SAMD9L ataxia-pancytopenia (ATXPC) syndrome is characterized by cerebellar ataxia, variable hematologic cytopenias, and predisposition to marrow failure, myelodysplasia, and myeloid leukemia, sometimes associated with monosomy 7. The onset of hematologic abnormalities has been reported as early as age three months. The cytopenias in all cell lineages range from mild to very severe. Onset of neurologic impairment is variable. Nystagmus, dysmetria, increased deep tendon reflexes, and clonus are common. Gait impairment and other neurologic abnormalities are slowly progressive.

Posterior column ataxia with retinitis pigmentosa (AXPC1) is an autosomal recessive neurologic disorder characterized by childhood-onset retinitis pigmentosa and later onset of gait ataxia due to sensory loss (summary by Ishiura et al., 2011).

A form of hereditary spastic paraplegia which usually presents in late adolescence or early adulthood as a pure phenotype of lower limb spasticity with hyperreflexia and extensor plantar responses, as well as mild bladder disturbances and pes cavus. Rarely, it can present as a complex phenotype with additional manifestations including epilepsy, variable peripheral neuropathy and/or memory impairment. Caused by mutations in the NIPA1 gene (15q11.2) encoding the magnesium transporter NIPA1.

Spastic paraplegia 7 (SPG7) is characterized by insidiously progressive bilateral leg weakness and spasticity. Most affected individuals have decreased vibration sense and cerebellar signs. Onset is mostly in adulthood, although symptoms may start as early as age 11 years and as late as age 72 years. Additional features including ataxia (gait and limbs), spastic dysarthria, dysphagia, pale optic disks, ataxia, nystagmus, strabismus, ptosis, hearing loss, motor and sensory neuropathy, amyotrophy, scoliosis, pes cavus, and urinary sphincter disturbances may be observed.

A pure form of hereditary spastic paraplegia with characteristics of a slowly progressive and relatively benign spastic paraplegia presenting in adulthood with spastic gait, lower limb hyperreflexia, extensor plantar responses, bladder dysfunction (urinary urgency and/or incontinence), and mild sensory and motor peripheral neuropathy.

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).

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is clinically characterized by a progressive cerebellar ataxia, peripheral neuropathy, and spasticity. Disease onset of classic ARSACS is often in early childhood, leading to delayed walking because of gait unsteadiness in very young toddlers, while an increasing number of individuals with disease onset in teenage or early-adult years are now being described. Typically the ataxia is followed by lower-limb spasticity and later by peripheral neuropathy – although pronounced peripheral neuropathy has been observed as a first sign of ARSACS. Oculomotor disturbances, dysarthria, and upper-limb ataxia develop with slower progression than the other findings. Brain imaging demonstrates atrophy of the superior vermis and the cerebellar hemisphere with additional findings on MRI, such as linear hypointensities in the pons and hyperintense rims around the thalami. Many affected individuals (though not all) have yellow streaks of hypermyelinated fibers radiating from the edges of the optic disc noted on ophthalmologic exam, and thickened retinal fibers can be demonstrated by optical coherence tomography. Mild intellectual disability, hearing loss, and urinary urgency and incontinence have been reported in some individuals.

Spinocerebellar ataxia-23 (SCA23) is an adult-onset autosomal dominant neurodegenerative disorder characterized by slowly progressive gait and limb ataxia, with variable additional features, including peripheral neuropathy and dysarthria (Bakalkin et al., 2010). For a general discussion of autosomal dominant spinocerebellar ataxia, see SCA1 (164400).

A rare hereditary spastic paraplegia with characteristics of progressive spastic paraplegia with pyramidal signs in the lower limbs, decreased vibration sense, and increased reflexes in the upper limbs. Caused by heterozygous mutation in the HSPD1 on chromosome 2q33.

Spastic paraplegia-12 is an autosomal dominant neurodegenerative disorder characterized by lower limb spasticity and hyperreflexia, resulting in walking difficulties. Some patients may have urinary symptoms and distal sensory impairment. The age at onset is variable and can range from childhood to adulthood (summary by Montenegro et al., 2012). For a general description and a discussion of genetic heterogeneity of autosomal dominant spastic paraplegia, see SPG3A (182600).

Spastic paraplegia 11 (SPG11) is characterized by progressive spasticity and weakness of the lower limbs frequently associated with the following: mild intellectual disability with learning difficulties in childhood and/or progressive cognitive decline; peripheral neuropathy; pseudobulbar involvement; and increased reflexes in the upper limbs. Less frequent findings include: cerebellar signs (ataxia, nystagmus, saccadic pursuit); retinal degeneration; pes cavus; scoliosis; and parkinsonism with characteristic brain MRI features that include thinning of the corpus callosum. Onset occurs mainly during infancy or adolescence (range: age 1-31 years) and in rare cases as late as age 60 years. Most affected individuals become wheelchair bound one or two decades after disease onset.

