Galactitol

Galactitol, also known as dulcitol, is a sugar alcohol that is a metabolic breakdown product of galactose[1][3]. It is formed from galactose by reduction in some living tissues and accumulates in urine and various tissues, such as the lens of the eye, in individuals deficient in certain enzymes like galactokinase[1]. Galactitol is a white, faintly sweet alcohol with the chemical formula C6H14O6[1][3].

Galactose is derived from lactose in food, such as dairy products, and is broken down by the enzyme lactase into glucose and galactose[3]. Galactitol is produced from galactose in a reaction catalyzed by aldose reductase[3]. It has a slightly sweet taste and can act as a metabotoxin, a neurotoxin, and a hepatotoxin when present in sufficiently high levels[3]. Chronically high levels of galactitol are associated with at least two inborn errors of metabolism, including galactosemia and galactosemia type II[3].

Galactosemia is a rare genetic metabolic disorder that affects an individual's ability to metabolize the sugar galactose properly[3]. Excess lactose consumption in individuals with galactose intolerance or galactosemia activates aldose reductase to produce galactitol, thus depleting NADPH and leading to lowered glutathione reductase activity[3]. As a result, hydrogen peroxide or other free radicals accumulate, causing serious oxidative damage to various cells and tissues[3]. In individuals with galactosemia, the enzymes needed for the further metabolism of galactose are severely diminished or missing entirely, leading to toxic levels of galactose 1-phosphate, galactitol, and galactonate[3].

High levels of galactitol in infants are specifically associated with hepatomegaly (an enlarged liver), cirrhosis, renal failure, cataracts, vomiting, seizure, hypoglycemia, lethargy, brain damage, and ovarian failure[3]. Galactitol is also known to accumulate in the eyes, causing cataracts, in individuals with galactokinase deficiency, a fairly common inherited recessive disorder[2].

Testing for galactitol involves newborn blood screening, testing for the enzyme in red blood cells, and gene analysis[2]. No special preparation is needed for this test, but potential complications include pain, bleeding, infection, and damage to tissues in the vicinity where blood is collected[2].

Citations:

[1] https://www.merriam-webster.com/medical/galactitol

[2] https://www.nicklauschildrens.org/treatments/galactitol

[3] https://hmdb.ca/metabolites/HMDB0000107

[4] https://pubchem.ncbi.nlm.nih.gov/compound/Galactitol

[5] https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/galactitol