BICD2 and autosomal dominant childhood-onset proximal spinal muscular atrophy with contractures: Dominant missense variants in the Bicaudal D2 Drosophila homolog 2 (BICD2) gene were initially described in autosomal dominant lower extremity-predominant spinal muscular atrophy 2 (SMALED2A;MIM#609797) [1] and its prenatal onset form (SMALED2B, MIM #618291) [2].