Parkinson's disease (PD) is a common neurodegenerative disease with its etiology still unknown. Clinically, most PD patients suffer from bradykinesia, resting tremor, rigidity, and postural instability, which could also be present in patients with other neurodegenerative conditions. Thus, analyses for relative gene alterations were performed to investigate the associations between PD and other neurodegenerative diseases. The results of the (CAG)n repeats expansion of ATXN2 and MJD1 gene in some PD patients described previously provided a better understanding of these associations.1–5 The high prevalence of SCA2 mutation in FPD1–5 and the report of Parkinsonism in a SCA3/MJD patient in Taiwan6 prompted us to determine the SCA2 and the SCA3/MJD frequency in PD patients in mainland China, assessing the necessity of SCA testing in Parkinsonism genetic analysis.
To investigate the prevalence and clinical feature(s) of Parkinson's disease (PD) patients with expanded (ATXN2 and MJD1) genes of spinocerebellar ataxia type 2 and 3 (SCA2 and SCA3/MJD) in a mainland Chinese population, CAG triplet repeat expansions of (SCA2 and SCA3/MJD) genes (ATXN2 and MJD1) were analyzed in a cohort of 452 PD patients, including 386 sporadic and 66 familial forms. Striatal dopamine transporter was evaluated in two SCA2 and two SCA3/MJD-positive family members, an idiopathic PD patient and a healthy control using carbon (C11) [11C]-radiolabeled-CFT positron emission tomography (PET). We found two patients in one familial PD (FPD) family (1.5%) and two sporadic PD patients (0.5%) with expanded CAG repeats in the ATXN2 locus, four patients in two FPD families (3%) and another three sporadic PD patients (0.8%) in the MJD1 locus. [11C]-CFT PET in detected members in SCA2 and SCA3/MJD families showed decrements of 11C-CFT uptake. These findings suggest that a mutation in SCA2 or SCA3/MJD may be one of the genetic causes of PD. © 2009 Movement Disorder Society
PATIENTS AND METHODS
Genetic analysis for expanded CAG repeats in the ATXN2 and MJD1 gene was carried out in 452 PD patients (including 386 sporadic and 66 index cases of familial forms; among the familial cases, 26 were compatible with autosomal dominant (AD) and 40 with autosomal recessive (AR) transmission) recruited over 6-years. All patients were under the supervision of the senior neurologist (B.-S.T.). All patients fulfilled the criteria of possible or probable PD proposed by Gelb et al.7 with a good and sustained response to levodopa (L-dopa). Informed consent was obtained from all the participants. Mutations in α-Synuclien and LRRk2 in the AD Parkinsonian families as well as Parkin, DJ-1, and Pink1 in the AR parkinsonian families were previously excluded by direct sequencing and gene dosage analyses.
For sizing of SCA2 and SCA3 expansions, fluorescence-polymerase chain reaction products were analyzed on an ABI-Prism 3100 automatic sequencer (PE Applied Biosystems, Foster City, CA) using the GS500 size standard. For sequence analysis of the ATXN2 and MJD1 alleles, “TA cloning” strategy were used as previously reported.1
[11C]-CFT PET Imaging
After obtaining informed consent, four affected members (AII-4, AIII-1, BI-2, and BII-2) from Families A and B, an idiopathic PD patient and a healthy control underwent the [11C]-CFT (2-b-carbomethoxy-3b-(4-fluorophenyl)tropane) Positron emission tomography (PET) using the methods previously described.8
Molecular Genetic Analysis
Among the total of 452 patients, two patients from an AD FPD family (Family A) (Fig. 1) and two sporadic patients (Cases S-1 and S-2) were identified to have an expanded SCA2 allele. Four symptomatic patients from two families (Families B and C) (Fig. 1) with AD FPD and three sporadic patients (Cases S-3, S-4, and S-5) were affected with SCA3/MJD. There were six males and five females with the onset age ranging from 25 to 67 years. The frequency of SCA2 and SCA3/MJD is 1.5 and 3% in FPD, and 0.5 and 0.8% in sporadic Parkinsonism, respectively.
