Fetal Brain MRI Findings in Myotonic Dystrophy and Considerations for Prenatal Genetic Testing.

Background: Congenital myotonic dystrophy type 1 (DM1) is a rare congenital neuromuscular disorder associated with high morbidity and potential early mortality requiring lifelong symptomatic management. Prenatal presentations of DM1 have been associated with nonspecific ultrasound findings such as clubbed foot, polyhydramnios, ventriculomegaly, and decreased fetal movement, but many cases of DM1 have no ultrasound anomalies.

Methods: We sought to compare the clinical course and prenatal imaging findings in two cases of DM1 using retrospective chart review.

Results: This report demonstrates potential expansion of the prenatal phenotype of DM1 including fetal SVT and frontal bossing. Both cases shared unique prenatal imaging features of lateral ventricle dilation involving the anterior bodies and frontal horns on fetal MRI.

Discussion: Because congenital DM1 is most often maternally inherited, attention to maternal symptoms, physical examination, and family history can be helpful in recognizing cases. Molecular diagnosis of DM1 requires specialized testing of the 3' untranslated region of the DMPK gene, and DM1 will not be detected by current standard prenatal genetic testing with microarray, karyotype, or exome sequencing.