Hello, I read about an autosomal recessive disease called "essential fructosuria", in which the enzyme fructokinase is absent and dietary fructose is phosphorylated by hexokinase to give fructose 6-phosphate. But why is this compound excreted instead of entering the glycolytic pathway? I mean, the third step of glycolysis is the conversion of fructose 6-phosphate (deriving from glucose) into fructose 1,6-bisphosphate, so why can't fructose 6-phosphate deriving from fructose be processed in the same way?

IIRC a higher rate of fructose remains unphosphorylated. I.e. in urine fructose is the characteristic metabolite being found in urine. Hexokinase has lower affinity for fructose and usually only converts fructose if glucose levels are low enough not to interfere.

Thanks