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
This study is a 12-month open-label extension (OLE) study of AT-007 in adult subjects with CG who previously participated in Study AT-007-1001 Part D and/or Part D Extension.~The study is designed to assess the long-term safety of AT-007 in subjects with CG as well as the pharmacodynamics (PD) (inhibition of galactitol) and PK of AT-007. The effect of 12-month treatment with AT-007 on the levels of galactose and other galactose metabolites in subjects with CG will also be evaluated.