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.

Disorders of intracellular cobalamin metabolism have a variable phenotype and age of onset that are influenced by the severity and location within the pathway of the defect. The prototype and best understood phenotype is cblC; it is also the most common of these disorders. The age of initial presentation of cblC spans a wide range: In utero with fetal presentation of nonimmune hydrops, cardiomyopathy, and intrauterine growth restriction. Newborns, who can have microcephaly, poor feeding, and encephalopathy. Infants, who can have poor feeding and slow growth, neurologic abnormality, and, rarely, hemolytic uremic syndrome (HUS). Toddlers, who can have poor growth, progressive microcephaly, cytopenias (including megaloblastic anemia), global developmental delay, encephalopathy, and neurologic signs such as hypotonia and seizures. Adolescents and adults, who can have neuropsychiatric symptoms, progressive cognitive decline, thromboembolic complications, and/or subacute combined degeneration of the spinal cord.

Extremely rare syndrome with features of spastic ataxia in association with bilateral congenital cataract, corneal dystrophy, and nonaxial myopia. It has been described in an inbred Bedouin family. Immunological abnormalities were frequent. Transmission is autosomal recessive and the disease is monogenic.

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.

A rare hereditary ataxia with characteristics of an apparently non-progressive or slowly progressive symmetrical ataxia of gait, pyramidal signs in the limbs, spasticity and hyperreflexia (especially in the lower limbs) together with dysarthria and impaired pupillary reaction to light, presenting as a fixed miosis. Nystagmus may also be present.

A rare genetic autosomal recessive spastic ataxia disease with characteristics of cerebellar ataxia, spasticity, cerebellar (and in some cases cerebral) atrophy, dystonia and leucoencephalopathy. Caused by homozygous or compound heterozygous complex genomic rearrangements involving the MARS2 gene on chromosome 2q33.

Autosomal recessive spastic ataxia-2 (SPAX2) is a neurologic disorder characterized by onset in the first 2 decades of cerebellar ataxia, dysarthria, and variable spasticity of the lower limbs. Cognition is not affected (summary by Dor et al., 2014). For a discussion of genetic heterogeneity of spastic ataxia, see SPAX1 (108600).

Hereditary spastic ataxia comprises a heterogeneous group of progressive neurodegenerative disorders characterized by lower-limb spasticity and generalized ataxia with dysarthria, impaired ocular movements, and gait disturbance. Spastic ataxia-1 (SPAX1) is an autosomal dominant form of the disorder with onset between the ages of 10 and 20 years. Other clinical features are supranuclear gaze palsy, hyperreflexia, hypertonicity, dystonia, pes cavus, mild ptosis, and decreased vibration sense in the lower limbs. Symptom severity is variable, but neither life span nor cognition is affected (summary by Meijer et al., 2002 and Bourassa et al., 2012). Genetic Heterogeneity of Spastic Ataxia See also SPAX2 (611302), caused by mutation in the KIF1C gene (603060) on chromosome 17p13; SPAX3 (611390), caused by rearrangements of the MARS2 gene (609728) on chromosome 2q33; SPAX4 (613672), caused by mutation in the MTPAP gene (613669) on chromosome 10p11; SPAX5 (614487), caused by mutation in the AFG3L2 gene (604581) on chromosome 18p11; SPAX6 (270550), caused by mutation in the SACS gene (604490) on chromosome 13q12; SPAX7 (108650); SPAX8 (617560), caused by mutation in the NKX6-2 gene (605955) on chromosome 8q21; SPAX9 (618438), caused by mutation in the CHP1 gene (606988) on chromosome 15q15; and SPAX10 (620666), caused by mutation in the COQ4 gene (612898) on chromosome 9q34.

A rare genetic autosomal recessive spastic ataxia disease with characteristics of the onset in early childhood of spastic paraparesis, cerebellar ataxia, dysarthria and optic atrophy. Caused by homozygous mutation in the MTPAP gene on chromosome 10p11.

