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Congenital myasthenic syndrome 1A(CMS1A)

MedGen UID:
419336
Concept ID:
C2931107
Disease or Syndrome
Synonyms: CMS IIa; CMS1A; MYASTHENIC SYNDROME, CONGENITAL, 1A, SLOW-CHANNEL; Myasthenic syndrome, congenital, type IIa
 
Gene (location): CHRNA1 (2q31.1)
 
Monarch Initiative: MONDO:0011088
OMIM®: 601462

Definition

Congenital myasthenic syndromes (CMS) are a group of inherited disorders affecting the neuromuscular junction (NMJ). Patients present clinically with onset of variable muscle weakness between infancy and adulthood. These disorders have been classified according to the location of the defect: presynaptic, synaptic, and postsynaptic, as well as by pathologic mechanism and electrophysiologic studies (i.e., acetylcholine receptor (AChR) deficiency, slow-channel or fast-channel kinetic defects at the AChR) (summary by Engel et al., 2003; Engel et al., 2015). Approximately 10% of CMS cases are presynaptic, 15% are synaptic, and 75% are postsynaptic, the majority of which are caused by AChR deficiency (Engel et al., 2003). Slow-channel congenital myasthenic syndrome (SCCMS) is a disorder of the postsynaptic NMJ characterized by early-onset progressive muscle weakness. The disorder results from kinetic abnormalities of the AChR channel, specifically prolonged opening and activity of the channel, which causes prolonged synaptic currents resulting in a depolarization block. This is associated with calcium overload, which may contribute to subsequent degeneration of the endplate and postsynaptic membrane. Treatment with quinine, quinidine, or fluoxetine may be helpful; acetylcholinesterase inhibitors and amifampridine should be avoided (summary by Engel et al., 2015). Genetic Heterogeneity of Congenital Myasthenic Syndromes Recessive mutations in subunits of the acetylcholine receptor are the most common cause of CMS (Harper, 2004). CMS1A and CMS1B (608930) are caused by mutation in the CHRNA1 gene (100690); CMS2A (616313) and CMS2C (616314) are caused by mutation in the CHRNB1 gene (100710) on 17p12; CMS3A (616321), CMS3B (616322), and CMS3C (616323) are caused by mutation in the CHRND gene (100720) on 2q33; and CMS4A (605809), CMS4B (616324), and CMS4C (608931) are caused by mutation in the CHRNE gene (100725) on 17p13. CMS5 (603034) is caused by mutation in the COLQ gene (603033) on 3p25; CMS6 (254210) is caused by mutation in the CHAT gene (118490) on 10q; CMS7 (616040) is caused by mutation in the SYT2 gene (600104) on 1q32; CMS8 (615120) is caused by mutation in the AGRN gene (103320) on 1p; CMS9 (616325) is caused by mutation in the MUSK gene (601296) on 9q31; CMS10 (254300) is caused by mutation in the DOK7 gene (610285) on 4p; CMS11 (616326) is caused by mutation in the RAPSN gene (601592) on 11p11; CMS12 (610542) is caused by mutation in the GFPT1 gene (138292) on 2p14; CMS13 (614750) is caused by mutation in the DPAGT1 gene (191350) on 11q23; CMS14 (616228) is caused by mutation in the ALG2 gene (607905) on 9q22; CMS15 (616227) is caused by mutation in the ALG14 gene (612866) on 1p21; CMS16 (614198) is caused by mutation in the SCN4A gene (603967) on 17q; CMS17 (616304) is caused by mutation in the LRP4 gene (604270) on 11p12; CMS18 (616330) is caused by mutation in the SNAP25 gene (600322) on 20p11; CMS19 (616720) is caused by mutation in the COL13A1 gene (120350) on 10q22; CMS20 (617143) is caused by mutation in the SLC5A7 gene (608761) on 2q12; CMS21 (617239) is caused by mutation in the SLC18A3 gene (600336) on 10q11; CMS22 (616224) is caused by mutation in the PREPL gene (609557) on 2p21; CMS23 (618197) is caused by mutation in the SLC25A1 gene (190315) on 22q11; CMS24 (618198) is caused by mutation in the MYO9A gene (604875) on 15q22; and CMS25 (618323) is caused by mutation in the VAMP1 gene (185880) on 12p13. [from OMIM]

