Journal of Neural Transmission

, Volume 115, Issue 5, pp 715–719

PARK2 mutations and clinical features in a Chinese population with early-onset Parkinson’s disease

Authors

    • Department of Aged Care and RehabilitationBankstown Hospital
    • Faculty of MedicineUniversity of New South Wales
  • Vincent Mok
    • Neurology Division, Department of Medicine and TherapeuticsPrince of Wales Hospital, The Chinese University of Hong Kong
  • Ping Wing Ng
    • Department of Medicine and GeriatricsUnited Christian Hospital
  • Jonas Yeung
    • Department of MedicineAHML Nethersole Hospital
  • John B. Kwok
    • Prince of Wales Medical Research Institute, University of New South Wales
  • Zhi Ming Fang
    • Cancer Care CentreSt George Hospital
  • Raymond Clarke
    • Cancer Care CentreSt George Hospital
  • Lawrence Wong
    • Neurology Division, Department of Medicine and TherapeuticsPrince of Wales Hospital, The Chinese University of Hong Kong
  • Peter R. Schofield
    • Prince of Wales Medical Research Institute, University of New South Wales
  • Nobutaka Hattori
    • Department of NeurologyJuntendo University, School of Medicine
Parkinson’s Disease and Allied Conditions - Original Article

DOI: 10.1007/s00702-007-0011-6

Cite this article as:
Chan, D.K.Y., Mok, V., Ng, P.W. et al. J Neural Transm (2008) 115: 715. doi:10.1007/s00702-007-0011-6
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Abstract

Our aim was to characterise PARK2 mutations and clinical features in Hong Kong Chinese with early-onset Parkinson’s disease. Subjects were recruited from two major hospitals. Detailed data included demographics, age of onset, duration of disease, neurological manifestations, complications and disease severity. Genetic analysis for PARK2 mutations was performed. Thirty-four patients were recruited (mean age of onset = 39 years; mean duration of disease = 10 years). Seven patients reported a family history. The salient clinical manifestations were resting tremor (33/34), bradykinesia (33/34), rigidity (30/34), postural instability (20/34), good response to l-dopa (33/34), asymmetry at onset (31/34) and sleep benefit (12/34). Motor complications were reported in a significant number of patients, and depression was the most common nonmotor complication. Five patients were identified to have PARK2 mutations. Two sisters were compound heterozygotes for an insertion and a deletion, a novel and rare 1 bp insertion/nonsense mutation c1378_1379insG (exon 12) and the entire deletion of exon 7. Another patient was homozygous for the entire deletion of exon 6. Two carriers were identified, one with a T1321C (Cys441Arg) missense mutation in exon 12 and another with a snp within intron 4. Our study reviewed a higher prevalence of PARK2 mutations in Chinese than that previously documented. A compound heterozygous mutation within two sisters with significant differences in age of onset and phenotypic manifestations suggest that modifier affects may be present in this family.

Keywords

Early-onset Parkinson’s diseasePARK2ChineseClinical features

Introduction

Parkinson’s disease (PD) is a complex neurodegenerative disease where the majority of cases are sporadic with symptoms appearing after the sixth decade of life. The condition is presumed to result from a complex interaction between genetic and environmental factors (Chan et al. 2004). However, autosomal dominant and recessive forms of PD are known to exist in a small minority of cases. The most common form of autosomal recessive PD is due to mutations in the PARK2 gene coding for the E3 ligase, parkin, which is associated with the ubiquitin-proteasome system (Shimura et al. 2000). Parkin mutations appear to be responsible for up to 77% of juvenile parkinsonism (onset <20 years), 49% of recessive familial cases of early-onset (<45 years) and 18% of isolated early-onset cases (Lücking et al. 2000).

PARK2 mutations have been found in Japanese (Kitada et al. 1998) and Caucasian populations (Lücking et al. 2000) and recently in three small series among Chinese populations where allelic mutation frequency ranges from 0% (Peng et al. 2003) and 6% (Wu et al. 2002) to 9% (Wu et al. 2005). Details of PARK2 mutations and their clinical characteristics are still lacking amongst young onset Chinese PD patients including those with a familial history. This is especially relevant in outpatient settings, as clinicians are often asked about the possibility of genetic testing for early-onset Chinese PD cases. With this in mind, we initiated a search for mutations of PARK2 in early-onset PD cases from outpatient clinics in Hong Kong.

