Information on the following diseases can be found in the Related Disorders section of this report:

• Hyperkalemic Periodic Paralysis
• Myotonic Dystrophy
• Thomsen Disease

Symptoms include muscle stiffness and weakness, mostly in the face, neck and upper extremities. The muscles are slow to relax after contracting (myotonia). This condition may become worse with exposure to cold.

Paramyotonia congenita is usually apparent during infancy and is not progressive. Individuals with this disorder do not have wasting of muscles (atrophy) or an increase of muscle bulk (hypertrophy).

This condition is transmitted as an autosomal dominant genetic trait. The malfunctioning gene has been tracked to the long arm of chromosome 17 (17q23.1-q25.3)

Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated "p" and a long arm designated "q". Chromosomes are further sub-divided into many bands that are numbered. For example, "chromosome 17q23.1-q25.3" refers to a region on the long arm of chromosome 17 between bands 23.1 and 25.3. The numbered bands specify the location of the thousands of genes that are present on each chromosome.

Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.

All individuals carry a few abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.

Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.

Paramyotonia congenita is a very rare disorder that affects males and females in equal numbers. A detailed study conducted in Germany concluded that the incidence of PMC was between 1 in 180,000 and 1 in 350,000. They note that the distribution of this disorder is not uniform since they found a region of the country in which the incidence was 1 in 8000.

Three large families with multiple generations of affected members have accounted for at least 60 patients with paramyotonia congenita.

Symptoms of the following disorders can be similar to those of Paramyotonia Congenita. Comparisons may be useful for a differential diagnosis:

Hyperkalemic Periodic Paralysis is rare disorder inherited as an autosomal dominant trait and typically detected during infancy. This disorder is characterized by periodic muscle weakness with or without muscles that do not relax after contracting (myotonia). Patients may have attacks once a week or several times a day. Typically the periods of muscle weakness last from one half an hour to an hour. This weakness may be found in the calves or thighs of the legs, lower back, arms, neck and/or eyelids. Periods of muscle weakness usually follow rest after exercise, hunger, infection, exposure to the cold and/or emotional stress. Permanent weakness and wasting of muscles may develop later on.

Myotonic Dystrophy is a rare disorder inherited as an autosomal dominant trait. This disorder involves the muscles, vision, and endocrine glands. Myotonic Dystrophy usually begins during young adulthood and is marked initially by an inability to relax muscles after contraction. Loss of muscle strength, mental deficiency, cataracts, reduction of testicular function, and frontal baldness are also symptomatic of this disorder. (For more information on this disorder, choose "Myotonic Dystrophy" as your search term in the Rare Disease Database.)

Thomsen Disease is a rare disorder inherited as an autosomal dominant trait. This neuromuscular disorder usually begins early in life. Difficulty in initiating movement combined with slowness of muscle relaxation are the primary symptoms. Muscle stiffness of the entire body may also occur. Thomsen Disease is generally a nonprogressive disorder. (For more information on this disorder, choose "Thomsen Disease" as your search term in the Rare Disease Database.)

Diagnosis
When paramyotonia congenita is suspected, a test is administered to test the capacity of muscles to conduct electricity (electromyography).

Treatment
The aim of treatment is to reduce the intensity of acute symptoms and to prevent, as far as possible, further attacks. Some attacks are so mild that treatment is not necessary. However, in other instances drug therapy is required.

Some patients with paramyotonia congenita may benefit from acetazolamide or thiazide diuretic drugs to reduce the number of paralytic attacks. Treatment with the drug tocainide may help reduce the cold-induced symptoms in some patients.

Genetic counseling may be of benefit for patients and their families. Other treatment is symptomatic and supportive.

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov

For information about clinical trials sponsored by private sources, contact:
www.centerwatch.com

McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). Baltimore, MD: The Johns Hopkins University Press; Paramyotonia Congenita of Von Eulenburg; PMC. Entry No: 168300; Last Edit: 8/26/2005.

TEXTBOOKS
Kasper, DL, Fauci AS, Longo DL, et al., eds. Harrison’s Principles of Internal Medicine. 16th ed. McGraw-Hill Companies. New York, NY; 2005:2526; 2537.

Rowland LP, ed. Merritt’s Neurology. 10th ed. Lippincott Williams & Wilkins. Philadelphia, PA. 2000:749.

Rimoin D, Connor JM, Pyeritz RP, Korf BR, eds. Emory and Rimoin’s Principles and Practice of Medical Genetics. 4th ed. Churchill Livingstone. New York, NY; 2002:3377-82.

JOURNAL ARTICLES
Weber MA, Nielles-Vallespin S, Huttner HB, Worhle JC, et al. Radiology. 2006;240:489-500.

Kurihara T. New classification and treatment for myotonic disorders. Intern Med. 2005;44:1027-32.

Vicart S, Sternberg D, Fontaine B, Meola G. Human skeletal muscle sodiym channelopathies. Neurol Sci. 2005;26:194-202

Fredericson M, Kim BJ, Date ES. Disabling foot cramping in a runner secondary to paramyotonia congenita: a case report. Foot Ankle Int. 2004;25

Kuntzer T. [Electrophysiological testing in muscle channelopathies] Rev Neurol (Paris). 2004;160(5 Pt 2):S49-54. French.

FROM THE INTERNET
Mosenkis A. Hyperkalemic periodic paralysis. Medical Encyclopedia. MedlinePlus. Update Date: 8/5/2004. 4pp.
www.nlm.nih.gov/medlineplus/ency/article/000316.htm

Frequently Asked Questions about Paramyotonia Congenita. Periodic Paralysis News Desk. Last updated March 2006. 4pp.
www.hkpp.org/faq/pmc.html

Emery AEH. Myotonias. Muscular Dystrophy Campaign. 2004. 3pp.
www.muscular-dystrophy.org/information_resources/factsheets/medical_conditions_factsheets/myotonias.html