Medicine – Primary Hyperlipidaemia Disorders

Primary hyperlipidaemias are inherited disorders of lipoprotein metabolism that cause abnormal elevation of LDL cholesterol, triglycerides, or both. They are important because they can lead to premature atherosclerotic cardiovascular disease, pancreatitis, or characteristic lipid deposits such as xanthomas.

The major disorders in the original notes are familial hypercholesterolaemia, familial hypertriglyceridaemia, lipoprotein lipase deficiency, and familial combined hyperlipidaemia.

1. Familial Hypercholesterolaemia

Familial hypercholesterolaemia – FH is an inherited disorder characterised by markedly elevated:

LDL cholesterol.

The classic form is usually inherited in an:

Autosomal dominant pattern.

2. Genetic Basis of Familial Hypercholesterolaemia

Most classical cases are caused by pathogenic variants affecting the:

LDL receptor – LDLR.

Other genes can also produce a similar phenotype, including:

APOB

and

PCSK9.

The underlying problem is impaired removal of LDL particles from the circulation.

3. LDL Receptor Defect

Normally LDL particles bind to:

LDL receptors on hepatocytes

and are removed from the blood.

When LDL receptor function is reduced:

LDL clearance falls.

Therefore LDL remains in the circulation for longer.

This leads to:

Markedly elevated plasma LDL cholesterol.

So the original statement that the LDL half-life is prolonged is broadly correct.

4. Heterozygous Familial Hypercholesterolaemia

A person with one affected allele typically has:

Heterozygous familial hypercholesterolaemia – HeFH.

The original prevalence of:

About 1 in 500

is an older traditional estimate.

Modern population studies suggest HeFH is more common, approximately:

Around 1 in 200–300 people, though prevalence varies between populations.

5. Cholesterol Levels in Heterozygous FH

The original notes give total cholesterol of:

9–15 mmol/L.

Patients with HeFH can indeed have very high cholesterol, but a fixed range is not required for diagnosis.

More important is:

Markedly elevated LDL cholesterol, especially from a young age, together with family history or physical signs.

6. Cardiovascular Risk in Heterozygous FH

Untreated HeFH greatly increases the risk of:

Premature atherosclerotic cardiovascular disease.

This includes:

Coronary artery disease.

Myocardial infarction.

The exact relative risk varies, so the older statement of a universal:

“six- to eightfold increase”

should be regarded as an approximate historical teaching point rather than a fixed figure.

7. Tendon Xanthomas

One of the most characteristic clinical signs of FH is:

Tendon xanthomas.

These are cholesterol deposits within tendons, especially:

Achilles tendons.

Extensor tendons of the hands.

They strongly suggest:

Familial hypercholesterolaemia.

8. Xanthelasma

Xanthelasma refers to yellow cholesterol-rich plaques around the eyelids.

It may occur in FH, but it is:

Less specific than tendon xanthomas.

Xanthelasma can also occur in people without severe inherited hypercholesterolaemia.

9. Corneal Arcus

Another possible feature is:

Corneal arcus.

In older adults this can be physiological, but in a young person it may support the presence of:

Severe hypercholesterolaemia.

10. Homozygous Familial Hypercholesterolaemia

Homozygous familial hypercholesterolaemia – HoFH is much rarer and far more severe.

Patients have profoundly impaired LDL receptor pathway function.

This results in extremely high LDL cholesterol from:

Early childhood.

11. Childhood Xanthomas

The original notes correctly describe:

Xanthomas in early childhood.

Children with HoFH can develop widespread xanthomas because cholesterol levels are extremely high from birth.

Sites may include:

Tendons.

Skin.

Pressure areas.

12. Childhood Cardiovascular Disease

Untreated HoFH can cause severe atherosclerosis very early in life.

Complications may include:

Aortic root disease.

Coronary artery disease.

Myocardial infarction during childhood or adolescence.

Therefore HoFH is a severe medical condition requiring specialist treatment.