CAG repeats in our PD patients with ATXN2 expansion had 36/22, 36/22, 36/22, and 37/22 CAG repeats (Table 1). The sequence of all the expanded CAG repeats was (CAG)n(CAA)(CAG)8. The 22 repeat alleles were all (CAG)13(CAA)(CAG)8. For PD patients with an expanded MJD1 allele, the CAG expansions ranged from 58 to 73 repeats (Table 1), and not interrupted by other trinucleotide variants.
|Age at symptom onset, years||42||35||29||37||46||25||40||39||67||36||38|
|Disease durationa, years||10||1||3||3||12||5||18||5||8||6||4|
|Abnormal gait or posture||+||+||−||+||+||+||+||−||+||+||+|
|UPDRS motor scoreoff||65||38||38||35||53||36||62||40||38||58||38|
|UPDRS motor scoreon||32||18||23||24||37||21||47||24||21||26||24|
|Hoehn and Yahr stage||4||2||1.5||1.5||3||3||4||3||3||3||1.5|
|No. of CAG repeats||36/22||36/22||37/22||36/22||65/14||69/18||73/14||67/14||58/20||64/14||67/14|
Table 1 also lists the main clinical and genetic features of 11 PD patients with an SCA2 or SCA3/MJD mutation. All the patients suffered from bradykinesia and rigidity; however resting tremor was absent in AIII-1, CII-3, and S-3. Asymmetric symptoms were lacking in two patients. Parkinsonism overlapped by ataxia as well as notable symptom variations was observed primarily in Family C. For example, CI-1 (Fig. 1), a septuagenarian, only noted a tremor in his left leg. No obvious bradykinesia was reported and his daily motor faculties were not affected until his death. CII-7 presented typical Parkinsonism that could be treated with dopaminergic medications. However, L-dopa did not alleviate bradykinesia or rigidity in CII-3, and on examination, obvious ataxia was observed. In Family B, BII-2 presented ataxic symptoms including intention tremor and slow saccades that did not observed in BI-2. It should be noted that the greater severity of ataxia presented larger expansions of CAG repeats in patients from both families. An earlier onset age in the younger generation was observed in Families B and C with SCA3/MJD (Fig. 1 and Table 1). The CAG repeats after the CAA and AAG variant were intact in Families B and C.
A marked bilateral and symmetrical decrement of 11C-CFT uptake was found in all detected patients and one idiopathic PD control (Fig. 2). The uptake of 11C-CFT was markedly reduced in the putamen and caudate, especially in the putamen. The simple ratios of the radioactivity of the caudate nucleus and the putamen, respective to that of the cerebellum, were calculated. The results of the ratios (mean ± SD) in four SCA patients, one IPD control and one healthy control were 1.27 ± 0.11, 1.23 and 3.66 in caudate, whereas 1.12 ± 0.25, 0.90 and 3.45 in putamen, respectively. Brain MRI scans on individuals AII-4, AIII-1, BI-2, and BII-2 were all normal (data not shown).
Recent reports suggest that CAG triplet expansions of ATXN2 and MJD1 genes can cause L-dopa responsive Parkinsonism.1–6 In our study, we studied a large cohort of PD patients, including 386 sporadic and 66 familial cases, confirming that SCA2 and SCA3/MJD mutations may exclusively manifest as L-dopa-responsive Parkinsonism. In contrast to the literature, in mainland China, we detected the SCA2 and SCA3/MJD mutation not only among familial cases but also in sporadic PD patients; as far as we know, this is the largest screening for SCA2 and SCA3/MJD expansions in a cohort of PD patients.
To date, all of the observations would suggest a prevalence (1.3–10%) and (0.4–0.5%) of SCA2 mutations among cases of familial and sporadic PD patients respectively.1–5, 9, 10 Both are similar to our result 1.5% and 0.5% respectively, suggesting that SCA2 is a rare genetic cause of sporadic than familial Parkinsonism in our population. The majority of reports of SCA3/MJD studies in Parkinsonism were cases of FPD with Chinese and African ethnicities.6, 11 But to date, no accurate frequency has been achieved in PD patients with SCA3/MJD mutation. In our study, we found the frequency of SCA3/MJD mutation is about 3% in FPD. Interestingly, we found SCA3/MJD also attributes to about 0.8% of sporadic PD patients in mainland China. As far as we know, this is the first report of SCA3/MJD mutation in sporadic PD patients.
