Dysmorphic features may include short stature,
low-set ears (40%), hypertelorism (36%), broad nasal root,
micrognathia (50%), prognathism, cleft palate or high arched palate
(10%), clinodactyly (70%), syndactyly (11%), and scoliosis
(11%). The main neurologic sign is periodic paralysis, which is not
necessarily related to hyperkalemia or hypokalemia and usually presents with
proximal muscle weakness (and not myotonia). Cardiac manifestations most
often are prolonged QT syndrome and symptomatic or asymptomatic ventricular
tachycardias. Patients have a higher risk for sudden cardiac death, although
the incidences of syncope and cardiac arrest are significantly lower than in
patients with type 1 and 2 long QT syndrome. Long QT Syndrome is
present in more than 70% of Andersen syndrome patients with the KCNJ2
mutation, and ventricular arrhythmias occur in 64%. Triggers for periodic
paralysis are inconsistent but may include rest after activities, periods of
inactivity, and sleep. Fasting, but also eating a large meal, and becoming
chilled are other common triggers. Chemical fumes and vapors containing
hydrocarbons (paint, gasoline, car exhaustion) have been described as
triggers in some patients. Even for an individual patient, potassium shifts
during attacks of weakness are inconsistent. This finding indicates that at
one point paralysis may be caused by hypokalemia (most common form 55%),
but the next time it may be triggered by hyperkalemia (22%).
Potassium-sensitive ACPPS patients may become weak and develop QTc
prolongation when they are hypokalemic. Carbonic anhydrase inhibitors are
used in this form of periodic paralysis to reduce the frequency and severity
of the attacks.