Bongers Ernie M H F, Shelton Luke M, Milatz Susanne, Verkaart Sjoerd, Bech Anneke P, Schoots Jeroen, Cornelissen Elisabeth A M, Bleich Markus, Hoenderop Joost G J, Wetzels Jack F M, Lugtenberg Dorien, Nijenhuis Tom
Departments of Human Genetics.
Physiology.
J Am Soc Nephrol. 2017 Oct;28(10):3118-3128. doi: 10.1681/ASN.2016080881. Epub 2017 Jul 3.
Mice lacking distal tubular expression of , the gene encoding the tight junction protein Claudin-10, show enhanced paracellular magnesium and calcium permeability and reduced sodium permeability in the thick ascending limb (TAL), leading to a urine concentrating defect. However, the function of renal Claudin-10 in humans remains undetermined. We identified and characterized mutations in two patients with a hypokalemic-alkalotic salt-losing nephropathy. The first patient was diagnosed with Bartter syndrome (BS) >30 years ago. At re-evaluation, we observed hypocalciuria and hypercalcemia, suggesting Gitelman syndrome (GS). However, serum magnesium was in the upper normal to hypermagnesemic range, thiazide responsiveness was not blunted, and genetic analyses did not show mutations in genes associated with GS or BS. Whole-exome sequencing revealed compound heterozygous sequence variants [c.446C>G (p.Pro149Arg) and c.465-1G>A (p.Glu157_Tyr192del)]. The patient had reduced urinary concentrating ability, with a preserved aquaporin-2 response to desmopressin and an intact response to furosemide. These findings were not in line with any other known salt-losing nephropathy. Subsequently, we identified a second unrelated patient showing a similar phenotype, in whom we detected compound heterozygous sequence variants [c.446C>G (p.(Pro149Arg) and c.217G>A (p.Asp73Asn)]. Cell surface biotinylation and immunofluorescence experiments in cells expressing the encoded mutants showed that only one mutation caused significant differences in Claudin-10 membrane localization and tight junction strand formation, indicating that these alterations do not fully explain the phenotype. These data suggest that pathogenic mutations affect TAL paracellular ion transport and cause a novel tight junction disease characterized by a non-BS, non-GS autosomal recessive hypokalemic-alkalotic salt-losing phenotype.
缺乏紧密连接蛋白Claudin-10的编码基因在远端肾小管表达的小鼠，其髓袢升支粗段（TAL）的细胞旁镁和钙通透性增强，钠通透性降低，导致尿液浓缩功能缺陷。然而，Claudin-10在人类肾脏中的功能仍未确定。我们在两名患有低钾性碱中毒失盐性肾病的患者中鉴定并表征了突变。第一名患者在30多年前被诊断为巴特综合征（BS）。在重新评估时，我们观察到低钙尿症和高钙血症，提示吉特曼综合征（GS）。然而，血清镁处于正常上限至高镁血症范围，噻嗪类药物反应未减弱，基因分析未显示与GS或BS相关基因的突变。全外显子测序揭示了复合杂合序列变异[c.446C>G（p.Pro149Arg）和c.465-1G>A（p.Glu157_Tyr192del）]。该患者的尿液浓缩能力降低，对去氨加压素的水通道蛋白-2反应保留，对呋塞米的反应完整。这些发现与任何其他已知的失盐性肾病均不一致。随后，我们鉴定了第二名无亲缘关系的患者，其表现出相似的表型，在该患者中我们检测到复合杂合序列变异[c.446C>G（p.（Pro149Arg）和c.217G>A（p.Asp73Asn）]。在表达编码突变体的细胞中进行的细胞表面生物素化和免疫荧光实验表明，只有一个突变导致Claudin-10膜定位和紧密连接链形成的显著差异，表明这些改变并不能完全解释该表型。这些数据表明，致病性突变影响TAL细胞旁离子转运，并导致一种以非BS、非GS常染色体隐性低钾性碱中毒失盐表型为特征的新型紧密连接疾病。
