HEREDITARY MYOKYMIA AND PAROXYSMAL ATAXIA LINKED TO CHROMOSOME-12 IS RESPONSIVE TO ACETAZOLAMIDE

A sixth family with autosomal dominantly inherited myokymia and paroxy smal ataxia is described. The syndrome in this family is linked to the recently discovered locus for inherited myokymia and paroxysmal ataxi a on the human chromosome 12p, and a missense mutation is shown in the KCNA1 gene. The attacks of ataxia in this family compare well with th ose of previously described families and similarly are precipitated by kinesigenic stimuli, exertion, and startle. Responsiveness of these a ttacks to low dose acetazolamide is confirmed, but some loss of effica cy occurs with prolonged treatment, and side effects are notable. Alth ough not all affected family members showed myokymia on clinical exami nation, electromyography invariably showed myokymic discharges, in one patient only after a short provocation with regional ischaemia. One a ffected family member also had attacks of paroxysmal kinesigenic chore oathetosis, responsive to carbamazepine.