B4GALNT1 and Parkinson disease: Of special interest was the observation that heterozygous mice (B4galnt1+/−), with only partial GM1 deficiency showed similar PD symptoms [71], similar in magnitude to the deficiencies observed in PD patients, e.g., occipital cortex, nigrostriatal neurons of the SNpc [12], and extra-CNS sites representing the PNS [9].