Rare. Sporadic transmission or of the following genes:

-        the RYR1 gene (19q13.1) ( autosomal dominant or recessive transmission) with a risk of susceptibility to malignant hyperthermia

-        the gene coding for selenoprotein N (SELENON) (1p36) (30 %)

-        the TTN gene (2q31.2) coding for titin, which can result in a severe cardiomyopathy; autosomal recessive transmission (see titinopathies)

-        the FXR1 gene (3q26.33); autosomal recessive transmission.

-        

The histological picture is that of multiple and small "cores" in the sarcomeres of type I and II fibers; however, this image is not very specific.

Clinically, four subgroups are described:

• (1) classical form (50 %): onset in infancy with hypotonia and muscle weakness. Respiratory failure out of proportion with the muscle weakness is not uncommon. Muscle contractures can cause: torticollis, kyphoscoliosis and spinal stiffness. Muscle pain during the exercise.
• (2) moderate form: neuromotor delay in infancy with distal weakness (only the hands are affected) and laxity of the  joints(sometimes RYR1 mutations)
• (3) arthrogryposic form of antenatal apparition
• (4) ophthalmoplegic form: in which the classical form is associated with external loculomotor problems.

Some children have cardiac A-V conduction disorders or restrictive cardiomyopathy (SEPN1 mutation).

A fatal case of malignant hyperthermia (without anesthesia exposure) observed 3 hours after oral intake of 2 mg of ondansetron in a 5-year-old boy with multiminicore myopathy due to new mutations in the RYR1 gene discovered following a crisis of malignant hyperthermia during the administration of sevoflurane at the age of 3 years: signs of sepsis were found at autopsy. This mutation could be able to generate spontaneous crises of HM. In addition, it is probably of a fortuitous association but  in vitro tests showed that high-dose HT2A agonists produce muscular contracture.

Anesthetic implications:

ECG and preoperative echocardiography; risk of malignant hyperthermia.

                                  

References : 

• Gordon CP, Litz S.
  Multicore myopathy in a patient with anhidrotic ectodermal dysplasia.
  Can J Anaesth 1992 ; 39 : 966-8.
• Docquier MA, Veyckemans F, Prudhomme S, Rossillon R.
  Anesthésie d'une enfant présentant une dysplasie anhydrotique ectodermique associée à une myopathie multicore.
  Can J Anaesth 2000; 47:449-53.
• Willemsen MAAP, van Oort AM, Sengers RCA, Gabreels FJM. 
  Multicore myopathy with restrictive cardiomyopathy. 
  Acta Paediatr 1997; 86:1271-4.
• Klingler W, Rueffert H, Lehmann-Horn F, Girard T, Hopkins PM. 
  Core myopathies and risk of malignant hyperthermia. 
  Anesth Analg 2009; 109: 1167-73.
• Gener B, Burns JM, Griffin S, Boyer EW. 
  Administration of ondansetron is associated with lethal outcome. 
  Pediatrics 2010; 125: e1514-7.
• Brislin RP, Theroux MC. 
  Core myopathies and malignant hyperthermia susceptibility : a review. 
  Pediatr Anesth 2013 ; 23 : 834-41.
• Christiaens F, Van den Bergh PYK. 
  Les myopathies congénitales. 
  Louvain Med 2014 ; 133 : 478-90. 
• North K, Wang C, Clarke N, Jungbluth H, Vainzof M, Dowling J et al. Approach to the diagnosis of congenital myopathies. Neuromuscul Disord 2014 ; 24 : 97-116. 
• Benarroch L, Bonne G, Rivier F, Hamroun D.
  The 2020 version of the gene table of neuromuscular disorders.
  Neuromusc Dis 2019 ; 29 : 980-1018 ou  http://www.musclegenetable.fr.   

                                                 

Updated: June 2021