These findings are in agreement with lower plasma levels of middle molecules (e.g., β2M, cystatin C, FGF-23, and β-trace proteins) and PBUTs (i.e., HA, IxS) reported in adult HD/PD patients with residual kidney function compared to those without [15,29,47,48,49,50,51,52]. Here, B2M is linked to Huntington disease.