Muscle Channelopathies Flashcards
Myotonia congenita - clinical features
sustained muscle tension in any skeletal muscle, but especially muscles in the legs.
Frequency of myotonia congenita
1 in 100,000 people worldwide, more common in scandinavia (1 in 10,000)
Myotonia congenita - gene
CLCN1
Mytonia congenita - inheritance
Thomsen disease is AD, Becker is AR
Myotonia congenita - etiology
Mutations in CLCN1 alter the structure and function of chloride channels, resulting in a reduction of chloride ions in skeletal muscles
Paramyotonia congenita - clinical features
individuals experience spells of muscle stiffness or myotonia, can be triggered by cold or exercise
Paramyotonia congenita - frequency
1 in 100,000
Paramyotonia congenita - gene
SCN4A
Paramyotonia congenita - inheritance
AD
Paramyotonia congenita - etiology
Mutations in SCN4A gene alters the structure of sodium channels and they cannot regulate the flow of sodium into muscle cells
Hyperkalemic periodic paralysis - clinical features
episodes of extreme muscle weakness or paralysis, usually in arm and leg muscles. Episodes increase in frequency until mid-adulthood
Hyperkalemic periodic paralysis - frequency
1 in 200,000
Hyperkalemic periodic paralysis - gene
SCN4A
Hyperkalemic periodic paralysis - inheritance
AD
Hyperkalemic periodic paralysis - etiology
Mutations in SCN4A causes sodium channels to stay open too long, allowing too much sodium into cells, triggering the body to dump potassium into the blood
Hypokalemic periodic paralysis - clinical features
episodes of extreme muscle weakness and temporary paralysis of arms and legs, which can last between a few hours to days
Hypokalemic periodic paralysis - frequency
1 in 100,000
Hypokalemic periodic paralysis - gene
CACNA1S, SCN4A, KCNJ2
Hypokalemic periodic paralysis - inheritance
AD
Hypokalemic periodic paralysis - etiology
SCN4A creates sodium channels, CACNA1S creates calcium channels, and KCNJ2 creates inward rectifier potassium channels
Andersen-Tawil Syndrome - clinical features
Periods of muscle weakness and paralysis, cardiac arrhythmias and prolonged QT interval, distinctive facial features and skeletal abnormalities
Andersen-Tawil Syndrome - frequency
1 in a million people
Andersen-Tawil Syndrome - gene
KCNJ2 accounts for about 60%
Andersen-Tawil Syndrome - inheritance
AD with a large de novo rate
Andersen-Tawil Syndrome - etiology
KCNJ2 encodes inward rectifier potassium channel 2
Management for muscle channelopathies
Participate in low intensity and low resistance exercises, annual visits to cardiologists, propofol & non-depolarizing anesthetics, MRI of leg muscles every 1-3 years, thyroid function tests
What things should people with muscle channelopathies avoid?
opiods and ACE-inhibitors, fasting, foods high in carbs or potassium, exposure to cold
Treatment for muscle channelopathies
aldosterone antagonists (potassium sparing), thiazides (potassium wasting), potassium supplements, carbonic anhydrase inhibitors, sodium channel blockers
Genetic testing for muscle channelopathies
molecular genetic testing (gene-targeted testing, comprehensive genomic testing) and test levels of serum creatine kinase concentration
