HTT and depressive symptom measurement: The CAG repeat lengths in ATXN7 and eight other polyglutamine disease-associated genes [ATXN1, ATXN2, ATXN3, calcium voltage-gated channel subunit alpha1 A (CACNA1A), ATXN7, TATA-box binding protein (TBP), atrophin 1 (ATN1), androgen receptor (AR), and huntingtin (HTT)] were measured by genotyping individual blood samples sourced from the Netherlands Study of Depression and Anxiety and the Netherlands Study of Depression from 2,165 depressed and 1,058 non-depressed older people (Lajoie and Snapp, 2013; Gardiner et al., 2017a).