In SCA2, CAG repeats are interrupted by CAA in the majority of normal alleles, whereas the expanded alleles of high range repeats consist of an uninterrupted stretch of CAG.10 Patients with SCA2-related Parkinsonism CAG repeats were interrupted by CAA, CCG, and CGG.2, 12, 13 In our PD patients, CAG repeat expansions were all (CAG)n(CAA)(CAG)8. Interestingly, the CAA interruptions in the normal alleles were all at the same site in the CAG stretch: the ninth site before the CAG end. Taken together, these data suggest that ethnicity may influence the intrinsic molecular structure, which may involve the Parkinsonian phenotype of SCA2.
Patients with SCA-related Parkinsonism always possess a smaller pathological CAG expansion and a later age of onset compared with the SCA “spinocerebellar” phenotype.13 The CAG repeats were 33 to 47 in patients with SCA2-associated Parkinsonism and 61 to 81 in patients with SCA3/MJD-associated Parkinsonism.1–6, 9–11 In our patients with SCA-associated Parkinsonism, the CAG repeat expansion were 36–37 in SCA2, 58–73 in SCA3/MJD. The “spinocerebellar” phenotypes of SCA2 and SCA3/MJD patients in mainland China, the CAG repeats were 42–47 and 68–83, respectively.14 In the two SCA3/MJD families reported here, patients of inter-generation (BII2) and intrageneration (CII3) with larger expansions presented more severe ataxia, consistent with the previous reports. Our finding further supports the theory that low-range CAG expansion repeats might have a role in determining phenotypes.1–3, 13 While some patients in the low-range expansion can also present with predominant ataxia.2 As a result, further studies are required to determine why CAG repeats in the low-range expansion manifest Parkinsonism in some patients and ataxia in others.
PET can permit the in vivo comparison of the underlying nigrostriatal deficit in familial and sporadic PD patients.8 There have been publications on PET research in SCA2 patients with Parkinsonism1, 5, 13; however, this is the first report on functional neuroimaging with a dopamine transporter ligand [11C]-CFT in SCA3/MJD presenting as Parkinsonism. A marked decrement of [11C]-CFT striatal uptake was in all detected patients. Interestingly, the motor disability in these four patients appeared less severe when compared with the magnitude of their [11C]-CFT striatal uptake decrement; especially for patients AIII-1 and BII-2. Although the disease duration in our patients (ranging 1–12 years) is rather diverse, the severe [11C]-CFT striatal uptake decrements are comparable with those reported in the other PET studies of patients with advanced PD.8
In summary, to the best of our knowledge, this is the largest screening for SCA2 and SCA3/MJD expansions in a cohort of PD patients. Our data confirm that mutation in SCA2 and SCA3/MJD is one of the genetic causes of familial and sporadic PD in mainland China, as a result, we suggest including this molecular test in the genetic screening of PD patients, especially those with family history. This is the first time the status of SCA3/MJD-associate Parkinsonism and the nigrostriatal dopaminergic system was evaluated using [11C]-radiolabeled-CFT PET. [11C]-radiolabeled-CFT PET can provide a useful way to measure the degree of nigrostriatal dopaminergic damage in SCA2 and SCA3/MJD-related Parkinsonism.
This work was supported by Projects in the National Science and Technology Pillar program in the Eleventh Five-year Plan Period (2006BAI05A07) (B.-S.T.), the National High-Tech Research and Development Program of China (863 Program) (2006AA02A408) (B.-S.T.), the Major State Basic Research Development Program of China (973 Program) (2006cb500700) (B.-S.T.), the National Key Technologies Research and Development Program of China (2004BA720A03) (B.-S.T.), the National Natural Science Foundation of China (B.-S.T.), and the Graduate degree thesis Innovation Foundation of Central South University (2008yb030) (J.-L.W.). We thank all the patients and family members for their generous participation in this work.
Study concept and design (Wang, Xiao, Tang); acquisition of data (Wang, Xiao, Cui, Lei, Song); analysis and interpretation of data (Guo, Shen, Jiang); drafting of the manuscript (Wang, Yan, Pan, Long); critical revision of the manuscript for important intellectual content (Yan, Pan, Xia, Tang); obtained funding (Tang); administrative, technical, and material support (Wang, Xiao, Cui, Lei, Song, Shen, Jiang, Yan, Pan, Xia, Tang); study supervision (Wang, Xiao, Shen, Jiang, Xia, Tang).