Compound heterozygous variants in Wiskott-Aldrich syndrome like (WASL) gene segregating in a family with early onset Parkinson's disease

BackgroundKnowledge of genetic determinants in Parkinson's disease is still limited. Familial forms of the disease continue to provide a rich resource to capture the genetic spectrum in disease pathogenesis, and this approach is exploited in this study.MethodsInformative members from a three-generation family of Indian ethnicity manifesting a likely autosomal recessive mode of inheritance of Parkinson's disease were used for whole exome sequencing. Variant data analysis and in vitro functional characterisation of variant(s) segregating with the phenotype were carried out in HEK-293 and SH-SY5Y cells using gene constructs of interest.ResultsTwo compound heterozygous variants, a rare missense (c.1139C > T:p.P380L) and a novel splice variant (c.1456 + 2 delTAGA, intron10) in Wiskott-Aldrich syndrome like gene (WASL, 7q31), both predicted to be deleterious were shared among the proband and two affected siblings. WASL, a gene not previously linked to a human Mendelian disorder is known to regulate actin polymerisation via Arp2/3 complex. Based on exon trapping assay using pSPL3 vector in HEK-293 cells, the splice variant showed skipping of exon10. Characterisation of the missense variant in SH-SY5Y cells demonstrated: i) significant alterations in neurite length and number; ii) decreased reactive oxygen species tolerance in mutation carrying cells on Tetrabutylphosphonium hydroxide induction and iii) increase in alpha-synuclein protein. Screening for WASL variants in two independent PD cohorts identified four individuals with heterozygous but none with biallelic variants.ConclusionWASL, with demonstrated functional relevance in neurons may be yet another strong candidate gene for autosomal recessive PD encouraging assessment of its contribution across populations.     

Genetic risk factors in Finnish patients with Parkinson's disease

IntroductionVariation contributing to the risk of Parkinson's disease (PD) has been identified in several genes and at several loci including GBA, SMPD1, LRRK2, POLG1, CHCHD10 and MAPT, but the frequencies of risk variants seem to vary according to ethnic background. Our aim was to analyze how variation in these genes contributes to PD in the Finnish population.MethodsThe subjects consisted of 527 Finnish patients with early-onset PD, 325 patients with late-onset PD and 403 population controls. We screened for known genetic risk variants in GBA, SMPD1, LRRK2, POLG1, CHCHD10 and MAPT. In addition, DNA from 225 patients with early-onset Parkinson's disease was subjected to whole exome sequencing (WES).ResultsWe detected a significant difference in the length variation of the CAG repeat in POLG1 between patients with early-onset PD compared to controls. The p.N370S and p.L444P variants in GBA contributed to a relative risk of 3.8 in early-onset PD and 2.5 in late-onset PD. WES revealed five variants in LRRK2 and SMPD1 that were found in the patients but not in the Finnish ExAC sequences. These are possible risk variants that require further confirmation. The p.G2019S variant in LRRK2, common in North African Arabs and Ashkenazi Jews, was not detected in any of the 849 PD patients.ConclusionsThe POLG1 CAG repeat length variation and the GBA p.L444P variant are associated with PD in the Finnish population.     

Transcranial sonography in patients with Parkinson's disease with glucocerebrosidase mutations

ObjectivesThe aim of this study was to search for possible differences in the findings of transcranial sonography (TCS) between groups of patients with glucocerebrosidase (GBA)-associated Parkinson's disease (PD) (4 patients with Gaucher disease type 1 and parkinsonism [GD+PD+] and 18 PD patients with heterozygous GBA mutations; [GBA+PD+]) and groups of 12 patients with Gaucher disease type 1 and no signs of parkinsonism (GD+PD?), 9 asymptomatic carriers of heterozygous GBA mutations (GBA+PD?), 32 sporadic PD patients (sPD), and 43 healthy controls.ResultsIn all groups of patients, except asymptomatic carriers of heterozygous GBA mutations (mean ± SD: 0.16 ± 0.03 cm²), the maximal areas of substantia nigra hyperechogenicity (aSN-max) was higher (GD+PD+: 0.28 ± 0.15 cm²; GD+PD?: 0.18 ± 0.06 cm²; GBA+PD+: 0.27 ± 0.06 cm²; sPD: 0.28 ± 0.10 cm²) when compared to controls (0.12 ± 0.08 cm²) (p = 0.001). In GBA-associated PD (GD+PD+ and GBA+PD+) and sPD, aSNmax values were very similar. Moderate or marked SN hyperechogenicity was present in 87.5% of sPD patients and in 83% of PD patients with heterozygous GBA mutations, but in only 11.6% of controls, and in 22.2% and 33.3% of patients from GBA+PD? and GD+PD? groups, respectively (p < 0.001). The prevalence of interrupted or missing echogenicity of the brainstem raphe differed between the groups (p = 0.046), while no difference was observed in the diameter of the third ventricle.ConclusionsTCS findings in GBA-associated PD were consistent to those of patients with sporadic PD.     

