The autosomal recessive (Becker) form of myotonia congenita.

In the last two decades, two genetically distinct forms of myotonia congenita have been identified--an autosomal dominant and an autosomal recessive form. The purpose of this review is to describe the features that enable us to distinguish between these two forms in the absence of sufficient genetic data. Thus far, it can be concluded that the only probable difference between the two forms is in the fatty-acid pattern of muscle phospholipids. Clinical, histologic, ultrastructural, and electromyographic investigation may prove helpful, but they alone cannot provide a reliable means of identifying the genotype in an individual patient.