Charcot-Marie-Tooth disease type 4B1 (CMT4B1) is a subtype of Charcot-Marie-Tooth disease type 4 characterized by an early childhood-onset of severe, demyelinating sensorimotor neuropathy, various degrees of complex myelin outfoldings seen on peripheral nerve biopsy, very slow, and often undetectable, nerve conduction velocities, and the typical CMT phenotype (i.e. distal muscle weakness and atrophy, sensory loss, and frequent pes cavus). Other reported features include facial weakness, vocal cord paresis, respiratory difficulties, and skeletal deformities (e.g. chest deformities, claw hands, pes equinovarus). The disease is Monarch Disease Ontology id MONDO_0011066 (Charcot-Marie-Tooth disease type 4B1). Also known as: CMT4B1, Charcot-Marie-Tooth disease type 4 caused by mutation in MTMR2, Charcot-Marie-Tooth neuropathy type 4B1, MTMR2 Charcot-Marie-Tooth disease type 4, autosomal recessive Charcot-Marie-Tooth disease with focally folded myelin sheaths type 4B1.