Genetic and Functional Analysis of Glycosyltransferase 8 Domain–Containing Protein 1 in Taiwanese Patients With Amyotrophic Lateral Sclerosis

Abstract

Background and ObjectivesTo investigate the frequency, spectrum, and molecular functional effect of glycosyltransferase 8 domain-containing protein 1 (GLT8D1) variations in Taiwanese patients with amyotrophic lateral sclerosis (ALS).MethodsWe performed genetic analyses of GLT8D1 in 410 unrelated patients with ALS by Sanger sequencing. The 410 patients were selected from a cohort of 477 unrelated patients with ALS after excluding variations in common ALS disease genes. Functional effects of the GLT8D1 variation were investigated by in vitro functional analysis.ResultsWe identified a novel heterozygous missense variation in GLT8D1, p.I290M (c.870C>G), in 1 single patient with familial ALS. The patient with the p.I290M variation had a spinal-onset ALS with disease onset at age 60 years and a survival of 6 years. Functional studies demonstrated that the variant I290M GLT8D1 protein was mislocalized to the endoplasmic reticulum (ER), provoked ER stress and unfolded protein response, compromised the glycosyltransferase activity, and led to an increased cytotoxicity.DiscussionGLT8D1 variations account for 0.2% (1/477) of the patients with ALS in Taiwan. These findings expand the spectrum of GLT8D1 variation and support the pathogenic role of GLT8D1 variations in ALS.

Integrative analysis of Lunatic Fringe variants associated with spondylocostal dysostosis type‐III

“…An alternative explanation is that variant LFNG is actually mislocalized to the endoplasmic reticulum (ER), as the diffuse pattern is characteristic of ER‐resident proteins (Figure 2B,C,F,G,I–K). 37,38 One explanatory mechanism could be misfolding in response to amino acid substitutions 39 . Indeed, previous evidence from disease‐causing variants in Glycosyltransferase 8 Domain–Containing Protein 1 ( GLT8D1 ), a GT‐A fold family, DxD motif‐ containing glycosyltransferase with a type‐II transmembrane domain with similarities to LFNG , has shown misfolding and persistence in the ER 38 .…”

“… 37,38 One explanatory mechanism could be misfolding in response to amino acid substitutions 39 . Indeed, previous evidence from disease‐causing variants in Glycosyltransferase 8 Domain–Containing Protein 1 ( GLT8D1 ), a GT‐A fold family, DxD motif‐ containing glycosyltransferase with a type‐II transmembrane domain with similarities to LFNG , has shown misfolding and persistence in the ER 38 . Since misfolding can arise from substitutions in various regions throughout the protein, findings corroborating this hypothesis may explain the wide spatial distribution of variants that result in mislocalization (Table 2).…”

GLT8D1 mutations cause amyotrophic lateral sclerosis via disruption of neurotrophin signalling within membrane lipid rafts

“…We previously described fully penetrant ALS-associated mutations within the gene encoding the glycosyltransferase GLT8D1 (Cooper-Knock et al, 2019). These findings have since been corroborated in a different population (Tsai et al, 2021). Discovered mutations are proximal to the substrate binding domain and impair GLT8D1 enzyme activity.…”

Glycosyltransferase 8 domain-containing protein 1 (GLT8D1) is a UDP-dependent galactosyltransferase

“…GXYLT1 and GXYLT2 were formerly known as GLT8D3 and GLT8D4, respectively; on the other hand, in mammals GLT8D1 has a closely related sequence homolog of unknown function (GLT8D2) 18 . In contrast to the glucosyl-or xylosyltransferase activity of the other mammalian GT8 enzymes, hydrolysis of UDP-galactose 9,15,19 and UDP-glucose 15 was reported for GLT8D1. So, the information concerning GLT8D1 activity and substrate specificity is still scarce.…”