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Recessive null-allele variants in MAG associated with spastic ataxia, nystagmus, neuropathy, and dystonia.

Parkinsonism Relat Disord. 2020;77:70-75. doi:10.1016/j.parkreldis.2020.06.027 [published online ahead of print, 2020 Jun 29].

Authors/Editors: Zech M, Brunet T, Škorvánek M, Blaschek A, Vill K, Hanker B, Hüning I, Haň V, Došekova P, Gdovinová Z, Alhaddad B, Berutti R, Strom TM, Růžička E, Kamsteeg EJ, van der Smagt JJ, Wagner M, Jech R, Winkelmann J.
Publication Date: 2020

07_zech

Abstract

Introduction The gene encoding myelin-associated glycoprotein (MAG) has been implicated in autosomal-recessive spastic paraplegia type 75. To date, only four families with biallelic missense variants in MAG have been reported. The genotypic and phenotypic spectrum of MAG-associated disease awaits further elucidation.

Methods Four unrelated patients with complex neurologic conditions underwent whole-exome sequencing within research or diagnostic settings. Following determination of the underlying genetic defects, in-depth phenotyping and literature review were performed.

Results In all case subjects, we detected ultra-rare homozygous or compound heterozygous variants in MAG. The observed nonsense (c.693C > A [p.Tyr231*], c.980G > A [p.Trp327*], c.1126C > T [p.Gln376*], and 1522C > T [p.Arg508*]) and frameshift (c.517_521dupAGCTG [p.Trp174*]) alleles were predicted to result in premature termination of protein translation. Affected patients presented with variable combinations of psychomotor delay, ataxia, eye movement abnormalities, spasticity, dystonia, and neuropathic symptoms. Cerebellar signs, nystagmus, and pyramidal tract dysfunction emerged as unifying features in the majority of MAG-mutated individuals identified to date.

Conclusions Our study is the first to describe biallelic null variants in MAG, confirming that loss of myelin-associated glycoprotein causes severe infancy-onset disease with central and peripheral nervous system involvement.

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