```html

Johnston Disease (Familial Hypercholesterolemia) – A Complete Medical Guide

Overview

Johnston disease is another name for **familial hypercholesterolemia (FH)**, an inherited disorder that causes markedly elevated low‑density lipoprotein cholesterol (LDL‑C) from birth. When untreated, the high LDL‑C accelerates atherosclerosis, leading to premature coronary artery disease (CAD) and sometimes valve disease.

• Genetics: Autosomal‑dominant inheritance (1‑copy of a defective gene is enough). Rarely, an autosomal‑recessive form exists.
• Who it affects: Both males and females of any ethnicity. Heterozygous FH (HeFH) occurs in ~1 in 250–300 people worldwide, making it one of the most common monogenic disorders. Homozygous FH (HoFH) is far rarer, ~1 in 300 000–500 000.
• Prevalence: In the United States, the CDC estimates >1.3 million individuals have HeFH, yet >90 % are undiagnosed. Global prevalence is similar, with higher detection rates in countries with cascade‑screening programs (e.g., the Netherlands, Norway).

Because LDL‑C is high from birth, cardiovascular disease can appear decades earlier than in the general population—often in the 30s for HeFH and even the teens for HoFH.

Symptoms

FH is primarily a laboratory diagnosis, but certain physical signs can appear, especially in the more severe homozygous form.

Cutaneous and Tendon Findings

• Tendon Xanthomas: Firm, yellowish nodules on the Achilles tendon, extensor tendons of the hands, or elbows. They are pathognomonic for FH.
• Xanthelasma: Lipid‑rich plaques on the eyelids; common in FH but also in other lipid disorders.
• Corneal Arcus: A gray‑white ring at the corneal periphery, often seen before age 45 in FH.

Cardiovascular Symptoms

• Chest pain (angina) or discomfort on exertion
• Shortness of breath with activity
• Palpitations or irregular heartbeat (due to myocardial ischemia)
• Sudden cardiac arrest (rare but possible in undiagnosed HoFH)

Other Possible Findings

• Fatigue or reduced exercise tolerance (secondary to limited cardiac output)
• Early‑onset peripheral arterial disease (claudication)

Causes and Risk Factors

Genetic Causes

The most common gene mutations affect the LDL receptor (LDLR) pathway:

• LDLR gene: >1 200 different pathogenic variants identified.
• APOB gene: Missense mutations impair LDL binding to its receptor.
• PCSK9 gain‑of‑function mutations: Increase degradation of LDL receptors.

In HoFH, the individual inherits two defective copies (either the same mutation from each parent or two different mutations).

Non‑Genetic Risk Modifiers

• High‑saturated‑fat diet → modest additive rise in LDL‑C.
• Obesity, metabolic syndrome, or type‑2 diabetes → further lipid abnormalities.
• Smoking → accelerates atherosclerotic plaque formation.
• Physical inactivity → worsens LDL‑C and HDL‑C balance.

Diagnosis

Early detection is crucial. Diagnosis combines clinical criteria, family history, and lab testing.

Screening Tests

• Lipid panel: LDL‑C ≥190 mg/dL (≥4.9 mmol/L) in adults without secondary causes strongly suggests FH. In children, LDL‑C ≥160 mg/dL (≥4.1 mmol/L) is a red flag.
• Genetic testing: Confirms pathogenic variant in LDLR, APOB, or PCSK9. Recommended for index cases and cascade screening of relatives.

Clinical Criteria

Several validated scoring systems exist. The most widely used is the Dutch Lipid Clinical Network (DLCN) criteria which assigns points for:

1. Family history of premature CAD or high cholesterol.
2. Personal history of premature CAD, cerebral vascular disease, or peripheral arterial disease.
3. Physical signs (xanthomas, corneal arcus).
4. Lipid levels.
5. Genetic test results.

A total >8 points = “definite FH,” 6–8 = “probable,” 3–5 = “possible.”

Additional Evaluations

• Cardiac imaging: Stress ECG, coronary CT angiography, or invasive coronary angiography to assess plaque burden.
• Carotid intima‑media thickness (CIMT) ultrasound: Detects early atherosclerosis.
• Liver function tests: Baseline before starting statins or PCSK9 inhibitors.

Treatment Options

Treatment aims to lower LDL‑C as early and as aggressively as possible.

First‑Line Medications

• Statins (HMG‑CoA reductase inhibitors): Reduce hepatic cholesterol synthesis, up‑regulating LDL receptors. High‑intensity atorvastatin 40–80 mg or rosuvastatin 20–40 mg can lower LDL‑C by 50–60 % in HeFH.
• Ezetimibe: Inhibits intestinal cholesterol absorption; adds ~15–20 % LDL‑C reduction when combined with a statin.