Additional description

From MedlinePlus Genetics
Congenital myasthenic syndrome is a group of conditions characterized by muscle weakness (myasthenia) that worsens with physical exertion. The muscle weakness typically begins in early childhood but can also appear in adolescence or adulthood. Facial muscles, including muscles that control the eyelids, muscles that move the eyes, and muscles used for chewing and swallowing, are most commonly affected. However, any of the muscles used for movement (skeletal muscles) can be affected in this condition. Due to muscle weakness, affected infants may have feeding difficulties. Development of motor skills such as crawling or walking may be delayed. The severity of the myasthenia varies greatly, with some people experiencing minor weakness and others having such severe weakness that they are unable to walk.

Some individuals have episodes of breathing problems that may be triggered by fevers or infection. Severely affected individuals may also experience short pauses in breathing (apnea) that can lead to a bluish appearance of the skin or lips (cyanosis).  https://medlineplus.gov/genetics/condition/congenital-myasthenic-syndrome

Clinical features

From HPO
Upper limb muscle weakness
MedGen UID:
305607
Concept ID:
C1698196
Finding
Weakness of the muscles of the arms.
Lower limb muscle weakness
MedGen UID:
324478
Concept ID:
C1836296
Finding
Weakness of the muscles of the legs.
Dysphagia
MedGen UID:
41440
Concept ID:
C0011168
Disease or Syndrome
Difficulty in swallowing.
Feeding difficulties
MedGen UID:
65429
Concept ID:
C0232466
Finding
Impaired ability to eat related to problems gathering food and getting ready to suck, chew, or swallow it.
Dysarthria
MedGen UID:
8510
Concept ID:
C0013362
Mental or Behavioral Dysfunction
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.
Fatigable weakness
MedGen UID:
451076
Concept ID:
C0947912
Disease or Syndrome
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.
Prolonged miniature endplate currents
MedGen UID:
350370
Concept ID:
C1864238
Finding
An abnormal prolongation of the miniature endplate potentials, i.e. the postsynaptic response to transmitter released from an individual vesicle at the neuromuscular junction.
Decreased size of nerve terminals
MedGen UID:
871144
Concept ID:
C4025615
Anatomical Abnormality
A reduction in the size of nerve terminals.
Hand muscle atrophy
MedGen UID:
116091
Concept ID:
C0239830
Finding
Muscular atrophy involving the muscles of the hand.
Diaphragmatic weakness
MedGen UID:
101067
Concept ID:
C0521532
Finding
A decrease in the strength of the diaphragm.
Generalized muscle weakness
MedGen UID:
155433
Concept ID:
C0746674
Sign or Symptom
Generalized weakness or decreased strength of the muscles, affecting both distal and proximal musculature.
Type 2 muscle fiber atrophy
MedGen UID:
355249
Concept ID:
C1864580
Pathologic Function
Atrophy (wasting) affecting primary type 2 muscle fibers. This feature in general can only be observed on muscle biopsy.
Intrinsic hand muscle atrophy
MedGen UID:
351202
Concept ID:
C1864716
Finding
Atrophy of the intrinsic muscle groups of the hand, comprising the thenar and hypothenar muscles; the interossei muscles; and the lumbrical muscles.
Intermittent episodes of respiratory insufficiency due to muscle weakness
MedGen UID:
813355
Concept ID:
C3807025
Finding
Anti-acetylcholine receptor antibody positivity
MedGen UID:
868186
Concept ID:
C4022578
Finding
The presence of autoantibodies (immunoglobulins) in the blood circulation that react against Ganglioside-monosialic acid (GM1), which is a type of glycosphingolipid with one sialic acid. GM1 is located on the outer layer of the plasma membrane, and plays a vital role in neurogenesis, nerve development, differentiation and repair after injury.
Impaired mastication
MedGen UID:
66779
Concept ID:
C0239043
Finding
An abnormal reduction in the ability to masticate (chew), i.e., in the ability to crush and ground food in preparation for swallowing.
High palate
MedGen UID:
66814
Concept ID:
C0240635
Congenital Abnormality
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).
Ptosis
MedGen UID:
2287
Concept ID:
C0005745
Disease or Syndrome
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).
Ophthalmoplegia
MedGen UID:
45205
Concept ID:
C0029089
Sign or Symptom
Paralysis of one or more extraocular muscles that are responsible for eye movements.
Ophthalmoparesis
MedGen UID:
155551
Concept ID:
C0751401
Sign or Symptom
Ophthalmoplegia is a paralysis or weakness of one or more of the muscles that control eye movement.

