Exploring a rare genetic disorder in a small country

Myotonia congenita type Becker is an autosomal recessive nondystrophic skeletal muscle disorder, caused by mutations in the CLCN1 gene. With a frequency of 0.6 per 100,000, myotonia congenita type Becker falls into the group of rare disorders. In the terms of a small country like Bulgaria, this means only single cases, seriously complicating the recognition and characterization of such a disorder. The present study encompasses the first genetically confirmed cases of Myotonia congenita type Becker in Bulgaria. The applied molecular genetic approach led to identification of the disease causing mutations in 78% of the tested families. In addition, two presumable endemic regions were studied, leading to identification of a significant carrier frequency in both regions of interest. These findings are from crucial importance for the inhabitants of the corresponding parts of Bulgaria in the terms of well-timed screening and adequate genetic counseling during family planning.