Recurrent syncope in the Andersen Tawil syndrome - Cardiac or neurological?

An 8-year-old female patient was referred to a paediatrician for assessment of an episode of global muscle weakness after a 100 m sprint. There was no loss of consciousness. Proximal hip muscles and shoulder girdle weakness was noted and the possibility of a myopathy was raised. Muscle biopsy demonstrated “ultra-structurally normal muscle fibres”. There was indolent progression of proximal muscle weakness over the years, with no diagnosis made. At the age of 18 the patient experienced three episodes of transient loss of consciousness over a two-week period. A witness described sudden “unresponsiveness and generalised muscle twitching”; a period of confusion consistent with a post-ictal period was noted. There was no urinary incontinence or tongue biting. No trigger was identified. Inpatient