- Impaired mastication (HP:0005216): An abnormal reduction in the ability to masticate (chew), i.e., in the ability to crush and ground food in preparation for swallowing. Evidence: PCS. Frequency: 1/4. (PMID:9158151)
- Type 2 muscle fiber atrophy (HP:0003554): Atrophy (wasting) affecting primary type 2 muscle fibers. This feature in general can only be observed on muscle biopsy. Evidence: IEA. (OMIM:601462)
- Middle age onset (HP:0003596): A type of adult onset with onset of symptoms at the age of 40 to 60 years. Evidence: PCS. Frequency: 1/4. (PMID:9158151)
- Fatigable weakness (HP:0003473): A type of weakness that occurs after a muscle group is used and lessens if the muscle group has some rest. That is, there is diminution of strength with repetitive muscle actions. Evidence: PCS. Frequency: 4/4. (PMID:9158151)
- Infantile onset (HP:0003593): Onset of signs or symptoms of disease between 28 days to one year of life. Evidence: PCS. Frequency: 1/4. (PMID:9158151)
- Lower limb muscle weakness (HP:0007340): Weakness of the muscles of the legs. Evidence: PCS. Frequency: 1/4. (PMID:9158151)
- 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:601462)
- Intrinsic hand muscle atrophy (HP:0008954): Atrophy of the intrinsic muscle groups of the hand, comprising the thenar and hypothenar muscles; the interossei muscles; and the lumbrical muscles. Evidence: PCS. Frequency: 1/4. (PMID:9158151)
- Ophthalmoparesis (HP:0000597): Ophthalmoplegia is a paralysis or weakness of one or more of the muscles that control eye movement. Evidence: IEA. (OMIM:601462)
- Dysphagia (HP:0002015): Difficulty in swallowing. Evidence: IEA. (OMIM:601462)
- Generalized muscle weakness (HP:0003324): Generalized weakness or decreased strength of the muscles, affecting both distal and proximal musculature. Evidence: PCS. Frequency: 2/4. (PMID:9158151)
- Juvenile onset (HP:0003621): Onset of signs or symptoms of disease between the age of 5 and 15 years. Evidence: PCS. Frequency: 1/4. (PMID:9158151)
- Decreased size of nerve terminals (HP:0003443): A reduction in the size of nerve terminals. Evidence: IEA. (OMIM:601462)
- Feeding difficulties (HP:0011968): Impaired ability to eat related to problems gathering food and getting ready to suck, chew, or swallow it. Evidence: TAS. (OMIM:601462)
- Upper limb muscle weakness (HP:0003484): Weakness of the muscles of the arms. Evidence: PCS. Frequency: 4/4. (PMID:9158151)
- Dysarthria (HP:0001260): Dysarthric speech is a general description referring to a neurological speech disorder characterized by poor articulation. Depending on the involved neurological structures, dysarthria may be further classified as spastic, flaccid, ataxic, hyperkinetic and hypokinetic, or mixed. Evidence: IEA. (OMIM:601462)
- Anti-neuromuscular Junction acetylcholine receptor antibody positivity (HP:0030208): The presence of autoantibodies (immunoglobulins) in the blood circulation that react against neuromuscular junction acetylcholine receptors. Evidence: PCS. Frequency: 0/4. (PMID:9158151)
- Intermediate young adult onset (HP:0025709): Onset of disease at an age of greater than or equal to 19 to under 25 years. Evidence: PCS. Frequency: 1/4. (PMID:9158151)
- Hand muscle atrophy (HP:0009130): Muscular atrophy involving the muscles of the hand. Evidence: PCS. Frequency: 3/4. (PMID:9158151)
- Diaphragmatic weakness (HP:0009113): A decrease in the strength of the diaphragm. Evidence: PCS. Frequency: 2/4. (PMID:9158151)
- 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: IEA. (OMIM:601462)
- Ophthalmoplegia (HP:0000602): Paralysis of one or more extraocular muscles that are responsible for eye movements. Evidence: TAS. (OMIM:601462)
- Intermittent episodes of respiratory insufficiency due to muscle weakness (HP:0004889). Evidence: IEA. (OMIM:601462)
- 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:9158151)
- Prolonged miniature endplate currents (HP:0003436): An abnormal prolongation of the miniature endplate potentials, i.e. the postsynaptic response to transmitter released from an individual vesicle at the neuromuscular junction. Evidence: PCS. (PMID:9158151)
These phenotypes are associated with the disease congenital myasthenic syndrome 1A (OMIM:601462).