MCC and depressive disorder: The biological mechanisms by which dietary biotin reduces the risk of anxiety and depression may involve the following aspects: Biotin serves as an essential coenzyme of five carboxylases for five carboxylases: acetyl CoA carboxylase 1 (ACC1) and 2 (ACC2), methylcrotonyl CoA carboxylase (MCC), propionyl CoA carboxylase (PCC), and pyruvate carboxylase (PC), playing pivotal roles in regulations of ATP production, Oxidative stress, immunological and inflammatory functions (11, 12, 14, 15, 37, 38).