IGHMBP2 and Charcot-Marie-Tooth disease axonal type 2S: Autosomal recessive mutations in the immunoglobulin μ-binding protein 2 gene (IGHMBP2) have been associated with two distinct phenotypes: spinal muscle atrophy with respiratory distress type 1 (SMARD1) and, more recently, Charcot-Marie-Tooth disease type 2S (CMT2S).