Comparison of phosphodiesterase 10A and dopamine transporter levels as markers of disease burden in early Parkinson's disease.

BACKGROUND: Recent work has shown loss of phosphodiesterase 10A levels in middle-stage and advanced treated patients with PD, which was associated with motor symptom severity. OBJECTIVES: To assess phosphodiesterase 10A levels in early PD and compare with loss of dopamine transporter as markers of disease burden. METHODS: Seventy-eight subjects were included in this study (17 early de novo, 15 early l-dopa-treated, 24 moderate-advanced l-dopa-treated patients with PD, and 22 healthy controls). All participants underwent [11 C]IMA107 PET, [11 C]PE2I PET, and 3-Tesla MRI scan. RESULTS: Early de novo PD patients showed loss of [11 C]IMA107 and of [11 C]PE2I binding in caudate and putamen (P < 0.001); early l-dopa-treated PD patients showed additional loss of [11 C]IMA107 in the caudate (P < 0.001; annual decline 3.6%) and putamen (P < 0.001; annual decline 2.8%), but loss of [11 C]PE2I only in the putamen (P < 0.001; annual decline 6.8%). Lower [11 C]IMA107 correlated with lower [11 C]PE2I in the caudate (rho = 0.51; P < 0.01) and putamen (rho = 0.53; P < 0.01). Longer disease duration correlated with lower [11 C]IMA107 in the caudate (rho = -0.72; P < 0.001) and putamen (rho = -0.48; P < 0.01), and with lower [11 C]PE2I only in the putamen (rho = -0.65; P < 0.001). Higher burden of motor symptoms correlated with lower [11 C]IMA107 in the caudate (rho = -0.42; P < 0.05) and putamen (rho = -0.41; P < 0.05), and with lower [11 C]PE2I only in the putamen (rho = -0.69; P < 0.001). CONCLUSION: Our findings demonstrate loss of phosphodiesterase 10A levels very early in the course of PD and is associated with the gradual and progressive increase of motor symptoms. Phosphodiesterase 10A imaging shows similar potential with dopamine transporter imaging to follow disease progression. © 2019 International Parkinson and Movement Disorder Society.

Nigrostriatal dysfunction in homozygous and heterozygous parkin gene carriers: an 18F-dopa PET progression study.

Little is known about the rate of progression of striatal dysfunction in subjects with parkin-linked parkinsonism. Being a heterozygous parkin gene carrier may confer susceptibility to Parkinson's disease (PD). In a previous (18)F-dopa PET study, we reported that 69% of carriers of a single parkin mutation showed subclinical loss of putamen dopaminergic function. Using serial (18)F-dopa PET, the present longitudinal study addresses rates of progression of nigrostriatal dysfunction in both compound heterozygous (parkin-linked parkinsonism) and single heterozygous parkin gene carriers. Three symptomatic patients who were compound heterozygotes for parkin gene mutations and six asymptomatic heterozygous carriers were clinically assessed and had (18)F-dopa PET at baseline and again after 5 years. The patients with symptomatic parkin showed a mean 0.5% annual reduction in putamen (18)F-dopa uptake over 5 years while caudate (18)F-dopa uptake declined by a mean annual rate of 2 %. The asymptomatic heterozygote gene carriers showed a mean 0.56% annual reduction in putamen and 0.62 % annual reduction in caudate (18)F-dopa uptake. Neurological examination at both baseline and follow-up showed no evidence of parkinsonism. Loss of nigrostriatal dysfunction in parkin-linked parkinsonism occurs at a very slow rate compared to the 9-12% annual loss of putamen (18)F-dopa uptake reported for idiopathic PD. Although subclinical reductions of striatal (18)F-dopa uptake are common in carriers of a single parkin mutation their slow rate of progression suggests that few if any of these will develop clinical parkinsonism.

Motor cortical physiology in patients and asymptomatic carriers of parkin gene mutations.

Autosomal recessive parkin (PARK2) gene-related parkinsonism may be phenotypically and pathophysiologically distinct from idiopathic Parkinson's disease (PD). Furthermore, asymptomatic subjects carrying a single parkin mutation ("parkin carriers") may show striatal dopaminergic dysfunction and increased cortical movement-related activation. Here, we used transcranial magnetic stimulation (TMS) to study corticospinal and intracortical excitability in manifesting parkin patients and asymptomatic carriers. We studied resting and active motor thresholds (RMT/AMT), central motor conduction time (CMCT), active recruitment curves, short-interval intracortical inhibition (SICI) and facilitation (ICF), SICI recruitment curve, and cortical silent period (CSP) in 8 patients "off" medication, 7 carriers, and two groups of age-matched controls (n = 21). Patients had longer CMCTs compared to controls with a significant negative correlation between CMCT duration and onset age (r = -0.83, P = 0.04). Carriers had increased RMT/AMT; the time course of SICI/ICF and the duration of CSP were normal in both patients and carriers; however slight abnormalities in the recruitment of SICI were found in the carriers. Prolonged CMCT and normal cortical inhibitory mechanisms in parkin patients may be of value in the differentiation from idiopathic PD. The subclinical electrophysiological abnormalities found in carriers may represent underlying compensatory mechanisms.

