Departamento de Bioquímica Clínica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, X5000HUA Córdoba, Argentina.
Centro de Investigaciones en Bioquímica Clínica e Inmunología-Consejo Nacional de Investigaciones Científicas y Técnicas, X5000HUA Córdoba, Argentina.
J Clin Endocrinol Metab. 2021 Jun 16;106(7):1867-1881. doi: 10.1210/clinem/dgab283.
Iodide transport defect (ITD) (Online Mendelian Inheritance in Man No. 274400) is an uncommon cause of dyshormonogenic congenital hypothyroidism due to loss-of-function variants in the SLC5A5 gene, which encodes the sodium/iodide symporter (NIS), causing deficient iodide accumulation in thyroid follicular cells.
This work aims to determine the molecular basis of a patient's ITD clinical phenotype.
The propositus was diagnosed with dyshormonogenic congenital hypothyroidism with minimal 99mTc-pertechnetate accumulation in a eutopic thyroid gland. The propositus SLC5A5 gene was sequenced. Functional in vitro characterization of the novel NIS variant was performed.
Sanger sequencing revealed a novel homozygous missense p.G561E NIS variant. Mechanistically, the G561E substitution reduces iodide uptake, because targeting of G561E NIS to the plasma membrane is reduced. Biochemical analyses revealed that G561E impairs the recognition of an adjacent tryptophan-acidic motif by the kinesin-1 subunit kinesin light chain 2 (KLC2), interfering with NIS maturation beyond the endoplasmic reticulum, and reducing iodide accumulation. Structural bioinformatic analysis suggests that G561E shifts the equilibrium of the unstructured tryptophan-acidic motif toward a more structured conformation unrecognizable to KLC2. Consistently, knockdown of Klc2 causes defective NIS maturation and consequently decreases iodide accumulation in rat thyroid cells. Morpholino knockdown of klc2 reduces thyroid hormone synthesis in zebrafish larvae leading to a hypothyroid state as revealed by expression profiling of key genes related to the hypothalamic-pituitary-thyroid axis.
We report a novel NIS pathogenic variant associated with dyshormonogenic congenital hypothyroidism. Detailed molecular characterization of G561E NIS uncovered the significance of KLC2 in thyroid physiology.
碘转运缺陷（ITD）（在线孟德尔遗传在人 No.274400）是一种由于 SLC5A5 基因的功能丧失变异导致的促激素性先天性甲状腺功能减退症的罕见病因，该基因编码钠/碘转运体（NIS），导致甲状腺滤泡细胞中碘的积累不足。
本工作旨在确定患者 ITD 临床表型的分子基础。
先证者被诊断为促激素性先天性甲状腺功能减退症，在正常位置的甲状腺中 99mTc 放射性碘摄取量最低。对先证者的 SLC5A5 基因进行测序。对新的 NIS 变体进行体外功能特征分析。
Sanger 测序显示一种新的纯合错义 p.G561E NIS 变体。从机制上讲，G561E 取代降低了碘的摄取，因为 G561E NIS 的靶向到质膜减少。生化分析表明，G561E 干扰了内质网以外的 NIS 成熟，使相邻的色氨酸酸性基序不能被驱动蛋白-1 亚基驱动蛋白轻链 2（KLC2）识别，从而减少了碘的积累。结构生物信息学分析表明，G561E 使无结构色氨酸酸性基序的平衡向更结构化的构象移动，使 KLC2 无法识别。一致地，Klc2 的敲低导致 NIS 成熟缺陷，从而减少了大鼠甲状腺细胞中的碘积累。klc2 的 morpholino 敲低导致斑马鱼幼虫甲状腺激素合成减少，如与下丘脑-垂体-甲状腺轴相关的关键基因的表达谱所示，表现为甲状腺功能减退状态。
我们报告了一种与促激素性先天性甲状腺功能减退症相关的新的 NIS 致病性变体。对 G561E NIS 的详细分子特征分析揭示了 KLC2 在甲状腺生理学中的重要性。
