A form of axonal Charcot-Marie-Tooth disease a peripheral sensorimotor neuropathy. Onset is in the first to sixth decade with a gait anomaly and a leg weakness that reaches the arms secondarily. Tendon reflexes are reduced or absent and after years all patients have a pes cavus. Other signs may be present including hearing loss and postural tremor.

The autosomal dominant TRPV4 disorders (previously considered to be clinically distinct phenotypes before their molecular basis was discovered) are now grouped into neuromuscular disorders and skeletal dysplasias; however, the overlap within each group is considerable. Affected individuals typically have either neuromuscular or skeletal manifestations alone, and in only rare instances an overlap syndrome has been reported. The three autosomal dominant neuromuscular disorders (mildest to most severe) are: Charcot-Marie-Tooth disease type 2C. Scapuloperoneal spinal muscular atrophy. Congenital distal spinal muscular atrophy. The autosomal dominant neuromuscular disorders are characterized by a congenital-onset, static, or later-onset progressive peripheral neuropathy with variable combinations of laryngeal dysfunction (i.e., vocal fold paresis), respiratory dysfunction, and joint contractures. The six autosomal dominant skeletal dysplasias (mildest to most severe) are: Familial digital arthropathy-brachydactyly. Autosomal dominant brachyolmia. Spondylometaphyseal dysplasia, Kozlowski type. Spondyloepiphyseal dysplasia, Maroteaux type. Parastremmatic dysplasia. Metatropic dysplasia. The skeletal dysplasia is characterized by brachydactyly (in all 6); the five that are more severe have short stature that varies from mild to severe with progressive spinal deformity and involvement of the long bones and pelvis. In the mildest of the autosomal dominant TRPV4 disorders life span is normal; in the most severe it is shortened. Bilateral progressive sensorineural hearing loss (SNHL) can occur with both autosomal dominant neuromuscular disorders and skeletal dysplasias.

HMSNR is an autosomal recessive progressive complex peripheral neuropathy characterized by onset in the first decade of distal lower limb weakness and muscle atrophy resulting in walking difficulties. Distal impairment of the upper limbs usually occurs later, as does proximal lower limb weakness. There is distal sensory impairment, with pes cavus and areflexia. Laboratory studies suggest that it is a myelinopathy resulting in reduced nerve conduction velocities in the demyelinating range as well as a length-dependent axonopathy (summary by Sevilla et al., 2013). For a discussion of genetic heterogeneity of autosomal recessive hereditary motor and sensory neuropathy, also known as Charcot-Marie-Tooth disease, see CMT4A (214400).

The spectrum of ANO5 muscle disease is a continuum that ranges from asymptomatic hyperCKemia and exercise-induced myalgia to proximal and/or distal muscle weakness. The most typical presentation is limb-girdle muscular dystrophy type 2L (LGMD2L) with late-onset proximal lower-limb weakness in the fourth or fifth decade (range 15-70 years). Less common is Miyoshi-like disease (Miyoshi muscular dystrophy 3) with early-adult-onset calf distal myopathy (around age 20 years). Incidental hyperCKemia may be present even earlier. Initial symptoms are walking difficulties, reduced sports performance, and difficulties in standing on toes as well as nonspecific exercise myalgia and/or burning sensation in the calf muscles. Muscle weakness and atrophy are frequently asymmetric. Cardiac findings can include cardiomyopathy and arrhythmias and/or left ventricular dysfunction. Bulbar or respiratory symptoms have not been reported. Females have milder disease manifestations than males. Disease progression is slow in both the LGMD and distal forms; ambulation is preserved until very late in the disease course. Life span is normal.

Any neuronopathy, distal hereditary motor in which the cause of the disease is a mutation in the HSPB3 gene.

Hereditary sensory and autonomic neuropathy type IC (HSAN1C) is an autosomal dominant neurologic disorder characterized by sensory neuropathy with variable autonomic and motor involvement. Most patients have adult onset of slowly progressive distal sensory impairment manifest as numbness, tingling, or pain, as well as distal muscle atrophy. Complications include ulceration and osteomyelitis. Some patients may have a more severe phenotype with onset in childhood. Electrophysiologic studies show a predominantly axonal neuropathy with some demyelinating features. Some patients may have evidence of central nervous system involvement, including macular telangiectasia type 2 and/or pyramidal signs. Affected individuals have increased levels of plasma 1-deoxysphingolipids (1-deoxySLs), which are thought to be neurotoxic. (summary by Rotthier et al., 2010, Gantner et al., 2019, and Triplett et al., 2019). Oral supplementation with serine decreases 1-deoxySL and may offer some clinical benefits (Fridman et al., 2019). For a discussion of genetic heterogeneity of HSAN, see HSAN1A (162400).