13. Familial Hypercholesterolaemia and Atherosclerosis

The central complication of FH is accelerated:

Atherosclerosis.

Persistently high LDL penetrates the arterial wall, contributing to plaque development and progressive narrowing or plaque rupture.

This explains why reducing LDL exposure as early as possible is a major goal in FH.

14. Treatment of Familial Hypercholesterolaemia

The original notes correctly include:

Diet

and

HMG-CoA reductase inhibitors – statins.

However, modern treatment is usually more intensive than diet plus statin alone.

Lifestyle measures remain useful, but genetic FH generally cannot be adequately treated by dietary modification alone.

15. Statins

Statins inhibit:

HMG-CoA reductase

in the liver.

This reduces hepatic cholesterol synthesis and increases hepatic expression of:

LDL receptors.

Therefore:

STATIN → ↑ LDL RECEPTOR ACTIVITY → ↓ PLASMA LDL.

High-intensity statin therapy is commonly a cornerstone of treatment.

16. Additional LDL-Lowering Therapy

If LDL remains elevated despite maximally tolerated statin therapy, additional agents may include:

Ezetimibe.

PCSK9-targeted therapy.

Other LDL-lowering treatments may be used in selected severe cases.

Patients with HoFH often need specialist treatment, potentially including more intensive pharmacological strategies and occasionally:

Lipoprotein apheresis.

17. Familial Hypertriglyceridaemia

Familial hypertriglyceridaemia is an inherited tendency toward elevated:

Triglycerides, usually carried mainly in VLDL particles.

It is often described as having:

Autosomal dominant familial clustering.

However, the genetics are usually more complex than a simple single-gene dominant disorder.

18. Turbid Plasma

When triglycerides are markedly elevated, plasma may appear:

Turbid or milky.

This is caused by large numbers of triglyceride-rich lipoprotein particles.

The more severe the triglyceride elevation, the more obvious the turbidity may become.

19. Eruptive Xanthomas

Severe hypertriglyceridaemia can cause:

Eruptive xanthomas.

These are small yellow-red papules, often appearing over:

Buttocks.

Back.

Extensor surfaces.

They can appear rapidly when triglycerides are extremely elevated.

20. Hypertriglyceridaemia and Pancreatitis

A major complication of severe hypertriglyceridaemia is:

Acute pancreatitis.

Risk increases substantially when triglycerides become very high.

Therefore:

SEVERE HYPERTRIGLYCERIDAEMIA + ABDOMINAL PAIN → CONSIDER ACUTE PANCREATITIS.

21. Hepatosplenomegaly

Very severe triglyceride-rich lipoprotein accumulation can produce:

Hepatomegaly

and sometimes:

Splenomegaly.

This is especially associated with severe chylomicronaemia syndromes rather than ordinary moderate familial hypertriglyceridaemia.

22. Retinal Changes

Severe hypertriglyceridaemia may produce:

Lipemia retinalis, where retinal vessels develop a creamy appearance.

The original note lists:

Retinal vein thrombosis.

Thrombotic events can occur in various metabolic settings, but lipemia retinalis is the more classic ocular association of extreme hypertriglyceridaemia.

23. Treatment of Familial Hypertriglyceridaemia

Treatment starts with:

Dietary modification.

Weight management.

Reduction or avoidance of alcohol.

Treatment of diabetes or other secondary contributors.

For significant persistent hypertriglyceridaemia, medications such as:

Fibrates

may be used.

24. Fibrates

Fibrates activate:

PPAR-α.

This increases fatty-acid oxidation and enhances metabolism of triglyceride-rich lipoproteins.

The overall effect is:

Lower plasma triglycerides.

Therefore:

FIBRATES → PARTICULARLY USEFUL FOR HIGH TRIGLYCERIDES.

25. Lipoprotein Lipase Deficiency

Lipoprotein lipase – LPL deficiency is a rare inherited disorder causing severe impairment of triglyceride-rich lipoprotein metabolism.

