Succinylacetone, also known as 4,6-dioxoheptanoic acid or SUAC, belongs to the class of compounds known as medium-chain keto acids and derivatives. These are keto acids with 6 to 12 carbon atoms. Succinylacetone is soluble (in water) and a weakly acidic compound (based on its pKa). Succinylacetone has been detected in amniotic fluid, blood, and urine. Within the cell, succinylacetone is primarily located in the cytoplasm (predicted from logP). Succinylacetone can be created by the oxidation of glycine, and is a precursor of methylglyoxal (Wikipedia). Succinylacetone is an abnormal tyrosine metabolite that arises from defects in the enzyme called fumarylacetoacetase (PMID: 16448836). Fumarylacetoacetase normally catalyzes the hydrolysis of 4-fumarylacetoacetate into fumarate and acetoacetate. If present in sufficiently high levels, succinylacetone can act as an acidogen, an oncometabolite, and a metabotoxin. An acidogen is an acidic compound that induces acidosis, which has multiple adverse effects on many organ systems. An oncometabolite is an endogenous metabolite that causes cancer. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of succinylacetone are associated with tyrosinemia type I. Type I tyrosinemia is an inherited metabolism disorder due to a shortage of the enzyme fumarylacetoacetate hydrolase that is needed to break down tyrosine. Patients usually develop features such as hepatic necrosis, renal tubular injury, and hypertrophic cardiomyopathy. Neurologic and dermatologic manifestations are also possible. The urine has an odour of cabbage or rancid butter. Succinylacetone is a keto-acid, which is a subclass of organic acids. Abnormally high levels of organic acids in the blood (organic acidemia), urine (organic aciduria), the brain, and other tissues lead to general metabolic acidosis. Acidosis typically occurs when arterial pH falls below 7.35. In infants with acidosis, the initial symptoms include poor feeding, vomiting, loss of appetite, weak muscle tone (hypotonia), and lack of energy (lethargy). These can progress to heart, liver, and kidney abnormalities, seizures, coma, and possibly death. These are also the characteristic symptoms of untreated tyrosinemia. Many affected children with organic acidemias experience intellectual disability or delayed development. Succinylacetone appears to function as an oncometabolite (similar in function to succinate, another oncometabolite) as patients with high levels of this compound often develop hepatocellular carcinoma (PMID: 20003495).