Pressler Carsten A, Heinzinger Jolanta, Jeck Nikola, Waldegger Petra, Pechmann Ulla, Reinalter Stephan, Konrad Martin, Beetz Rolf, Seyberth Hannsjörg W, Waldegger Siegfried
Department of Pediatrics, Philipps University of Marburg, Marburg, Germany.
J Am Soc Nephrol. 2006 Aug;17(8):2136-42. doi: 10.1681/ASN.2005101071. Epub 2006 Jun 28.
Genetic defects of the Na+-K+-2Cl- (NKCC2) sodium potassium chloride co-transporter result in severe, prenatal-onset renal salt wasting accompanied by polyhydramnios, prematurity, and life-threatening hypovolemia of the neonate (antenatal Bartter syndrome or hyperprostaglandin E syndrome). Herein are described two brothers who presented with hyperuricemia, mild metabolic alkalosis, low serum potassium levels, and bilateral medullary nephrocalcinosis at the ages of 13 and 15 yr. Impaired function of sodium chloride reabsorption along the thick ascending limb of Henle's loop was deduced from a reduced increase in diuresis and urinary chloride excretion upon application of furosemide. Molecular genetic analysis revealed that the brothers were compound heterozygotes for mutations in the SLC12A1 gene coding for the NKCC2 co-transporter. Functional analysis of the mutated rat NKCC2 protein by tracer-flux assays after heterologous expression in Xenopus oocytes revealed significant residual transport activity of the NKCC2 p.F177Y mutant construct in contrast to no activity of the NKCC2-D918fs frameshift mutant construct. However, coexpression of the two mutants was not significantly different from that of NKCC2-F177Y alone or wild type. Membrane expression of NKCC2-F177Y as determined by luminometric surface quantification was not significantly different from wild-type protein, pointing to an intrinsic partial transport defect caused by the p.F177Y mutation. The partial function of NKCC2-F177Y, which is not negatively affected by NKCC2-D918fs, therefore explains a mild and late-onset phenotype and for the first time establishes a mild phenotype-associated SLC12A1 gene mutation.
钠-钾-2氯共转运体（NKCC2）的基因缺陷会导致严重的产前肾盐耗竭，并伴有羊水过多、早产和危及新生儿生命的低血容量（产前巴特综合征或高前列腺素E综合征）。本文描述了两名兄弟，他们在13岁和15岁时出现高尿酸血症、轻度代谢性碱中毒、低钾血症和双侧髓质肾钙质沉着症。应用呋塞米后利尿和尿氯排泄增加减少，提示亨利袢厚升支氯化钠重吸收功能受损。分子遗传学分析显示，这两名兄弟是编码NKCC2共转运体的SLC12A1基因突变的复合杂合子。在非洲爪蟾卵母细胞中异源表达后，通过示踪通量测定对突变的大鼠NKCC2蛋白进行功能分析，结果显示NKCC2 p.F177Y突变体构建体具有显著的残余转运活性，而NKCC2-D918fs移码突变体构建体则无活性。然而，两个突变体的共表达与单独的NKCC2-F177Y或野生型没有显著差异。通过发光表面定量测定的NKCC2-F177Y的膜表达与野生型蛋白没有显著差异，表明p.F177Y突变导致了内在的部分转运缺陷。因此，NKCC2-F177Y的部分功能不受NKCC2-D918fs的负面影响，这解释了一种轻度和迟发性表型，并首次建立了一种与轻度表型相关的SLC12A1基因突变。
