Deficiency of RET phosphorylation, an indicator of failed GDNF signaling, was identified in the substantia nigra of sPD subjects and also in the GM1-deficient B4Galnt1+/− mice; in the latter GDNF signaling was restored by LIGA20, a membrane-permeable analog of GM113. This evidence concerns the gene B4GALNT1 and Platelet storage pool disease.