Complex sentence: Creatine is needed for many tissues in the body to store and use energy properly, and the effects of guanidinoacetate methyltransferase deficiency are most severe in organs and tissues that require large amounts of energy, such as the brain and muscles.
Split into simpler sentences: Creatine is needed for many tissues in the body to be able to store and use energy properly. The effects of guanidinoacetate methyltransferase deficiency are most severe in organs and tissues that require large amounts of energy, such as the brain and muscles.