Why diarrhea/vomiting in galactosemia?

[Ven0m]

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KLN biochem didn't really explain the mechanism - just that it's due to improper metabolism.

I know that galactosemia = deficiency of either galactokinase or galactose-1P uridyl transferase and I understand its consequences in the liver and brain and how it builds up in the blood.

But why diarrhea/vomiting? Is it because intestinal mucosa cells aren't metabolizing galactose correctly, resulting in galactose accumulation within the intestinal lumen, causing osmotic draw -> diarrhea? But then why vomiting?

 

[Redbarron21]

So I have a proposed mechanism for the vomiting after reading the chapter on galactosemia in Nelson Textbook of Pediatrics 20th edition (2015).

Enzyme deficiency -> buildup of galactose 1 phosphate in brain -> osmotic fluid shift -> hydrocephalus (they specifically say pseudotumor cerebri and bulging fontanelle in the book) -> disturbance of chemoreceptor trigger zone at base of 4th ventricle -> vomiting.

 

[Redbarron21]

Also the E. Coli association with galactosemia is a favorite test question in pediatrics. Not sure about Step 1 though.

 

[Ven0m]

So I have a proposed mechanism for the vomiting after reading the chapter on galactosemia in Nelson Textbook of Pediatrics 20th edition (2015).

Enzyme deficiency -> buildup of galactose 1 phosphate in brain -> osmotic fluid shift -> hydrocephalus (they specifically say pseudotumor cerebri and bulging fontanelle in the book) -> disturbance of chemoreceptor trigger zone at base of 4th ventricle -> vomiting.

Why would a build up of galactose 1 phosphate in the brain cause an osmotic fluid shift if the galactose 1 phosphate is in the neurons, not the extracellular space? Or do the cells actually swell?