- Myotonia (HP:0002486): An involuntary and painless delay in the relaxation of skeletal muscle following contraction or electrical stimulation. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:614)
- EMG abnormality (HP:0003457): Abnormal results of investigations using electromyography (EMG). Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:614)
- Muscle stiffness (HP:0003552): A condition in which muscles cannot be moved quickly without accompanying pain or spasm. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:614)
- Myotonia with warm-up phenomenon (HP:0003740): Myotonia that occurs after a period of rest and decreases with continuing exercise. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:614)
- EMG: myotonic discharges (HP:0100284): High frequency discharges in electromyography (EMG) that vary in amplitude and frequency, waxing and waning continuously with firing frequencies ranging from 150/second down to 20/second and producing a sound that has been referred to as a dive bomber sound. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:614)
- Myalgia (HP:0003326): Pain in muscle. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:614)
- Skeletal muscle hypertrophy (HP:0003712): Abnormal increase in muscle size and mass not due to training. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:614)
- Clumsiness (HP:0002312): Lack of physical coordination resulting in an abnormal tendency to drop items or bump into objects. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:614)
- Muscle spasm (HP:0003394): Sudden and involuntary contractions of one or more muscles. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:614)
- EMG: myopathic abnormalities (HP:0003458): The presence of abnormal electromyographic patterns indicative of myopathy, such as small-short polyphasic motor unit potentials. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:614)
- Feeding difficulties in infancy (HP:0008872): Impaired feeding performance of an infant as manifested by difficulties such as weak and ineffective sucking, brief bursts of sucking, and falling asleep during sucking. There may be difficulties with chewing or maintaining attention. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:614)
- Progressive distal muscle weakness (HP:0009063): Progressively reduced strength of the distal musculature. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:614)
- Dysphagia (HP:0002015): Difficulty in swallowing. Evidence: TAS. Frequency: Very rare (HP:0040284). (ORPHA:614)
- Arrhythmia (HP:0011675): Any cardiac rhythm other than the normal sinus rhythm. Such a rhythm may be either of sinus or ectopic origin and either regular or irregular. An arrhythmia may be due to a disturbance in impulse formation or conduction or both. Evidence: TAS. Frequency: Very rare (HP:0040284). (ORPHA:614)
- Cardiac conduction abnormality (HP:0031546): Any anomaly of the progression of electrical impulses through the heart. Evidence: TAS. Frequency: Very rare (HP:0040284). (ORPHA:614)
These phenotypes are associated with the disease Thomsen and Becker disease (ORPHA:614).