Clinical and molecular genetic findings of hereditary Parkinson's patients from Turkey

IntroductionThe majority of Parkinson's disease (PD) ensue late-onset with a complex spectrum of environmental and genetic risk factors. Awareness of genetic causes in patients with PD is essential for genetic counseling and future genotype-oriented therapeutic developments.MethodsLarge pathogenic changes in eight PD-related genes and small pathogenic sequence variants in 22 PD-related genes were investigated simultaneously in 82 PD patients from 79 families where clinical evaluations were performed. The phenotypic characteristics of the patients with molecular changes were examined for genotype-phenotype relations.ResultsPathogenic variants in SNCA, PRKN, DJ-1, FBXO7, and GBA genes were determined in 25 patients from 24 families (24/79, 30%). Associated variants were found in PRKN in 14, SNCA in three, FBXO7 in two, and DJ-1 in one patient. A novel homozygous deletion (c.491delT, p.(V164Dfs*13) (SCV001733595)) leading to protein truncation in the PRKN gene was identified in two patients from the same family. Furthermore, heterozygous GBA gene variants were detected in five patients from different families.ConclusionIt has been shown that the most common cause of genetically transmitted PD is the PRKN gene, while LRRK2 does not play an essential role in this selected population. It has been suggested that even if the autosomal recessive inheritance is expected, genes with autosomal dominant effects such as SNCA should not be overlooked and suggested for investigation. Our study is also the first for evaluating the pathogenic GBA variants’ frequency in PD patients from Turkey.     

Glucocerebrosidase mutations in primary parkinsonism

IntroductionMutations in the lysosomal glucocerebrosidase (GBA) gene increase the risk of Parkinson's Disease (PD). We determined the frequency and relative risk of major GBA mutations in a large series of Italian patients with primary parkinsonism.MethodsWe studied 2766 unrelated consecutive patients with clinical diagnosis of primary degenerative parkinsonism (including 2350 PD), and 1111 controls. The entire cohort was screened for mutations in GBA exons 9 and 10, covering approximately 70% of mutations, including the two most frequent defects, p.N370S and p.L444P.ResultsFour known mutations were identified in heterozygous state: 3 missense mutations (p.N370S, p.L444P, and p.D443N), and the splicing mutation IVS10+1G>T, which results in the in-frame exon-10 skipping. Molecular characterization of 2 additional rare variants, potentially interfering with splicing, suggested a neutral effect. GBA mutations were more frequent in PD (4.5%, RR = 7.2, CI = 3.3–15.3) and in Dementia with Lewy Bodies (DLB) (13.8%, RR = 21.9, CI = 6.8–70.7) than in controls (0.63%). but not in the other forms of parkinsonism such as Progressive Supranuclear Palsy (PSP, 2%), and Corticobasal Degeneration (CBD, 0%). Considering only the PD group, GBA-carriers were younger at onset (52 ± 10 vs. 57 ± 10 years, P < 0.0001) and were more likely to have a positive family history of PD (34% vs. 20%, P < 0.001).ConclusionGBA dysfunction is relevant for synucleinopathies, such as PD and DLB, except for MSA, in which pathology involves oligodendrocytes, and the tauopathies PSP and CBD. The risk of developing DLB is three-fold higher than PD, suggesting a more aggressive phenotype.     

