Transmission of maternal muscle-specific tyrosine kinase (MuSK) to offspring: report of two cases.

Familial occurrence of myasthenia gravis is uncommon and reports of maternal transmission of muscle-specific tyrosine kinase (MuSK) antibody myasthenia are rarer still. We report two families with maternal transmission of MuSK antibody myasthenia gravis to the offspring by different mechanisms. The first family demonstrates transmission genetic susceptibility of inheriting myasthenia gravis from MuSK antibodies, whereas the second one demonstrates transplacental transmission of MuSK antibodies at birth.