Hyperkalemic Periodic Paralysis
Nondystrophic myotonias are a group of disorders characterized by skeletal muscle excitability leading to failure of muscle relaxation after activation or contraction leading to stiffness. Individuals with these conditions may experience periodic cramping followed by weakness, stiffness, and fatigue. Temporary paralysis may occur in some cases. Triggers may include cold, stress, or exercise. These symptoms often appear early in life between infancy and childhood, but onset may be in adulthood in rare cases. Unlike its counterpart, dystrophic myotonia, nondystrophic myotonias are not usually progressive and most often do not involve other organ systems.
Nondystrophic myotonias are often linked to pathogenic variants in the SCN4A or CLCN1 genes. Our panel also includes evaluation of genes associated with related conditions such as rippling muscle disease, periodic paralysis, and Schwartz-Jampel syndrome, a syndromic condition characterized by myotonia.
Who is this test for?
This panel may be appropriate for anyone with a personal or family history of nondystrophic myotonia. Patients exhibiting symptoms of myotonia without any signs of progressive muscle-weakening can also benefit from this test. Nondystrophic myotonia should be a consideration particularly when the associated symptoms are triggered by cold temperatures, exercise, viral infection, eating certain foods, or fasting.
What are the potential benefits for my patient?
Nondystrophic myotonia is extremely rare and there are no FDA-approved therapeutic treatments for it at this time. This also makes it harder to diagnose as it is frequently overlooked. Genetic testing is useful not only for assisting with diagnoses but also for identifying the specific type of nondystrophic myotonia present and developing an appropriate treatment plan.
Genetic testing for nondystrophic myotonia can:
- Establish or confirm the appropriate diagnosis
- Identify risks for additional related symptoms
- Connect patients to relevant resources & support
- Result in more personalized treatment and symptom management
- Inform family members about their own risk factors
- Provide options for family planning