Genetic analysis of TRIM family genes for early-onset Parkinson's disease in Chinese population

IntroductionAmounting evidence has suggested the Tripartite Motif (TRIM) family proteins as related to Parkinson's disease (PD). However, many of the risk genes were still awaiting further explorations, and their genetic role in PD has not been investigated yet.MethodsHere, we aimed to systematically evaluate the genetic associations of TRIMs with PD in a large Chinese early-onset PD (EOPD, age at onset < 50 years) cohort. We identified rare variants (minor allele frequency < 0.01) in 743 unrelated EOPD patients using whole exome sequencing, and evaluated the association between rare variants and EOPD at allele and gene levels.ResultsTotally 123 rare variants were identified in 13 TRIM protein family members, including TRIM3, TRIM6, TRIM8, TRIM9, TRIM10, TRIM11, TRIM17, TRIM24, TRIM27, TRIM28, TRIM34, TRIM40 and TRIM41. At the allele level, three variants were nominally associated with PD, namely p.R65H in TRIM10, p.P467S in TRIM11, and p.I425V in TRIM24. Gene-based burden analysis showed a clear enrichment of rare variants of TRIM24 in EOPD.ConclusionThese results demonstrate TRIM24 as a potential risk gene for PD, provide a better understanding for the genetic involvement of TRIM protein family members in EOPD and broaden the current mutation spectrum of PD.     

GBA variation and susceptibility to multiple system atrophy

IntroductionGenetic variants in the glucocerebrosidase (GBA) gene have been previously associated with susceptibility to synucleinopathies. The risk is well-established in Lewy body disease but is not as confirmed for multiple system atrophy (MSA). We aim to evaluate associations between exonic variants in GBA and risk of neuropathologically-confirmed multiple system atrophy (MSA).MethodsSanger gene sequencing of GBA was performed on 167 pathologically confirmed MSA patients collected at Mayo Clinic Florida Brain Bank, and data were extracted from whole-genome sequencing of 834 clinical controls. Common GBA variants were assessed for association with MSA. Rare GBA variants (and also all GBA variants) were collapsed together and evaluated for association with MSA risk using a gene-burden test.ResultsA total of 17 exonic GBA variants were observed, including a novel p.Q112X variant that is likely pathogenic in a patient with mixed parkinsonism-cerebellar subtype MSA. The more common p.N409S and p.L483P variants that recessively cause Gaucher's disease (GD), and are associated with risk of Lewy body disease, were not observed. When collapsing across all GBA variants, the presence of any GBA variant was significantly more frequent in MSA patients than in controls (OR = 1.90, P = 0.031). However, this association was driven by p.T408M, which had a significantly higher frequency in MSA patients compared to controls (OR = 4.21, P = 0.002). There was no significant association with risk of MSA for the p.E365K variant (OR = 0.79, P = 0.72).ConclusionsOther than the specific GBA p.T408M variant, coding GBA variants are not associated with risk of MSA.     

Glucocerebrosidase enzyme activity in GBA mutation Parkinson’s disease

Mutations in the glucocerebrosidase (GBA1) gene, the most common genetic contributor to Parkinson’s disease (PD), are associated with an increased risk of PD in heterozygous and homozygous carriers. While glucocerebrosidase enzyme (GCase) activity is consistently low in Gaucher disease, there is a range of leukocyte GCase activity in healthy heterozygous GBA1 mutation carriers. To determine whether GCase activity may be a marker for PD with heterozygous GBA1 mutations (GBA1 mutation PD, GBA PD), GBA PD patients (n = 15) were compared to PD patients without heterozygous GBA1 mutations (idiopathic PD; n = 8), heterozygous GBA1 carriers without PD (asymptomatic carriers; n = 4), and biallelic mutation carriers with PD (Gaucher disease with PD, GD1 PD; n = 3) in a pilot study. GCase activity (nmol/mg protein/hour) in GD1 PD (median [interquartile range]; minimum–maximum: 6.4 [5.7]; 5.3–11) was lower than that of GBA PD (16.0 [7.0]; 11–40) (p = 0.01), while GCase activity in GBA PD was lower than idiopathic PD (28.5 [15.0]; 16–56) (p = 0.01) and asymptomatic carriers (25.5 [2.5]; 23–27) (p = 0.04). Therefore, GCase activity appears to be a possible marker of heterozygous GBA1 mutation PD, and larger studies are warranted. Prospective studies are also necessary to determine whether lower GCase activity precedes development of PD.     

