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Abstract：
Spondyloepiphyseal dysplasia tarda (SEDT) is a condition involving late-onset, X-linked recessive skeletal dysplasia caused by mutations in the TRAPPC2 gene. In this paper, we identified a novel nonsense variant in a SEDT pedigree and analyzed the function of the variant in an attempt to explain the new pathogenesis of the TRAPPC2 protein in SEDT. Briefly, DNA and RNA samples from the peripheral blood of SEDT individuals were prepared. The causative variant in the Chinese SEDT family was identified by clinic whole-exome sequencing analysis. Then, we observed the mRNA expression of TRAPPC2 in patients and the mutant TRAPPC2 level in vitro and analyzed the protein stability and subcellular distribution by cell fluorescence and Western blotting. We also investigated the effect of TRAPPC2 knockdown on the expression and secretion of COL2A1 in SW1353 cells or primary human chondrocytes. Herein, we found a nonsense variant, c.91A>T, of the TRAPPC2 gene in the pedigree. TRAPPC2 mRNA expression levels were significantly decreased in the available peripheral blood cell samples of two affected patients. An in vitro study showed that the mutant plasmid exhibited significantly lower mRNA and protein of TRAPPC2, and the mutant protein changed its membrane distribution. TRAPPC2 knockdown resulted in decreased COL2A1 expression and collagen II secretions. Our data indicate that the novel nonsense variant, c.91A>T, of the TRAPPC2 gene is the cause of SEDT in this pedigree. The variant results in a lowered expression of TRAPPC2 and then affects the COL2A1 expression and collagen II secretions, which may explain the mechanism of loss of function of the variant.
摘要：
脊柱骨phy发育不良（SEDT）是一种涉及迟发性的疾病，由TRAPPC2基因突变引起的X连锁隐性骨骼发育不良。在本文中,我们在SEDT家系中鉴定了一个新的无义变体,并分析了该变体的功能,试图解释SEDT中TRAPPC2蛋白的新发病机制.简而言之，制备来自SEDT个体的外周血的DNA和RNA样品。通过临床全外显子组测序分析鉴定了中国SEDT家族的致病变异。然后，我们观察了患者体内TRAPPC2的mRNA表达和突变的TRAPPC2水平，并通过细胞荧光和Western印迹分析了蛋白质的稳定性和亚细胞分布。我们还研究了TRAPPC2敲低对SW1353细胞或原代人软骨细胞中COL2A1表达和分泌的影响。在这里，我们发现了一个无意义的变体，c.91A>T，系谱中的TRAPPC2基因。在两名受影响患者的可用外周血细胞样品中，TRAPPC2mRNA表达水平显着降低。体外研究表明，突变质粒显示出TRAPPC2的mRNA和蛋白显着降低，突变蛋白改变了其膜分布。TRAPPC2敲低导致COL2A1表达和胶原II分泌减少。我们的数据表明，新的无意义变体，c.91A>T，TRAPPC2基因是该谱系中SEDT的原因。该变体导致TRAPPC2的表达降低，然后影响COL2A1表达和胶原蛋白II分泌，这可以解释变体功能丧失的机制。