Methods

Patients of Chinese descent were recruited from the outpatient departments of two major Hong Kong hospitals, the Prince of Wales Hospital and United Christian Hospital. The former is a major teaching hospital with a catchment population of 1.3 million and the latter is an affiliated teaching hospital with a catchment population of six hundred thousand. Patients were examined and diagnosed by accredited neurologists.

The inclusion criteria were as follows:
  1. 1.

    Chinese patients with PD as defined by the presence of at least 2 of the following features: bradykinesia, tremor at rest, rigidity or postural instability.

     
  2. 2.

    Both patients with familial history or sporadic cases with the age of onset of ≤45 years were recruited.

     
Exclusion criteria were patients with all other causes of parkinsonism including Parkinson Plus Syndrome, vascular causes, drug-induced parkinsonism or inherited metabolic diseases such as Wilson’s disease and hypothyroidism.

All patients provided informed consent and the data collected included the following: demographics, age of onset of PD, duration of illness, presence of symmetrical signs and dystonia at onset, sleep benefit, other medical comorbidities and medications (duration and dosage). The presence of dyskinesia, off-phenomenon and other complications including cognitive impairment, depression and hallucinations were also documented. A detailed neurological examination was carried out and severity of disease was classified using UPDRS as well as modified Hoehn & Yahr stage.

Genetic analysis

The coding sequence of the Park 2 gene was screened for nucleotide substitutions and small-scale genetic rearrangements ((100 bp) by PCR amplification of genomic DNA templates using previously published exonic primers (Hattori et al. 1998).

PCR products were purified using the Wizard SV gel purification system (Promega) before bidirectional sequencing using BigDye V3.1 chemistry (AB, Forster City, CA, USA). PCR to detect exonic deletions were performed in 25 μL reactions containing 100 ng of genomic DNA, 0.25 μM of each primer, 200 μM of dNTPs and 1× PCR buffer with 5% DMSO and 0.25 U Blue GoTaq polymerase (Promega). All PCR reactions used five touch-down cycles at 95°C for 30 s denaturation, at 62°C for 30 s annealing and at 70°C for 50 s extension after initial denaturation of samples at 95°C for 3 min, followed by 27 cycles at 95°C for 30 s denaturation, at 56°C for 30 s annealing and at 70°C for 50 s extension (Corbett Research CG1-96). At the conclusion of cycling, samples remained at 72°C for 10 min as a final extension step. PCR products were resolved by electrophoresis in 1.4% agarose gels for the presence or absence of the target exons (Hattori et al. 1998). PARK2 gene mutations were numbered relative to PARK2 mRNA sequence NM_004562.1 (Genbank).

Micro-deletion analysis

We employed copy number variation (CNV) analysis to identify micro-deletions and wherever possible we confirmed these deletions using routine PCR.

Results

A total of 34 patients were recruited. There were 13 females and 21 males. The mean age of the patients was 49 years (SD 5.7), the mean age of onset was 39 years (SD 6.0) and mean duration of disease was 10 years (SD 6.2).

Seven cases reported a family history, two had one parent diagnosed by neurologists to have parkinsonism and five had one sibling suffering from the disease confirmed by neurologists. Of the five patients who had a sibling with the disease, two were sisters. Consanguineous marriage was known in one patient but the proband did not have a family history of parkinsonism. The salient clinical manifestations of the 34 patients are summarised in Table 1.

