Liddle Syndrome

Liddle syndrome is a rare autosomal dominant monogenic form of hypertension caused by gain-of-function mutations in the epithelial sodium channel (ENaC) in the distal nephron. These mutations increase aldosterone-independent sodium reabsorption, causing extracellular volume expansion, hypertension, hypokalemia, and metabolic alkalosis with suppressed plasma renin and aldosterone levels. Because it mimics mineralocorticoid excess despite low aldosterone, it is called pseudohyperaldosteronism.

1. Epidemiology

1. Rare disorder and an uncommon cause of early-onset or resistant hypertension
2. Can present in childhood, adolescence, or adulthood, though many cases are recognized between ages 11 and 31 years
3. No clear sex or racial predilection has been established
4. Hypertension is present in most patients, while hypokalemia is common but not universal
5. Variable penetrance and phenotypic heterogeneity may delay diagnosis or lead to misclassification as essential hypertension or primary hyperaldosteronism

2. Genetics

1. Inheritance is autosomal dominant with variable penetrance
2. ENaC is composed of 3 subunits encoded by:
• SCNN1A (α)
• SCNN1B (β)
• SCNN1G (γ)
3. Most classic disease-causing mutations involve the β or γ subunits, especially the PY motif
4. The PY motif is required for binding of Nedd4-2, an E3 ubiquitin ligase that normally mediates ENaC ubiquitination and degradation
5. Most mutations impair channel degradation, though a minority increase open-state probability of ENaC

3. Pathophysiology

3.1 Normal ENaC Regulation

1. ENaC is located on the apical membrane of principal cells in the distal nephron/collecting duct
2. Under normal conditions, Nedd4-2 binds the PY motif of ENaC and promotes ubiquitination, internalization, and degradation
3. Aldosterone increases ENaC activity partly through SGK1, which phosphorylates Nedd4-2 and reduces its ability to downregulate ENaC
4. This increases ENaC surface expression and sodium reabsorption

3.2 In Liddle Syndrome

1. Mutated ENaC cannot be properly regulated by Nedd4-2
2. ENaC degradation is impaired, resulting in increased channel density on the apical membrane
3. The channel remains constitutively active independent of aldosterone
4. This produces a physiologic state resembling aldosterone excess despite low aldosterone levels

3.3 Physiologic Consequences

1. ↑ Na⁺ reabsorption → extracellular volume expansion
2. Volume expansion → hypertension
3. Negative feedback on the RAAS → low renin and low aldosterone
4. Increased distal sodium entry creates a lumen-negative potential, promoting urinary K⁺ secretion → hypokalemia
5. Enhanced H⁺ secretion contributes to metabolic alkalosis

3.4 Core Concept

ENaC gain-of-function → ↑ Na⁺ reabsorption in the distal nephron → extracellular volume expansion → ↓ renin and ↓ aldosterone → ↑ distal Na⁺-dependent K⁺ and H⁺ secretion → hypokalemia + metabolic alkalosis

4. Clinical Features

4.1 Symptoms

1. Many patients are initially asymptomatic
2. Early-onset or resistant hypertension is the most typical presentation
3. Symptoms of hypokalemia may include:
• Muscle weakness
• Fatigue
• Polyuria
• Polydipsia
4. Hypertension-related complaints may include headache or dizziness
5. Severe untreated disease may predispose to arrhythmias and cardiovascular complications

4.2 Signs

1. Hypertension
2. Usually volume expanded physiologically but without overt edema
3. Hypokalemia on laboratory evaluation
4. In longstanding or undertreated disease, evidence of target-organ injury may be present:
• Left ventricular hypertrophy
• Retinopathy
• Chronic kidney disease

5. Laboratory Findings

Parameter	Typical Finding
Sodium	Usually normal; occasionally mildly ↑
Potassium	↓, but may be normal
Bicarbonate	↑ (metabolic alkalosis)
Plasma renin activity	↓
Aldosterone	↓ or low-normal
Urinary potassium	↑

Important: normal potassium does not exclude Liddle syndrome.

6. Diagnosis

6.1 Suspect in

1. A young patient with early-onset or resistant hypertension
2. Hypokalemia with or without metabolic alkalosis
3. Low renin + low or low-normal aldosterone
4. Positive family history of similar hypertension, hypokalemia, or confirmed Liddle syndrome

6.2 Confirmatory Evaluation

1. Biochemical profile showing hyporeninemic, hypoaldosteronemic hypertension
2. Genetic testing demonstrating pathogenic variants in SCNN1A, SCNN1B, or SCNN1G
3. In selected cases, broader sequencing such as whole-exome sequencing may be considered

6.3 Differential Diagnosis

Other causes of low-renin hypertension, especially with low aldosterone, include:

1. Apparent mineralocorticoid excess
• 11β-HSD2 deficiency
• Licorice ingestion
2. 11β-hydroxylase deficiency
3. 17α-hydroxylase deficiency
4. Mineralocorticoid receptor-activating mutation
5. Glucocorticoid resistance
6. Ectopic ACTH production
7. Gordon syndrome
• distinguished by hyperkalemia and metabolic acidosis, not hypokalemic metabolic alkalosis

7. Management

7.1 Nonpharmacologic

1. Dietary sodium restriction is recommended
2. Salt restriction has a synergistic effect with ENaC blockers

7.2 First-Line Pharmacologic Therapy

1. Amiloride is the treatment of choice
2. Triamterene is an effective alternative
3. These agents directly inhibit ENaC and address the primary defect

7.3 Key Therapeutic Principle

1. Spironolactone is ineffective because Liddle syndrome is not caused by excess aldosterone
2. The defect is ENaC activation independent of mineralocorticoid signaling

7.4 Additional Antihypertensive Therapy

1. If blood pressure remains above goal, additional agents may be added:
• Calcium channel blockers
• β-blockers
• Vasodilators
2. Thiazides should be used cautiously because they may worsen hypokalemia and may appear in fixed-dose combinations

7.5 Monitoring / Special Considerations

1. Monitor:
• Blood pressure
• Serum potassium
• Renal function
2. Hyperkalemia is uncommon when renal function is normal, but monitoring remains necessary
3. Amiloride also blocks lithium entry through ENaC and may help in lithium-induced nephrogenic diabetes insipidus
4. In pregnancy, amiloride has been used and dose adjustment may be required in selected patients

8. Prognosis

1. Prognosis is generally good with early recognition and appropriate ENaC-blocking therapy
2. Delayed diagnosis or undertreatment may result in persistent hypertension and progressive end-organ damage
3. Reported complications include:
• Left ventricular hypertrophy
• Myocardial infarction
• Stroke or TIA
• Heart failure
• Chronic kidney disease
• Arrhythmias
4. Early diagnosis and targeted therapy help prevent or delay cardiovascular and renal complications

9. Family Screening and Counseling

1. Because the disorder is autosomal dominant, screening of family members is recommended
2. Patients should be counseled regarding:
• Importance of medication adherence
• Low-sodium diet
• Regular follow-up for blood pressure, potassium, and renal function
3. Genetic counseling may be appropriate, especially in families with early-onset hypertension

10. Clinical Pearls

👉 Young patient with resistant hypertension + low renin + low aldosterone = think Liddle syndrome; Liddle syndrome: ↓ renin, ↓ aldosterone, ENaC gain-of-function, responds to amiloride/triamterene