Blood Sample Collection and Analysis

Morning blood samples were collected from all study participants between 2013 and 2014 (n = 102), according to standard procedures. After preparation of serum and plasma, samples were stored at −80°C until assayed. All participants were fasting at the time for the blood sample collection. For the subgroup of HD-diagnosed patients who underwent the CBGT program, blood samples were also collected following their final CBT session (approximately 2 months after the baseline blood samples). Routine blood analysis was performed by the Clinical Chemistry Laboratory at the Karolinska University Hospital using standard procedures. The oxytocin level in blood plasma was determined by radioimmunoassay (Antibody: RRID:AB_2894933; https://antibodyregistry.org/search.php?q=AB_2894933) at the Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, Mölndal, Sweden. Further assay details were published previously (20). The assay’s lower limit of detection was 5 pM. The intra- and interassay coefficients of variation were 14% and 8%, 10% and 15%, and 12% and 10% at 12, 31, and 60 pM, respectively.