Five patients were identified to have mutations in PARK2. The mutations and clinical characteristics of these patients are summarised in Table 2. In one family, two sisters were compound heterozygotes for an insertion and a deletion, a novel 1 bp insertion c1378_1379insG within the coding region of exon 12 and the entire deletion of exon 7 (c.735_871del) including codons 245_291. Another patient was homozygous for the entire deletion of exon 6 (c.619_734) including codons 207_244. Two carriers were identified, one with a T1321C (Cys441Arg) missense mutation in exon 12 and another with a single nucleotide polymorphism within intron 4 (IVS4 + 10T > C). The last three patients did not report any family history.
Table 1

 Summary of salient clinical features of 34 patients with early-onset PD

Clinical features

Number of patients/total number

Cardinal features

 Resting tremor

33/34

 Bradykinesia

33/34

 Rigidity

30/34

 Postural instability

20/34

Good response to l-dopa

33/34

Asymmetry at onset

31/34

Dystonia at onset

3/34

Motor complications

 Wearing off

17/34

 l-dopa-induced dyskinesia

3/34

 Freezing

13/34

Sleep benefit

12/34

Motor scale

 Mean score of UPDRS Part II on/off

8/18 (n = 34/27)

 Part III on/off

24/39 (n = 26/12)

 Modified Hoehn & Yahr stage off

3 (n = 34)

Nonmotor complications

 Incontinence

3/34

 Cognitive impairment with MMSE £ 24

7/33 (one had missing data)

 Depression

13/34

 Hallucinations

4/34

Table 2

 Summary of genetic and phenotypic characteristics of early-onset PD patients with PARK2 variants

PARK2 mutation

T1321C heterozygote (Cys441Arg) (exon 12)

Homologous deletion of exon 6 (codons 207_244)

Compound heterozygotes insertion (c.1378_1379insG – exon 12) & deletion of Exon 7 (codons 245_291)

T > C (IVS4 + 10) (intron 4)

Patient 1

Patient 2

Patient 3

Patient 4

Patient 5

Sex

M

F

F

F

M

Age of onset

41

30

35

17

38

Duration

4

16

21

29

2

Family history

No

No

Yes

Yes

No

Asymmetry at onset

No

Yes

Yes

No

Yes

Dystonia at onset

No

No

No

Yes

No

Sleep benefit

Yes

No

No

No

No

Cardinal features

 Resting tremor

Yes

Yes

Yes

Yes

Yes

 Bradykinesia

Yes

Yes

No

Yes

Yes

 Rigidity

Yes

Yes

Yes

Yes

No

 Postural instability

No

Yes

No

No

No

 l-dopa response

Yes

Yes

Yes

Yes

Yes

 l-dopa-induced dyskinesia

No

No

Yes

Yes

No

Motor or autonomic complications

 Gait freezing

No

Yes

No

Yes

No

 Orthostatic hypotension

No

No

No

No

No

 Incontinence

No

No

No

No

No

Psychiatric complications

 Hallucinations

No

No

No

No

No

 Dementia (MMSE out of 30)

30

28

27

 

29

 Depression

No

No

No

No

No

UPDRS Part II

 On phase

0

3

3

1

5

 Off phase

3

12

6

UPDRS Part III

 On phase

17

13

0

22

 Off phase

33

Modified Hoehn & Yahr

 Off stage

2

2

3

4

2

The mean age of onset of PARK2 mutation-positive patients was 27.3 years (SD 9.3) (only including three patients with both alleles affected) and 32.2 years (SD 9.4) (including all five patients). Mean duration of disease is as follows: 22 years (SD 6.6) (only including three patients with both alleles affected); 14.4 years (SD 11.4) (including all five patients). Mean age of onset of PARK2-negative patients is 40.4 years (SD 4.4). Mean duration of disease is 9.1 years (SD 4.7).

Discussion

Current data on PARK2 mutation and phenotypic characteristics in Chinese is very limited. Our study has added further information and has found PARK2 mutations in 5 out of 34 early-onset cases. The frequency of PARK2 mutations is 8 out of 68 alleles (one patient had a homologous deletion), two sisters were heterozygous for a compound mutation (an insertion and a deletion), one patient was heterozygous for a missense mutation and one was heterozygous for a polymorphism within intron 4. The frequency of PARK2 mutations in 11.7% of our early-onset patients is higher than the 0–6% previously reported by Peng et al. (2003) and Wu et al. (2002). Despite this, the frequency of PARK2 mutations is still lower than the 18–49% range reported for Caucasian populations (Mata et al. 2004). Apart from smaller sample sizes and older age as cut-off point for early onset (age 50 years versus age 45 years) (Peng et al. 2003, Wu et al. 2002), the previous Chinese studies used mutation screening methods, which may have under-scored deletions or duplications. Therefore, we believe that this study more closely reflects the frequency of PARK2 mutations amongst early-onset Chinese PD patients in an outpatient setting while acknowledging that it is possible that not all the mutant variants may be pathogenic.

