There are now many lines of evidence to suggest that E326K has a role in determining the course of PD. Even though it is not a recognised cause of Gaucher's disease, it has come up frequently in genetic studies looking at PD-related GBA variants and functional work supports the claim... my experience fits with the observations in this study and those of others... the tendency is towards akinetic rigidity, gait problems and cognitive impairment, rather than a tremor predominant form of PD...
JAMA Neurol. 2016 Aug 29. doi: 10.1001/jamaneurol.2016.2245. [Epub ahead of print]
Davis MY, Johnson CO, Leverenz JB, Weintraub D, Trojanowski JQ, Chen-Plotkin A, Van Deerlin VM, Quinn JF, Chung KA, Peterson-Hiller AL, Rosenthal LS, Dawson TM, Albert MS, Goldman JG, Stebbins GT, Bernard B, Wszolek ZK, Ross OA, Dickson DW, Eidelberg D, Mattis PJ, Niethammer M, Yearout D, Hu SC, Cholerton BA, Smith M, Mata IF, Montine TJ, Edwards KL, Zabetian CP.
Parkinson disease (PD) is heterogeneous in symptom manifestation and rate of progression. Identifying factors that influence disease progression could provide mechanistic insight, improve prognostic accuracy, and elucidate novel therapeutic targets.
To determine whether GBA mutations and the E326K polymorphism modify PD symptom progression.
DESIGN, SETTING, AND PARTICIPANTS:
The entire GBA coding region was screened for mutations and E326K in 740 patients with PD enrolled at 7 sites from the PD Cognitive Genetics Consortium. Detailed longitudinal motor and cognitive assessments were performed with patients in the on state.
MAIN OUTCOMES AND MEASURES:
Linear regression was used to test for an association between GBA genotype and motor progression, with the Movement Disorder Society-sponsored version of the Unified Parkinson's Disease Rating Scale Part III (MDS-UPDRS III) score at the last assessment as the outcome and GBA genotype as the independent variable, with adjustment for levodopa equivalent dose, sex, age, disease duration, MDS-UPDRS III score at the first assessment, duration of follow-up, and site. Similar methods were used to examine the association between genotype and tremor and postural instability and gait difficulty (PIGD) scores. To examine the effect of GBA genotype on cognitive progression, patients were classified into those with conversion to mild cognitive impairment or dementia during the study (progression) and those without progression. The association between GBA genotype and progression status was then tested using logistic regression, adjusting for sex, age, disease duration, duration of follow-up, years of education, and site.
Of the total sample of 733 patients who underwent successful genotyping, 226 (30.8%) were women and 507 (69.2%) were men (mean [SD] age, 68.1 [8.8] years). The mean (SD) duration of follow-up was 3.0 (1.7) years. GBA mutations (β = 4.65; 95% CI, 1.72-7.58; P = .002), E326K (β = 3.42; 95% CI, 0.66-6.17; P = .02), and GBA variants combined as a single group (β = 4.01; 95% CI, 1.95-6.07; P = 1.5 × 10-4) were associated with a more rapid decline in MDS-UPDRS III score. Combined GBA variants (β = 0.38; 95% CI, 0.23-0.53; P = .01) and E326K (β = 0.64; 95% CI, 0.43-0.86; P = .002) were associated with faster progression in PIGD scores, but not in tremor scores. A significantly higher proportion of E326K carriers (10 of 21 [47.6%]; P = .01) and GBA variant carriers (15 of 39 [38.5%]; P = .04) progressed to mild cognitive impairment or dementia.
CONCLUSIONS AND RELEVANCE:
GBA variants predict a more rapid progression of cognitive dysfunction and motor symptoms in patients with PD, with a greater effect on PIGD than tremor. Thus, GBA variants influence the heterogeneity in symptom progression observed in PD.