Sclerosteosis is a severe sclerosing bone dysplasia characterized by progressive skeletal overgrowth. Syndactyly is a variable manifestation. The disorder is rare and the majority of affected individuals have been reported in the Afrikaner population of South Africa (summary by Brunkow et al., 2001). For a discussion of genetic heterogeneity of sclerosteosis, see SOST1 (269500).

Spastic ataxia-5 (SPAX5) is an autosomal recessive neurodegenerative disorder characterized by early-onset spasticity resulting in significantly impaired ambulation, cerebellar ataxia, oculomotor apraxia, dystonia, and myoclonic epilepsy (summary by Pierson et al., 2011). For a discussion of genetic heterogeneity of spastic ataxia, see SPAX1 (108600).

Childhood-onset spasticity with hyperglycinemia is an autosomal recessive disorder characterized by onset of slowly progressive spasticity that results in impaired gait in the first decade of life. Imaging of the central nervous system shows leukodystrophy and/or lesions in the upper spinal cord. More variable features include visual defects and mild learning disabilities. Serum glycine is increased, but CSF glycine is only mildly increased or normal; serum lactate is normal. The disorder represents a form of 'variant' nonketotic hyperglycinemia and is distinct from classic nonketotic hyperglycinemia (NKH, or GCE; 605899), which is characterized by significantly increased CSF glycine. Several forms of 'variant' NKH, including SPAHGC, appear to result from defects of mitochondrial lipoate biosynthesis (summary by Baker et al., 2014).

Spinocerebellar ataxia-42 (SCA42) is an autosomal dominant neurologic disorder characterized predominantly by gait instability and additional cerebellar signs such as dysarthria, nystagmus, and saccadic pursuits. The age at onset and severity of the disorder is highly variable. The disorder is slowly progressive (Coutelier et al., 2015). For a general discussion of autosomal dominant spinocerebellar ataxia, see SCA1 (164400).

Progressive myoclonic epilepsy-10 (EPM10) is an autosomal recessive neurodegenerative disorder characterized by onset of progressive myoclonus, ataxia, spasticity, dysarthria, and cognitive decline in the first decade of life. The severity is variable, but some patients may become mute and bedridden with psychosis (summary by Turnbull et al., 2012). For a general phenotypic description and a discussion of genetic heterogeneity of progressive myoclonic epilepsy, see EPM1A (254800).

Autosomal recessive spinocerebellar ataxia-27 (SCAR27) is an adult-onset neurologic disorder characterized by gait difficulties and other cerebellar signs, such as eye movement abnormalities, dysarthria, and difficulty writing. The disorder is progressive, and some patients may lose independent ambulation. Additional features include spasticity of the lower limbs and cognitive impairment. Brain imaging shows cerebellar atrophy (summary by Eidhof et al., 2018).

Intellectual developmental disorder with autistic features and language delay, with or without seizures (IDDALDS), is a neurodevelopmental disorder characterized by global developmental delay, variable intellectual disability, impaired speech development, and behavioral abnormalities, most commonly on the autism spectrum. About half of patients develop seizures; brain imaging is typically normal. Additional features are highly variable, but may include chronic constipation, walking difficulties, and dysmorphic facial features (summary by Guo et al., 2019).

Mitochondrial complex V deficiency nuclear type 4A (MC5DN4A) is an autosomal dominant metabolic disorder characterized by poor feeding and failure to thrive in early infancy. Laboratory studies show increased serum lactate, alanine, and ammonia, suggesting mitochondrial dysfunction. Some affected individuals show spontaneous resolution of these symptoms in early childhood and have subsequent normal growth and development, whereas others show developmental delay with impaired intellectual development and movement abnormalities, including dystonia, ataxia, or spasticity; these neurologic deficits are persistent (Lines et al., 2021, Zech et al., 2022). For a discussion of genetic heterogeneity of mitochondrial complex V deficiency, nuclear types, see MC5DN1 (604273).