Spastic paraplegia-10 (SPG10) is an autosomal dominant neurologic disorder with variable manifestations. Some patients have onset of a 'pure' spastic paraplegia, with lower limb spasticity, hyperreflexia, extensor plantar responses, and variable involvement of the upper limbs beginning in childhood or young adulthood. Some patients show distal sensory impairment, which can be part of the 'pure' phenotype. However, some patients also show an axonal sensorimotor peripheral neuropathy with distal sensory impairment and distal muscle atrophy reminiscent of Charcot-Marie-Tooth disease type 2 (see, e.g., CMT2A, 118210). Rarely, patients with KIF5A mutations may have additional neurologic features, including parkinsonism or cognitive decline, consistent with a 'complicated' phenotype. Spastic paraplegia and peripheral neuropathy in isolation may represent extreme ends of the phenotypic spectrum of KIF5A mutations (summary by Goizet et al., 2009 and Crimella et al., 2012). For a general phenotypic description and a discussion of genetic heterogeneity of autosomal dominant spastic paraplegia, see SPG3A (182600).

Hereditary spastic paraplegia 8 (SPG8) is a slowly progressive pure spastic paraplegia of the lower limbs (i.e., pyramidal signs including hyperreflexia, spasticity, and occasionally clonus without other neurologic findings). Some affected individuals have urinary urgency that usually becomes apparent at the same time as the spasticity. Onset is between ages ten and 59 years. Affected individuals often become wheelchair dependent. While intra- and interfamilial phenotypic variability is high, SPG8 is typically more severe than other types of hereditary spastic paraplegia.

Spastic paraplegia 4 (SPG4; also known as SPAST-HSP) is characterized by insidiously progressive bilateral lower-limb gait spasticity. More than 50% of affected individuals have some weakness in the legs and impaired vibration sense at the ankles. Sphincter disturbances are very common. Onset is insidious, mostly in young adulthood, although symptoms may start as early as age one year and as late as age 76 years. Intrafamilial variation is considerable.

A complex hereditary spastic paraplegia with characteristics of mild to severe lower limbs spasticity, hyperreflexia, extensor plantar responses, pes cavus and significant wasting and weakness of the small hand muscles. Impaired vibration sensation, temporal lobe epilepsy and cognitive dysfunction were also reported.

Autosomal recessive spastic paraplegia-46 (SPG46) is a neurodegenerative disorder characterized by onset in childhood of slowly progressive spastic paraplegia and cerebellar signs. Some patients have cognitive impairment, cataracts, and cerebral, cerebellar, and corpus callosum atrophy on brain imaging (summary by Boukhris et al., 2010 and Martin et al., 2013). For a discussion of genetic heterogeneity of autosomal recessive spastic paraplegia, see SPG5A (270800).

The spectrum of BSCL2-related neurologic disorders includes Silver syndrome and variants of Charcot-Marie-Tooth neuropathy type 2, distal hereditary motor neuropathy (dHMN) type V, and spastic paraplegia 17. Features of these disorders include onset of symptoms ranging from the first to the seventh decade, slow disease progression, upper motor neuron involvement (gait disturbance with pyramidal signs ranging from mild to severe spasticity with hyperreflexia in the lower limbs and variable extensor plantar responses), lower motor neuron involvement (amyotrophy of the peroneal muscles and small muscles of the hand), and pes cavus and other foot deformities. Disease severity is variable among and within families.

Spastic paraplegia 3A (SPG3A; also known as ATL1-HSP) is characterized by progressive bilateral and mostly symmetric spasticity and weakness of the legs. Compared to other forms of autosomal dominant hereditary spastic paraplegia (HSP), in which diminished vibration sense (caused by degeneration of the corticospinal tracts and dorsal columns) and urinary bladder hyperactivity are present in all affected individuals, these findings occur in a minority of individuals with SPG3A. The average age of onset is four years. More than 80% of reported individuals manifest spastic gait before the end of the first decade of life. Most persons with early-onset ATL1-HSP have a "pure" ("uncomplicated") HSP; however, complicated HSP with axonal motor neuropathy and/or distal amyotrophy with lower motor neuron involvement (Silver syndrome phenotype) has been observed. The rate of progression in ATL1-HSP is slow, and wheelchair dependency or need for a walking aid (cane, walker, or wheelchair) is relatively rare.

A complex form of hereditary spastic paraplegia, with onset in childhood or adulthood of progressive spastic paraplegia (with spastic gait, spasticity, lower limb weakness, pes cavus and urinary urgency) associated with the additional manifestation of peripheral sensorimotor neuropathy. The SPG36 phenotype has been mapped to a locus on chromosome 12q23-q24.

A pure form of hereditary spastic paraplegia with a childhood to adulthood-onset of slowly progressive spastic gait, extensor plantar responses, brisk tendon reflexes in arms and legs, decreased vibration sense at ankles and urinary dysfunction. Ankle clonus is also reported in some patients.

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).

Hereditary spastic paraplegia-72A (SPG72A) is a pure form of spastic paraplegia with onset of difficulty walking and stiff legs associated with hyperreflexia and extensor plantar responses in early childhood. The disorder is slowly progressive, and some patients develop the need for assistance in walking. Some patients may have pes cavus or sphincter disturbances. Cognition, speech, and ocular function are normal (summary by Esteves et al., 2014). For a discussion of genetic heterogeneity of autosomal dominant spastic paraplegia, see SPG3A (182600).