Lethal multiple pterygium syndrome, large cystic hygroma, and cleft palate: Rare and severe fetal presentations of RYR1- and NEB-related congenital myopathies.

Congenital myopathies are a genetically heterogeneous group of neuromuscular disorders that commonly present with congenital hypotonia and weakness but can also present broadly. The most severe presentation is neonatal with arthrogryposis and, rarely, fetal akinesia and pterygia, features also seen in lethal multiple pterygium syndrome (LMPS). We describe two fetuses with similar phenotype, including hydrops fetalis, large cystic hygromas, bilateral talipes, and fetal akinesia in the second trimester. Genetic diagnoses were made using exome sequencing. Both fetuses had a severe form of congenital myopathy. In the first fetus, we identified two novel compound heterozygous likely pathogenic variants consistent with autosomal recessive RYR1-related congenital myopathy (congenital myopathy 1B). In the second fetus, we identified two likely pathogenic variants, one of which is novel, likely in trans consistent with a diagnosis of autosomal recessive NEB-related congenital myopathy. Reaching a genetic diagnosis for these fetuses allowed the families to receive accurate genetic counseling for future pregnancies. These fetuses highlight the genetic and phenotypic heterogeneity of LMPS, and support a broad approach to genetic testing.