Mutations in the gene LRRK2 encoding dardarin (PARK8) cause familial Parkinson's disease: clinical, pathological, olfactory and functional imaging and genetic data.

We have established that the frequency of LRRK2 mutations in a series of 118 cases of familial Parkinson's disease is 5.1%. In the largest family with autosomal dominant, late-onset Parkinson's disease where affected subjects share a Y1699C missense mutation we provide a detailed clinical, pathological and imaging report. The phenotype in this large British kindred included asymmetrical, levodopa-responsive parkinsonism where unilateral leg tremor at onset and foot dystonia were prominent features. There was no significant abnormality of cognition but there was prominent behavioural disorder. We observed a lower age of onset in successive generations. Histopathology in one patient showed substantia nigra cell loss and Lewy body formation, with small numbers of cortical Lewy bodies. 18F-dopa positron emission tomography (PET) in another patient showed a pattern of nigrostriatal dysfunction typical of idiopathic Parkinson's disease. 18F-dopa-PET scans in unaffected family members prior to identifying the disease locus did not detect subclinical nigrostriatal dysfunction. Olfaction was assessed in affected subjects and Lewy bodies were identified in the olfactory bulb as well as cortex and brainstem of one deceased patient. In order to assess the role of mutations in this gene in other familial cases we undertook a mutation screen of all 51 exons of LRRK2 in 117 other smaller British kindreds with familial Parkinson's disease. The commonest mutation was G2019S and we also identified two novel mutations, R1941H and T2356I, in the coding sequence. These data suggest that parkinsonism caused by mutations in LRRK2 is likely to represent the commonest locus for autosomal dominant Parkinson's disease with a phenotype, pathology and in vivo imaging similar to idiopathic, late-onset Parkinson's disease.

Marfan syndrome presenting with headache and coincidental ophthalmic artery aneurysm.

A 24-year-old Ugandan woman was referred for a neurology opinion after complaining of a year long history of right-sided retro-orbital stabbing pain. Brain imaging revealed a coincidental 3 mm left ophthalmic artery aneurysm. Marfanoid habitus was noted; after further investigations she was diagnosed with mild aortic root dilatation, subtle lens dislocation and Marfan syndrome. Her symptoms were secondary to temporomandibular joint dysfunction, an under-recognised complication of Marfan syndrome. Her ophthalmic artery aneurysm is likely to be a coincidental finding.

In vivo assessment of brain monoamine systems in parkin gene carriers: a PET study.

PET studies in parkin-linked parkinsonism have generally been performed to assess striatal dopaminergic dysfunction and very little is known about the involvement of other monoaminergic structures in these patients. Measurements of (18)F-dopa uptake into serotonergic and noradrenergic structures provide an indication of the functional integrity of these nerve terminals. We used (18)F-dopa PET to assess changes in brain monoaminergic function associated with parkin mutations. Twelve patients with parkin-linked parkinsonism and 12 asymptomatic parkin heterozygotes were included in the study. Eleven healthy controls, 12 patients with idiopathic Parkinson's disease (IPD), and four patients with PINK1 mutations were also investigated for comparison. parkin patients and IPD patients were matched for striatal dopaminergic dysfunction, as measured by (18)F-dopa uptake. Compared to controls, parkin patients showed significant (18)F-dopa reductions in the caudate, putamen, ventral striatum, locus coeruleus, midbrain raphe, and pallidum. The same structures showed reduced uptake in IPD patients, who additionally had significant reductions in hypothalamus, ventral anterior thalamus, and pineal gland. Direct comparison of parkin with IPD patients showed that hypothalamus was targeted in IPD and midbrain raphe in parkin disease. Patients with PINK1 mutation and several parkin heterozygotes also showed monoaminergic dysfunction. These findings suggest that parkin patients and IPD patients with similar striatal dysfunction have different patterns of monoaminergic involvement, with more widespread dysfunction in IPD.

Upregulation of dopamine D2 receptors in dopaminergic drug-naive patients with Parkin gene mutations.

