- Easy fatigability (HP:0003388): Increased susceptibility to fatigue. Evidence: TAS. (OMIM:615120)
- Childhood onset (HP:0011463): Onset of disease at the age of between 1 and 5 years. Evidence: PCS. Frequency: 2/2. (PMID:19631309)
- Ptosis (HP:0000508): The upper eyelid margin is positioned 3 mm or more lower than usual and covers the superior portion of the iris (objective); or, the upper lid margin obscures at least part of the pupil (subjective). Evidence: PCS. Frequency: 2/2. (PMID:19631309)
- Difficulty running (HP:0009046): Reduced ability to run. Evidence: PCS. Frequency: 2/2. (PMID:19631309)
- 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:19631309)
- High palate (HP:0000218): Height of the palate more than 2 SD above the mean (objective) or palatal height at the level of the first permanent molar more than twice the height of the teeth (subjective). Evidence: TAS. Frequency: Occasional (HP:0040283). (OMIM:615120)
- Respiratory insufficiency (HP:0002093). Evidence: TAS. Frequency: Occasional (HP:0040283). (OMIM:615120)
- Narrow chest (HP:0000774): Reduced width of the chest from side to side, associated with a reduced distance from the sternal notch to the tip of the shoulder. Evidence: TAS. (OMIM:615120)
- Proximal muscle weakness (HP:0003701): A lack of strength of the proximal muscles. Evidence: PCS. Frequency: 1/2. (PMID:19631309)
- Weakness of facial musculature (HP:0030319): Reduced strength of one or more muscles innervated by the facial nerve (the seventh cranial nerve). Evidence: PCS. Frequency: 2/2. (PMID:19631309)
- EMG: decremental response of compound muscle action potential to repetitive nerve stimulation (HP:0003403): A compound muscle action potential (CMAP) is a type of electromyography (EMG). CMAP refers to a group of almost simultaneous action potentials from several muscle fibers in the same area evoked by stimulation of the supplying motor nerve and are recorded as one multipeaked summated action potential. This abnormality refers to a greater than normal decrease in the amplitude during the course of the investigation. Evidence: PCS. Frequency: 2/2. (PMID:19631309)
These phenotypes are associated with the disease congenital myasthenic syndrome 8 (OMIM:615120).