How Often Is Congenital Myasthenic Syndrome Misdiagnosed as Seronegative MG?

Approximately 10% of patients with myasthenia gravis (MG) do not have autoantibodies against acetylcholine receptor, muscle-specific kinase, or lipoprotein receptor–related protein 4 and are considered seronegative. An unknown proportion of seronegative patients may actually have congenital myasthenic syndrome, which requires different treatment. These researchers assessed 50 out of 100 adult patients from multiple centers who were previously diagnosed with seronegative myasthenia gravis (median age, 35) and conducted whole-exome sequencing and targeted gene analysis to identify mutations associated with congenital myasthenic syndromes. The MG diagnosis was based on fatigable weakness and abnormal repetitive nerve stimulation or resp…