spinal muscular atrophy with lower extremity predominance 2b spinal muscular atrophy with lower extremity predominance 2b spinal muscular atrophy with lower extremity predominance 2b (smaled2b) is a rare neuromuscular disorder characterised by generalised muscle weakness. spinal muscular atrophy with lower extremity predominance 2bother nameslower extremity-predominant spinal muscular atrophy type 2b, smaled2bspinal muscular atrophy with lower extremity predominance 2b is inherited in an autosomal dominant manner.specialtyneurologysymptomsgeneralised severe hypotonia at birthusual onsetinfancydurationlifetimecausesmutations in bicd2 genediagnostic methodmolecular testprognosislife limiting indications decreased foetal movement is apparent already before birth. the child is born with a generalised muscle weakness (hypotonia) and contractures resembling arthrogryposis multiplex congenita, respiratory insufficiency, and sometimes facial deformations. the disorder is frequently fatal in early childhood. cause the disease is caused by a mutation in the bicd2 gene and is passed on in an autosomal dominant manner. there is no known cure to smaled2b.