Skeletal muscle channelopathies

Question 1

Myotonia

Answer 1

Muscle stiffness
Uncontrolled APs - tetanus
Shows warm-up phenomenon

Question 2

Paramyotonia

Answer 2

Muscle stiffness
Paradoxical myotonia
Uncontrolled APs - tetanus
Worsens with exercise

Question 3

Muscle weakness

Answer 3

Periodic paralyiss
Unexcitability
Individuals can still function normally

Question 4

Malignant hyperthermia

Answer 4

Mutations in skeletal RyRs
Hypersensitisation of Ca release
Increased release/sensitivity, hyper metabolism, hyperthermia, muscle contraction + rigidity (ventilation problems), hyperaemia, hyperkalemia

If survive - rhabdomyolysis (irreversible damage to skeletal muscle)

Question 5

Thompson myotonia

Myotonia Congenita

Answer 5

Dominant - need 1 allele to show phenotype

1 protein effects dimer - both pores

Question 6

Becker myotonia

Myotonia Congenita

Answer 6

Recessive - need 2 alleles to show phenotype
2 proteins (subunits) affected

Question 7

Potassium-aggravated myotonia (PAM)

Answer 7

Sodium channel myotonia - muscle rigidity
Helped by exercise
Not associated with weakness

Question 8

Paramytonia congenita

Answer 8

Sodium channel myotonia - muscle rigidity
Autosomal dominant
Exacerbated with exercise
Short-lasting weakness

Question 9

Hyperkaliemic periodic paralysis (HyperPP)

Answer 9

Sodium channel mutations
Autosomal dominant
Triggered by K+-rich food
High [K+] serum during weakness
Loss of excitability

Question 10

Hypokaliemic periodic paralysis (HypoPP)

Answer 10

Sodium channel mutations
Triggered by low K+ food
K+-rich food is a remedy

Question 11

Congenital myasthenic syndrome (CMS)

Answer 11

Defective neuromuscular transmission
Associated with nAChRs
Similar to Grave’s disease