Essential fructosuria

• Involves a defect in fructokinase. Autosomal recessive.
• A benign, asymptomatic condition (fructokinase deficiency is kinder), since fructose is not trapped in cells. Hexokinase becomes 1° pathway for converting fructose to fructose-6-phosphate.
• Symptoms: fructose appears in blood and urine.
• Disorders of fructose metabolism cause milder symptoms than analogous disorders of galactose metabolism.

Hereditary fructose intolerance

• Hereditary deficiency of aldolase B. Autosomal recessive.
• Fructose-1-phosphate accumulates, causing a ↓ in available phosphate, which results in inhibition of glycogenolysis and gluconeogenesis. Symptoms present following consumption of fruit, juice, or honey. Urine dipstick will be ⊝ (tests for glucose only); reducing sugar can be detected in the urine (nonspecific test for inborn errors of carbohydrate metabolism).
• Symptoms: hypoglycemia, jaundice, cirrhosis, vomiting.
• Treatment: ↓ intake of both fructose and sucrose (glucose + fructose).