The phenotypic spectrum of GARS1-associated axonal neuropathy ranges from GARS1 infantile-onset SMA (GARS1-iSMA) to GARS1 adolescent- or early adult-onset hereditary motor/sensory neuropathy (GARS1-HMSN). GARS1-iSMA. Age of onset ranges from the neonatal period to the toddler years. Initial manifestations are typically respiratory distress, poor feeding, and muscle weakness (distal greater than proximal). Weakness is slowly progressive, ultimately requiring mechanical ventilation and feeding via gastrostomy tube. GARS1-HMSN. Age of onset is most commonly during the second decade (range eight to 36 years). Initial manifestations are typically muscle weakness in the hands sometimes with sensory deficits. Lower limb involvement (seen in ~50% of individuals) ranges from weakness and atrophy of the extensor digitorum brevis and weakness of toe dorsiflexors to classic peroneal muscular atrophy with foot drop and a high steppage gait.

A form of axonal Charcot-Marie-Tooth disease, a peripheral sensorimotor neuropathy with symmetric weakness primarily occurring in the lower limbs and reaching the arms only after 5 to 10 years, occasional and predominantly distal sensory loss and reduced tendon reflexes. Presents with gait anomaly between the first and sixth decade and early onset is generally associated to a more severe phenotype that may include foot drop.

Spastic paraplegia-5A (SPG5A) is an autosomal recessive neurologic disorder with a wide phenotypic spectrum. Some patients have pure spastic paraplegia affecting only gait, whereas others may have a complicated phenotype with additional manifestations, including optic atrophy or cerebellar ataxia (summary by Arnoldi et al., 2012). The hereditary spastic paraplegias (SPG) are a group of clinically and genetically diverse disorders characterized by progressive, usually severe, lower extremity spasticity; see reviews of Fink et al. (1996) and Fink (1997). Inheritance is most often autosomal dominant (see 182600), but X-linked (see 303350) and autosomal recessive forms also occur. Genetic Heterogeneity of Autosomal Recessive Spastic Paraplegia Autosomal recessive forms of SPG include SPG7 (607259), caused by mutation in the paraplegin gene (602783) on chromosome 16q24; SPG9B (616586), caused by mutation in the ALDH18A1 gene (138250) on 10q24; SPG11 (604360), caused by mutation in the spatacsin gene (610844) on 15q21; SPG15 (270700), caused by mutation in the ZFYVE26 gene (612012) on 14q24; SPG18 (611225), caused by mutation in the ERLIN2 gene (611605) on 8p11; SPG20 (275900), caused by mutation in the spartin gene (607111) on 13q12; SPG21 (248900), caused by mutation in the maspardin gene (608181) on 15q21; SPG26 (609195), caused by mutation in the B4GALNT1 gene (601873) on 12q13; SPG28 (609340), caused by mutation in the DDHD1 gene (614603) on 14q22; SPG30 (610357), caused by mutation in the KIF1A gene (601255) on 2q37; SPG35 (612319), caused by mutation in the FA2H gene (611026) on 16q23; SPG39 (612020), caused by mutation in the PNPLA6 gene (603197) on 19p13; SPG43 (615043), caused by mutation in the C19ORF12 gene (614297) on 19q12; SPG44 (613206), caused by mutation in the GJC2 gene (608803) on 1q42; SPG45 (613162), caused by mutation in the NT5C2 gene (600417) on 10q24; SPG46 (614409), caused by mutation in the GBA2 gene (609471) on 9p13; SPG48 (613647), caused by mutation in the KIAA0415 gene (613653) on 7p22; SPG50 (612936), caused by mutation in the AP4M1 gene (602296) on 7q22; SPG51 (613744), caused by mutation in the AP4E1 gene (607244) on 15q21; SPG52 (614067), caused by mutation in the AP4S1 gene (607243) on 14q12; SPG53 (614898), caused by mutation in the VPS37A gene (609927) on 8p22; SPG54 (615033), caused by mutation in the DDHD2 gene (615003) on 8p11; SPG55 (615035), caused by mutation in the MTRFR gene on 12q24; SPG56 (615030), caused by mutation in the CYP2U1 gene (610670) on 4q25; SPG57 (615658), caused by mutation in the TFG gene (602498) on 3q12; SPG61 (615685), caused by mutation in the ARL6IP1 gene (607669) on 1p12; SPG62 (615681), caused by mutation in the ERLIN1 gene on 10q24; SPG63 (615686), caused by mutation in the AMPD2 gene (102771) on 1p13; SPG64 (615683), caused by mutation in the ENTPD1 gene (601752) on 10q24; SPG72 (615625), caused by mutation in the REEP2 gene (609347) on 5q31; SPG74 (616451), caused by mutation in the IBA57 gene (615316) on 1q42; SPG75 (616680), caused by mutation in the MAG gene (159460) on 19q13; SPG76 (616907), caused by mutation in the CAPN1 gene (114220) on 11q13; SPG77 (617046), caused by mutation in the FARS2 gene (611592) on 6p25; SPG78 (617225), caused by mutation in the ATP13A2 gene (610513) on 1p36; SPG79 (615491), caused by mutation in the UCHL1 gene (191342) on 4p13; SPG81 (618768), caused by mutation in the SELENOI gene (607915) on 2p23; SPG82 (618770), caused by mutation in the PCYT2 gene (602679) on 17q25; SPG83 (619027), caused by mutation in the HPDL gene (618994) on 1p34; SPG84 (619621), caused by mutation in the PI4KA gene (600286) on 22q11; SPG85 (619686), caused by mutation in the RNF170 gene (614649) on 8p11; SPG86 (619735), caused by mutation in the ABHD16A gene (142620) on 6p21; SPG87 (619966), caused by mutation in the TMEM63C gene (619953) on 14q24; SPG89 (620379), caused by mutation in the AMFR gene (603243) on 16q13; and SPG90B (620417), caused by mutation in the SPTSSA gene (613540) on 14q13. Additional autosomal recessive forms of SPG have been mapped to chromosomes 3q (SPG14; 605229), 13q14 (SPG24; 607584), 6q (SPG25; 608220), and 10q22 (SPG27; 609041). A disorder that was formerly designated SPG49 has been reclassified as hereditary sensory and autonomic neuropathy-9 with developmental delay (HSAN9; 615031).

