These include chronic ataxia disorders (SCA-14, SCA-27, SCA-35, SCA-42, AOA2, CAPOS,), genetic epilepsy syndromes (KCNA2, SCN2A, PRRT2, TBC1D24), GLUT-1, mitochondrial disorders (PDHA1, PDHX, TPK1, DARS2, ACO2), metabolic disorders [aminoacidopathies (Maple syrup urine disease: BCKDHA, BCKDHB, DBT; Hartnup disease: SLC6A19), urea cycle defects (type I citrullinemia: ASS1), thiamine metabolism defects (thiamine pyrophosphate deficiency: TPK1) biotin metabolism (biotinidase deficiency: BTD),] and others (KCND3, NALCN, FHM2/ATP1A2, PACS1, CEP290). The gene discussed is TPK1; the disease is Hartnup disease.