Severe congenital nephrogenic diabetes insipidus in a compound heterozygote with a new large deletion of the AQP2 gene. A case report

Abstract

Background: Congenital nephrogenic diabetes insipidus (NDI) is a rare condition characterized by severe polyuria, due to the inability of the kidneys to concentrate urine in response to arginine vasopressin (AVP). In the majority of the cases, the disease shows an X-linked inherited pattern, although an autosomal recessive inheritance was also observed.

Methods: We report a patient with a severe NDI diagnosed during the neonatal period. Because the patient was female without a family history of congenital NDI, her disease was thought to exhibit an autosomal recessive form.

Results: A full mutation analysis of AVP receptor 2 (AVPR2; MIM#300538) gene showed no mutations. However, direct Sanger sequencing of the aquaporin 2 (AQP2) revealed an apparently homozygous mutation at nucleotide position NM_000486.5:c.374C>T (p.Thr125Met) in exon 2. Further customized multiplex ligation-dependent probe amplification (MLPA), single-nucleotide polymorphism (SNP) array analysis, and long-range polymerase chain reaction (PCR) followed by Sanger sequencing showed a heterozygous exonic deletion comprising exons 2, 3, and partially 4 of AQP2.

Conclusion: This is the first case of a compound heterozygote patient with a missense mutation involving NM_000486.5:exon2:c.374C>T (p.Thr125Met) and a gross deletion of at least exons 2, 3, and partially 4 on the AQP2 to present with a severe NDI phenotype.

Keywords: (SNP) array; aquaporin 2 gene; compound heterozygous mutation; exonic deletion; nephrogenic diabetes insipidus; p.T125M mutation; polyuria.

Figure 1

(a) Left panel: sequence electropherograms of AQP2 exon 2, showing the nucleotide change NM_000486.5:exon2:c.374C>T (p.Thr125Met) (red arrow) in the proband (upper panel), her father (middle panel), and the wild‐type sequence in her mother (bottom panel). Right panel: MLPA analysis showing AQP2 dosage of the proband (up), her father (middle), and her mother (down). C: control sample; In: intron; UTR: untranslated region. (b) (SNP) array analysis in the proband using CytoSNP 850K (Illumina, USA). Allele frequency and log R ratio of the SNPs within AQP2 in chromosome 12 have shown. (c) Delimitation of breakpoints for deletion at AQP2 region using specific primers (available upon request), long‐range PCR, and Sanger sequencing in an ABI 3070 XL. (d) Mutation pedigree in the family. (e) Predicted G‐quadruplex sequences in the patient included herein using QGRS software. Analysis was performed within 100 bp at the breakpoint site. (f) Overview of sequence motifs at the delineated breakpoints. Whole junction fragment analysis was performed with BLASTN application, University of California Santa Cruz Genome Browser, Sequencher DNA Sequence Analysis Software, and RepeatMasker application

Figure 2

Schematic representation of mutations found in the proband within AQP2 using different technologies. (a) Structure of aquaporin 2 embedded in the cell membrane reporting the protein mutations by deletion that cause nephrogenic diabetes insipidus (in blue). (b) The location of the identified deletion of at least exons 2, 3, and 4 is marked in red in the AQP2 protein