Dopamine D2 receptor binding and cerebral glucose metabolism recover after D-penicillamine-therapy in Wilson's disease

Distribution of non-ceruloplasmin-bound copper after i.v. 64Cu injection studied with PET/CT in patients with Wilson disease

Background & Aims

In Wilson disease (WD), copper accumulation and increased non-ceruloplasmin-bound copper in plasma lead to liver and brain pathology. To better understand the fate of non-ceruloplasmin-bound copper, we used PET/CT to examine the whole-body distribution of intravenously injected 64-copper (64Cu).

Methods

Eight patients with WD, five heterozygotes, and nine healthy controls were examined by dynamic PET/CT for 90 min and static PET/CT up to 20 h after injection. We measured 64Cu activity in blood and tissue and quantified the kinetics by compartmental analysis.

Results

Initially, a large fraction of injected 64Cu was distributed to extrahepatic tissues, especially skeletal muscle. Thus, across groups, extrahepatic tissues accounted for 45-58% of the injected dose (%ID) after 10 min, and 45-55% after 1 h. Kinetic analysis showed rapid exchange of 64Cu between blood and muscle as well as adipose tissue, with 64Cu retention in a secondary compartment, possibly mitochondria. This way, muscle and adipose tissue may protect the brain from spikes in non-ceruloplasmin-bound copper. Tiny amounts of cerebral 64Cu were detected (0.2%ID after 90 min and 0.3%ID after 6 h), suggesting tight control of cerebral copper in accordance with a cerebral clearance that is 2-3-fold lower than in muscle. Compared to controls, patients with WD accumulated more hepatic copper 6-20 h after injection, and also renal copper at 6 h.

Conclusion

Non-ceruloplasmin-bound copper is initially distributed into a number of tissues before being redistributed slowly to the eliminating organ, the liver. Cerebral uptake of copper is extremely slow and likely highly regulated. Our findings provide new insights into the mechanisms of copper control.

Impact and implications

Maintaining non-ceruloplasmin-bound copper within the normal range is an important treatment goal in WD as this "free" copper is considered toxic to the liver and brain. We found that intravenously injected non-ceruloplasmin-bound copper quickly distributed to a number of tissues, especially skeletal muscle, subcutaneous fat, and the liver, while uptake into the brain was slow. This study offers new insights into the mechanisms of copper control, which may encourage further research into potential new treatment targets.

Clinical trial number

2016-001975-59.

Neurological Manifestations of Wilson's Disease: Pathophysiology and Localization of Each Component

Wilson's disease (WD) is an autosomal recessive disease that presents mainly with hepatic, neurological, and psychiatric manifestations. Neurological manifestations have been described in the past. Nevertheless, the pathophysiology and the clinical relevance of these manifestations have not been described in great detail in the medical literature. We aim to consolidate the knowledge about the neurological manifestations of WD and present the pathophysiology of each neurological manifestation of the disease. We will give a brief definition, the provenance, and the pathophysiology of the neurological conditions. We collected data from the National Library of Medicine (PubMed) using regular keywords and medical subject headings. Studies were selected applying the following inclusion/exclusion criteria: (1) studies that used exclusively human subjects, (2) papers published in English, and (3) papers from 1990 onward. The exclusion criteria were (1) studies that used animals, (2) papers not published in English, and (3) papers published before 1990. Additional studies were included via reference lists of identified papers and related articles featured in PubMed and Google Scholar. Copper toxicity is the principal factor for brain degeneration seen in WD. Parkinsonism seen in WD has been associated with a nigrostriatal dopaminergic deficit. Resting tremor may have the same pathophysiology as parkinsonism. Action tremor is related to an accumulation of copper in the cerebellum's vermis and hemispheres. At the same time, essential tremor can be explained due to affection of the dentate nucleus. Choreoathetosis is produced due to increased activity of the direct pathway. We did not find specifically associated pathophysiology related to dysarthria. We assume that multiple parts of the brain are involved in that problem. Putamen nucleus damage is the leading cause that explains dystonia seen in WD along with the globus palidus. We did not find a specific localization for seizures in WD, but the pathology seems to be related to decreased levels of B6 and direct toxicity of copper on the brain.

