Neurologic syndrome associated with homozygous mutation at MAG sialic acid binding site.

Abstract

The MAG gene encodes myelin‐associated glycoprotein (MAG), an abundant protein involved in axon–glial interactions and myelination during nerve regeneration. Several members of a consanguineous family with a clinical syndrome reminiscent of Pelizaeus–Merzbacher disease and demyelinating leukodystrophy on brain MRI were recently found to harbor a homozygous missense p.Ser133Arg MAG mutation. Here, we report two brothers from a nonconsanguineous family afflicted with progressive cognitive impairment, neuropathy, ataxia, nystagmus, and gait disorder. Exome sequencing revealed the homozygous missense mutation p.Arg118His in MAG. This Arg118 residue in immunoglobulin domain 1 is critical for sialic acid binding, providing a compelling mechanistic basis for disease pathogenesis.