g.:
    • Ezetimibe ^[17]
    • PCSK9 inhibitor, e.g., evolocumab or alirocumab
    • Bile acid sequestrant, e.g., colesevelam
    • Lomitapide (in patients with homozygous familial hypercholesterolemia)

Severe hypertriglyceridemia ^[1][6][17]

For children, see “Management of pediatric dyslipidemia.”

• Indication: fasting triglycerides > 500 mg/dL
• First-line treatment
  • Fibrates, e.g., fenofibrate or gemfibrozil
  • OR omega-3 fatty acids, e.g., icosapent ethyl or omega-3-acid ethyl esters
• Subsequent treatment if triglycerides remain > 500 mg/dL ^[1]
  • Fibrates PLUS omega-3 fatty acids (recommended)
  • Consider adding niacin. ^[5]

Treatment with statins may still be indicated in patients with LDL cholesterol < 190 mg/dL and/or triglycerides < 500 mg/dL, depending on ASCVD risk.

Xanthoma and xanthelasma ^[30][31]

• Treatment may be considered for cosmetic reasons, but recurrence is common.
• Methods include surgical, laser, and/or topical therapy.

• Hepatic steatosis: associated with abetalipoproteinemia
• Hypertriglyceridemia-induced pancreatitis
  • May occur in severe hypertriglyceridemia (typically > 1,000 mg/dL)
  • Associated conditions include hyperlipoproteinemia types I and IV.
• ASCVD
  • Manifests with secondary diseases, e.g.:
    • Coronary heart disease
    • Myocardial infarction
    • Stroke
    • Peripheral arterial disease
    • Carotid artery stenosis
    • Cholesterol embolization syndrome
  • Hyperlipoproteinemia types II, III; , and IV are associated with premature atherosclerosis.

We list the most important complications. The selection is not exhaustive.

Epidemiology

Approximately 20% of individuals aged 6–19 years have abnormal lipid values. ^[32]

Etiology ^[33]

• Obesity (most common cause)
• Familial dyslipidemias
• Other causes: See “Secondary causes of dyslipidemia.”

Risk factors for pediatric dyslipidemia ^[5][33][34]

• Family history
  • Parent with total cholesterol ≥ 120 mg/dL or known dyslipidemia
  • First- or second-degree relative with premature ASCVD ^[33]
• High risk factors
  • BMI ≥ 97th percentile
  • Pediatric hypertension meeting criteria for pharmacotherapy
  • Diabetes
  • Kawasaki disease with coronary aneurysms
  • Heart transplant
  • Chronic kidney disease (including kidney transplant)
  • Cigarette smoking
• Moderate risk factors
  • BMI 95–96th percentile
  • Pediatric hypertension not meeting criteria for pharmacotherapy
  • Kawasaki disease with regressed coronary aneurysms
  • Nephrotic syndrome
  • Inflammatory conditions: SLE, JIA
  • HIV
  • HDL < 40 mg/dL

Other conditions, especially cardiac conditions, may also increase risk and affect management. ^[34]

Clinical features ^[33][34]

• Dyslipidemia is usually asymptomatic.
• Patients with severe dyslipidemia (e.g., those with homozygous familial dyslipidemia) may present with: ^[27][35][36]
  • Xanthomas (cutaneous, interdigital, tendinous)
  • Clinical ASCVD

Pediatric dyslipidemia screening ^{[5][33][34][37]}

Screening methods

• Targeted screening: recommended for all children
  • Starting at 2 years of age, screen for risk factors for pediatric dyslipidemia at well-child visits. ^[37]
  • When risk factors are first recognized, obtain a lipid panel (preferably fasting). ^[5][33][34]
  • If the lipid panel is normal and risks persist, repeat the lipid panel regularly (e.g., every 3–5 years) throughout childhood. ^[5][34]
• Universal lipid panel screening: recommended by some societies in addition to targeted screening ^[5][33][38]
  • First screening: once between 9 and 11 years
  • Second screening: once between 17 and 21 years

Next steps

• Screening with nonfasting lipid panel: total cholesterol > 200 mg/dL, non-HDL > 145 mg/dL, and/or HDL < 45 mg/dL ^[34]
• Screening with FLP: See “Diagnostics for pediatric dyslipidemia” for cutoff levels.

For individuals with a family history suggesting premature ASCVD and/or inherited hyperlipoproteinemia, obtain a screening lipid panel as early as 2 years of age. ^[17]

Diagnostics for pediatric dyslipidemia ^[33]

The average of two FLPs, obtained 2–12 weeks apart, must meet criteria for hypercholesterolemia and/or hypertriglyceridemia.