Wilson disease: neurologic features

Wilson disease (WD) is a neurodegenerative disorder, which presents as a spectrum of neurologic manifestations that includes tremor, bradykinesia, rigidity, dystonia, chorea, dysarthria, and dysphagia, together with a combination of neurologic symptoms that can easily lead to misdiagnosis. An early diagnosis of WD, and appropriate anticopper treatment, usually leads to a marked improvement in patient health. Conversely, delayed diagnosis can result in persistent pathology, which, left untreated, can ultimately prove lethal. The aim of this chapter is to present a detailed description of the neurologic features of WD, including their evaluation, together with relevant ophthalmologic examinations, brain neuroimaging, and other laboratory measurements that show the extent of the involvement of the nervous system.

Wilson disease - currently used anticopper therapy

Wilson disease (WD) is a genetic disorder of copper metabolism that can be treated successfully with pharmacologic treatment. Two groups of drugs are currently used: chelators (e.g., d-penicillamine and trientine), which increase urinary copper excretion, and zinc salts, which inhibit copper absorption in the digestive tract. The mechanisms of action lead to a negative copper balance, stopping pathologic accumulation of copper in the tissues and clearing affected organs of copper overload. Due to a lack of prospective clinical trials, the use of drugs depends mainly on center experience and the accessibility in different countries or regions. This chapter presents the different reports and recommendations regarding WD treatment. In addition to the different expert opinions on pharmacologic agents, there are a few axioms regarding WD treatment: treatment should start immediately after diagnosis, even in clinically presymptomatic cases; the patient should be treated for life, making compliance a key factor in treatment success; and the treatment should be monitored regularly via liver and hematologic tests, neurologic examination, and copper metabolism, modifying the treatment accordingly. Other drugs proposed for WD treatment (e.g., tetrathiomolybdate) are in clinical trials and lack current recommendations. Thus, only the currently available options for WD pharmacologic treatment are discussed.

Symptomatic treatment of neurologic symptoms in Wilson disease

Wilson disease (WD) is a potentially treatable neurodegenerative disorder. In the majority of cases, treatment with drugs that induce a negative copper balance (usually chelators or zinc salts) leads to improvements in liver function and neurologic signs. However, some patients show severe neurologic symptoms at diagnosis, such as tremor, dystonia, parkinsonism, and chorea. In this patient group, some neurologic deficits may persist despite adequate treatment, and further neurologic deterioration may be observed after treatment initiation. Such patients may require additional treatment to alleviate neurologic symptoms. Apart from general recommendations for WD anticopper treatment, there are currently no guidelines for managing neurologic symptoms in WD. The aim of this chapter is to summarize possible treatments of neurologic symptoms in WD based on the presently available medical literature.

Genetic and degenerative disorders primarily causing other movement disorders

In this chapter, we will discuss the contributions of structural and functional imaging to the diagnosis and management of genetic and degenerative diseases that lead to the occurrence of movement disorders. We will mainly focus on Huntington's disease, Wilson's disease, dystonia, and neurodegeneration with brain iron accumulation, as they are the more commonly encountered clinical conditions within this group.

Early neurological worsening in patients with Wilson's disease

BACKGROUND

Early neurological worsening during treatment initiation for Wilson's disease (WD) is an unresolved problem. Our aim was to establish the frequency and outcome of early neurological worsening in patients with WD.

METHODS

We analyzed 143 symptomatic patients diagnosed with WD between 2005 and 2009. Early neurological deterioration was based on worsening on the Unified Wilson's Disease Score Scale, scored at baseline through 6 months or occurrence of new neurological symptoms. Reversibility of worsening was followed up to 24 months.

RESULTS

Early neurological worsening was observed in 11.1% (16/143) and involved only patients with neurological signs at diagnosis. Mean time to worsening from treatment initiation was 2.3 ± 1.9 months. Neurological deterioration was completely reversible in 53% (8/15) and partially in 13% (2/15) of patients over 9.2 ± 5.2 months. Patients who experienced early deterioration had significantly more severe baseline neurological deficit, higher prevalence of thalamic (66% vs 29%) and brain stem (73% vs 33%) lesions seen on baseline magnetic resonance imaging, and more often used concomitant dopamine receptor antagonists (46% vs 5%). Disease duration, treatment type (d-penicillamine or zinc sulfate), type of neurological manifestations, initial copper metabolism results, and liver function parameters did not differ between evaluated groups.

