Comparing the effects of GBA variants and onset age on clinical features and progression in Parkinson's disease

OBJECTIVE

Glucosylceramidase (GBA) variants and onset age significantly affect clinical phenotype and progression in Parkinson's disease (PD). The current study compared clinical characteristics at baseline and cognitive and motor progression over time among patients having GBA-related PD (GBA-PD), early-onset idiopathic PD (early-iPD), and late-onset idiopathic PD (late-iPD).

METHODS

We recruited 88 GBA-PD, 167 early-iPD, and 488 late-iPD patients in this study. A subset of 50 GBA-PD, 81 early-iPD, and 223 late-iPD patients was followed up at least once, with a 3.0-year mean follow-up time. Linear mixed-effects models helped evaluate the rate of change in the Unified Parkinson's Disease Rating Scale motor and Montreal Cognitive Assessment scores.

RESULTS

At baseline, the GBA-PD group showed more severe motor deficits and non-motor symptoms (NMSs) than the early-iPD group and more NMSs than the late-iPD group. Moreover, the GBA-PD group had more significant cognitive and motor progression, particularly bradykinesia and axial impairment, than the early-iPD and late-iPD groups at follow-up. However, the early-onset GBA-PD (early-GBA-PD) group was similar to the late-onset GBA-PD (late-GBA-PD) group in baseline clinical features and cognitive and motor progression.

CONCLUSION

GBA-PD patients exhibited faster cognitive and motor deterioration than early-iPD and late-iPD patients. Thus, subtype classification based on genetic characteristics rather than age at onset could enhance the prediction of PD disease progression.

Prevalence and Genotype-Phenotype Correlations of GBA-Related Parkinson's Disease in a Large Chinese Cohort

Background and purpose

Variants in the glucocerebrosidase (GBA) gene are recognized as a common and important genetic risk factor for Parkinson disease (PD). However, the impact of variant severity on the clinical phenotype of PD in the Chinese population remains unclear. Thus, the present study aimed to determine the frequency of GBA‐related PD (GBA‐PD) and the relationship of GBA variant severity with clinical characteristics in a large Chinese cohort.

Methods

Long‐range polymerase chain reaction and next generation sequencing were performed for the entire GBA gene. GBA variant severity was classified into five classes: mild, severe, risk, complex, and unknown.

Results

Among the total 737 PD patients, 47 GBA variants were detected in 79 (10.72%) patients, and the most common GBA variants were R163Q, L444P, and R120W. Complete demographic and clinical data were obtained for 673 patients, which revealed that 18.50% of early onset PD patients had GBA variants. Compared with patients without GBA variants, GBA‐PD patients experienced PD onset an average of 4 years earlier and had more severe motor and nonmotor symptoms. Patients carrying severe and complex variants had a higher burden of nonmotor symptoms, especially depression, and more mood/cognitive and gastrointestinal symptoms than patients carrying mild variants.

Conclusions

GBA‐PD is highly prevalent in the Chinese population. The severity of GBA variants underlies distinct phenotypic spectrums, with PD patients carrying severe and complex variants seeming to have similar phenotypes. PD patient stratification by GBA variant severity should become a prerequisite for selecting specific treatments.

POLG R964C and GBA L444P mutations in familial Parkinson's disease: Case report and literature review

Polymerase gamma (POLG) is an enzyme responsible for the replication and repair of mitochondrial DNA. Mutations in POLG may cause variable clinical manifestations, including parkinsonism, epilepsy, cerebellar ataxia, neuropathy, and progressive external ophthalmoplegia. However, mutations of this gene are rare in patients with typical Parkinson's disease (PD). We report a man (current age: 59 years) without any underlying disease presenting with right-hand tremor at the age of 39 years, followed by slow movement, rigidity, and postural instability. He developed motor fluctuation and levodopa-induced dyskinesia 8 years later. At the age of 58 years, cognitive decline and visual hallucination ensued; he was institutionalized thereafter. We used multiplex ligation-dependent probe amplification, which demonstrated no large deletions or duplications of relevant PD genes. Next, targeted sequencing panel covering 51 genes causative for PD was applied for the proband; it revealed a heterozygous missense substitution R964C in POLG and a heterozygous missense substitution L444P in GBA. The patient's father, who had been diagnosed as having PD and type 2 diabetes mellitus at the age of 70 years, demonstrated identical mutations. This is the first report of familial PD combined with POLG R964C and GBA L444P mutations. Two pathogenic gene mutations potentially cause double hit in pathological neurodegeneration. This finding extends our understanding of the PD genotype-phenotype correlation.

Evaluation of the detection of GBA missense mutations and other variants using the Oxford Nanopore MinION

BACKGROUND

Mutations in GBA cause Gaucher disease when biallelic and are strong risk factors for Parkinson's disease when heterozygous. GBA analysis is complicated by the nearby pseudogene. We aimed to design and validate a method for sequencing GBA using long reads.

METHODS

We sequenced GBA on the Oxford Nanopore MinION as an 8.9 kb amplicon from 102 individuals, including patients with Parkinson's and Gaucher diseases. We used NanoOK for quality metrics, NGMLR to align data (after comparing with GraphMap), Nanopolish and Sniffles to call variants, and WhatsHap for phasing.

RESULTS

We detected all known missense mutations in these samples, including the common p.N409S (N370S) and p.L483P (L444P) in multiple samples, and nine rarer ones, as well as a splicing and a truncating mutation, and intronic SNPs. We demonstrated the ability to phase mutations, confirm compound heterozygosity, and assign haplotypes. We also detected two known risk variants in some Parkinson's patients. Rare false positives were easily identified and filtered, with the Nanopolish quality score adjusted for the number of reads a very robust discriminator. In two individuals carrying a recombinant allele, we were able to detect and fully define it in one carrier, where it included a 55-base pair deletion, but not in another one, suggesting a limitation of the PCR enrichment method. Missense mutations were detected at the correct zygosity, except for the case where the RecNciI one was missed.

CONCLUSION

The Oxford Nanopore MinION can detect missense mutations and an exonic deletion in this difficult gene, with the added advantages of phasing and intronic analysis. It can be used as an efficient research tool, but additional work is required to exclude all recombinants.