• Persistent hypercholesterolemia is diagnosed with either:
  • LDL measurements
    • Elevated: ≥ 130 mg/dL
    • Borderline: 110–129 mg/dL
  • Non-HDL measurements
    • Elevated: ≥ 145 mg/dL
    • Borderline: 120–144 mg/dL
• Persistent hypertriglyceridemia is diagnosed with triglyceride levels.
  • Children aged < 10 years
    • Elevated: ≥ 100 mg/dL
    • Borderline: 75–99 mg/dL
  • Children aged 10–19 years
    • Elevated: ≥ 130 mg/dL
    • Borderline: 90–129 mg/dL

Pediatric dyslipidemia most commonly involves moderately to severely elevated triglycerides, normal to mildly elevated LDL, reduced HDL, and obesity. ^[33]

Management of pediatric dyslipidemia ^[5][33][34]

Initial management

• Educate patients and caregivers on the risk of accelerated atherosclerosis and coronary artery disease.
• Thoroughly assess for risk factors for pediatric dyslipidemia.
• Immediately refer to a pediatric lipid specialist for:
  • LDL ≥ 250 mg/dL
  • Triglyceride average ≥ 500 mg/dL or a single triglyceride level ≥ 1000 mg/dL ^[33]
  • Suspected or confirmed familial hypercholesterolemia (FH) ^[34]
  • Complex and/or multiple risk factors (e.g., significant cardiac history) ^[33][34]
• Initiate lifestyle interventions to address modifiable risk factors.
  • Dietary changes
    • Start CHILD-1 diet and refer to a dietician.
    • If no improvement after 3 months, escalate to the CHILD-2 diet.
  • Counseling on regular exercise
  • Counseling on smoking cessation, if applicable
• Optimize treatment of underlying conditions.

Triglyceride levels ≥ 500 mg/dL increase the risk of pancreatitis. ^[33]

Ongoing management of pediatric dyslipidemia ^[33]

Recheck an FLP after 6 months of lifestyle interventions to guide further management.

• Hypercholesterolemia
  • Start statin therapy for children for any of the following:
    • LDL ≥ 250 mg/dL; immediately refer to a lipid specialist
    • LDL 190–249 mg/dL regardless of risk factors
    • LDL 160–189 mg/dL with either
      • A positive family history
      • ≥ 1 high risk factor for pediatric dyslipidemia and either 2 moderate risk factors or clinical ASCVD
    • LDL 130–159 mg/dL with either
      • ≥ 2 high risk factors for pediatric dyslipidemia
      • 1 high risk factor and either 2 moderate risk factors or clinical ASCVD
  • Continue CHILD-2-LDL diet and lifestyle changes for either of the following:
    • LDL 130–189 mg/dL with no risk factors; repeat FLP every 6 months
    • LDL < 130 mg/dL regardless of risk factors; repeat FLP every 12 months
• Hypertriglyceridemia
  • Refer to a lipid specialist for either of the following:
    • Triglycerides ≥ 500 mg/dL (immediate referral)
    • Triglycerides 200–499 mg/dL and non-HDL ≥ 145 mg/dL and LDL < 130 mg/dL
  • Continue CHILD-2 diet and lifestyle interventions for any of the following:
    • Triglycerides 200–499 mg/dL and non-HDL < 145 mg/dL: Consider adding omega-3-fish oil.
    • Triglycerides elevated but < 200 mg/dL : Intensify CHILD-2-TG diet , weight loss, and repeat FLP in 6 months.
    • Triglycerides < 100 mg/dL if < 10 years or < 130 mg/dL if 10–19 years; repeat FLP every 12 months.

Statin therapy for children ^[33]

• Indications
  • First-line pharmacotherapy for elevated LDL in individuals > 10 years
  • Specialists may consider statin therapy for patients with hypertriglyceridemia.
• Initiation: Start at a low dose and uptitrate after 3 months based on FLP results and tolerability. ^[33]
• Monitoring studies
  • Baseline studies: Obtain creatine kinase, ALT, and AST.
  • Following initiation or dose change: Obtain FLP, ALT, AST 4 weeks later.
  • Stable dose ^[33]
    • Check FLP, ALT, and AST in 8 weeks
    • Then every 3–4 months in the first year
    • Then every 6 months
  • If symptoms of myopathy develop, stop the statin and check a creatine kinase level.
• Referral indications: not meeting treatment goals despite optimal therapy

Statin therapy is not routinely recommended for children < 10 years of age but may be considered by a specialist. ^[33] Statins are contraindicated in pregnancy. Counsel individuals who can become pregnant on highly effective contraception methods. ^[33]

Advanced management

Specialists may consider the following.

• Alternative or adjunctive pharmacotherapy ^[5][33][34]
  • Hypercholesterolemia: ezetimibe, bile acid sequestrant, PCSK9 inhibitors, LDL apheresis
  • Hypertriglyceridemia: fibrate (off-label), niacin, and/or omega-3 fatty acids
• Genetic testing: for familial dyslipidemia genetic variants in the patient and possibly family members ^[17]

Prevention ^[33]

• At every well-child visit, discuss:
  • Pediatric lifestyle recommendations (e.g., counseling on regular exercise, limited screen time)
  • Pediatric nutrition
• Children with risk factors for dyslipidemia: Recommend the CHILD-1 diet.

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