Scapulohumeroperoneal myopathy is an autosomal dominant muscle disorder characterized by slowly progressive muscle weakness and atrophy affecting both proximal and distal muscles of the upper and lower limbs. Onset is usually in the first decade and can be as early as infancy, although some patients do not notice symptoms until young adulthood. There is marked variability in severity (summary by Zukosky et al., 2015).

Charcot-Marie-Tooth disease type 2FF (CMT2FF) is an autosomal dominant progressive axonal sensorimotor peripheral neuropathy characterized by early-childhood onset of difficulties walking or running due to atrophy and weakness of the lower limbs. Most patients have foot and ankle deformities, requiring surgery or walking aids. Some patients lose independent ambulation. There is also prominent involvement of the upper limbs, with weakness and atrophy of the forearm, wrist, and intrinsic hand muscles. Proximal muscle function is preserved. Affected individuals have variable distal sensory impairment. Most patients have hyporeflexia, although brisk reflexes, suggesting upper motor involvement, have been described in 1 family. Sural nerve biopsy showed abnormal myelination (Rebelo et al., 2021). For a phenotypic description and a discussion of genetic heterogeneity of axonal CMT type 2, see CMT2A (118210).

Charcot-Marie-Tooth disease type 2Z (CMT2Z) is an autosomal dominant axonal peripheral neuropathy characterized by onset, usually in the first decade, of distal lower limb muscle weakness and sensory impairment. The disorder is progressive, and affected individuals tend to develop upper limb and proximal muscle involvement in an asymmetric pattern, resulting in severe disability late in adulthood. Rare occurrence of global developmental delay with impaired intellectual development or learning difficulties has been observed. In some instances, the same mutation may result in different phenotypic manifestations (CMT2Z or DIGFAN), which highlights the clinical spectrum associated with MORC2 mutations and may render the classification of patients into one or the other disorder challenging (summary by Sevilla et al., 2016, Ando et al., 2017, Guillen Sacoto et al., 2020). For a phenotypic description and a discussion of genetic heterogeneity of axonal CMT, see CMT2A1 (118210).

Autosomal recessive distal hereditary motor neuronopathy-6 (HMNR6) is a neuromuscular disorder characterized by onset of distal muscle weakness in early infancy. Affected individuals often present at birth with distal joint contractures or foot deformities and show delayed motor development, often with inability to walk or frequent falls. Hypo- or hyperreflexia may be observed; limb muscle atrophy may also be present. Patients often show respiratory distress or diaphragmatic palsy. Electrophysiologic studies are consistent with a peripheral motor neuropathy without sensory involvement (Maroofian et al., 2019). For a discussion of genetic heterogeneity of autosomal recessive distal HMN, see HMNR1 (604320).