Extremely rare. Congenital myopathy in the Samaritan population (Jewish religious group, also present in Syria) where the rate of inbreeding is very high. A mutation of the RYR1 gene is responsible for this myopathy; the concentration of RYR1 receptors is decreased in the affected muscles but the organisation of the excitation/contraction coupling proteins (caveolin, dysferlin) is also abnormal.

This myopathy is clinically characterized by the fact it improves with age (around 2 years), unlike other myopathies.

Clinical presentation:

-        major hypotonia at birth, sometimes requiring artificial ventilation; skin of a pasty consistency

-        motor developmental delay but hypotonia and muscle weakness improves gradually with age

Histologically, the picture is partly compatible with the centronuclear and the central core congenital myopathies.

One patient presented moderate and transient hyperthermia after anesthesia.

Anesthetic implications:

avoid succinylcholine; risk of malignant hyperthermia and of halogenated-induced rhabdomyolysis ?

References : 

-         Böhm J, Leshinsky-Silver E, Vassilopoulos S, Le Gras S, Lerman-Sagie L et al. 
Samaritan myopathy, an ultimately benign congenital myopathy, is caused by a RYR1 mutation. 
Acta Neuropathol 2012; 124: 575-81.

-        Lev D, Sadeh M, Watemberg N, Dabby R et al. 
A benign congenital myopathy in an inbred Samaritan family. 
Eur J Pediatr Neurol 2006; 10: 182-5.

Updated: September 2018