Congenital myasthenic syndrome due to rapsyn deficiency: three cases with arthrogryposis and bulbar symptoms.

We report the cases of 3 children with postsynaptic congenital myasthenic syndrome with acetylcholine receptor deficiency due to rapsyn deficiency. Symptoms began at the neonatal period with hypotonia, arthrogryposis, bulbar symptoms, and respiratory distress. Two of the 3 children needed tracheostomy and gastrostomy. Electromyograms showed a decremental response to repetitive stimulation. Muscle biopsies were normal or showed type I fiber preponderance. Genetic studies identified mutations in the rapsyn gene (RAPSN). The 3 patients were heterozygous for N88 K and a second mutation (either Y86X, 1083_1084 dupCT or IVS4-2 A > G). The patients responded favorably to anticholinesterase treatment, with a clear improvement of clinical symptoms, especially the bulbar symptoms of apneas and swallowing disturbances. This paper underlines the importance of anticholinesterase medication in patients with congenital myasthenic syndrome due to rapsyn deficiency.