D-Arabitol is a polyol. Polyols are sugar alcohols linked to the pentose phosphate pathway (PPP). They are classified on the basis of the number of carbon atoms. Polyols occur in body fluids. A patient with leukoencephalopathy and peripheral neuropathy has been identified as suffering from ribose-5-phosphate isomerase (RPI) deficiency, a defect in the PPP. In this disorder, highly elevated concentrations of the C5 polyols such as D-arabitol are found in body fluids. In addition, transaldolase deficiency, another defect in the PPP, has been diagnosed in a patient with mainly liver problems among others. This patient had increased concentrations of polyols, mainly D-arabitol. So far, the pathophysiological role of polyols is relatively unknown. It is thought that D-arabitol is a metabolic end-product in humans. The strong brain-CSF-plasma gradient of polyols in the patient with RPI deficiency suggested a primary metabolic disorder. The mechanisms of brain and neuronal damage in RPI deficiency remain to be elucidated. A neurotoxic effect due to the accumulation of the polyols may play a role. D-Arabitol is a product of the enzyme D-arabinitol 4-dehydrogenase (EC 1.1.1.11) in the pentose and glucuronate interconversion pathway :1181-3). D-Arabitol has also been found to be a fungal metabolite, urinary D-Arabinitol is a marker for invasive candidiasis or infection by Candida fungal species. It can also a metabolite in Debaryomyces, Pichia and Zygosaccharomyces.