Molecular analysis in patients with nephrolithiasis (NL) and/or nephrocalcinosis (NC) enables more accurate evaluation of underlying etiologies. The existing clinical evidence regarding genetic testing in adults with NL comprises only a few cohort studies. We retrospectively analyzed 49 adult patients diagnosed with NL and/or NC from a single center, on whom we performed a genetic test using a nephrolithiasis panel. We reviewed the phenotype of the patients and compared the cases with positive and negative molecular diagnosis. In total, 49 adult patients with NL and/or NC underwent genetic testing. Of the tested patients, 29 (59.2%) patients had 24 abnormal variants in 14 genes. Mendelian diseases were diagnosed in 14 (28.6%) cases: cystinuria (SLC3A1, SLC7A9; n = 4), hereditary distal renal tubular acidosis (SLC4A1; n = 3), Dent disease (CLCN5; n = 2), familial hypomagnesaemia with hypercalciuria and nephrocalcinosis (CLDN16; n = 1), infantile hypercalcemia type 1 (CYP24A1; n = 1), primary hyperoxaluria type 1 (AGXT; n = 1), Bartter syndrome type 2 (KCNJ1; n = 1), and autosomal dominant tubulointerstitial kidney disease (UMOD; n = 1). Eight (16.3%) patients had pathogenic or likely pathogenic monoallelic variants as predisposing factors for NL and/or NC, and seven (14.3%) had biallelic or monoallelic variants of uncertain significance. Patients with positive genetic tests had a lower estimated glomerular filtration rate (p = 0.03) and more frequent NL associated with NC (p = 0.007) and were unlikely to have arterial hypertension (p = 0.03) when compared with patients with negative tests. Our study shows an increased effectiveness of molecular diagnosis and highlights the benefits of genetic testing. NL associated with NC and the presence of chronic kidney disease are the characteristics that should prompt the clinician to suspect an inherited form of NL and/or NC.

Nephrocalcinosis is associated with conditions that cause hypercalcemia and the increased urinary excretion of calcium, phosphate, and/or oxalate. A monogenic etiology is found in almost 30% of childhood-onset nephrocalcinosis which is also a common manifestation of primary hyperparathyroidism. We discuss a child with nephrocalcinosis and features mimicking primary hyperparathyroidism. A 7-year-old girl presented with nephrocalcinosis. Hypercalciuria, hyperphosphaturia, mild hypercalcemia, hypophosphatemia and elevated parathyroid hormone levels along with normal serum creatinine and absence of hypokalemic alkalosis suggested primary hyperparathyroidism. However, she was ultimately diagnosed with Bartter syndrome type 2 based on the presence of homozygous pathogenic variation in KCNJ1gene. This is the second reported case of late-onset Bartter syndrome type 2 without hypokalemic alkalosis. Patients with Bartter syndrome may present with high parathyroid hormone levels and hypercalcemia in addition to hypercalciuria. Thus, the present case suggests that the KCNJ1 gene should be included in genetic analysis even in older children with isolated nephrocalcinosis.

Nephrocalcinosis is a characteristic feature of both type 1 and type 2 Bartter syndrome. Bartter syndrome type 2 presents antenatally and very early in life. Late-onset presentation with isolated nephrocalcinosis is extremely rare. We describe an 11-year-old girl with incidentally detected medullary nephrocalcinosis on renal ultrasonography. She was clinically suspected to have primary hyperoxaluria based on high urine oxalate. However, clinical exome sequencing revealed a pathogenic missense variant in the KCNJ1 gene leading to the molecular diagnosis of Bartter syndrome type 2. Both parents were heterozygous carriers of the same variant. Subsequent investigations did reveal a mild Bartter syndrome phenotype with mild metabolic alkalosis, high urine chloride and high renin and aldosterone. Our case illustrates phenotypic heterogeneity of Bartter syndrome type 2 and the usefulness of genetic testing in establishing the correct diagnosis and guiding further management in such cases.

A 30+6/7-week infant was born by vaginal delivery to a 21-year-old primigravida with pregnancy complicated by polyhydramnios. The infant developed polyuria and significant weight loss in the first 2 weeks of life despite appropriate fluid management. He developed hyponatraemia, hypochloraemia, transient hyperkalaemia and prerenal azotaemia with metabolic acidosis. On further evaluation, he had elevated plasma renin and aldosterone levels. Bartter syndrome was considered in the differential diagnosis. Bartter syndrome gene panel revealed a rare compound heterozygous mutation in exon 2 of the KCNJ1 gene (Lys186Glu/Thr71Met), suggesting antenatal Bartter syndrome (type 2). The infant developed late-onset hypokalaemia and metabolic alkalosis by week 4 of life. He regained birth weight by week 3 of life but failed to thrive (10-20 g/kg/day) despite high caloric intake (140 kcal/kg/day). His electrolyte abnormalities gradually improved, and he was discharged home without the need for electrolyte supplements or medications.

Bartter syndrome type 2 (BS2) is an autosomal recessive renal tubular disorder, which is caused by the mutations in KCNJ1. This study was designed to analyze and describe the genotype and clinical features of five Chinese probands with BS2. Identify KCNJ1 gene variants by the next generation sequencing and evaluate their mutation effects according to 2015 American College of Medical Genetics and Genomics (ACMG) standards and guidelines. Ten variants including eight novel ones of KCNJ1 gene were found, the most common type was missense variant. The common symptoms and signs from high to low incidence were: polydipsia and polyuria (5/5), one of them (1/5) presented with diabetes insipidus; maternal polyhydramnios and premature delivery (4/5); growth retardation (3/5). Two patients presented with hypochloremic metabolic alkalosis and hypokalemia; whereas the acid-base disturbance was absent in the others. One patient had evident parathyroid hormone (PTH) resistance (hypocalcemia, hyperphosphatemia and markedly elevated PTH levels), three presented with PTH overacting (hypercalcemia, hypophosphatemia and mild elevated PTH levels), and one showed normal blood calcium and phosphorus concentrations with high-normal PTH levels. All patients had nephrocalcinosis and/or hypercalciuria, and one of them complicated with nephrolithiasis. Indomethacin has significant therapeutic effect on the growth retardation, polydipsia and polyuria and treatment was associated with a decrease in urine calcium excretion, normalization of electrolyte disturbance and PTH parameters. Ten variants of KCNJ1 gene were identified in five Chinese probands. These patients had atypical BS phenotype lacking evident metabolic alkalosis and/or manifesting with PTH overaction/resistance, which reminds clinicians to carefully differentiate BS2 with other parathyroid disorders. This is the first report of BS2 from Chinese populations.