Department of Pediatrics and Adolescent Medicine, Aarhus University Hospital, Aarhus, Denmark.
Department of Biomedicine, Aarhus University, Aarhus, Denmark.
Neuroendocrinology. 2018;107(2):167-180. doi: 10.1159/000491579. Epub 2018 Jun 27.
Autosomal dominant familial neurohypophyseal diabetes insipidus (adFNDI) is characterized by severe polyuria and polydipsia and is caused by variations in the gene encoding the AVP prohormone. This study aimed to ascertain a correct diagnosis, to identify the underlying genetic cause of adFNDI in a Swedish family, and to test the hypothesis that the identified synonymous exonic variant in the AVP gene (c.324G>A) causes missplicing and endoplasmic reticulum (ER) retention of the prohormone.
DESIGN/PATIENTS: Three affected family members were admitted for fluid deprivation test and dDAVP (1-deamino-8-d-arginine-vasopressin) challenge test. Direct sequencing of the AVP gene was performed in the affected subjects, and genotyping of the identified variant was performed in family members. The variant was examined by expression of AVP minigenes containing the entire coding regions as well as intron 2 of AVP.
METHODS/RESULTS: Clinical tests revealed significant phenotypical variation with both complete and partial adFNDI phenotype. DNA analysis revealed a synonymous c.324G>A substitution in one allele of the AVP gene in affected family members only. Cellular studies revealed both normally spliced and misspliced pre-mRNA in cells transfected with the AVP c.324G>A minigene. Confocal laser scanning microscopy showed collective localization of the variant prohormone to ER and vesicular structures at the tip of cellular processes.
We identified a synonymous variant affecting the second nucleotide of exon 3 in the AVP gene (c.324G>A) in a family in which adFNDI segregates. Notably, we showed that this variant causes partial missplicing of pre-mRNA, resulting in accumulation of the variant prohormone in ER. Our study suggests that even a small amount of aberrant mRNA might be sufficient to disturb cellular function, resulting in adFNDI.
常染色体显性遗传性神经垂体性尿崩症（adFNDI）的特征是严重的多尿和多饮，由 AVP 前体激素基因变异引起。本研究旨在确定一个瑞典家族的 adFNDI 的正确诊断，确定 adFNDI 的潜在遗传原因，并检验所识别的 AVP 基因中的同义外显子变异（c.324G>A）是否导致前体激素的错配和内质网（ER）滞留的假说。
设计/患者：三名受影响的家庭成员接受了液体剥夺试验和 dDAVP（1-脱氨基-8-D-精氨酸血管加压素）挑战试验。对受影响的个体进行了 AVP 基因的直接测序，并对家族成员进行了所识别变异的基因分型。通过含有 AVP 完整编码区和 AVP 内含子 2 的 AVP 小基因的表达来检查该变异。
方法/结果：临床检查显示，表型变化明显，既有完全性也有部分性 adFNDI 表型。DNA 分析显示，受影响的家族成员只有一个 AVP 基因的等位基因存在同义 c.324G>A 取代。细胞研究显示，用 AVP c.324G>A 小基因转染的细胞中存在正常剪接和错配前体 mRNA。共聚焦激光扫描显微镜显示，变异前体激素在细胞过程尖端聚集到 ER 和囊泡结构。
我们在一个 adFNDI 分离的家族中鉴定了一个位于 AVP 基因外显子 3 的第二个核苷酸的同义变异（c.324G>A）。值得注意的是，我们表明该变异导致前体 mRNA 的部分错配，导致变异前体激素在 ER 中的积累。我们的研究表明，即使是少量的异常 mRNA 也足以扰乱细胞功能，导致 adFNDI。
