Different defects in the same gene on chromosome 17 appear to cause paramyotonia congenita and at least one form of myotonia congenita, as well as hyperkalemic periodic paralysis.
What is the difference between myotonia congenita and paramyotonia congenita?
Myotonia congenita and paramyotonia congenita differ from each other in the age of onset, muscles affected and the form of myotonia present.
Paramyotonia congenita causes a type of myotonia in which exposure to cold brings on prolonged muscle contraction in the face, forearms and hands.
However, it differs from myotonia congenita in being more readily triggered by cold and in that the myotonia in paramyotonia congenita becomes worse rather than better with repetitive activity.
A number of different defects in this same gene have been found to be associated with hyperkalemic periodic paralysis, at least one form of myotonia congenita and paramyotonia congenita.
Central core disease, some forms of myotonia congenita, myotubular myopathy (possibly), some forms of nemaline myopathy, paramyotonia congenita and periodic paralysis follow the autosomal dominant pattern.
Another diagnostic test is the electro-myogram (EMG), which is particularly helpful in the diagnosis of myotonia congenita or paramyotonia congenita.
With paramyotonia congenita, specific treatment of the symptoms is often unnecessary.
Thus far, locations of the defective genes responsible for central core disease, hyperkalemic periodic paralysis, paramyotonia congenita and at least three forms of myotonia congenita are known.