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- PATIENTS AND METHODS
Myocardial 123Metaiodobenzylguanidine (MIBG) enables the assessment of postganglionic sympathetic cardiac innervation. MIBG uptake is decreased in nearly all patients with Parkinson's disease (PD). Our objective was to evaluate MIBG uptake in patients with genetic PD. We investigated MIBG uptake in 14 patients with PD associated with mutations in different genes (Parkin, DJ-1, PINK1, and leucine-rich repeat kinase 2 -LRRK2), in 15 patients with idiopathic PD, and 10 control subjects. The myocardial MIGB uptake was preserved in 3 of the 4 Parkin-associated Parkinsonisms, in 1 of the 2 patients with DJ-1 mutations, in 1 of the 2 brothers with PINK1 mutations, in 3 of the 6 unrelated patients with Gly2019Ser mutation in the LRRK2 gene, whereas it was impaired in all patients with idiopathic PD. MIBG was preserved in all control subjects. Our study shows that myocardial MIGB uptake was normal in 8 of 14 patients with genetic PD, suggesting that cardiac sympathetic denervation occurs less frequently in genetic PD than in idiopathic PD. Our findings also demonstrate that MIGB uptake has a heterogeneous pattern in genetic PD, because it was differently impaired in patients with different mutations in the same gene or with the same gene mutation. © 2007 Movement Disorder Society
In addition to motor symptoms, autonomic abnormalities have been reported in Parkinson's disease (PD). Recently, several studies have investigated the usefulness of myocardial scintigraphy with 123Metaiodobenzylguanidine (MIGB) in assessing the sympathetic nerve terminals in PD demonstrating that MIGB is decreased in nearly all patients with PD.1–4 The reduction of MIGB uptake, which indicates cardiac sympathetic denervation,5 was also seen in PD patients at the earliest stage of the disease and in PD patients without significant autonomic dysfunction suggesting that postganglionic damage may occur early in PD.6, 7 Differing from PD, other studies showed normal MIGB uptake in multiple system atrophy and in patients with progressive supranuclear palsy, suggesting that myocardial scintigraphy may be helpful in differentiating PD from these parkinsonian syndromes.4–6, 8 Recently, it has been reported that MIGB was normal in 4 patients with early-onset PD (EOPD) and mutations in the Parkin gene,9, 10 while it was reduced in patients with EOPD carrying mutations in the α-synuclein gene.11 In our report, we studied the myocardial scintigraphy with MIGB in patients with PD associated with mutations in Parkin, DJ-1, PINK1, and leucine-rich repeat kinase 2 (LRRK2) genes.
PATIENTS AND METHODS
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- PATIENTS AND METHODS
Our study involved 14 patients with genetic PD, 15 patients with idiopathic PD, and 10 control subjects. Of the 14 patients with genetic PD, 4 (2 of whom were siblings) carried Parkin mutations; 2 unrelated patients carried DJ-1 mutations, 2 brothers carried PINK1 mutations, and 6 (1 with a family history and 5 apparently sporadic) carried the Gly2019Ser mutation in the LRRK2 gene. Patients with idiopathic PD were negative for Gly2019Ser and Ile2020Thr mutations in the LRRK2 gene. PD was diagnosed according to the criteria of the UK Parkinson's disease Society Brain Bank. All patients were assessed using the Unified Parkinson's Disease Rating Scale motor score (UPDRS-ME), and Hoehn and Yahr (H&Y) rating scales in an “off” phase (off medications overnight). Autonomic testing was performed on all patients. The sympathetic skin response was recorded from the palmar hand surfaces in response to electrical stimuli applied to the median nerve at the wrist. Heart rate responses to respiratory change (deep breathing test) and the standing test for postural hypotension assessment were also performed as previously described.12 All patients were treated with levodopa plus dopa decarboxylase inhibitor with or without dopamine agonists (4 of the 14 genetic PD patients and 5 of the 15 patients with idiopathic PD were taking dopamine agonists; one of the patients with genetic PD was taking amantadine). Cerebral magnetic resonance imaging was normal in all patients. Ten healthy subjects also participated in our study. Exclusion criteria for patients and controls were: diabetes, a history of neuropathy, previous relevant cardiac disease, or any other medical condition that could affect the autonomic nervous system or the myocardial MIBG uptake. No subject was taking drugs known to interfere with MIBG uptake in sympathetic nerve terminals. Written informed consent was obtained from each participant in the study.