Second‑Line / Adjunct Therapies

• PCSK9 inhibitors (evolocumab, alirocumab): Monoclonal antibodies that prevent LDL‑R degradation. They can lower LDL‑C an additional 50–60 % and are approved for both HeFH and HoFH (if residual LDL‑R activity).
• Bile‑acid sequestrants (cholestyramine, colesevelam): Reduce enterohepatic recirculation of bile acids, modestly lowering LDL‑C (10‑15 %).
• Microsomal triglyceride transfer protein (MTP) inhibitor – lomitapide: Approved for HoFH; reduces LDL‑C by up to 50 % but carries risk of hepatic steatosis.
• Gene‑silencing therapy – inclisiran: Small interfering RNA that reduces PCSK9 synthesis; administered twice yearly after loading doses.

Lipid‑Apheresis

For HoFH or severe HeFH refractory to maximal drug therapy, LDL‑apheresis removes LDL particles directly from the bloodstream. Typical sessions (once or twice weekly) can reduce LDL‑C by 60–70 % temporarily.

Lifestyle Modifications

• Diet: Adopt a heart‑healthy diet—American Heart Association (AHA) Step 1 or Step 2 diet—rich in fruits, vegetables, whole grains, legumes, nuts, and fish; limit saturated fat (<7 % of total calories), trans fat, and dietary cholesterol.
• Physical activity: At least 150 min/week of moderate‑intensity aerobic exercise (e.g., brisk walking, cycling) plus resistance training twice weekly.
• Weight management: Achieve/maintain BMI 18.5–24.9 kg/m².
• Smoking cessation: Eliminates a major accelerator of atherosclerosis.

Living with Johnston disease (familial hypercholesterolemia)

Daily Management Tips

• Medication adherence: Set alarms or use pill‑organizer apps; never skip doses.
• Regular labs: Check fasting lipid panel every 3–6 months while titrating therapy; liver enzymes and CK (creatine kinase) annually if on high‑dose statins.
• Family screening: Cascade testing of first‑degree relatives is essential; early detection saves lives.
• Vaccinations: Flu and COVID‑19 vaccines reduce systemic inflammation that can destabilize plaques.
• Mind‑body health: Stress management (mindfulness, yoga) may favorably influence lipid metabolism.
• Insurance and financial assistance: Many biologics (PCSK9 inhibitors) have patient‑assistance programs; work with a lipid specialist to navigate coverage.

Follow‑Up Schedule

Visit Type	Frequency	Purpose
Primary‑care or lipid clinic	Every 3–6 months	Lipid panel, medication tolerance, counseling
Cardiology (if CAD present)	Every 6–12 months	Stress testing or imaging, medication optimization
Liver function/CK tests	Annually (or sooner if symptoms)	Monitor statin safety

Prevention

While the genetic defect cannot be removed, secondary risk can be minimized.

• Early detection: Universal cholesterol screening at ages 9–11 and again at 17–21 (per AAP recommendations) catches many cases before disease manifests.
• Cascade testing: Inform all relatives; each first‑degree relative has a 50 % chance of inheriting the mutation.
• Maintain a heart‑healthy lifestyle throughout life—even with medication, diet and exercise lower residual risk.
• Control comorbidities: Keep blood pressure <130/80 mmHg, HbA1c <7 % if diabetic, and maintain optimal weight.

Complications

If untreated or undertreated, the chronic high LDL‑C accelerates atherosclerosis and leads to:

• Premature coronary artery disease: Angina, myocardial infarction, sudden cardiac death; average age of first MI in HeFH ≈ 45 years, in HoFH ≈ 20 years.
• Peripheral arterial disease: Claudication, critical limb ischemia.
• Stroke: Ischemic events from carotid or intracranial atherosclerosis.
• Aortic valve disease: Early‑onset aortic stenosis or regurgitation due to lipid deposition.
• Liver disease: Rarely, hepatic steatosis from high‑dose lipid‑lowering agents.
• Psychosocial impact: Anxiety or depression related to chronic medication use and family screening.

When to Seek Emergency Care

References

• Mayo Clinic. “Familial hypercholesterolemia.” https://www.mayoclinic.org
• National Heart, Lung, and Blood Institute. “Familial Hypercholesterolemia.” https://www.nhlbi.nih.gov
• American College of Cardiology/American Heart Association. “2023 Guideline for the Management of Blood Cholesterol.” Circulation
• World Health Organization. “Global brief on familial hypercholesterolemia.” 2022. WHO
• Cleveland Clinic. “Lipid Apheresis.” https://my.clevelandclinic.org
• Nordestgaard BG et al. “Familial hypercholesterolemia is underdiagnosed and undertreated in the general population.” *J Clin Invest.* 2021;131(10):e146200.

```