Review and Analysis of Two Gitelman Syndrome Pedigrees Complicated with Proteinuria or Hashimoto's Thyroiditis Caused by Compound Heterozygous SLC12A3 Mutations

Abstract

Gitelman syndrome (GS) is an autosomal recessive inherited salt-losing renal tubular disease, which is caused by a pathogenic mutation of SLC12A3 encoding thiazide-sensitive Na-Cl cotransporter, which leads to disturbance of sodium and chlorine reabsorption in renal distal convoluted tubules, resulting in phenotypes such as hypovolemia, renin angiotensin aldosterone system (RAAS) activation, hypokalemia, and metabolic alkalosis. In this study, two GS families with proteinuria or Hashimoto's thyroiditis were analyzed for genetic-phenotypic association. Sanger sequencing revealed that two probands carried SLC12A3 compound heterozygous mutations, and proband A carried two pathogenic mutations: missense mutation Arg83Gln, splicing mutation, or frameshift mutation NC_000016.10:g.56872655_56872667 (gcggacatttttg>accgaaaatttt) in exon 8. Proband B carries two missense mutations: novel Asp839Val and Arg904Gln. Both probands manifested hypokalemia, hypomagnesemia, hypocalcinuria, metabolic alkalosis, and RAAS activation; in addition, the proband A exhibited decreased urinary chloride, phosphorus, and increased magnesium ions excretion, complicated with Hashimoto's Thyroiditis, while the proband B exhibited enhanced urine sodium excretion and proteinuria. The older sister of proband B with GS also had Hashimoto's thyroiditis. Electron microscopy revealed swelling and vacuolar degeneration of glomerular epithelial cells, diffuse proliferation of mesangial cells and matrix, accompanied by a small amount of low-density electron-dense deposition, and segmental fusion of epithelial cell foot processes in proband B. Light microscopy showed mild mesangial hyperplasia in the focal segment of the glomerulus, hyperplasia, and hypertrophy of juxtaglomerular apparatus cells, mild renal tubulointerstitial lesions, and one glomerular sclerosis. So, long-term hypokalemia of GS can cause kidney damage and may also be susceptible to thyroid disease.

Figure 1

(a) Family A genetic pedigree map; black indicates a carrier of the Arg83Gln mutation, gray indicates a carrier of the mutation of SLC12A3 NC_000016.9:g.56872655_56872667 (gcggacatttttg>accgaaaatttt), the arrow indicates the proband, the square indicates male, and the circle indicates female; (b) family B genetic pedigree map; black indicates a carrier of the Asp839Val mutation, gray indicates a carrier of the Arg904Gln mutation, the arrow indicates the proband, the square indicates male, and the circle indicates female; (c–e) pathological electron microscopic examination of renal biopsy shows swelling and vacuolar degeneration of glomerular epithelial cells, diffuse proliferation of mesangial cells and matrix, accompanied by a small amount of low-density electron dense deposition, swelling, and vacuolar degeneration in the visceral epithelial cells, segmental fusion of epithelial cells foot processes. (f–i) Pathological light microscopic examination of renal biopsy shows mild mesangial hyperplasia in the focal segment of the glomerulus, hyperplasia, and hypertrophy of juxtaglomerular apparatus cells, mild renal tubulointerstitial lesions, and one glomerular sclerosis (h). (f) HE staining ×200; (g, h) PAM staining ×200; (i) PAS staining ×200.

Figure 2

Sanger sequencing image of Pedigree A mutation type. (a) The NP_001119580.2:p.Arg83Gln (NM_001126108.2:c.248G>A, rs768527231) heterozygous mutant type in SLC12A3 exon1; (b) the corresponding wild type; (c) the NC_000016.10:g.56872655_56872667 (gcggacatttttg>accgaaaatttt, rs1215667472) heterozygous mutant type in exon8; (d) the clone of the mutant type at the corresponding position; and (e) the clone of the wild type at the corresponding position.

Figure 3

Sanger sequencing diagram of Pedigree B mutation type. (a) The Asp839Val (c.2516A>T) heterozygous mutant type in SLC12A3 exon21; (b) the corresponding wild type; (c) the NP_001119580.2:p.Arg904Gln (NM_001126108.2:c.2711G>A, rs11643718) heterozygous mutant type in exon23; (d) the wild type at the corresponding position.