Myocardial MIBG scintigraphy was performed at rest. A total of 111 MBq of 123I-MIGB (Amersham, Eindhoven, NL) was injected intravenously in 60 s. Data were collected using a dual head gamma camera (Axis, Picker, Bedford, OH) at 10 min (early image) and 240 min (delayed image) after the isotope injection. Static planar imaging and regional MIBG uptake were obtained with 128 × 128 matrix. Only planar images in thoracic anterior view were used for quantitative evaluation. Regions of interest (ROI) were drawn around the whole heart and mediastinum of the anterior image, and tracer uptake was measured within each ROI to calculate the heart/mediastinum (H/M) ratio. The H/M ratio from early and delayed images was evaluated in all subjects, and values were considered abnormal if they were more than three standard deviations below the respective control mean. Regional MIBG uptake was assessed using single-photon emission tomography (SPECT) on the three axes display (short axis, vertical long axis, and horizontal long axis). Images were evaluated by an investigator who was blinded to the patients' diagnosis.
Blood samples for genetic analysis were collected after obtaining informed consent from all the patients and controls. DNA was prepared using standard methods. We investigated 14 patients for Parkin, DJ-1, and PINK1, and 29 patients for Gly2019Ser and Ile2020Thr mutations in the LRRK2 gene. For sequence analysis, the coding region of Parkin, DJ-1, PINK1, and the exon 41 of the LRRK2 gene were amplified by PCR using intronic primers. Dideoxy cycle sequencing was performed with ABI PRISM sequencing kit according to the manufacturer's protocols. This was followed by exon sequencing on ABI 3130-XL Avant automated DNA sequence analyzers.
The differences in continuous variables (mean age and H/M ratio) between idiopathic PD, genetic PD, and controls were assessed using one-way analysis of variance, followed by unpaired t test corrected according to Bonferroni for multiple comparisons. χ2 test was used to compare sex distribution among groups. The difference in Hoehn-Yahr and UPDRS-ME scores between idiopathic and genetic PD groups were assessed using Mann-Whitney U test, while unpaired t test was calculated for age at onset and levodopa dosage. Mann-Whitney U test and unpaired t test were also used to compare genetic PD patients with low and normal H/M ratios.
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Characteristics of patients and controls are shown in Tables 1 and 2. All patients with PD (genetic and idiopathic) had a good response to levodopa. Only one patient with genetic PD (LRRK2-I) had autonomic dysfunction (sympathetic skin response absent; deep breathing test and postural evaluation of blood pressure were abnormal), whereas dysautonomia was never found in sporadic PD patients.
Table 1. Characteristic and H/M ratio in patients with genetic and idiopathic Parkinson's disease (PD), and controls
|Variables||Genetic PD (N = 14)||Idiopathic PD (N = 15)||Controls (N = 10)||P-value|
|Mean age ± SD, yr||58.29 ± 12.46||69.47 ± 6.41||63.10 ± 5.53||0.007|
|Sex (N, % male)||8 (57.1)||9 (60.0)||5 (50.0)||0.883|
|Mean age ± SD at onset, yr||41.57 ± 11.99||66.33 ± 6.83||–||<0.001|
|Duration of the disease, mean ± SD, yr||16.80 ± 11.90||3.13 ± 3.64||–||<0.001|
|Hoehn–Yahr median (range)||2.5 (2-4)||2.0 (1-4)||–||0.001|
|UPDRS-ME||38.29 ± 14.69||22.93 ± 12.84||–||<0.001|
|Dosage of levodopa (mg/daily, mean ± SD)||566.07 ± 166.30||426.67 ± 237.45||–||0.08|
|H/M ratio mean ± SD (range)|| || || || |
| Early image||1.45 ± 0.30 (1.13-2.0)||1.16 ± 0.02 (1.13-1.19)||1.69 ± 015 (1.47-1.94)||<0.001|
| Delayed image||1.61 ± 0.40 (1.13-2.0)||1.17 ± 0.02 (1.13-1.19)||1.98 ± 0.06 (1.91-2.07)||<0.001|
Table 2. H/M ratio in patients with genetic Parkinson's disease
|Gene||Sex/Age||Onset||H-Y||Therapy (mg/die)||Mutation||H/M ratio|
|Parkin|| || || || || || || |
|I||M/39||30||3.0||LD 600||202-203delAG hom.||1.46||2.0|
