Types Two types of<unk>  exist, an autosomal dominant form and an autosomal recessive form. Autosomal dominant<unk>  (OMIM #160800) is also called Thomsen disease, after Danish/German physician Asmus Julius Thomas Thomsen (1815–1896), who himself had the disease and who wrote the first description of it in the medical literature (in 1876). Autosomal recessive<unk>  (OMIM #255700) is also called generalized<unk> , recessive generalized<unk>  (RGM), Becker disease, and Becker<unk> , after the German professor Peter Emil Becker, who discovered its recessive nature. The term<unk> l in its sense of "clinically apparent from birth" applies only to Thomsen disease, as the clinical onset of Becker<unk>  may be delayed up to the age of 4 to 6 years. But in either form of<unk> , the term's strictest sense reflects that the disease is genetically present from birth, although the clinical onset may be delayed. With the advent of genetic testing, it has recently been found that some typically recessive mutations may occur in a dominant fashion in some individuals. The reason for this is not known. Because several CLCN1 mutations can cause either Becker disease or Thomsen disease, doctors usually rely on characteristic signs and symptoms to distinguish the two forms of<unk> . However,<unk>  caused by CLCN1 mutations can occasionally be clinically indistinguishable from<unk>  caused by sodium channel mutations (SCN4A mutations) resulting in the similar disease paramyotonia<unk> . A so-called Finnish heritage disease,<unk> l<unk>  is more common in Finland and among ethnic Finns. A molecular study of the CLCN1 gene in 24 families in northern Finland, including 46 affected individuals, showed that although the inheritance appeared to be dominant (Thomsen type), in fact it is recessive (Becker type). Differential diagnosis Sodium channel<unk> s (SCN4A) * Potassium-aggravated<unk>  (acetazolamide responsive<unk>  * Paramyotonia<unk>  * Hyperkalemic periodic paralysis Dystrophies *<unk>  dystrophy <unk>  muscular dystrophy: Type 1 and Type 2) Potassium channel disorders (KCNJ2) * Andersen-Tawil syndrome Other disorders * Thyroid disorders * Neuromyotonia (Isaacs Syndrome) * Schwartz–Jampel syndrome * Stiff person syndrome * Brody myopathy (Brody Disease, Brody's Disease, Brody's Myopathy)
Myotonia congenita
Myotonic dystrophy
Paramyotonia congenita
Periodic paralysis
Klumpke paralysis
Quadrigia
Cardiofaciocutaneous syndrome
Hyperkalemic periodic paralysis