AT-007 in Adult Subjects With Classic Galactosemia (CG)

Primary: \- To evaluate the long-term safety of 12-month oral administration of AT-007 in adult subjects with Classic Galactosemia (CG) Secondary: * To evaluate the long-term inhibition of galactitol, a biomarker of aldose reductase (AR) activity, induced by 12-month oral administration of AT-007 to adult subjects with CG * To evaluate the pharmacokinetic (PK) parameters of 12-month oral administration of AT-007 in adult subjects with CG Exploratory: * To evaluate the effect of 12-month oral administration of AT-007 on the levels of galactose and its other metabolites in adult subjects with CG * To evaluate the burden of illness (BOI) of adult subjects with CG * To evaluate quality of life (QOL) measures of adult subjects with CG * To evaluate the effect of 12-month oral administration of AT-007 on the BOI and QOL of adult subjects with CG