Andersen-Tawil syndrome. ATS. Long QT syndrome 7. LQT7. Potassium-sensitive periodic paralysis, ventricular ectopy, and dysmorphic features.
Incidence
About 40-60% of cases of Andersen-Tawil syndrome are caused by mutations in the KCNJ2 gene. The cause of the remaining cases remains unknown. This condition is inherited in an autosomal dominant pattern although sporadic cases have been reported. Penetrance is extremely variable.
Clinical Characteristics
Andersen-Tawil syndrome is 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. It is type of long QT syndrome and is also considered a rare form of periodic paralysis. It causes episodes of muscle weakness, changes in heart rhythm (arrhythmia), and developmental abnormalities. Physical abnormalities associated with this condition typically affect the head, face, and limbs. About 60% of cases of Andersen-Tawil syndrome are caused by mutations in the KCNJ2 gene. The cause of the remaining cases remains unknown. This condition is inherited in an autosomal dominant pattern. Physical abnormalities associated with Andersen-Tawil syndrome typically affect the head, face, and limbs. These features often include a very small lower jaw (micrognathia), dental abnormalities, low-set ears, widely spaced eyes, and unusual curving of the fingers or toes (clinodactyly). Some affected people also have short stature and an abnormal curvature of the spine (scoliosis)
Precipitants
Attacks may be triggered by low (or high) potassium, taking potassium supplement (in some patients), exercise, rest after exercise, sleep or other factors which vary from patient.
Provocation Tests
Provocation tests are not recommended. However an exercise EKG will usually be used to help make the diagnosis. The goal of the exercise test is to allow the individual to exercise for 10 or more minutes without reaching a heart rate in excess of 150-160 beats per minute while hooked up to a heart monitor. This exercise often \"uncovers\" a long QT interval which doesn\'t show up when the patient is at rest.
Diagnostic Procedures
The diagnosis of Andersen-Tawil syndrome might be suspected in individuals with either:1. Two of the following three criteria: a) Periodic paralysis. b) Symptomatic cardiac arrhythmias or evidence of enlarged U-waves, ventricular ectopy, or a prolonged QTc or QUc interval on electrocardiogram (ECG). c) Characteristic facial features, dental abnormalities, small hands and feet, and at least two of the following: Low-set ears, Widely spaced eyes, Small lower jaw (mandible), Fifth-digit clinodactyly (curved pinky finger), Syndactyly.
or 2. One of the above three criteria in addition to at least one other family member who meets two of the three criteria. The presence of a mutation in the KCNJ2 gene confirms the diagnosis of Andersen-Tawil syndrome. Genetic testing can identify mutations in only about 40% to 60% of clinically diagnosed ATS patients, as many mutations have yet to be identified.