TPP1 and autosomal recessive spinocerebellar ataxia 7: Diagnosis is usually confirmed by deficiency of TPP1 activity in leukocytes and/or identification of pathogenic mutations in TPP1. Interestingly, TPP1 mutations which partially affect enzyme activity, have also been described in patients with spinocerebellar ataxia autosomal recessive 7 (SCAR7; OMID 609270).