|II||M/47||37||2.0||LD 500||exon 3del hom.||1.73||1.92|
|IIIa||F/54||42||2.0||LD 600b||exon 3-4del hom.||1.15||1.15|
|IVa||M/59||43||2.5||LD 600b||exon 3-4del hom.||1.73||1.96|
| || || || || || || || |
|DJ-1|| || || || || || || |
|I||M/47||38||2.5||LD 750||g.159 C/G and IVS4+2insA||1.45||1.97|
|II||M/38||24||3.0||LD 750||g.168_185 dup hom. and E163K hom.||1.16||1.16|
| || || || || || || || |
|PINK-1|| || || || || || || |
|Ia||M/74||29||4.0||LD 500||889delG hom.||1.18||1.19|
|IIa||M/68||28||3.0||LD 500||889delG hom.||1.68||1.93|
| || || || || || || || |
|LRRK2|| || || || || || || |
|I||F/74||54||4.0||LD 750||Gly2019Ser het.||1.13||1.13|
|II||F/66||53||2.5||LD 500b||Gly2019Ser het.||1.18||1.19|
|III||F/62||43||3.0||LD 625||Gly2019Ser het||1.15||1.15|
|IV||M/50||42||2.0||LD 250||Gly2019Ser het||1.58||1.97|
|V||F/68||66||2.0||LD 250b||Gly2019Ser het.||1.77||1.85|
|VI||F/70||53||4.0||LD 750||Gly2019Ser hom.||2.0||2.0|
Mutation analyses showed three different mutations in the Parkin gene (a homozygous exon 3del in a subject with apparently sporadic EOPD, a homozygous 202-203delAG in another subject with apparently sporadic EOPD, and a homozygous exon 3-4del in two siblings with EOPD); a previously described homozygous mutation in exon 7 (E163K) and a homozygous mutation (g.168_185dup) in the promoter region of the DJ-1 gene in a patient with EOPD, dementia and amyotrophic lateral sclerosis,13 and two novel DJ-1 mutations, in a double heterozygous state (g.159 C/G, IVS4 + 2insA), in a patient with apparently sporadic EOPD (Tarantino P, et al., 2006; personal communication); a novel homozygous deletion 889delG mutation in the PINK-1 gene in 2 brothers with early-onset PD (Cirò Candiano IC, et al., 2006; personal communication). Mutation analysis of the Gly2019Ser in the LRRK2 gene showed the presence of the mutation in a homozygous state in a patient with familial late-onset PD (consanguineous parents, and deceased affected relatives in both maternal and parental ascendants; a living sibling with PD with the same homozygous genotype), and the presence of the mutation in a heterozygous state in 5 other patients with apparently sporadic late-onset PD (Table 2).
In the control group, the H/M ratio (mean ± SD) was 1.69 ± 0.15 in the early and 1.98 ± 0.06 in the delayed images, and the lower normal limit of the ratio (mean minus three SDs) was set at 1.23 and 1.81, respectively. The H/M ratio was significantly lower in the idiopathic PD group (early: 1.16 ± 0.02; delayed: 1.17 ± 0.02) than in both the genetic group (early: 1.45 ± 0.30; delayed: 1.61 ± 0.40, P < 0.001) and the control group (early: 1.69 ± 0.15; delayed: 1.98 ± 0.06, P < 0.001) (Table 1). In all idiopathic PD patients, the H/M ratios both in the early and delayed images were more than three standard deviations below the respective control mean. The H/M ratio of the genetic PD group significantly differed from that of the control group (early: P = 0.017; delayed: P = 0.003). However, patients with genetic PD showed a heterogeneous pattern of cardiac MIBG uptake. Indeed, 8 of 14 showed a normal MIBG uptake (early: 1.67 ± 0.18; delayed: 1.95 ± 0.05), whereas the remaining 6 patients had a decreased MIBG uptake (early: 1.16 ± 0.02; delayed: 1.16 ± 0.02), which was more than three SDs below the respective control mean (Table 2). More in detail, 3 of 4 patients carrying homozygous Parkin mutation, 1 of the 2 patients with DJ-1 mutations, 1 of the 2 brothers with PINK1 mutations, and 3 of 6 patients carrying the Gly2019Ser mutation in the LRRK2 gene had normal MIBG uptake, while the remaining 6 genetic PD patients (1 carrying homozygous Parkin mutations, 1 with DJ-1 mutations, 1 with PINK1 mutations, and 3 with LRRK2 mutations) showed markedly reduced cardiac tracer uptake (Table 2). MIGB uptake was also different in the affected siblings carrying homozygous mutations in the Parkin gene (see Fig. 1), and in the 2 affected brothers with homozygous PINK1 mutations (see Fig. 2).
