Essential fructosuria

Essential fructosuria (also known as hepatic fructokinase deficiency or ketohexokinase deficiency) is a rare, benign inborn error of carbohydrate metabolism caused by a deficiency of the enzyme fructokinase (ketohexokinase) in the liver, intestine, and kidney. This enzyme is responsible for the first step in fructose metabolism — the phosphorylation of fructose to fructose-1-phosphate. When fructokinase is deficient, ingested fructose cannot be properly metabolized and accumulates in the blood, leading to fructosemia and subsequent excretion of fructose in the urine (fructosuria). The condition is entirely asymptomatic and does not cause any organ damage or clinical complications. Essential fructosuria is typically discovered incidentally when routine urine testing detects a reducing substance that is not glucose. This finding can sometimes lead to misdiagnosis of diabetes mellitus if the reducing substance is not properly identified. The condition affects no body systems in a clinically meaningful way, and individuals with essential fructosuria have a normal life expectancy and require no dietary restrictions or medical treatment. Approximately 10–20% of ingested fructose is excreted in the urine, while the remainder is slowly metabolized through alternative metabolic pathways such as conversion by hexokinase. It is important to distinguish essential fructosuria from hereditary fructose intolerance (aldolase B deficiency), which is a serious and potentially life-threatening condition. No treatment is necessary for essential fructosuria, and the prognosis is excellent. Genetic counseling may be offered to affected families, though the condition carries no health burden.

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