Arboleda-Tham syndrome (ARTHS) is an autosomal dominant disorder with the core features of impaired intellectual development, speech delay, microcephaly, cardiac anomalies, and gastrointestinal complications (summary by Kennedy et al., 2019).

MFN2 hereditary motor and sensory neuropathy (MFN2-HMSN) is a classic axonal peripheral sensorimotor neuropathy, inherited in either an autosomal dominant (AD) manner (~90%) or an autosomal recessive (AR) manner (~10%). MFN2-HMSN is characterized by more severe involvement of the lower extremities than the upper extremities, distal upper-extremity involvement as the neuropathy progresses, more prominent motor deficits than sensory deficits, and normal (>42 m/s) or only slightly decreased nerve conduction velocities (NCVs). Postural tremor is common. Median onset is age 12 years in the AD form and age eight years in the AR form. The prevalence of optic atrophy is approximately 7% in the AD form and approximately 20% in the AR form.

Axonal Charcot-Marie-Tooth disease type 2CC is an autosomal dominant peripheral neuropathy that predominantly affects the lower limbs, resulting in muscle weakness and atrophy and gait impairment. Other features include distal sensory impairment and less severe involvement of the upper limbs. The age at onset and severity are variable (summary by Rebelo et al., 2016). For a phenotypic description and a discussion of genetic heterogeneity of axonal CMT type 2, see CMT2A (118210).

The phenotypic spectrum of GARS1-associated axonal neuropathy ranges from GARS1 infantile-onset SMA (GARS1-iSMA) to GARS1 adolescent- or early adult-onset hereditary motor/sensory neuropathy (GARS1-HMSN). GARS1-iSMA. Age of onset ranges from the neonatal period to the toddler years. Initial manifestations are typically respiratory distress, poor feeding, and muscle weakness (distal greater than proximal). Weakness is slowly progressive, ultimately requiring mechanical ventilation and feeding via gastrostomy tube. GARS1-HMSN. Age of onset is most commonly during the second decade (range eight to 36 years). Initial manifestations are typically muscle weakness in the hands sometimes with sensory deficits. Lower limb involvement (seen in ~50% of individuals) ranges from weakness and atrophy of the extensor digitorum brevis and weakness of toe dorsiflexors to classic peroneal muscular atrophy with foot drop and a high steppage gait.