Metabolic disorders arise from the accumulation of proteins, lipids, glycogen, urea, calcium stones, and toxic substances, etc. Each of these molecules has specific metabolic pathways and metabolic substances (enzymes, proteins) in action. Agents in performing their tasks cause the accumulation of molecules in the blood and other places. Some examples of metabolic disorders are Gaucher's disease, hereditary tyrosinemia, hereditary orotaciduria, and Fabry's disease.
Metabolic diseases are a broad category and there are several metabolic disorders caused by clinically simple defects and difficult-to-treat genetic disorders. Obesity, for example, is the most common type of metabolic disorder and is closely related to metabolic syndrome (a group of clinical conditions such as high blood sugar and triglycerides). According to the World Health Organization (WHO), more than 650 million people over the age of 18 were obese in 2016.