Identification of compound mutations of SLC12A3 gene in a Chinese pedigree with Gitelman syndrome exhibiting Bartter syndrome-liked phenotypes

Abstract

Background: Gitelman syndrome is a rare salt-losing renal tubular disorder associated with mutation of SLC12A3 gene, which encodes the Na-Cl co-transporter (NCCT). Gitelman syndrome is characterized by hypokalemia, metabolic alkalosis, hypomagnesemia, hypocalciuria, and renin-angiotensin-aldosterone system (RAAS) activation. Different SLC12A3 variants may lead to phenotypic variability and severity.

Methods: In this study, we reported the clinical features and genetic analysis of a Chinese pedigree diagnosed with Gitelman syndrome.

Results: The proband exhibited hypokalaemia, hypomagnesemia, metabolic alkalosis, but hypercalciuria and kidney stone formation. The increased urinary calcium excretion made it confused to Bartter syndrome. The persistent renal potassium wasting resulted in renal tubular lesions, and might affect urinary calcium reabsorption and excretion. Genetic analysis revealed mutations of SLC12A3 gene with c.433C > T (p.Arg145Cys), c.1077C > G (p.Asn359Lys), and c.1666C > T (p.Pro556Ser). Potential alterations of structure and function of NCCT protein due to those genetic variations of SLC12A3 are predicted. Interestingly, one sibling of the proband carried the same mutant sites and exhibited similar clinical features with milder phenotypes of hypokalemia and hypomagnesemia, but hypocalciuria rather than hypercalciuria. Family members with at least one wild type copy of SLC12A3 had normal biochemistry. With administration of spironolactone, potassium chloride and magnesium supplement, the serum potassium and magnesium were maintained within normal ranges.

Conclusions: In this study, we identified compound mutations of SLC12A3 associated with varieties of clinical features. Further efforts are needed to investigate the diversity in clinical manifestations of Gitelman syndrome and its correlation with specific SLC12A3 mutations.

Keywords: Gitelman syndrome; Hypercalciuria; Hypokalemia; SLC12A3.

Fig. 1

Imaging manifestations and renal biopsy to show renal lesions. A-D Computed tomography (CT) scan of the proband. Arrows to show renal calcification. C and D are the magnification of A and B, respectively. E-H Renal pathomorphism of the patient to show renal tubular lesions. E. Hematoxylin-eosin (HE) staining. F. Periodic acid Schiff (PAS) staining. G. Sliver methenamine (SM) staining. H. Congo red staining. Those show renal tubular atrophy, epithelial cell edema, and the thickening of basal membrane. The vacuolar degeneration of tubular epithelial cells and loss of brush border were observed. SM and Congo red staining were negative. (× 200) Arrowheads in panel E indicate degenerated tubular epithelial cells. The scale bar in panel E-H stands for 100 μm

Fig. 2

Genetic analysis of SLC12A3 mutations in the pedigree of Gitelman syndrome. A Pedigree of the family structure. Marked symbols to show patients carried compound heterozygous mutations of SLC12A3. Mutations of c.433 C > T and c.1666 C > T was presented as black, and c.1077 C > G was showed as grey. Circles present females, and squares present males. Arrow shows proband. The III-1 and III-2 show normal phenotypes, without features of Gitelman syndrome. B Sequencing results of variants of SLC12A3. The patient (II-6, proband) and his mother (I-2), brother (II-2) and sisters (II-1; II-4; II-5) carried heterozygous mutation of C433T (Arg145Cys) and C1666T (Pro556Ser) in Exon 3 and 13 of SLC12A3, respectively. Heterozygous mutation of C1077G (Asn359Lys) in Exon 8 was detected in the patient (II-6, proband), his father (I-1), his son (III-2), and the sister with Gitelman syndrome (II-4). Arrows indicate heterozygous nucleotide substitutions

Fig. 3

The model structure of Na-Cl cotransporter (NCCT) protein with variants induced by novel mutations of SLC12A3 to show potential influence. The differences of modeled structure compared to wild type (A) were indicated in circles. The visible differences of protein structure was induced by (B) co-existence of c.433 C > T (p.Arg145Cys) and c.1666 C > T (p.Pro556Ser), or (C) c.1077 C > G (p.Asn359Lys) lead to differences from wild type protein structure. It may induce the alteration of the function of NCCT