HTT and Huntington disease: Thiodiglycol has also been detected in urine samples from individuals not exposed to HD and is therefore not useful as a definitive marker for HD exposure.11 In contrast, HD metabolites from the glutathione (GSH)/beta-lyase pathway are specific for HD exposure.10, 11 These observations suggest that GSH depletion occurs in humans, and that GSH-HD/beta-lyase pathway metabolites provide a specific and useful biomarker for diagnosing HD exposure.