Influences of Pregnancy on Different Genetic Subtypes of Non-Dystrophic Myotonia and Periodic Paralysis.

Background: There are only few reports of pregnancy and delivery in non-dystrophic myotonia or periodic paralysis caused by CLCN1 or SCN4A gene mutations.

Methods: We report the medical histories and personal attitudes of 5 unrelated German patients, 2 following autosomal recessive inheritance (case 1; most likely and case 2; confirmed Becker disease) and 3 following autosomal dominant inheritance (case 3; CLCN1 mutation, cases 4-5; SCN4A mutations), who delivered a total of 9 children.

Results: Apart from case 5 with periodic paralysis, who had 5 early miscarriages and pre-eclampsia resulting in cesarean delivery, there was no evidence of increased obstetric complication rates, and neonatal outcome was favorable. In all patients, there was aggravation of myotonia or weakness in pregnancy, followed by a short-term improvement after delivery in cases 2 and 3. Mexiletine medication improved the clinical features significantly in case 2 but was unable to control pregnancy-related deterioration. In case 4 (and her sister) and case 5, there was a clear disease aggravation in pregnancy resulting in hospitalization or repeated neurological examinations.

Conclusion: Pregnancy can be regarded as a strong triggering factor in inherited non-dystrophic myotonias and periodic paralysis, regardless of the underlying gene defect.