The age of onset of patients with PARK2 mutations in our study varied from 17 to 41 years of age (17, 30, 35, 38 and 41 years where the former three had both alleles affected). The mean age, age of onset and duration of disease [mean (SD)] in the three patients who had PARK2 mutations in both alleles were 49 (5.8), 27 (9.3) and 22 (6.6) years, respectively (if the two heterozygotes were included, the mean age, the mean age of onset and the mean duration of disease would be 47, 32 and 14 years, respectively). All patients with PARK2 mutations had good responses to l-dopa. These clinical features are similar to previous findings in the literature. We also found the mean age of onset to be older and duration of disease to be shorter in the PARK2-negative group: mean age 50 (5.6), mean age of onset 40 (4.4) and mean duration 9 (4.7) years. Together these results support a correlation between PARK2 mutations and an earlier age of onset in Chinese PD patients.

Another interesting finding was the significantly different phenotypic manifestations in two sister siblings, which were heterozygous for the same compound PARK2 mutations. Both siblings were heterozygous for a novel insertion c1378_1379insG and a deletion (entire exon 7). The deletion of exon 7 deletes codons 245_291 and puts one of the PARK2 alleles out of frame. The single nucleotide insertion/nonsense mutation in these two sisters also causes a frame shift within exon 12, which is likely to inactivate and extend the length of this PARK2 allele. The differences in the age of onset and clinical features of the two sisters suggest that the novel mutation may have a dominant negative affect or alternatively some other modifier may be involved. The younger of the two sisters had a juvenile age of onset (17 years) compared to the older sister who had a later age of early onset (35 years) closer to the mean age of onset (39 years) for this series. The presentation of more severe symptoms in association with the juvenile age of onset in the form of dystonia and symmetrical signs at onset (Table 2) may indicate an association between age of onset and severity of presentation in this case. PARK2 is thought to play a role in the ubiquitin-proteasome pathway in the degradation of protein substrates (Shimura et al. 2000). Perhaps other modifying factors such as genetic, epigenetic or environmental factors might have caused the mark differences in phenotypic manifestations between these sisters.

Among the 20% PD patients with a family history, 29% (2/7) had PARK2 mutations. If parents were excluded (that is only siblings were counted), the percentage was as high as 40% (2/5). About 80% of our cases were without a family history of PD and could represent PD of sporadic onset. However, among this subgroup of patients, we found three patients with PARK2 mutations (3/27), one was homozygote for a deletion of exon 6 (codons 207 to 244), which puts both alleles out of frame. The other two cases were heterozygotes, one had a missense mutation in exon 12 and the other a snp within intron 4. This represents 7.4% of total alleles studied (4/54). Stratifying this subgroup by age of onset (≤30 years old or >30 years) revealed a higher percentage of mutations, 33% or 1/3 present in the younger age of onset group (≤ 30 years old) compared to 8.3% or 2/24 in the older age of onset (>30 years old). The high frequencies of PARK2 mutations found amongst patients with family history or isolated PD with younger age of onset is in accord to the findings of Lücking et al. (2002).

In conclusion, we find a higher frequency of PARK2 mutations amongst Chinese with early-onset PD compared to previous descriptions. Our finding of a high frequency of mutations in patients with positive family history or isolated PD with younger onset age closely reflects the finding reported by Lücking et al. The mutations identified in this Chinese series with early-onset PD are mostly different from those reported elsewhere. Substantial differences in the clinical manifestations of two affected sisters (both compound PARK2 heterozygotes) suggest that other modifying factors may influence phenotypic features in this case of inherited PD. Further mutation-screening of PARK2 in early-onset patients in the Chinese population may improve our understanding of factors affecting age of onset where clinically indicated or appropriate.

Acknowledgments

We are indebted to the valuable support and advice from Prof. Richard Kay and Dr. Edward Leung.

Copyright information

© Springer-Verlag 2007