It is classically inherited in an:

Autosomal recessive pattern.

26. Normal Function of Lipoprotein Lipase

LPL is located on vascular endothelial surfaces, especially in:

Adipose tissue.

Skeletal muscle.

It hydrolyses triglycerides contained in:

Chylomicrons

and

VLDL.

This releases fatty acids for uptake into tissues.

27. LPL Deficiency

When LPL activity is severely deficient:

Chylomicrons cannot be cleared normally.

Therefore chylomicrons accumulate in plasma.

The result is:

Severe hypertriglyceridaemia.

This is part of the syndrome often termed:

Familial chylomicronaemia syndrome.

28. Clinical Features of LPL Deficiency

Patients may develop symptoms from childhood, including:

Recurrent pancreatitis.

Eruptive xanthomas.

Lipemia retinalis.

Hepatosplenomegaly.

Blood or plasma may appear:

Milky or lactescent.

29. Pancreatitis in LPL Deficiency

Recurrent acute pancreatitis is one of the most important complications.

Therefore:

CHILD/YOUNG PERSON + EXTREME TRIGLYCERIDES + RECURRENT PANCREATITIS → THINK FAMILIAL CHYLOMICRONAEMIA.

30. Treatment of LPL Deficiency

Management differs from ordinary hypertriglyceridaemia.

The cornerstone is a:

Very-low-fat diet

to reduce formation of dietary chylomicrons.

Alcohol and other triglyceride-raising factors should be avoided.

Because the primary defect is severe impairment of the LPL pathway, traditional triglyceride-lowering drugs such as fibrates may have:

Limited effectiveness in true complete LPL deficiency.

This is an important distinction from ordinary familial hypertriglyceridaemia.

31. Familial Combined Hyperlipidaemia

Familial combined hyperlipidaemia – FCHL is a common inherited dyslipidaemia associated with increased production of:

ApoB-containing lipoproteins.

Affected family members may show different lipid patterns.

32. Lipid Pattern in Familial Combined Hyperlipidaemia

Patients may have:

High LDL cholesterol.

High triglycerides.

or

Both elevated cholesterol and triglycerides.

The lipid phenotype may vary over time and between relatives.

Therefore the original description of:

Elevated cholesterol and triglycerides

is broadly correct, but not every patient necessarily has both raised simultaneously.

33. ApoB in Familial Combined Hyperlipidaemia

A characteristic feature is often:

Elevated apolipoprotein B – ApoB.

This reflects an increased number of:

Atherogenic lipoprotein particles.

This contributes to the disorder’s strong association with premature cardiovascular disease.

34. Atherosclerosis in Familial Combined Hyperlipidaemia

The major clinical concern is:

Premature atherosclerosis.

Patients have increased risk of:

Coronary artery disease

and other atherosclerotic cardiovascular disease.

Unlike classic FH, tendon xanthomas are generally:

Not characteristic.

35. Familial Combined Hyperlipidaemia and Metabolic Factors

FCHL often coexists with features such as:

Obesity.

Insulin resistance.

Hypertension.

These factors may worsen the lipid phenotype and cardiovascular risk.

36. Treatment of Familial Combined Hyperlipidaemia

Treatment focuses on reducing overall cardiovascular risk.

This includes:

Diet and weight management.

Exercise.

Smoking cessation.

Management of diabetes and hypertension.

LDL-lowering therapy, often with statins.

Additional triglyceride-lowering therapy may be considered according to the lipid pattern.

37. Familial Hypercholesterolaemia – Note Form

Inheritance:

Usually autosomal dominant.

Typical defect:

LDL receptor pathway.

↓

Reduced LDL clearance.

↓

Markedly increased LDL cholesterol.

Heterozygous FH:

Commoner than old 1:500 estimate; roughly 1:200–300 in many populations.

Premature coronary disease.

Tendon xanthomas.

Xanthelasma may occur.

Premature corneal arcus may occur.

Homozygous FH:

Very rare.

Extremely high LDL from childhood.