Spastic paraplegia-54 (SPG54) is a complicated form of spastic paraplegia, a neurodegenerative disorder affecting fibers of the corticospinal tract. Affected individuals have delayed psychomotor development, intellectual disability, and early-onset spasticity of the lower limbs. Brain MRI shows a thin corpus callosum and periventricular white matter lesions. Brain magnetic resonance spectroscopy shows an abnormal lipid peak (summary by Schuurs-Hoeijmakers et al., 2012). For a general phenotypic description and a discussion of genetic heterogeneity of autosomal recessive spastic paraplegia, see 270800.

HMND9 is an autosomal dominant neurologic disorder characterized by juvenile onset of slowly progressive distal muscle weakness and atrophy affecting both the lower and upper limbs (summary by Tsai et al., 2017). For a general phenotypic description and a discussion of genetic heterogeneity of autosomal dominant distal HMN, see HMND1 (182960).

CMTDIF is an autosomal dominant neurologic disorder characterized by onset around adolescence of slowly progressive distal muscle atrophy and weakness affecting the upper and lower limbs and resulting in steppage gait. There is distal sensory impairment with decreased reflexes. Nerve conduction velocities are variable, ranging from the demyelinating to the axonal range (summary by Soong et al., 2013). For a discussion of genetic heterogeneity of CMTDI, see 606482.

Autosomal recessive distal hereditary motor neuronopathy-8 (HMNR8), or sorbitol dehydrogenase deficiency with peripheral neuropathy (SORDD), is characterized by onset of distal muscle weakness mainly affecting the lower limbs and resulting in difficulty walking. Onset of symptoms is usually in the first or second decades of life, although later adult onset has been reported; the disorder is slowly progressive. Nerve conduction velocities are most consistent with an axonal process. More variable features include distal sensory impairment, upper limb tremor, and scoliosis. Laboratory studies show increased serum sorbitol (summary by Cortese et al., 2020). For a general phenotypic description and a discussion of genetic heterogeneity of autosomal recessive HMN, see HMNR1 (604320).

Mitochondrial form of axonal Charcot-Marie-Tooth disease-1 (CMTMA1) is inherited only through the maternal line. The disorder is characterized by onset of distal muscle weakness and atrophy mainly affecting the lower limbs and resulting in difficulty walking in the second decade of life, although both earlier and later onset can occur. Upper limb involvement often develops with time, and affected individuals have weakness and atrophy of the intrinsic hand muscles. Other features may include distal sensory impairment, foot deformities, scoliosis, hypo- or hyperreflexia, spastic paraparesis, and neurogenic bladder. Electrophysiologic studies are compatible with an axonal sensorimotor peripheral neuropathy, and muscle and nerve biopsy show evidence of mitochondrial dysfunction with decreased activities of respiratory complexes, mtDNA deletions, and mitochondrial hyperplasia (summary by Fay et al., 2020).

Autosomal recessive distal hereditary motor neuronopathy-7 (HMNR7) is characterized by onset of lower leg weakness in the first decade. Affected individuals have difficulty climbing stairs and problems standing on the heels. Some patients have later onset well into the adult years. Most patients have foot deformities, and some may have leg muscle atrophy. The disorder is slowly progressive and often involves the upper limbs. Muscle biopsy and electrophysiologic studies are consistent with both a myopathic process and an axonal motor neuropathy. Sensory abnormalities are not typically present, and patients remain ambulatory. The phenotype shows phenotypic overlap with distal hereditary motor neuropathy, but can distinguished by the presence of myopathic features (summary by Deschauer et al., 2021 and Pagnamenta et al., 2021). For a discussion of genetic heterogeneity of autosomal recessive HMN, see HMNR1 (604320).

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).

Autosomal recessive limb-girdle muscular dystrophy-27 (LGMDR27) is characterized by progressive muscle weakness primarily affecting the lower limbs and resulting in walking difficulty or loss of ambulation. The age at onset is highly variable, from infancy to young adulthood. Patients with infantile onset may have a more severe disease course with rapid progression. Upper limb involvement and distal muscle weakness may also occur. Additional more variable features include neck muscle weakness, scoliosis, and joint contractures. Less common features include impaired intellectual development or speech delay, cardiomyopathy, and cardiac arrhythmia. Muscle biopsy shows nonspecific dystrophic changes (Coppens et al., 2021). For a discussion of genetic heterogeneity of autosomal recessive limb-girdle muscular dystrophy, see LGMDR1 (253600).