Contribution of coding/non-coding variants in NUS1 to late-onset sporadic Parkinson's disease

IntroductionA recent study reported that rare variants in NUS1 were associated with Parkinson's disease (PD). We aimed to assess the relative contribution of rare and common coding/non-coding variants of NUS1 to late-onset PD patients (LOPD).MethodsWhole genome sequencing data were analyzed for target NUS1 regions, derived from a cohort of 1962 cases and 1279 controls. The genetic association analyses were performed using logistic regression analysis and Sequence Kernel association test. Expression quantitative trait loci (eQTL) analysis was conducted to further explore the association of variants with NUS1 expression based on the data from GTEx database.ResultsWe identified 18 rare coding variants. p.Y131C was first identified in LOPD. However, no significant burden of rare NUS1 coding variants in LOPD was found. The rare variant sets of two regulatory elements (GH06J117605 and GH06J117674) were significantly enriched in LOPD even after Bonferroni correction (adjusted P = 0.013; adjusted P = 0.010). Considering the joint effect of rare and common variants, all variant sets within GH06J117605 and GH06J117674 showed association with LOPD but were no longer significant after Bonferroni correction. None of the common variants within coding/non-coding regions were significant after Bonferroni correction. The eQTL results suggested these variants in GH06J117605 and GH06J117674 could potentially have eQTL effects on the brain tissues.ConclusionsThese findings provide novel insight into the role of NUS1 regulatory regions in the development of LOPD and indicate that the variants in regulatory elements of NUS1 may be associated with LOPD by influencing the gene expression level.     

A new alpha-synuclein missense variant (Thr72Met) in two Turkish families with Parkinson's disease

IntroductionMissense variants and multiplications of the alpha-synuclein gene (SNCA) are established as rare causes of autosomal dominant forms of Parkinson's Disease (PD).MethodsTwo families of Turkish origins with PD were studied; the SNCA coding region was analyzed by Sanger sequencing, and by whole exome sequencing (WES) in the index patient of the first and the second family, respectively. Co-segregation studies and haplotype analysis across the SNCA locus were carried out. Functional studies included in vitro thioflavin-T aggregation assay and in silico structural modelling of the alpha-synuclein (α-syn) protein.ResultsWe identified a novel heterozygous SNCA variant, c.215C > T (p.Thr72Met), segregating with PD in a total of four members in the two families. A shared haplotype across the SNCA locus was found among variant carriers, suggestive of a common ancestor. We next showed that the Thr72Met α-syn displays enhanced aggregation in-vitro, compared to the wild-type species. In silico analysis of a tetrameric α-syn structural model revealed that Threonine 72 lies in the tetrameric interface, and substitution with the much larger methionine residue could potentially destabilize the tetramer.ConclusionWe present clinical, genetic, and functional data supporting a causative role of the SNCA c.215C > T (p.Thr72Met) variant in familial PD. Testing for this variant in patients with PD, especially of Turkish origin, might detect additional carriers. Further functional analyses might offer new insights into the shared biochemical properties of the PD-causing SNCA missense variants, and how they lead to neurodegeneration.     

Variant R244H in Na+/Mg2+ exchanger SLC41A1 in Taiwanese Parkinson's disease is associated with loss of Mg2+ efflux function

BackgroundSequence variants in SLC41A1 have been reported to be associated with Parkinson's disease (PD). This study investigates whether the genetic variants in SLC41A1 contribute to Taiwanese PD.MethodsWe sequenced SLC41A1 cDNA fragments from 80 patients with early onset PD. A cohort of PD and ethnically matched controls were examined for the sequence variant. The effect of variation on Mg²⁺ homeostasis was further examined using stably induced 293 cells expressing recombinant wild type and variant SLC41A1.ResultsA novel heterozygous R244H in the SLC41A1 gene was identified in one early onset PD patient, which not present either in 479 PD patients or 525 normal controls with age onset >50. Both wild type and R244H SLC41A1-V5-His proteins were co-localized to areas of the plasma membrane that were stained using wheat germ agglutinin (WGA). Fluorescent probe mag-fluo-4 staining indicated that R244H SLC41A1 is dysfunctional in Mg²⁺ efflux.ConclusionsThis study has shown loss of Mg²⁺ efflux function consequent to SLC41A1 R244H variant and SLC41A1 coding variants seem to be rare in Taiwanese PD.     

