Safety and Pharmacokinetics of AT-007 in Healthy Subjects and in Adult Subjects With Classic Galactosemia

This study is a first-in-human, randomized, placebo-controlled, 4-Part, single ascending dose (SAD) and multiple ascending dose (MAD) study in healthy adult subjects and adult subjects with Classic Galactosemia.

The study is designed to assess the safety and PK of AT-007 in healthy subjects and subjects with Classic Galactosemia as well as the effect of AT-007 on biomarkers of galactose metabolism (galactose, galactitol, and other galactose metabolites) in subjects with Classic Galactosemia. This study consists of 4 parts: * Part A (SAD) in 32 healthy subjects. Once daily oral escalating dose (6 active, 2 placebo). * Part B and C (MAD for 7 days) in 36 healthy subjects. Once daily multiple daily dosing (8 active, 2 placebo per each dose cohort). * Part D (SAD followed by MAD for 27 days) in 18 subjects with Classic Galactosemia. Once daily followed by multiple daily oral dosing (6 active, 2 placebo for each dose cohort).