The ?/? hydrolase superfamily comprise diverse members that are involved in important biochemical processes and related to various diseases. They have unrelated sequences, various substrates, and different kinds of catalytic activities, yet they share the same canonical ?/? hydrolase fold, which consists of an eightstranded parallel ?/? structure. They are also characterized by a catalytic triad composed of a histidine, an acid and a nucleophile. Members of this superfamily are often drug targets for treating diseases, such as diabetes, Alzheimer’s disease, obesity and blood clotting disorders. The abhydrolase domain-containing protein 9 (ABHD9), also designated epoxide hydrolase 3 (EPHX3), is a 360 amino acid protein and a member of the ?/? hydrolase superfamily. The gene encoding ABHD9 maps to chromosome 19, which consists of over 63 million bases, houses approximately 1,400 genes and is recognized for having the greatest gene density of the human chromosomes.