Childhood xanthomas.

Very premature coronary and aortic atherosclerosis.

MI can occur in childhood/adolescence.

Treatment:

Lifestyle measures.

High-intensity statin.

Ezetimibe.

PCSK9-targeted therapy when needed.

Specialist therapy/apheresis in severe HoFH.

38. Familial Hypertriglyceridaemia – Note Form

Main abnormality:

Raised triglycerides, usually VLDL predominant.

Possible features when severe:

Turbid plasma.

Eruptive xanthomas.

Pancreatitis.

Lipemia retinalis.

Hepatomegaly ± splenomegaly.

Treatment:

Diet.

Weight loss where appropriate.

Avoid excess alcohol.

Control diabetes.

Fibrates for suitable patients.

39. Lipoprotein Lipase Deficiency – Note Form

Inheritance:

Autosomal recessive.

Defect:

LPL pathway failure.

↓

Failure to clear chylomicron triglyceride normally.

↓

Extreme hypertriglyceridaemia.

Clinical features:

Childhood onset.

Milky plasma.

Eruptive xanthomas.

Lipemia retinalis.

Hepatosplenomegaly.

Recurrent pancreatitis.

Treatment:

Very-low-fat diet is central.

Traditional fibrates may be relatively ineffective in complete LPL deficiency.

40. Familial Combined Hyperlipidaemia – Note Form

Lipid abnormality:

↑ LDL cholesterol.

or

↑ Triglycerides.

or

↑ Both.

Typical additional clue:

↑ ApoB.

Major complication:

Premature atherosclerotic cardiovascular disease.

Tendon xanthomas:

Generally absent, helping distinguish it from classical FH.

41. Important Corrections to the Original Notes

The traditional prevalence:

“Heterozygous FH ≈ 1 in 500”

is now considered too low.

Modern estimates are closer to:

ABOUT 1 IN 200–300, depending on the population.

The original fixed cholesterol range:

9–15 mmol/L

can occur in HeFH, but diagnosis is not based on a single universal cholesterol range. The key abnormality is:

MARKEDLY ELEVATED LDL FROM A YOUNG AGE.

The older statement of:

“six- to eightfold increased IHD risk”

captures the substantial risk but should not be treated as a fixed value for every patient.

The clinically important message is:

UNTREATED FH → MARKEDLY INCREASED PREMATURE ASCVD RISK.

For severe hypertriglyceridaemia, the classic retinal manifestation is:

LIPEMIA RETINALIS

rather than retinal vein thrombosis as the defining association.

LPL deficiency should be distinguished from ordinary familial hypertriglyceridaemia.

In true LPL deficiency:

CHYLOMICRONS ACCUMULATE MASSIVELY

and treatment is centred on:

STRICT DIETARY FAT RESTRICTION.

Familial combined hyperlipidaemia may cause raised cholesterol, triglycerides, or both—not necessarily both in every affected person.

Key Clinical Pattern

For rapid recall:

FAMILIAL HYPERCHOLESTEROLAEMIA → VERY HIGH LDL + TENDON XANTHOMAS + PREMATURE CORONARY DISEASE.

HOMOZYGOUS FH → CHILDHOOD XANTHOMAS + VERY EARLY ATHEROSCLEROSIS/MI.

FAMILIAL HYPERTRIGLYCERIDAEMIA → HIGH TG + PANCREATITIS RISK.

LPL DEFICIENCY → AR + CHYLOMICRONS + EXTREME TG + RECURRENT PANCREATITIS.

FAMILIAL COMBINED HYPERLIPIDAEMIA → ↑ LDL AND/OR ↑ TG + ↑ ApoB + PREMATURE ATHEROSCLEROSIS.

The easiest final distinction is:

TENDON XANTHOMA → THINK FAMILIAL HYPERCHOLESTEROLAEMIA.

ERUPTIVE XANTHOMA + PANCREATITIS → THINK SEVERE HYPERTRIGLYCERIDAEMIA.