CONDITION REFERENCE
Congenital myasthenic syndromes
Information from MedlinePlus Genetics about this condition and how it can be inherited.
About this condition
Congenital myasthenic syndromes are a group of conditions that are characterized by weak muscles that tire easily (myasthenia). In people with these conditions, myasthenia typically begins shortly after birth or during early childhood. The most commonly affected muscles are the muscles in the head and neck (bulbar muscles) that control chewing and swallowing, speech, and facial expressions; the muscles that move the eyes and eyelids; and the muscles in the arms and legs. However, any of the muscles used for movement (skeletal muscles) can be affected.
In individuals with congenital myasthenic syndromes, episodes of severe weakness or breathing problems may be triggered by fevers, infection, or tiring physical activity. The severity of the myasthenia varies greatly, from minor muscle weakness to severe weakness that may require wheelchair assistance.
Babies with congenital myasthenic syndromes may have feeding difficulties. Some affected babies may also experience short pauses in breathing (apnea) that can lead to a bluish appearance of the skin or lips (cyanosis). In severe instances, a lack of movement before birth can lead to joint deformities (contractures) that cause joint stiffness (arthrogryposis) and impair movement.
Children with congenital myasthenic syndromes may have speech problems (dysarthria) or swallowing difficulties (dysphagia). The development of motor skills, such as crawling or walking, may be delayed in these children.
Inheritance
- Autosomal recessive
- Autosomal dominant
A condition can have several forms with different inheritance patterns. Each pattern may apply to a different gene or form of the condition.
Related genes
MedlinePlus lists these genes for this condition. Open a gene page to read any available ClinGen reviews and ClinVar records.
YOUR DNA FILE
What can your DNA file tell you?
Your DNA file only includes the positions your test checked and reported. Consumer DNA kits usually test selected positions. Sequencing files can also leave out positions that were not reported or where the test could not give a result.
A variant missing from your file does not mean you tested negative for it. A ClinVar classification applies to a particular variant and the condition or finding it was reported for. It does not apply to everyone with that gene. An uncertain finding cannot establish a diagnosis.
BioDecode reads supported DNA files on your computer. It cannot fill gaps in your test, diagnose a condition or replace clinical testing.
Sources and dates
The source information on this page last changed on 2026-09-18.
MedlinePlus Source details
Source release: Fri, 18 Sep 2026 05:17:13 GMT
Source publication: 2026-02-13
Source review: 2026-02
SHA-256: fdc8bd614310c12718379cef6569962e5d0e791cecabcc355b53a72816ac263a
About the library sources · Latest validated release · Record 54c2473e46fd