Variants of SLC18A3 leading to congenital myasthenic syndrome in two children with varying presentations

This report describes the variation in presentation of two unrelated patients found to have a rare form of presynaptic congenital myasthenic syndrome. Both patients presented with hypotonia, ptosis, poor weight gain and apneic episodes. Through whole exome sequencing, our patients were found to have the same likely pathogenic biallelic variants in W315X and I200N of SLC18A3, encoding vesicular acetylcholine transporter (VAChT). These specific variants in SLC18A3 have not been previously described in the literature. We illustrate the variety in clinical presentation and course of children with mutations in SLC18A3, leading to presynaptic congenital myasthenic syndrome through VAChT deficiency.