Table 1.

Summary of HA features.

Disease	OMIM ID	Location	Gene/Locus	Inheritance	Clinical Features and Phenotype
Spinocerebellar ataxia type 1 (SCA1)	#164400	6p22.3	ATXN1	Autosomal-dominant	Cerebellar ataxia (characterized by Purkinje neuron and dentate nucleus neuron loss) with variable involvement of the brainstem and spinal cord. Cognitive decline has been also observed
Spinocerebellar ataxia type 2 (SCA2)	#183090	12q24.12	ATXN2	Autosomal-dominant	Cerebellar ataxia (characterized by olivopontocerebellar degeneration) associated with oculomotor defects, parkinsonism, cognitive impairment, and peripheral neuropathy
Spinocerebellar ataxia type 3 or Machado–Joseph Disease (SCA3 or MJD)	#109150	14q32.12	ATXN3	Autosomal-dominant	Cerebellar ataxia (characterized by the degeneration of deep cerebellar nuclei neurons) with pyramidal and extrapyramidal signs. In some cases, peripheral neuropathy and parkinsonism have been also detected
Spinocerebellar ataxia type 6 (SCA6)	#183086	19q13.13	CACNA1A	Autosomal-dominant	Pure cerebellar ataxia characterized by Purkinje neuron degeneration. In a few cases, basal ganglia dysfunction has been reported
Spinocerebellar ataxia type 7 (SCA7)	#164500	3p14.1	ATXN7	Autosomal-dominant	Cerebellar ataxia, dysarthria, spasticity, and peculiarly retinal degeneration
Spinocerebellar ataxia type 17 (SCA17)	#607136	6q27	TBP	Autosomal-dominant	Cerebellar ataxia (characterized by Purkinje neuron loss) associated with the degeneration of different other brain region (cerebral cortex, basal ganglia, and cingulate and hippocampal gyri) resulting in pyramidal signs, psychiatric dysfunction, and dementia
Spinocerebellar ataxia type 27B or GAA-FGF17 ataxia (SCA27B)	#620174	13q33.1	FGF14	Autosomal-dominant	Cerebellar ataxia (characterized by Purkinje neuron loss, in particular in the vermis) in combination with nystagmus, dysarthria, vertigo, spasticity, or peripheral axonal neuropathy
Friedreich’s ataxia (FA)	#229300	9q21.11	FXN	Autosomal-recessive	Progressive gait and limb ataxia, dysarthria, polyneuropathy, and sensory loss due to the dysfunction of the spinocerebellar and pyramidal tracts and the dorsal column. Cerebellum is barely affected, with only dentate nucleus neuron loss
Cerebellar ataxia with neuropathy and vestibular areflexia syndrome (CANVAS)	#614575	4p14	RFC1	Autosomal-recessive	Cerebellar ataxia (characterized by imbalance) associated with bilateral vestibulopathy, sensory neuropathy, and, occasionally, autonomic dysfunction and chronic cough
Autosomal-recessive spastic ataxia of Charlevoix-Saguenay (ARSACS)	#270550	13q12.12	SACS	Autosomal-recessive	Cerebellar ataxia (characterized by Purkinje neuron degeneration) later associated with pyramidal tract signs, spasticity, and peripheral neuropathy
Ataxia–telangiectasia (AT)	#208900	11q22.3	ATM	Autosomal-recessive	Cerebellar ataxia and progressive degeneration of different neuronal populations associated with oculomotor apraxia, extrapyramidal movements, and immunodeficiency
Autosomal-recessive ataxia type 2 (ARCA2)	#612016	1q42.13	ADCK3	Autosomal-recessive	Cerebellar ataxia combined with exercise intolerance, dystonia, epilepsy, and intellectual disability
Episodic ataxia 1 (EA1)	#160120	12p13.32	KCNA1	Autosomal-dominant	Periodic short ataxia and myokymia attacks
Episodic ataxia 2 (EA2)	#108500	19qp13.13	CACNA1A	Autosomal-dominant	Long intermittent ataxic events
Fragile X-associated tremor/ataxia syndrome (FXTAS)	#300623	Xq27.3	FMR1	X-linked dominant	Cerebellar ataxia accompanied by tremor, peripheral neuropathy, cognitive decline, and psychiatric signs
Joubert syndrome	#213300	9q34.3	INPP5E	Autosomal-recessive	Ataxia (caused by cerebellum and brainstem malformations), ocular motor apraxia, and non-neurological signs such as breathing impairment, kidney, and liver alterations