LMX1B and Parkinson disease: With this in mind, it is noteworthy that Lmx1a expression declines with age in the mouse brain (Doucet-Beaupre et al., 2016; Laguna et al., 2015), while patient brain LMX1B levels have been reported to inversely correlate with PD progression (Laguna et al., 2015; Xia et al., 2016).