Figure 1. Myocardial 123Metaiodobenzylguanidine (MIBG) planar anterior view and regional radiolabeled MIBG uptake 4 hr p.i., in siblings with homozygous exon 3-4 Parkin mutations. Planar anterior view of the Parkin-III patient (a) showed severe decrease of cardiac MIBG uptake, whereas MIBG uptake was normal in the Parkin-IV patient (b). Regional MIBG uptake in the Parkin-IV patient (c) showed high MIBG activity in all the regions of the heart.
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Figure 2. Myocardial 123Metaiodobenzylguanidine (MIBG) planar anterior view and regional radiolabeled MIBG uptake 4 hr p.i., in 2 brothers with homozygous PINK1 mutations. Planar anterior view of the patient PINK1-I (a) showed severe decrease of cardiac MIBG uptake, whereas MIBG uptake was normal in the PINK1-II patient (b). Regional MIBG uptake in the PINK1-II patient (c) showed high MIBG activity in all the regions of the heart.
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When genetic PD patients were categorized according to H/M ratio, no significant differences for any considered variable were found between patients with low H/M ratio (N = 6; age, mean 61.33 ± 13.72, P = 0.459; disease duration, mean 20.50 ± 12.44, P = 0.332; H-Y, median 3.0, range 2–4, P = 0.257; age at onset, mean 40.83 ± 12.25, P = 0.850; levodopa dosage, mean 620.8 ± 112.3, P = 0.304) and those with normal H/M ratio (N = 8; age, mean 56.12 ± 11.76; disease duration, mean 14.00 ± 11.49; H-Y, median 2.5, range 2–4; age at onset 42.12 ± 12.41; ledovopa dosage, mean 525.0 ± 194.6).
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- PATIENTS AND METHODS
Our study demonstrates that 8 of 14 patients with genetic PD due to mutations in different genes had preserved MIBG uptake, while all idiopathic PD patients showed markedly reduced cardiac MIBG uptake. Indeed, MIBG was normal in 3 of 4 patients with Parkin-associated Parkinsonism, in 1 of the patients with DJ-1 mutations, in 1 of the 2 brothers with PINK1 mutations, and in 3 of the 6 patients with the Gly2019Ser mutation in the LRRK2 gene.
MIBG is an analog of the norepinephrine with mechanisms of uptake and storage similar to those of the endogenous neurotransmitter.14 MIBG uptake reflects presynaptic sympathetic system integrity, and reduced myocardial uptake of the tracer suggests cardiac sympathetic dysfunction or denervation.15
There is evidence that most patients with PD display a marked decrease in cardiac MIBG uptake.1–4 Reduced MIBG uptake has been demonstrated in PD either in the early and in the late phases of the disease or in absence of autonomic dysfunction, indicating that MIBG myocardial scintigraphy may contribute to the early diagnosis of PD, and to the early detection of silent autonomic dysfunction.6, 7
A recent study4 conducted in a large series of patients with idiopathic PD showed that cardiac MIBG H/M ratio was lower in patients with more advanced disease, indicating that myocardial MIBG uptake may be inversely related to the severity of PD. At variance with this observation, our findings demonstrate that genetic PD group had a Hoehn-Yahr score and a MIBG H/M ratio higher than idiopathic PD group, and that genetic PD patients with a normal H/M ratio did not differ clinically from genetic PD patients with decreased MIBG uptake, suggesting that in patients with genetic PD postganglionic sympathetic denervation occurs independently from the severity of the disease.
