Transient antenatal Bartter's Syndrome and X-linked polyhydramnios: insights from the genetics of a rare condition

Identification of a novel intronic mutation of MAGED2 gene in a Chinese family with antenatal Bartter syndrome

BACKGROUND

Antenatal Bartter syndrome is a life-threatening disease caused by a mutation in the MAGED2 gene located on chromosome Xp11. It is characterized by severe polyhydramnios and extreme prematurity. While most reported mutations are located in the exon region, variations in the intron region are rarely reported.

METHODS

In our study, we employed whole exome sequencing and Sanger sequencing to genotype members of this family. Additionally, a minigene assay was conducted to evaluate the impact of genetic variants on splicing.

RESULTS

Our findings reveal a novel intronic variant (NM_177433.3:c.1271 + 4_1271 + 7delAGTA) in intron 10 of the MAGED2 gene. Further analysis using the minigene assay demonstrated that this variant activated an intronic cryptic splice site, resulting in a 96 bp insertion in mature mRNA.

CONCLUSIONS

Our results indicate that the novel intronic variant (c.1271 + 4_1271 + 7delAGTA) in intron 10 of the MAGED2 gene is pathogenic. This expands the mutation spectrum of MAGED2 and highlights the significance of intronic sequence analysis.

A novel MAGED2 variant in a Chinese preterm newborn with transient antenatal Bartter's syndrome with 4 years follow-up

Background

Transient antenatal Bartter’s syndrome caused by MAGED2 mutation is a rare X-linked recessive renal tubular disorder. Cases reported are mostly infants, and the long-term prognosis of the disease is still under investigation.

Case presentation

We encountered a preterm male infant with polyhydramnios, polyuria, salt loss, hypercalciuria, nephrocalcinosis and alkalosis. Antenatal Bartter’s syndrome was suspected, but these clinical symptoms surprisingly disappeared after about 2 months. This led to the clinical diagnosis of transient antenatal Bartter’s syndrome. Gene analysis in this patient disclosed a novel variant (c.1598C > T, p.Ala533Val) in exon 12 of MAGED2 gene, and his mother was a heterozygous carrier. This patient was followed up in clinic for 4 years without recurrence of imbalance of potassium, sodium and chloride. His height and weight were in normal range, and all laboratory examinations and nephrotic ultrasound were also normal.

Conclusions

We reported the first Chinese case of transient antenatal Bartter’s syndrome caused by MAGED2 mutation. The 4-year follow-up of our case further demonstrates the benign prognosis of the disease and indicates that early recognition of this phenotype could avoid unnecessary treatments.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02553-1.

Molecular Basis, Diagnostic Challenges and Therapeutic Approaches of Bartter and Gitelman Syndromes: A Primer for Clinicians

Gitelman and Bartter syndromes are rare inherited diseases that belong to the category of renal tubulopathies. The genes associated with these pathologies encode electrolyte transport proteins located in the nephron, particularly in the Distal Convoluted Tubule and Ascending Loop of Henle. Therefore, both syndromes are characterized by alterations in the secretion and reabsorption processes that occur in these regions. Patients suffer from deficiencies in the concentration of electrolytes in the blood and urine, which leads to different systemic consequences related to these salt-wasting processes. The main clinical features of both syndromes are hypokalemia, hypochloremia, metabolic alkalosis, hyperreninemia and hyperaldosteronism. Despite having a different molecular etiology, Gitelman and Bartter syndromes share a relevant number of clinical symptoms, and they have similar therapeutic approaches. The main basis of their treatment consists of electrolytes supplements accompanied by dietary changes. Specifically for Bartter syndrome, the use of non-steroidal anti-inflammatory drugs is also strongly supported. This review aims to address the latest diagnostic challenges and therapeutic approaches, as well as relevant recent research on the biology of the proteins involved in disease. Finally, we highlight several objectives to continue advancing in the characterization of both etiologies.

