SLC18A3 variants lead to fetal akinesia deformation sequence early in pregnancy

Fetal akinesia deformation sequence (FADS) and lethal multiple pterygium syndrome (LMPS) are clinically overlapping syndromes manifesting with reduced or absent fetal movement, arthrogryposis, and several anomalies during fetal life. The etiology of these syndromes is heterogeneous, and in many cases it remains unknown. In order to determine the genetic etiology of FADS in two fetuses with fetal akinesia, arthrogryposis, edema, and partial cleft palate, we utilized exome sequencing. Our investigations revealed a homozygous nonsense variant [c.1116C>A, p.(Cys372Ter)] in the SLC18A3 gene, which encodes for the vesicular acetylcholine transporter (VAChT) responsible for active transport of acetylcholine in the neuromuscular junction. This is the first description of a nonsense variant in the SLC18A3 gene, as only missense variants and whole gene deletions have been previously identified in patients. The previously detected SLC18A3 defects have been associated with congenital myasthenic syndromes, and therefore our findings extend the clinical spectrum of SLC18A3 defects to severe prenatal phenotypes. Our findings suggest that nonsense variants in SLC18A3 cause a more severe phenotype than missense variants and are in line with previous studies showing a lethal phenotype in VAChT knockout mice. Our results underline the importance of including SLC18A3 sequencing in the differential diagnostics of fetuses with arthrogryposis, FADS, or LMPS of unknown etiology.