A Seed Sequence Variant in miR-145-5p causes Multisystem Smooth Muscle Dysfunction Syndrome (MSMDS)

Multisystem smooth muscle dysfunction syndrome (MSMDS) is a smooth muscle myopathy with major dysfunction in multiple organ systems. Described cases have been exclusively associated with recurrent missense variants at amino acid position 179 in the ACTA2 gene. We describe a patient with multiple major manifestations of MSMDS including steno-occlusive cerebrovascular arteriopathy, prune belly syndrome, gastrointestinal dysmotility, bladder dysfunction, and pupillary hyporeactivity without variation in ACTA2. Whole genome sequencing revealed a single nucleotide variant contained within the seed sequence of MIR145, which encodes the smooth muscle associated microRNA; hsa-miR-145-5p. RNA expression analysis on patient-derived fibroblasts was consistent with actin cytoskeletal dysfunction, and mutant miR-145-5p was unable to mediate cytoskeletal modulation of smooth muscle cells. MSMDS can be caused by a loss-of-function mutation in the smooth muscle differentiation factor, miR-145-5p, the first described non-coding genetic vasculopathy. Overall design: RNAseq of human fibroblast and primary VSMCs