Inclusion Criteria:

For mother: adult mother with confirmed pregnancy no later than week 23+6 and genetically confirmed as carrier of an EDA mutation

• For fetal subject : male fetal subject with confirmed diagnosis of XLHED
• For untreated relative: untreated male relative subject aged between 6 months and 75 years with the same EDA mutation as the treated subject

Exclusion Criteria:

• For mother: any evidence of active maternal infection associated with a risk of preterm birth and/or congenital anomalies of prenatal and postnatal risk to the child. Documented maternal HIV infection. Any pre-existing maternal medical condition that increases the risk of preterm birth or increases the risk of a serious untoward event occurring to the mother during pregnancy. Any pregnancy disorder associated with an increased risk of preterm birth, and/or maternal, fetal or neonatal morbidity/mortality.
• For fetal subject : second major anatomic anomaly (not related to the underlying XLHED) that contributes to a significant morbidity or mortality risk, or echocardiogram or ultrasonography or other findings that indicate a high risk of fetal demise or risk of preterm birth. Any condition other than XLHED that is likely to have an impact on the number of tooth germs. Any other medical condition which in the opinion of the investigator would not allow for safe conduct of the study for the subject, or that would interfere with efficacy assessments.
• For untreated relative: carrier of an hypomorphic EDA mutation. Known hypersensitivity to pilocarpine or pilocarpine-like muscarinic agonists. Presence of an implanted device (e.g., defibrillator, neurostimulator, pacemaker). Previous treatment with the study intervention by any route of administration prior to study start.