Are there any new treatments for myotonia congentia?

No- but new types: Myotonia congenita used to be divided into either thomson or becker's disease. It now appears that there are over 80 mutations (in the chloride channel gene or a sodium channel gene) that contribute to a diagnosis of typical or atypical myotonia congenita. Identifying the particular gene mutation will lead to better personalized treatment options.

Not really: But most patients with myotonia congenita do not require medicines. If the myotonia is severe and limits function, medications which may help include anti-arrhythmics and anti-epileptics. Mexilitine and Phenytoin have shown successes. Very specialized area, and best to see pediatric neurologist.