DPAGT1-CDG: Functional analysis of disease-causing pathogenic mutations and role of endoplasmic reticulum stress

Abstract

Pathogenic mutations in DPAGT1 are manifested as two possible phenotypes: congenital disorder of glycosylation DPAGT1-CDG (also known as CDG-Ij), and limb-girdle congenital myasthenic syndrome (CMS) with tubular aggregates. UDP-N-acetylglucosamine-dolichyl-phosphate N-acetylglucosamine phosphotransferase (GPT), the protein encoded by DPAGT1, is an endoplasmic reticulum (ER)-resident protein involved in an initial step in the N-glycosylation pathway. The aim of the present study was to examine the effect of six variants in DPAGT1 detected in patients with DPAGT1-CDG, and the role of endoplasmic reticulum stress, as part of the search for therapeutic strategies to use against DPAGT1-CDG. The effect of the six mutations, i.e., c.358C>A (p.Leu120Met), c.791T>G (p.Val264Gly), c.901C>T (p.Arg301Cys), c.902G>A (p.Arg301His), c.1154T>G (p.Leu385Arg), and of the novel mutation c.329T>C (p.Phe110Ser), were examined via the analysis of DPAGT1 transcriptional profiles and GTP levels in patient-derived fibroblasts. In addition, the transient expression of different mutations was analysed in COS-7 cells. The results obtained, together with those of bioinformatic studies, revealed these mutations to affect the splicing process, the stability of GTP, or the ability of this protein to correctly localise in the ER membrane. The unfolded protein response (UPR; the response to ER stress) was found not to be active in patient-derived fibroblasts, unlike that seen in cells from patients with PMM2-CDG or DPM1-CDG. Even so, the fibroblasts of patients with DPAGT1-CDG seemed to be more sensitive to the stressor tunicamycin. The present work improves our knowledge of DPAGT1-CDG and provides bases for developing tailored splicing and folding therapies.

<p>Effect of Genetic Testing on Diagnosing Gastrointestinal Pediatric Patients with Previously Undiagnosed Diseases</p>

“…Pathogenic variants in DPAGT1 are known to manifest two distinct phenotypes, either limb-girdle congenital myasthenic syndrome (CMS) with tubular aggregates, or congenital disorder of glycosylation (DPAGT1-CDG). 26 Interestingly, in this study, our proband shared the same homozygous missense variant and diagnosis that has been reported only once before; where a Spanish non-consanguineous family had a baby boy with similar clinical features and prognosis as proband II-2. 27 Although this variant has only been reported once before, we believe it harbors a deleterious outcome.…”

Congenital myasthenic syndrome in China: genetic and myopathological characterization

“…Selective limb-girdle weakness devoid of ocular muscles was frequently observed in patients with GFPT1 and GMPPB mutations. Such unspecific myopathy in CMS was usually related to defects in the glycosylation pathway 18,[23][24] and the agrin-LRP4-MuSK signaling pathway. [1][2]5,13,22 Unlike other patients with CHAT mutations, 7 our case had prominent exercise intolerance and mild lower limb weakness without any episodes of respiratory insufficiency or ptosis, even up to childhood.…”

Clinical and molecular diagnosis of non‐phosphomannomutase 2 N‐linked congenital disorders of glycosylation in Spain

“…The 25 patients examined in this work belonged to 23 families. Eight of these patients have been previously described, [8][9][10][11][12][13][14][15] All 25 patients were referred for analysis by their specialist physicians (most of whom belonged to the Spanish CDG Consortium). The present study was approved by the Ethics Committee of the Universidad Autónoma de Madrid.…”