DPAGT1 myasthenia and myopathy

Abstract

Objective: To investigate patients with DPAGT1 (UDP-N-acetylglucosamine-dolichyl-phosphate N-acetylglucosaminephosphotransferase 1)-associated myasthenic syndrome. Methods:We performed exome and Sanger sequencing, determined glycoprotein expression in patient muscles, assessed pathogenicity of the mutant proteins by examining their expression and enzymatic activity in transfected cells, evaluated structural changes in muscle and the neuromuscular junction, and examined electrophysiologic aspects of neuromuscular transmission in vitro.Results: Patients 1 and 2, 16 and 14 years of age, had progressive fatigable weakness since infancy and are intellectually disabled. Patient 3, a less severely affected brother of patient 1, also has autistic features. Each patient harbors 2 novel heteroallelic mutations in DPAGT1, an enzyme subserving protein N-glycosylation. Patients 1 and 3 harbor Met1Leu, which reduces protein expression, and His375Tyr, which decreases enzyme activity. Patient 2 carries Val264Met, which abolishes enzyme activity, and a synonymous Leu120Leu mutation that markedly augments exon skipping, resulting in some skipped and infrequent nonskipped alleles. Therefore, the nonskipped allele rescues the phenotype. Intracellular microelectrode studies indicate combined pre-and postsynaptic defects of neuromuscular transmission with evidence for somatic mosaicism in patient 2. Structural studies reveal hypoplastic endplates, fiber-type disproportion, tubular aggregates, and degeneration of muscle fiber organelles resulting in autophagocytosis.Conclusions: DPAGT1 myasthenia affects multiple parameters of neuromuscular transmission, causes fiber-type disproportion and an autophagic myopathy, and can be associated with intellectual disability. We speculate that hypoglycosylation of synapse-specific proteins causes defects in central as well as motor synapses. Neurology ® 2014;82:1822-1830 GLOSSARY AChE 5 acetylcholinesterase; AChR 5 acetylcholine receptor; a-bgt 5 a-bungarotoxin; cDNA 5 complementary DNA; CMS 5 congenital myasthenic syndrome; 3,4-DAP 5 3,4-diaminopyridine; DPAGT1 5 UDP-N-acetylglucosamine-dolichylphosphate N-acetylglucosaminephosphotransferase 1; EP 5 endplate; MEPC 5 miniature endplate current; MEPP 5 miniature endplate potential; STIM1 5 stromal interaction molecule 1.Congenital myasthenic syndromes (CMS) are heterogeneous disorders in which the safety margin of neuromuscular transmission is compromised by one or more specific mechanisms. Most CMS are caused by defects in endplate (EP)-specific proteins.1 Recently, however, it became apparent that proteins distributed in many tissues, namely the intermediate filament linker plectin 2 and enzymes subserving glycosylation of nascent peptides such as GFPT1, 3,4 DPAGT1, 5 ALG2, and ALG14, 6 are also CMS targets. GFPT1 is the initial and ratelimiting enzyme in the biosynthesis of N-acetylglucosamine, an essential substrate for O-and N-glycosylation.7 DPAGT1 catalyzes the first step, ALG14 in concert with ALG13 catalyzes the second step, and A...

Clinical utility gene card for: DPAGT1 defective congenital disorder of glycosylation

“…Twenty-five variants have been reported: twenty-one missense variants, three splicing variants and one duplication vari ant [1][2][3][4][5][6][7][8][9][10][11] (www.lovd.nl/DPAGT1). The standard reference sequence indicating reported variants (ENSG00000172269) and a reference for exon numbering (ENST00000354202) can be found at http://www.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The frequency and the prevalence of the disease are not known.…”

“…3,8,[10][11][12]14,15 The multisystem presentation (28 patients) is, as a rule, a severe disease. Twenty-three patients died between 6 weeks and 5 years.…”

Clinical and genetic basis of congenital myasthenic syndromes

“…Allelic conditions include CDG type Ij. Muscle biopsy shows small tubular aggregates, fiber type disproportion with small caliber type 1 fibers and autophagic vacuolar myopathy, resembling similar patterns to STIM1-related myopathies 3,41,42 .…”

Splicing Aberrations in Congenital Myasthenic Syndromes

“…Screening using a minigene is labor-intensive and is not realistic. To seek for an alternative to in cellulo and in vitro analyses, we analyzed hidden scenarios of the branch point [48], the 3' splice site [49], and the 5' splice site [50] by exploiting in silico analysis methods. Tools to predict RNA-binding proteins for specific cis-elements are also available online [29,42], and further development of such tools will facilitate identification of splicing mutations and their underlying mechanisms.…”