Enzyme deficiencies occur when the body lacks specific enzymes needed for various biochemical reactions. Enzymes are proteins that help speed up chemical processes, such as breaking down food or detoxifying substances. When an enzyme is deficient, it can lead to the accumulation of harmful substances or the inability to properly digest nutrients, resulting in various health issues. Common examples of enzyme deficiencies include lactase deficiency, which causes lactose intolerance, and phenylalanine hydroxylase deficiency, leading to phenylketonuria (PKU). These conditions can often be managed through dietary changes or enzyme replacement therapies, depending on the specific deficiency and its effects on the body.