Types
Periodic paralysis is an autosomal dominant myopathy with considerable variation in penetrance, leading to a spectrum of familial phenotypes (only one parent needs to carry the gene mutation to affect the children, but not all family members who share the gene are affected to the same degree). Specific diseases include:
- Hypokalemic periodic paralysis (Online 'Mendelian Inheritance in Man' (OMIM) 170400), where potassium leaks into the muscle cells from the bloodstream.
- Hyperkalemic periodic paralysis (Online 'Mendelian Inheritance in Man' (OMIM) 170500), where potassium leaks out of the cells into the bloodstream.
- Paramyotonia congenita (Online 'Mendelian Inheritance in Man' (OMIM) 168300), a form which often accompanies hyperkalemic periodic paralysis, but may present alone. The primary symptom of paramyotonia congenita is muscle contracture which develops during exercise or activity. Paramyotonia congenita attacks may also be triggered by a low level of potassium in the bloodstream. This means people with both hyperkalemic periodic paralysis and paramyotonia congenita can have attacks with fluctuations of potassium up or down.
- Andersen-Tawil syndrome (Online 'Mendelian Inheritance in Man' (OMIM) 170390), a form of periodic paralysis that includes significant heart rhythm problems, fainting and risk of sudden death. Potassium levels may be low, high, or normal during attacks of ATS. Patients with ATS may also have skeletal abnormalities like scoliosis (curvature of the spine), webbing between the second and third toes or fingers (syndactyly), crooked fingers (clinodactyly), a small jaw (micrognathia) and low-set ears.
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