Functional Characterization of PHEX Gene Variants in Children With X-Linked Hypophosphatemic Rickets Shows No Evidence of Genotype-Phenotype Correlation
Functional Characterization of PHEX Gene Variants in Children With X-Linked Hypophosphatemic Rickets Shows No Evidence of Genotype-Phenotype Correlation
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X 连锁低磷血症性佝偻病儿童 PHEX 基因变异的功能特征显示没有基因型-表型相关性的证据
DOI：
10.1002/jbmr.4035
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发表时间：
2020-05-12
影响因子：
6.2
通讯作者：
Zhang, Aihua
中科院分区：
文献类型：
--
作者：
Zheng, Bixia;Wang, Chunli;Zhang, Aihua
X连锁低磷血症（XLHR）是由磷酸盐调节内肽酶同源物X连锁（PHEX）基因的功能缺失突变引起的。关于XLHR基因型-表型相关性存在相当大的争议。本研究描述了53例XLHR患儿的临床特征和分子遗传学基础。总共鉴定了47种不同的突变，其中27种先前未在文献中描述或输入人类基因突变数据库（HGMD）。在XLHR患者中观察到截断变异的高患病率（72.34%）。在我们的队列中，XLHR的临床表现和严重程度没有显示截短和非截短突变类型之间的明显相关性。为了进一步描述这种非显著性趋势背后的PHEX变体的特征，我们评估了10种PHEX变体对蛋白质表达、细胞运输和内肽酶活性的影响。我们的结果表明，p.Arg567*，p.Gln714* 和p.Arg747* 的无义突变导致蛋白质分子量降低和运输缺陷。在7个非截短突变中，p.Cys77Tyr、p.Cys85Ser、p.Ile281Lys、p.Ile333del、p.Ala514Pro和p.Gly572Ser突变体不分泌到培养基中，并以未成熟形式保持捕获在细胞内，而p.Gly553Glu突变体被末端糖基化并分泌到培养基中。我们进一步评估了内肽酶活性的p.Gly553Glu突变体使用淬灭的荧光肽底物，并显示，活性的p.Gly553Glu显着降低到13%相比，野生型，这表明催化功能的破坏。这些数据不仅支持临床结果显示疾病严重程度和PHEX突变类型之间没有相关性，而且还提供了对XLHR发病机制的有用分子见解。(c)2020年美国骨与矿物质研究学会。
X-linked hypophosphatemia (XLHR) is caused by loss-of-function mutations in the phosphate regulating endopeptidase homolog X-linked (PHEX) gene. Considerable controversy exists regarding genotype-phenotype correlations in XLHR. The present study describes the clinical features and molecular genetic bases of 53 pediatric patients with XLHR. Overall, 47 different mutations were identified, of which 27 were not previously described in the literature or entered in the Human Gene Mutation Database (HGMD). A high prevalence (72.34%) of truncating variants was observed in XLHR patients. The clinical presentation and severity of XLHR did not show an evident correlation between the truncating and non-truncating mutation types in our cohort. To further delineate the characteristics of PHEX variants underlying this nonsignificant trend, we assessed the effects of 10 PHEX variants on protein expression, cellular trafficking, and endopeptidase activity. Our results showed that the nonsense mutations p.Arg567*, p.Gln714*, and p.Arg747* caused a reduction of protein molecular weight and a trafficking defect. Among seven non-truncating mutations, the p.Cys77Tyr, p.Cys85Ser, p.Ile281Lys, p.Ile333del, p.Ala514Pro, and p.Gly572Ser mutants were not secreted into the medium and remained trapped inside cells in an immature form, whereas the p.Gly553Glu mutant was terminally glycosylated and secreted into the medium. We further assessed the endopeptidase activity of the p.Gly553Glu mutant using a quenched fluorogenic peptide substrate and revealed that the activity of p.Gly553Glu significantly reduced to 13% compared with the wild type, which indicated disruption of catalytic function. These data not only support the clinical results showing no correlation between disease severity and the type of PHEX mutation but also provide helpful molecular insights into the pathogenesis of XLHR. (c) 2020 American Society for Bone and Mineral Research.