HTT and Kennedy disease: To date, glutamine expansions have been described in the following human proteins: huntingtin (Htt); Sca1, Sca2, Sca3, Sca6, Sca7, and Sca17 (different types of spinocerebellar ataxia); androgen receptor protein (spinobulbar muscular atrophy); and atrophin-1 (dentatorubro-pallidoluysian atrophy).