- EMG: myotonic runs (HP:0003730): Spontaneous, repetitive electrical activity demonstrated by electromyography (EMG). Evidence: PCS. Frequency: 2/2. (PMID:34938096)
- Dysphagia (HP:0002015): Difficulty in swallowing. Evidence: TAS. (OMIM:255700)
- Muscle hypertrophy of the lower extremities (HP:0008968): Muscle hypertrophy primarily affecting the legs. Evidence: TAS. (OMIM:255700)
- Juvenile onset (HP:0003621): Onset of signs or symptoms of disease between the age of 5 and 15 years. Evidence: PCS. (PMID:18337100)
- Muscle stiffness (HP:0003552): A condition in which muscles cannot be moved quickly without accompanying pain or spasm. Evidence: PCS. Frequency: 25/27. (PMID:18337100)
- Myotonia (HP:0002486): An involuntary and painless delay in the relaxation of skeletal muscle following contraction or electrical stimulation. Evidence: PCS. Frequency: 2/2. (PMID:34938096)
- Myotonia with warm-up phenomenon (HP:0003740): Myotonia that occurs after a period of rest and decreases with continuing exercise. Evidence: PCS. Frequency: 29/29. (PMID:18337100;PMID:34938096)
- Percussion myotonia (HP:0010548): A localized myotonic contraction in a muscle in reaction to percussion (tapping with the examiner's finger, a rubber percussion hammer, or a similar object). Evidence: PCS. Frequency: 26/27. (PMID:18337100)
- Childhood onset (HP:0011463): Onset of disease at the age of between 1 and 5 years. Evidence: PCS. Frequency: 12/12. (PMID:18337100;PMID:34938096)
- Young adult onset (HP:0011462): Onset of disease at the age of between 16 and 40 years. Evidence: PCS. (PMID:18337100)
- Autosomal recessive inheritance (HP:0000007): A mode of inheritance that is observed for traits related to a gene encoded on one of the autosomes (i.e., the human chromosomes 1-22) in which a trait manifests in individuals with two pathogenic alleles, either homozygotes (two copies of the same mutant allele) or compound heterozygotes (whereby each copy of a gene has a distinct mutant allele). Evidence: PCS. (PMID:1379744)
- Muscle weakness (HP:0001324): Reduced strength of muscles. Evidence: PCS. Frequency: 2/2. (PMID:34938096)
- Skeletal muscle hypertrophy (HP:0003712): Abnormal increase in muscle size and mass not due to training. Evidence: PCS. Frequency: 17/29. (PMID:18337100;PMID:34938096)
- Lid lag on downgaze (HP:0025605): Delayed descent of the upper eyelid on downgaze. Also described by some authors as von Graefe sign. Evidence: PCS. Frequency: 7/27. (PMID:18337100)
- Myalgia (HP:0003326): Pain in muscle. Evidence: PCS. Frequency: 13/29. (PMID:18337100;PMID:34938096)
These phenotypes are associated with the disease myotonia congenita, autosomal recessive (OMIM:255700).