A Case Report and Literature Review of a Novel Mutation in the MAGED2 Gene of a Patient With Severe Transient Polyhydramnios

Background: Polyhydramnios occurs frequently during pregnancy. Mutations in the MAGED2 gene can cause X-linked acute early-onset polyhydramnios with a severe but transient form of antenatal Bartter's syndrome. Case Presentation: Here, we report a new novel frameshift mutation c.733_734delCT (p. Leu245GlufsTer4) in the MAGED2 gene (NM_177433.1) that caused prenatal polyhydramnios, but did not cause polyuria after birth. Follow-up was conducted for 2 months, and the baby's growth and development were normal, without polyuria and renal impairment. In addition, we identified all individuals with MAGED2 mutations reported in the literature before March 2021. Conclusion: We report a new case with a novel variant of the MAGED2 gene that caused severe hydramnios but with a good result and summary clinical characteristics in a newborn with antenatal Bartter's syndrome caused by an MAGED2 mutation. Good prenatal diagnosis and genetic consultation can improve pregnancy monitoring and newborn management.

Salt-Losing Tubulopathies in Children: What's New, What's Controversial?

Renal tubulopathies provide insights into the inner workings of the kidney, yet also pose therapeutic challenges. Because of the central nature of sodium in tubular transport physiology, disorders of sodium handling may affect virtually all aspects of the homeostatic functions of the kidney. Yet, owing to the rarity of these disorders, little clinical evidence regarding treatment exists. Consequently, treatment can vary widely between individual physicians and centers and is based mainly on understanding of renal physiology, reported clinical observations, and individual experiences. Salt-losing tubulopathies can affect all tubular segments, from the proximal tubule to the collecting duct. But the more frequently observed disorders are Bartter and Gitelman syndrome, which affect salt transport in the thick ascending limb of Henle's loop and/or the distal convoluted tubule, and these disorders generate the greatest controversies regarding management. Here, we review clinical and molecular aspects of salt-losing tubulopathies and discuss novel insights provided mainly by genetic investigations and retrospective clinical reviews. Additionally, we discuss controversial topics in the management of these disorders to highlight areas of importance for future clinical trials. International collaboration will be required to perform clinical studies to inform the treatment of these rare disorders.

Prevalence of Novel MAGED2 Mutations in Antenatal Bartter Syndrome

BACKGROUND AND OBJECTIVES

Mutations in the MAGED2 gene, located on the X chromosome, have been recently detected in males with a transient form of antenatal Bartter syndrome or with idiopathic polyhydramnios. The aim of this study is to analyze the proportion of the population with mutations in this gene in a French cohort of patients with antenatal Bartter syndrome.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The French cohort of patients with antenatal Bartter syndrome encompasses 171 families. Mutations in genes responsible for types 1-4 have been detected in 75% of cases. In patients without identified genetic cause (n=42), transient antenatal Bartter syndrome was reported in 12 cases. We analyzed the MAGED2 gene in the entire cohort of negative cases by Sanger sequencing and retrospectively collected clinical data regarding pregnancy as well as the postnatal outcome for positive cases.

RESULTS

We detected mutations in MAGED2 in 17 patients, including the 12 with transient antenatal Bartter syndrome, from 16 families. Fifteen different mutations were detected (one whole deletion, three frameshift, three splicing, three nonsense, two inframe deletions, and three missense); 13 of these mutations had not been previously described. Interestingly, two patients are females; in one of these patients our data are consistent with selective inactivation of chromosome X explaining the severity. The phenotypic presentation in our patients was variable and less severe than that of the originally described cases.

CONCLUSIONS

MAGED2 mutations explained 9% of cases of antenatal Bartter syndrome in a French cohort, and accounted for 38% of patients without other characterized mutations and for 44% of male probands of negative cases. Our study confirmed previously published data and showed that females can be affected. As a result, this gene must be included in the screening of the most severe clinical form of Bartter syndrome.