Exome-wide rare variant analysis in familial essential tremor

IntroductionEssential tremor (ET) is one of the most common movement disorders. Despite its high prevalence and heritability, its genetic etiology remains elusive with only a few susceptibility genes identified and poorly replicated. Our aim was to find novel candidate genes involved in ET predisposition through whole exome sequencing.MethodsWe studied eight multigenerational families (N = 40 individuals) with an autosomal-dominant inheritance using a comprehensive strategy combining whole exome sequencing followed by case-control association testing of prioritized variants in a separate cohort comprising 521 ET cases and 596 controls. We further performed gene-based burden analyses in an additional dataset comprising 789 ET patients and 770 healthy individuals to investigate whether there was an enrichment of rare deleterious variants within our candidate genes.ResultsFifteen variants co-segregated with disease status in at least one of the families, among which rs749875462 in CCDC183, rs535864157 in MMP10 and rs114285050 in GPR151 showed a nominal association with ET. However, we found no significant enrichment of rare variants within these genes in cases compared with controls. Interestingly, MMP10 protein is involved in the inflammatory response to neuronal damage and has been previously associated with other neurological disorders.ConclusionsWe prioritized a set of promising genes, especially MMP10, for further genetic and functional studies in ET. Our study suggests that rare deleterious coding variants that markedly increase susceptibility to ET are likely to be found in many genes. Future studies are needed to replicate and further infer biological mechanisms and potential disease causality for our identified genes.     

The LRRK2 G2385R variant is a risk factor for sporadic Parkinson's disease in the Korean population

The G2385R (SNP accession no. rs34778348) and R1628P (rs33949390) variants of leucine-rich repeat kinase 2 (LRRK2, PARK8) are emerging as an important risk factor for Parkinson's disease (PD) in the ethnic Chinese and Japanese populations. The purpose of this study was to investigate whether these variants are a genetic risk factor in sporadic PD patients in the Korean population. A total of 923 patients and 422 healthy subjects were included. The variants were screened by a SNaPshot assay. The LRRK2 G2385R variant was detected in 82 PD patients (8.9%, two homozygous and 80 heterozygous) and in 21 normal controls (5.0%, all heterozygous). The frequency of the LRRK2 G2385R variant in PD was significantly higher than in normal controls (adjusted odds ratio 1.83, p = 0.0170, 95% confidence interval 1.11–3.00). There were no differences in the mean age at onset or gender between the G2385R carriers and the non-carriers in PD patients. The LRRK2 R1628P variant was very rare (0.78% in patients versus 0.26% in controls) in the tested 384 patient–control pairs, and was not a significant risk factor. This study supports that the LRRK2 G2385R variant may be a genetic risk factor for sporadic PD in the Korean population.     

Familial periodic paralysis associated with a rare KCNJ5 variant that supposed to have incomplete penetrance

BackgroundThe periodic paralyses are a group of skeletal muscle channelopathies caused by variants in several ion channel genes. Potassium Inwardly Rectifying Channel Subfamily J Member 5 (KCNJ5) encodes the G-protein–activated inwardly rectifying potassium channel 4 (Kir3.4) and the heterozygous KCNJ5 variants cause familial hyperaldosteronism and long QT syndrome (LQTS). Recent studies suggested that variants in KCNJ5 are also causative for Andersen-Tawil syndrome, which showed periodic paralysis and characteristic electrocardiogram features.Clinical report.We found a heterozygous KCNJ5 variant c.1159G > C, p.(Gly387Arg) in an individual with familial periodic paralysis using exome sequencing. Sanger sequencing revealed that this variant was inherited from his affected mother. The same variant had been previously found in two cases of familial LQTS or Andersen-Tawil syndrome, and functional analysis suggested that this variant might have loss of function effect on channel activity. However, the allele frequency of c.1159G > C variant in an East Asian population of public databases ranged from 0.21% to 0.25%, indicating possible incomplete penetrance.ConclusionsOur two patients expand the phenotypic spectrum associated with the c.1159G > C KCNJ5 variant, though the variant has very low penetrance.     

Transcranial sonography and functional imaging in glucocerebrosidase mutation Parkinson disease