Nonprogressive neurodevelopmental disorder with spasticity and transient opisthotonus (NEDSTO) is an autosomal recessive complex neurologic disorder characterized by delay of gross motor milestones, particularly walking, associated with axial hypotonia and peripheral spasticity apparent from infancy or early childhood. Affected individuals often show transient opisthotonic posturing in infancy, and later show abnormal involuntary movements, including chorea, dystonia, and dyspraxia. Some patients have impaired intellectual development, although the severity is highly variable; most have speech delay and articulation difficulties and a happy overall demeanor. Brain imaging shows myelination defects in some patients. The disorder is nonprogressive, and many patients may catch up developmentally in the second or third decades (summary by Wagner et al., 2020).

Distal myopathy-5 (MPD5) is an autosomal recessive, slowly progressive muscle disorder characterized by adolescent onset of distal muscle weakness and atrophy predominantly affecting the lower limbs. Other features include facial weakness and hyporeflexia. Patients remain ambulatory even after long disease duration (summary by Park et al., 2016).

Charcot-Marie-Tooth disease type 2X (CMT2X) is an autosomal recessive, slowly progressive, axonal peripheral sensorimotor neuropathy characterized by lower limb muscle weakness and atrophy associated with distal sensory impairment and gait difficulties. Some patients also have involvement of the upper limbs. Onset usually occurs in the first 2 decades of life, although later onset can also occur (summary by Montecchiani et al., 2016) For a phenotypic description and a discussion of genetic heterogeneity of axonal CMT, see CMT2A1 (118210).

Charcot-Marie-Tooth disease type 2Y is an autosomal dominant peripheral neuropathy characterized by distal muscle weakness and atrophy associated with length-dependent sensory loss. Most patients have involvement of both the lower and upper limbs. The age at onset and the severity of the disorder are highly variable (summary by Gonzalez et al., 2014). For a phenotypic description and a discussion of genetic heterogeneity of axonal CMT, see CMT2A1 (118210).

X-linked adult-onset distal myopathy-7 (MPD7) is an X-linked recessive disorder that affects only males. It is characterized by onset of distal muscle weakness predominantly affecting the lower limbs between 20 and 60 years of age. The disorder is slowly progressive, with most affected individuals developing distal upper limb involvement and some developing proximal muscle involvement, although patients remain ambulatory. Muscle biopsy shows variable myopathic changes as well as sarcoplasmic inclusions that may represent abnormally aggregated proteins (summary by Johari et al., 2021).

Demyelinating Charcot-Marie-Tooth disease-1H (CMT1H) is an autosomal dominant peripheral sensorimotor neuropathy with onset usually in adulthood (third to fifth decades). Affected individuals present with foot deformities, upper or lower limb sensory disturbances, and motor deficits, mainly impaired gait. Of note, many patients complain of unpleasant sensory sensations in the upper extremities and hands. The disorder is slowly progressive and becomes more apparent with age, although patients usually remain ambulatory. Other features include hypo- or areflexia, limb muscle weakness, and impaired gait. Electrophysiologic studies are consistent with a demyelinating polyneuropathy. Rare patients may have hyperelastic skin or develop age-related macular degeneration (summary by Auer-Grumbach et al., 2011 and Safka Brozkova et al., 2020) For a discussion of genetic heterogeneity of autosomal dominant Charcot-Marie-Tooth disease type 1, see CMT1B (118200).

Myopathy with myalgia, increased serum creatine kinase, and with or without episodic rhabdomyolysis (MMCKR) is an autosomal recessive disorder of skeletal muscle characterized by the onset of muscle cramping and stiffness on exertion in infancy or early childhood, although later (even adult) onset has also been reported. The features remit with rest, but some individuals develop mild proximal or distal muscle weakness. Rare affected individuals may demonstrate cardiac involvement, including left ventricular dysfunction or rhythm abnormalities. Laboratory studies show increased baseline serum creatine kinase levels with episodic spikes that may coincide with rhabdomyolysis. EMG shows myopathic changes, and muscle biopsy shows nonspecific myopathic or degenerative features (Lopes Abath Neto et al., 2021; Salzer-Sheelo et al., 2022).