X-linked transient antenatal Bartter syndrome related to MAGED2 gene: enriching the phenotypic description and pathophysiologic investigation.

Purpose: Transient Bartter syndrome related to pathogenic variants of MAGED2 is the most recently described antenatal Bartter syndrome. Despite its transient nature, it is the most severe form of Bartter syndrome in the perinatal period. Our aim was to describe 14 new cases and to try to explain the incomplete penetrance in women.

Methods: We report on 14 new cases, including 3 females, and review the 40 cases described to date. We tested the hypothesis that MAGED2 is transcriptionally regulated by differential methylation of its CpG-rich promotor by pyrosequencing of DNA samples extracted from fetal and adult leukocytes and kidney samples.

Results: Analysis of the data from 54 symptomatic patients showed spontaneous resolution of symptoms in 27% of cases, persistent complications in 41% of cases and fatality in 32% of cases. Clinical anomalies were reported in 76% of patients, mostly renal anomalies (52%), cardiovascular anomalies (29%) and dysmorphic features (13%). A developmental delay was reported in 24% of patients. Variants were found in all regions of the gene. Methylation analysis of the MAGED2 CpG-rich promotor showed a correlation with gender, independent of age, tissue or presence of symptoms, excluding a role for this mechanism in the incomplete penetrance in women.

Conclusion: This work enriches the phenotypic and genetic description of this recently described disease, and deepens our understanding of the pathophysiological role and regulation of MAGED2. Finally, by describing the wide range of outcomes in patients, this work opens the discussion on genetic counseling offered to families.