[Functional characterization of SLC12A1 gene variants in 3 patients with Bartter syndrome type â ].

Objective: To clarify the molecular basis of patients with Bartter syndrome type I and explore the therapeutic effect of trafficking-defective variations by chemical chaperone 4-Phenylbutyric acid(4-PBA). Methods: The clinical characteristics, laboratory findings and genetic data of 3 patients diagnosed with Bartter syndrome type I who were admitted to Department of Nephrology, Children's Hospital of Nanjing Medical University from 2017 to 2018 were retrospectively analyzed. Wild type and variant SLC12A1 gene constructs were transiently overexpressed in HEK293 cells. Western blotting was used to detect the expression levels of Na+-K+-2Cl-cotransporter(NKCC2) protein. Immunofluorescent staining was applied to investigate the subcellular localization of NKCC2 protein. In addition, the effect of the chemical chaperone 4-PBA on the expression and localization of the SLC12A1 gene variants was investigated. Unpaired t test was used for statistical analysis of 4-PBA treatment. Results: All the 3 patients (2 males and 1 female), aged 3.0, 4.0 and 1.2 years, respectively. All patients had antenatal onset with polyhydramnios and were born prematurely. After birth, all patients presented with hypochlorine alkalosis accompanied by hypokalemia and hyponatremia. Sequencing analysis revealed that the 3 patients were homozygotes or compound heterozygotes for variants in the SLC12A1 gene. In HEK293 cells, the surface expression of NKCC2 in 3 variants (p.L463S, p.L479V, p.507-510del) are all lower than in wild type (0.718±0.039, 0.287±0.081, 0.025±0.156 vs. 1.001±0.028, t=5.92, 8.35, 30.49, all P<0.01). Moreover, the total protein expression of p.L479V and p.507-510del group were all lower than that in wild type group (0.630±0.032, 0.043±0.003 vs. 1.000±0.111, t=3.21, 8.65, all P<0.05). 4-PBA treatment increased the mature protein expression level of the p.L463S and p. L479V group in 4-PBA treatment group are all higher than the untreated group (0.459±0.018 vs. 1.123±0.024, 0.053±0.012 vs. 1.256±0.037, t=2.75, 18.35, all P<0.05). Cytoplasmic retention of the L479V and 507-510del variants were observed by immunofluorescent staining. 4-PBA treatment could rescue a number of NKCC2 L479V variants to the membrane. Conclusions: The 3 SLC12A1 variants cause expression or subcellular localization defects of the protein. The findings that plasma membrane expression and activity can be rescued by 4PBA might help to develop novel therapeutic strategy for Bartter syndrome type Ⅰ.

[Clinical features and genetic variants of Dent disease in 10 children].

Objective: To summarize the clinical features and genetic analysis results of 10 children with Dent disease. Methods: The clinical data and gene test results of 10 boys aged from 8 months to 12 years with Dent disease diagnosed in Children's Hospital of Nanjing Medical University from January 2014 to July 2017 were analyzed retrospectively. Results: All patients had insidious onset, 5 cases were found to have proteinuria on routine urine examination after hospitalization duo to other diseases, 4 cases were admitted to hospital because increased foams in the urine, and 1 case was found to have proteinuria on health checkup. All cases presented with low molecular weight proteinuria, urine protein electrophoresis showed that the proportion of low molecular weight protein was greater than 50%, 7 cases had nephrotic-range proteinuria, but none had hypoproteinemia. Six cases had hypercalciuria, 3 cases had nephrocalcinosis, 1 case had nephrolithiasis, 2 cases had glomerular microscopic hematuria, in 1 case urine glucose wa weakly positive but blood glucose was normal. All patients had normal renal function, normal serum calcium, no hypophosphoremia and none had rickets. Genetic analysis results showed that 7 patients with variants in the CLCN5 gene, including 2 nonsense variants (p.R637X, p.Y143X), 3 missense variants (p.A540D, p.G135E, p.G703V), 1 deletion variant (exons 9, 10, 11, 12, 13, 1 missing), and 1 frameshift variant (p.T260Tfs*10). Three cases had missense variants of OCRL gene (p.I274T, p.I371T, p.F399S). Except for p.R637X and p.I274T, the other 8 cases had newly discovered variants. Five patients underwent a renal biopsy, the biopsy revealed focal global glomerulosclerosis in 3 patients, mild mesangial proliferative glomerulonephritis in 1 patient and renal minimal change in 1 patient. Mild focal tubular atrophy and interstitial fibrosis were noted in three cases. Mild segmental foot process effacement was noted under electron microscope in all five cases. Conclusions: All the children with Dent disease had insidious onset, low molecular weight proteinuria is the main clinical manifestation, most cases presented with nephrotic-range proteinuria, but there was no hypoalbuminemia, some cases were not associated with hypercalciuria. The pathogenic genes in most cases were CLCN5 and a few were OCRL. The types of genetic variation include missense variant, nonsense variant, deletion variant and frameshift variant. Although Dent disease is a renal tubular disease, renal biopsy suggests that most cases are associated with glomerular lesions.