PDF(Pubmed)
Abstract：
Hereditary spastic paraplegia (HSP) is a heterogeneous group of neurological disorders that are characterized by progressive spasticity and weakness in the lower limbs. SPG26 is a complicated form of HSP, which includes not only weakness in the lower limbs, but also cognitive impairment, developmental delay, cerebellar ataxia, dysarthria, and peripheral neuropathy, and is caused by biallelic mutations in the B4GALNT1 (beta-1,4-N-acetylgalactosaminyltransferase 1) gene. The B4GALNT1 gene encodes ganglioside GM2/GD2 synthase (GM2S), which catalyzes the transfer of N-acetylgalactosamine to lactosylceramide, GM3, and GD3 to generate GA2, GM2, and GD2, respectively. The present study attempted to characterize a novel B4GALNT1 variant (NM_001478.5:c.937G>A p.Asp313Asn) detected in a patient with progressive multi-system neurodegeneration as well as deleterious variants found in the general population in Japan. Peripheral blood T cells from our patient lacked the ability for activation-induced ganglioside expression assessed by cell surface cholera toxin binding. Structural predictions suggested that the amino acid substitution, p.Asp313Asn, impaired binding to the donor substrate UDP-GalNAc. An in vitro enzyme assay demonstrated that the variant protein did not exhibit GM2S activity, leading to the diagnosis of HSP26. This is the first case diagnosed with SPG26 in Japan. We then extracted 10 novel missense variants of B4GALNT1 from the whole-genome reference panel jMorp (8.3KJPN) of the Tohoku medical megabank organization, which were predicted to be deleterious by Polyphen-2 and SIFT programs. We performed a functional evaluation of these variants and demonstrated that many showed perturbed subcellular localization. Five of these variants exhibited no or significantly decreased GM2S activity with less than 10% activity of the wild-type protein, indicating that they are carrier variants for HSP26. These results provide the basis for molecular analyses of B4GALNT1 variants present in the Japanese population and will help improve the molecular diagnosis of patients suspected of having HSP.
摘要：
遗传性痉挛性截瘫（HSP）是一组异质性的神经系统疾病，其特征是下肢进行性痉挛和虚弱。SPG26是一种复杂的HSP，这不仅包括下肢的虚弱，还有认知障碍，发育迟缓,小脑共济失调,构音障碍,和周围神经病变，并且是由B4GALNT1（β-1,4-N-乙酰氨基半乳糖转移酶1）基因中的双等位基因突变引起的。B4GALNT1基因编码神经节苷脂GM2/GD2合酶（GM2S），催化N-乙酰半乳糖胺向乳糖基神经酰胺的转移，GM3和GD3分别生成GA2、GM2和GD2。本研究试图表征在患有进行性多系统神经变性的患者中检测到的新型B4GALNT1变体(NM_001478.5:c.937G>Ap.Asp313Asn)以及在日本普通人群中发现的有害变体。我们患者的外周血T细胞缺乏通过细胞表面霍乱毒素结合评估的活化诱导的神经节苷脂表达的能力。结构预测表明氨基酸取代，p.Asp313Asn,与供体底物UDP-GalNAc的结合受损。体外酶分析表明，该变体蛋白不表现出GM2S活性，导致HSP26的诊断。这是日本首例诊断为SPG26的病例。然后，我们从东北医疗大型银行组织的全基因组参考小组jMorp（8.3KJPN）中提取了B4GALNT1的10个新的错义变体，Polyphen-2和SIFT程序预测是有害的。我们对这些变体进行了功能评估，并证明许多变体显示出扰动的亚细胞定位。这些变体中的五种没有或显著降低了GM2S活性，野生型蛋白的活性低于10%，表明它们是HSP26的载体变体。这些结果为日本人群中存在的B4GALNT1变体的分子分析提供了基础，并将有助于改善怀疑患有HSP的患者的分子诊断。
