Enzymes are obviously a very important component in our body. One enzyme that you might look at is lactase which is the enzyme needed to produce lactose in our body. Lactose intolerance comes from the inability to process lactose because an insufficient amount of lactase. The amount of this enzyme also decreases as we age so older people are less able to handle lactose. There are side effects of lactose intolerance including gastrointestinal distress and bloating. Without the ability to break down lactose, the lactose can ferment into lactic acid, CH4 and CO2. The links below provide additional information about lactose, lactase, and lactose intolerance.
Galactosemia is another. Lack of the necessary enzyme leads to a build up of galactose which can cause jaundice, liver damage, mental retardation and liver failure.
is there any other disease or effect other than lactose intollerance?