#OMIM170390 – https://omim.org/entry/170390

Also known as: Andersen syndrome; Long QT syndrome; Andersen cardiodysrhythmic periodic paralysis; Periodic paralysis, potassium-sensitive cardiodysrhythmic type

1. The Disease:

A rare disorder characterized by periodic muscle paralysis, prolongation of the QT interval with a variety of ventricular arrhythmias (leading to predisposition to sudden cardiac death) and characteristic physical features: short stature, scoliosis, low-set ears, hypertelorism, broad nasal root, micrognathia, clinodactyly, brachydactyly and syndactyly.

2. The symptoms:

ATS is characterized by a triad of: episodic flaccid muscle weakness (i.e., periodic paralysis); ventricular arrhythmias and prolonged QT interval; and anomalies including low-set ears, widely spaced eyes, small mandible, fifth digit clinodactyly, syndactyly, short stature, and scoliosis. Lack of early signs or symptoms does not exclude the diagnosis.

  • Affected individuals present in the first or second decade with either cardiac symptoms (palpitations and/or syncope) or weakness that occurs spontaneously following prolonged rest or following rest after exertion. Mild permanent weakness is common.
  • Mild learning difficulties and a distinct neurocognitive phenotype(i.e., deficits in executive function and abstract reasoning) have been described.

3. Actions to take in case of early diagnosis

  • Babies with a positive genetic test (1 pathogenic variants in heterozygous state in the KCNJ2 gene), should continue breastfeeding.
  • The diagnosis is based on genetic results, clinical features, and EKG abnormalities.
  • ATS is a lifelong condition that requires lifetime management and regular follow-up with a paediatrician specialist in cardiology, geneticist, and a multidisciplinary approach to care.
  • Treatment of manifestations: For episodic weakness: if serum potassium concentration is low (<3.0 mmol/L), administration of oral potassium (20-30 mEq/L) every 15-30 minutes (not to exceed 200 mEq in a 12-hour period) until the serum concentration normalizes; if a relative drop in serum potassium within the normal range causes episodic paralysis, an individual potassium replacement regimen with a goal of maintaining serum potassium levels in the high range of normal can be considered; if serum potassium concentration is high, ingesting carbohydrates may lower serum potassium levels. Mild exercise may shorten or reduce the severity of the attack.
  • Prevention of primary manifestations: Reduction in frequency and severity of episodic attacks of weakness with lifestyle/dietary modification to avoid known triggers; use of carbonic anhydrase inhibitors; daily use of slow-release potassium supplements; implantable cardioverter-defibrillator for those with tachycardia-induced syncope. Empiric treatment with flecainide should be considered for significant, frequent ventricular arrhythmias in the setting of reduced left ventricular function.
  • Prevention of secondary complications: Cautious use of antiarrhythmic drugs that may paradoxically exacerbate the neuromuscular symptoms.
  • Surveillance: Annual screening of asymptomatic individuals with a KCNJ2pathogenic variant with a 12-lead EKG and 24-hour Holter monitoring.
  • Agents/circumstances to avoid: Medications known to prolong QT intervals; salbutamol inhalers (may exacerbate cardiac arrhythmias); thiazide and other potassium-wasting diuretics (may provoke drug-induced hypokalaemia and could aggravate the QT interval prolongation).
  • Genetic counselling is highly recommended for family planning and evaluation of at-risk family members.

4. For more informations :

Biblio: https://www.ncbi.nlm.nih.gov/books/NBK1264/