A novel compound heterozygous variant of the SLC12A3 gene in Gitelman syndrome pedigree

Abstract

Background: Gitelman syndrome (GS) is an autosomal recessive disorder caused by genic mutations of SLC12A3 (Solute carrier family 12 member 3), which encodes the Na-Cl cotransporter (NCC), and presents with characteristic metabolic abnormalities, including hypokalemia, metabolic alkalosis, hypomagnesemia, and hypocalciuria. In this study, we report a case of a GS pedigree, including analysis of GS-associated gene mutations.

Methods: We performed next-generation sequencing analysis and Sanger sequencing to explore the SLC12A3 mutations in a GS pedigree that included a 35-year-old female patient with GS and five family members within three generations. Furthermore, we summarized their clinical manifestations and analyzed laboratory parameters related to GS.

Results: The female proband (the patient with GS) presented with intermittent fatigue and transient periods of tetany, along with significant hypokalemia, hypomagnesemia, and hypocalciuria. All other members of the pedigree had normal laboratory results without obvious GS-related symptoms. Genetic analysis of the SLC12A3 gene identified two novel missense mutations (c.1919A > G, p.N640S in exon 15; c.2522A > G, p.D841G in exon 21) in the patient with GS. Moreover, we demonstrated that her mother, younger maternal uncle, and cousin were carriers of one mutation (c.1919A > G), and her father was the carrier of the other (c.2522A > G).

Conclusion: This is the first report of these two novel pathogenic variants of SLC12A3 and their contribution to GS. Further functional studies are particularly warranted to explore the underlying molecular mechanisms.

Keywords: Compound heterozygous; Gitelman syndrome; Pedigree; SLC12A3.

Fig. 1

Sequencing diagram of SLC12A3 gene Exon 15. a Exon 15 wild-type (DNA and amino acid sequences, GRCh37.p13); (b) Exon 15 heterozygous mutation type, A1919G, AAC → AGC, Asn640Ser (N640S); (c) Exon 15 wild-type (Sanger sequencing); (d) Exon 15 heterozygous mutation type (Sanger sequencing)

Fig. 2

Sequencing diagram of SLC12A3 gene Exon 21. a Exon 21 wild-type (DNA and amino acid sequences, GRCh37. p13); (b) Exon 21 heterozygous mutation, A2522G, GAC → GGC, Asp841Gly (D841G); (c) Exon 21 wild-type (Sanger sequencing); (d) Exon 21 heterozygous mutation type (Sanger sequencing)

Fig. 3

Predicted topological localization of Na-Cl cotransporter (NCC) mutations. Schematic representation of NCC protein with the intercellular N- and C-terminal domains and with squares 1 to 12 indicating the 12 transmembrane segments.^[9^] Arrows indicate the position of the selected mutations

Fig. 4

Pedigree chart of the proband’s family. The arrow indicates the proband. Filled symbols indicate subjects affected by gene mutations (c.1919A > G is marked as black and c.2522A > G is marked as grey). Men are indicated by squares, and women are indicated by circles. III1, the proband, III2, sister, III3, cousin, II1, father, II2, mother, II3, elder uncle, II4, younger uncle

Fig. 5

Effect of SLC12A3 mutations on the modeled structure of the Na-Cl cotransporter (NCC) protein. Compared to the wild-type (a), c.1919A > G (b) alone caused three visible differences in the protein structure (marked with red and black frames), whereas c.2522A > G (c) alone led to one further difference (marked with a brown frame). Coexistence of c.1919A > G and c.2522A > G (d) resulted in three more differences (marked with purple frames)