Myotonia Congenita - CLCN1

Klinische Symptomatik

The most common clinical symptom of Myotonia congenita is muscle rigidity. The disease begins in childhood and all muscle groups, including eye musculature, facial muscles and the tongue can be affected. Rigidity can improve with repetitive movement (the so-called "warm up phenomenon"). The muscles are typically hypertrophied. Men are generally more often affected than women. The autosomal recessive form of the disease is associated with a more pronounced muscle rigidity than the dominant form. Patients may develop mild proximal muscle weakness accompanied by periods of acute paralysis. The age of onset varies greatly, ranging from early childhood to adulthood.

There is an probably increased risk of anesthesia in patients presenting with myotonia congenita, particularly caused by a hypersensitivity against depolarising muscle relaxants. Prior to an anesthesia, the anesthetist must be informed when a muscle diesease is present to choose a trigger free anesthesia.

Genetik

Myotonia congenita is most often caused by mutations in the CLCN1 gene (muscular chloride channel 1 gene). Autosomal dominant (Thomsen) and recessive (Becker) mutations in the CLCN1 gene can cause various phenotypes. A sequence analysis of the CLCN1 gene can detects 95% of all disease-inducing mutations. The prevalence of de novo mutations in the dominant form is unknown.

Differential diagnostics:

CLCN1-negtive patients suspicion of myotonia/paramyotonia and an autosomal dominant inheritance: SCN4A, DMPK (DM1) or ZNF9 (DM2, PROMM) mutation analysis.

Häufigkeit

Exact prevalence is not known.

Prevalence is between 1 : 10 000 (in Scandinavia) and 1 : 100 000 (worldwide).

 

Diagnostik