Spinocerebellar Ataxia Type 2

The proportion with SCA patients with SCA2 ranges from 4% in the Portugal (0% in Russia) to 47% in Italy, and is 15% for US SCA patients. The mean age of onset of SCA2 is in the 4th decade, but is more rapidly progressive when onset occurs before age 20. A form of infantile-onset SCA2 has been recognized associated with extreme expansions of SCA2 alleles, in which children have infantile spasms, severe hypotonia, pigmentary retinopathy, dysphagia, failure to thrive, and usually die before 2 years of age. In adult-onset SCA2 confinement to wheelchair may occur 10-20 years after onset, and death may occur 10-30 years after onset. Death may be due to respiratory or autonomic failure.

SCA2 is characterized by slowly progressive ataxia sometimes with leg stiffness and/or painful leg muscle cramps at night. Mild dementia has been reported, which appears to be predominantly an impairment of executive functions. Examination may reveal very mild dysarthria, slowed, hypometric or totally absent saccades, supranuclear ophthalmoplegia, fasiculations in the face and tongue, dystonia and chorea and segmental or total loss of reflexes. SCA2 is caused by an expansion in CAG repeat in the SCA2 gene on 12q23-24.1 that leads to an elongated tract of glutamine residues within a novel protein, ataxin-2. The diagnosis of SCA2 is established by the demonstration of an expansion in one CAG repeat alleles in the SCA2 locus greater than or equal to 34 repeats in an ataxia patient.