- EMG: myotonic runs (HP:0003730): Spontaneous, repetitive electrical activity demonstrated by electromyography (EMG). Evidence: PCS. (PMID:18337100)
- 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: 7/9. (PMID:18337100)
- Myotonia with warm-up phenomenon (HP:0003740): Myotonia that occurs after a period of rest and decreases with continuing exercise. Evidence: PCS. Frequency: 9/9. (PMID:18337100)
- Myotonia (HP:0002486): An involuntary and painless delay in the relaxation of skeletal muscle following contraction or electrical stimulation. Evidence: PCS. Frequency: 7/9. (PMID:18337100)
- Handgrip myotonia (HP:0012899): Difficulty releasing one's grip associated with prolonged first handgrip relaxation times. Evidence: PCS. Frequency: 5/9. (PMID:18337100)
- 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: 4/9. (PMID:18337100)
- Early young adult onset (HP:0025708): Onset of disease at an age of greater than or equal to 16 to under 19 years. Evidence: PCS. (PMID:18337100)
- Childhood onset (HP:0011463): Onset of disease at the age of between 1 and 5 years. Evidence: PCS. (PMID:18337100)
- Skeletal muscle hypertrophy (HP:0003712): Abnormal increase in muscle size and mass not due to training. Evidence: PCS. Frequency: 7/9. (PMID:18337100)
- Muscle weakness (HP:0001324): Reduced strength of muscles. Evidence: PCS. Frequency: 0/9. (PMID:18337100)
- 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: 1/9. (PMID:18337100)
- Autosomal dominant inheritance (HP:0000006): 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 heterozygotes. In the context of medical genetics, an autosomal dominant disorder is caused when a single copy of the mutant allele is present. Males and females are affected equally, and can both transmit the disorder with a risk of 50% for each child of inheriting the mutant allele. Evidence: PCS. (PMID:18337100)
- Myalgia (HP:0003326): Pain in muscle. Evidence: PCS. Frequency: 1/9. (PMID:18337100)
These phenotypes are associated with the disease myotonia congenita, autosomal dominant (OMIM:160800).