Medicated patients with Parkinsonism and parkin gene mutations have been reported to show a significant decrease in striatal dopamine D2 receptors (D2R) in comparison to medicated idiopathic Parkinson's disease (IPD) patients with similar age and disease severity. The aim of this study was to verify whether the genetic defect per se is responsible for this decrease. We have studied with [11C]raclopride (RAC) positron emission tomography (PET) in a group of 14 sporadic patients with parkin-linked Parkinsonism, 6 of whom had never received levodopa or dopamine agonists. The remaining 8 patients had been treated with levodopa for at least 5 years. Presynaptic striatal [18F]dopa storage was not significantly different between these two groups of patients. In untreated parkin-positive patients, significant putaminal increases in RAC-binding potential (BP) were found in comparison to an age-matched healthy control group by using a classical region of interest approach and statistical parametric mapping. In contrast, levodopa-treated parkin-positive patients showed significant decreases in RAC-BP in the caudate and putamen when compared to an age-matched healthy control group. The RAC PET findings revealed that striatal D2R upregulation occurs in dopaminergic drug-naive parkin-positive patients, in a similar fashion to the upregulation reported in drug-naive IPD. D2R downregulation observed in medicated parkin-positive patients, therefore, is not caused primarily by the genetic defect itself. Parkin-positive patients appear to have a greater susceptibility to the exposure to dopaminergic medication than IPD patients, which in turn might be an indirect effect of their genetic mutation.

Nigral degeneration and striatal dopaminergic dysfunction in idiopathic and Parkin-linked Parkinson's disease.

We have used MR segmented inversion recovery ratio imaging (SIRRIM) of the substantia nigra pars compacta to detect and correlate nigral signal change in idiopathic Parkinson's disease (PD) and parkin patients with striatal (18)F-dopa uptake. Nine PD patients, nine parkin patients, and eight control subjects were studied with a combination of MR inversion recovery sequences sensitive to nigral cell loss. Blinded independent observer rating and quantified nigral signal analysis were performed on all subjects. Striatal regions of interest were defined on T(1)-weighted MRI co-registered to (18)F-dopa positron emission tomography. On blinded observer rating of the SIRRIM dorsal and ventral nigral images, 25% (2/8) of control subjects, 44% (4/9) of PD patients, and 67% (6/9) of parkin patients were classified as abnormal. Quantified total nigral signal intensities were reduced to a greater extent in the parkin compared to PD patients. There was a greater predilection for signal reduction in the ventral nigral slice of the PD compared to the parkin patient group, who showed a more uniform involvement. All PD and parkin patients were discriminated from controls on the basis of caudate and putamen (18)F-dopa Ki reductions. Our results suggest that MR segmented inversion recovery ratio imaging shows poor sensitivity for discriminating parkin and idiopathic PD patients from normal controls. Where nigral signal abnormalities were seen, parkin patients manifested generalized nigral cell loss with widespread striatal dopamine terminal dysfunction compared with the lateral nigral targeting seen in PD and selective loss of putamen (18)F-dopa uptake.

Parkinsonism and nigrostriatal dysfunction are associated with spinocerebellar ataxia type 6 (SCA6).

SCA6 is a slowly progressive, late-onset cerebellar ataxia due to a trinucleotide expansion in the CACNA1A gene. We describe two unrelated cases that presented with Parkinsonism and cerebellar ataxia. One case was L-dopa-responsive with a pattern of (18)F-dopa uptake similar to Parkinson's disease, and the second case was not L-dopa-responsive and had an atypical pattern of nigrostriatal dysfunction. We suggest that SCA6, in common with SCA2 and SCA3, may be associated with Parkinsonism attributable to nigral loss and dopaminergic dysfunction. Moreover, isolated cases may be confused with multiple system atrophy.

Parkin disease in a Brazilian kindred: Manifesting heterozygotes and clinical follow-up over 10 years.

We report on a large Brazilian kindred with young-onset parkinsonism due to either a homozygous or heterozygous mutation in parkin. A total of 6 members were affected: 5 were homozygous and 1 heterozygous for a deletion in exon 4. Two other heterozygotes also had extrapyramidal signs. All affected subjects showed characteristic features of parkin disease with foot dystonia and an excellent response to levodopa complicated by motor fluctuations and dyskinesia within 3 years of therapy. Careful clinical follow-up over 10 years showed the phenotype was similar in all the homozygotes with asymmetrical limb bradykinesia and early walking difficulties. Some acceleration of disability was observed in some of the cases as they entered the third decade of illness, but dementia was absent.