BackgroundHeterozygous glucocerebrosidase (GBA) mutations are the leading genetic risk factor for Parkinson disease, yet imaging correlates, particularly transcranial sonography, have not been extensively described.MethodsTo determine whether GBA mutation heterozygotes with Parkinson disease demonstrate hyperechogenicity of the substantia nigra, transcranial sonography was performed in Ashkenazi Jewish Parkinson disease subjects, tested for the eight most common Gaucher disease mutations and the LRRK2 G2019S mutation, and in controls. [¹⁸F]-fluorodeoxyglucose or [¹⁸F]-fluorodopa positron emission tomography is also reported from a subset of Parkinson disease subjects with heterozygous GBA mutations.ResultsParkinson disease subjects with heterozygous GBA mutations (n = 23) had a greater median maximal area of substantia nigral echogenicity compared to controls (n = 34, aSNmax = 0.30 vs. 0.18, p = 0.007). There was no difference in median maximal area of nigral echogenicity between Parkinson disease groups defined by GBA and LRRK2 genotype: GBA heterozygotes; GBA homozygotes/compound heterozygotes (n = 4, aSNmax = 0.27); subjects without LRRK2 or GBA mutations (n = 32, aSNmax = 0.27); LRRK2 heterozygotes/homozygotes without GBA mutations (n = 27, aSNmax = 0.28); and GBA heterozygotes/LRRK2 heterozygotes (n = 4, aSNmax = 0.32, overall p = 0.63). In secondary analyses among Parkinson disease subjects with GBA mutations, maximal area of nigral echogenicity did not differ based on GBA mutation severity or mutation number. [¹⁸F]-fluorodeoxyglucose (n = 3) and [¹⁸F]-fluorodopa (n = 2) positron emission tomography in Parkinson disease subjects with heterozygous GBA mutations was consistent with findings in idiopathic Parkinson disease.ConclusionsBoth transcranial sonography and positron emission tomography are abnormal in GBA mutation associated Parkinson disease, similar to other Parkinson disease subjects.     

Screening of LRP10 mutations in Parkinson's disease patients from Italy

IntroductionParkinson's disease (PD) belongs to a family of neurodegenerative diseases characterized by alpha-synuclein accumulation in neurons, whose etiopathogenesis remains largely uncovered. Recently, LRP10 has been associated with PD, Parkinson's disease Dementia (PDD) and Dementia with Lewy Bodies (DLB) by linkage analysis and positional cloning in an Italian family with late-onset PD. After the first characterization of a LRP10 pathogenic variant, other eight mutations have been detected in an international series of 660 probands with either a clinical or pathological diagnosis of PD, PDD or DLB. However, the results of following replication studies were inconclusive and the pathogenic role of LRP10 is still debated. The aim of this study is to sequence the LRP10 gene in an Italian cohort of clinically-diagnosed PD patients and to compare the frequency of the identified variants with the ones found in a large cohort of Italian exomes.MethodsA cohort of 664 PD patients was analyzed by targeted Next Generation Sequencing approach. Identified LRP10 variants were subsequently confirmed by Sanger sequencing and searched for in an in-house database including 3596 Italian exomes.ResultsWe identified three PD patients carrying a rare heterozygous, potentially pathogenic variant (p.R296C, p.R549Q, p.R661C). None of them was detected in 3596 Italian exomes. Two of them (p.R296C and p.R661C) have been previously reported in one sporadic PD and one definite Progressive supranuclear palsy patients respectively. All three carriers had late-onset PD responsive to levodopa, characterized by both motor and non-motor features, but no cognitive impairment.ConclusionWe report three rare possibly-pathogenic LRP10 variants in PD patients from Italy. Further investigations are required to definitively establish their role in alpha-synucleinopathies.     

Low frequency of GCH1 and TH mutations in Parkinson's disease

BackgroundThe causes of Parkinson's disease (PD) are unknown in the majority of patients. The GCH1 gene encodes GTP-cyclohydrolase I, an important enzyme in dopamine synthesis. Co-occurrence of dopa-responsive dystonia (DRD) and a PD phenotype has been reported in families with GCH1 mutations. Recently, rare coding variants in GCH1 were found to be enriched in PD patients, indicating a role for the enzyme in the neurodegenerative process.MethodsTo further elucidate the contribution of GCH1 mutations to sporadic PD, we examined its coding exons in a targeted deep sequencing study of 509 PD patients (mean age at onset 56.7 ± 12.0 years) and 230 controls. We further included the tyrosine hydroxylase gene TH, also known to cause DRD. Gene dose assessments were performed to screen for large copy number variants in a subset of 48 patients with early-onset PD.ResultsNo putatively pathogenic GCH1 mutations were found. The frequency of rare heterozygous variants in the TH gene was 0.69% (7/1018) in the patient group and 0.22% (1/460) in the control group (p = 0.45).ConclusionsPrevious studies have found that coding variants in the GCH1 gene may be considered a risk factor for PD. Our study indicates that mutations in GCH1 are rare in late-onset PD. Several patients carried heterozygous variants in the TH gene that may affect protein function. Our study was not designed to determine with certainty if any of these variants play a role as risk factors for late-onset PD.