Recent clinical studies

Etiology

Bauché S, Vellieux G, Sternberg D, Fontenille MJ, De Bruyckere E, Davoine CS, Brochier G, Messéant J, Wolf L, Fardeau M, Lacène E, Romero N, Koenig J, Fournier E, Hantaï D, Streichenberger N, Manel V, Lacour A, Nadaj-Pakleza A, Sukno S, Bouhour F, Laforêt P, Fontaine B, Strochlic L, Eymard B, Chevessier F, Stojkovic T, Nicole S
J Neurol 2017 Aug;264(8):1791-1803. Epub 2017 Jul 15 doi: 10.1007/s00415-017-8569-x. PMID: 28712002
Compton AG, Albrecht DE, Seto JT, Cooper ST, Ilkovski B, Jones KJ, Challis D, Mowat D, Ranscht B, Bahlo M, Froehner SC, North KN
Am J Hum Genet 2008 Dec;83(6):714-24. Epub 2008 Nov 20 doi: 10.1016/j.ajhg.2008.10.022. PMID: 19026398Free PMC Article
Maselli RA, Books W, Dunne V
Ann N Y Acad Sci 2003 Sep;998:18-28. doi: 10.1196/annals.1254.004. PMID: 14592859
Navarro C, Teijeira S
Acta Myol 2003 May;22(1):11-4. PMID: 12966699

Diagnosis

Montagnese F, Klupp E, Karampinos DC, Biskup S, Gläser D, Kirschke JS, Schoser B
Muscle Nerve 2017 Aug;56(2):334-340. Epub 2017 Feb 23 doi: 10.1002/mus.25485. PMID: 27874200
Bestue-Cardiel M, Sáenz de Cabezón-Alvarez A, Capablo-Liesa JL, López-Pisón J, Peña-Segura JL, Martin-Martinez J, Engel AG
Neurology 2005 Jul 12;65(1):144-6. doi: 10.1212/01.wnl.0000167132.35865.31. PMID: 16009904

Therapy

Bestue-Cardiel M, Sáenz de Cabezón-Alvarez A, Capablo-Liesa JL, López-Pisón J, Peña-Segura JL, Martin-Martinez J, Engel AG
Neurology 2005 Jul 12;65(1):144-6. doi: 10.1212/01.wnl.0000167132.35865.31. PMID: 16009904

Prognosis

Bauché S, Vellieux G, Sternberg D, Fontenille MJ, De Bruyckere E, Davoine CS, Brochier G, Messéant J, Wolf L, Fardeau M, Lacène E, Romero N, Koenig J, Fournier E, Hantaï D, Streichenberger N, Manel V, Lacour A, Nadaj-Pakleza A, Sukno S, Bouhour F, Laforêt P, Fontaine B, Strochlic L, Eymard B, Chevessier F, Stojkovic T, Nicole S
J Neurol 2017 Aug;264(8):1791-1803. Epub 2017 Jul 15 doi: 10.1007/s00415-017-8569-x. PMID: 28712002

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