Our findings extend previous studies conducted in a few patients with Parkin-associated Parkinsonism with no Lewy body pathology who showed preserved cardiac MIBG uptake.9, 10 Postmortem examination showed that tyrosine hydroxylase (TH)-immunoreactive nerve fibers in the epicardium were well preserved in patients with homozygous mutations in the Parkin gene,9 while these nerve fibers were markedly reduced or absent in subjects with idiopathic PD and pathologically confirmed Lewy body,9, 16 suggesting that the integrity of cardiac sympathetic nerves in Parkin-associated Parkinsonism may be related to the absence of Lewy body pathology, and may account for normal cardiac MIGB uptake. In accordance with these observations, pathologic evidences have demonstrated the presence of Lewy bodies in the sympathetic ganglia17 and in the postganglionic sympathetic nerves in the heart18 from patients with PD, indicating that Lewy body pathology itself might cause profound cardiac sympathetic denervation and low MIBG uptake.
Our study also shows that genetic PD patients displayed a heterogeneous pattern of cardiac MIBG uptake. Indeed, MIBG uptake varied among PD patients with mutations in different genes, among unrelated patients with different mutations in the same gene (1 of 2 patients with DJ-1 mutations, and 1 of the 4 Parkin-mutated patients had reduced cardiac MIBG uptake), and also among unrelated patients carrying the same gene mutation (3 of 6 patients carrying the Gly2019Ser mutation in the LRRK2 gene had markedly decreased cardiac MIBG uptake, whereas it was normal in the remaining 3 patients). Similar results have been recently reported in 5 patients from three small families from Japan with LRRK2 mutations.19 Two of these patients from the same family carrying the Gly2019Ser in the LRRK2 gene and 1 patient from another family with the Ile2020Thr mutation had normal cardiac MIBG uptake, while the remaining 2 patients from the third family carrying the Ile2020Thr mutation had decreased cardiac MIBG uptake.
Why genetic PD displays a heterogeneous pattern of cardiac MIBG uptake is still unknown. On the basis of the above-mentioned studies showing a link between Lewy pathology, cardiac sympathetic degeneration, and low MIBG uptake,5, 10, 17, 18 it can be hypothesized that genetic PD without Lewy bodies might show a normal cardiac MIBG uptake, while patients with genetic PD and Lewy body pathology might have decreased MIBG uptake. Recent studies in PD patients with mutation in Parkin or LRRK2 genes showed a pleomorphic range of pathologies with or without Lewy bodies. Indeed, Parkin-associated Parkinsonisms usually lack Lewy body pathology,20–22 but patients with mutations in the Parkin gene with Lewy bodies in the brain have been recently reported.23, 24 Similarly, it has been reported that PD patients with the Gly2019Ser may or may not have Lewy body pathology in the brain,25–28 while individuals with familial PD carrying other LRRK2 mutations, such as Ile2020Thr, Tyr1699Cys, do not have Lewy bodies in the brain.29, 30 Taken together, these findings suggest that genetic PD patients carrying the same gene mutation or different mutations in the same gene may have pleomorphic neuropathology (positive or negative Lewy bodies), which in turn might cause heterogeneous cardiac MIBG uptake.
It is noteworthy that a heterogeneous MIBG uptake was observed in our siblings with homozygous Parkin mutations (1 of them had normal cardiac MIBG uptake) and in the 2 brothers with homozygous PINK1 mutations (1 subject had normal MIBG while his brother showed markedly decreased cardiac MIBG uptake), suggesting that the same gene mutation might be associated with pleomorphic Lewy pathology also in individuals from the same family. Pathologic evidence supports this hypothesis. Indeed, some authors19 reported that 1 patient with Ile2020Thr mutation in the LRRK2 gene from the Sagamihara family had Lewy body pathology, while most of the other members of his family were negative for Lewy bodies.
There are some limitations to this study. We lack pathologic data, and we do not know whether our patients with genetic PD and impaired MIBG cardiac uptake have Lewy body pathology in the brain and sympathetic nerve endings. However, at present, very few pathologic data have been reported on sympathetic nerve fibers in genetic PD, and no evidence exists concerning pathologic findings in brain and sympathetic nerve endings in subjects with homozygous PINK1 or DJ-1 mutations.
In conclusion, differing from idiopathic PD, patients with genetic PD can show normal or decreased cardiac MIBG uptake, suggesting that cardiac MIBG scintigraphy is not useful to distinguish patients with genetic PD from those with idiopathic PD. Whether this heterogeneous pattern of cardiac MIBG uptake is related to the presence or the absence of Lewy body pathology in cardiac sympathetic nerves remains to be determined.