CONCLUSIONS

Neurological worsening at the beginning of anti-copper therapy may occur in over 10% of WD patients. Special attention should be paid to those with severe initial neurological manifestations, advanced brain injury and using dopamine receptor antagonists. Type of anti-copper therapy did not show clear association with early neurological worsening.

Association of dopamine receptor gene polymorphisms with the clinical course of Wilson disease

BACKGROUND

Dopamine receptor D2 (DRD2) polymorphisms are proposed to be important factors in the presentation of neuropsychiatric symptoms in many disorders, including decreased striatum levels of dopamine D2 receptors in Wilson disease. The present study investigated the association between DRD2 gene polymorphisms and clinical manifestation of Wilson disease.

METHODS

Analyzing data from 97 symptomatic Wilson disease patients, we investigated the DRD2 gene polymorphisms rs1800497, rs1799732, and rs12364283. We assessed the polymorphisms impact on the phenotypic presentation of the disease.

RESULTS

Generally, the DRD2 gene polymorphisms had no impact on the hepatic or neuropsychiatric clinical presentation of Wilson disease. However, rs1799732 deletion allele carriers with neuropsychiatric symptoms had earlier onset of WD symptoms by almost 6 years compared with individuals without this allele (22.5 vs. 28.3 years; P < 0.05). This unfavorable effect of the rs1799732 polymorphism was even more pronounced among adenosine triphosphatase 7B gene (ATP7B) p.H1069Q homozygous patients, in whom carriership of the deletion allele was related to earlier initial neuropsychiatric manifestation by 14 years (18.4 vs. 32.2 years; P < 0.01).

CONCLUSIONS

Genetic variation of DRD2, specifically the rs1799732 polymorphism, may produce an earlier clinical presentation of Wilson disease neuropsychiatric symptoms and signs that occur in the course of dopaminergic system impairment due to copper accumulation in the brain. We speculate that this effect may be due to the impact of DRD2 polymorphism on dopamine D2 receptor density, but further studies are needed to understand the mechanisms of such phenotypic effects.

Neurologic Wilson's disease

Despite a long history, Wilson's disease, an autosomal recessive disease caused by mutations in the ATP7B gene, remains a commonly misdiagnosed import disease. Mutations in ATP7B result in abnormal copper metabolism and subsequent toxic accumulation of copper. Clinical manifestations of neurologic Wilson's disease include variable combinations of dysarthria, dystonia, tremor, and choreoathetosis. Among neurodegenerative diseases, it is unusual in that misdiagnosis and delay in treatment are clinically relevant because treatments can prevent and cure Wilson's disease, if they are given appropriately. If left untreated, Wilson's disease progresses to hepatic failure or severe neurologic disability and death, while those adequately treated have normal life spans. This review focuses on the neurologic features of Wilson's disease, its diagnosis, and treatment options.

Extrapyramidal symptoms in Wilson's disease are associated with olfactory dysfunction

Wilson's disease is a rare autosomal recessive disorder characterized by the accumulation of copper, mainly in the liver and the brain. As copper accumulation in the brain leads to disturbances in basal ganglia function, neurological-type patients typically present with hypo- and hyperkinetic extrapyramidal symptoms, with Parkinsonism being very common. Although there are numerous reports on olfactory deficits in primary neurodegenerative disorders, olfactory function has not been investigated in metabolic disorders presenting with extrapyramidal features. Twenty-four patients with Wilson's disease participated in the investigation. All patients were treated pharmacologically. They comprised patients with liver disease alone (including mild enzyme elevation in asymptomatic individuals; n = 11) and/or neurological symptoms (n = 13) at the time of testing. Twenty-one patients underwent both [18F]fluoro-2-deoxy-D-glucose positron emission tomography ([18F]FDG-PET) and magnetic resonance imaging (MRI). The severity of extrapyramidal symptoms was judged using a clinical score system ranging from 0 (no symptoms) to 3 (severe symptoms). In all patients, psychophysical testing was performed using the Sniffin' Sticks, which involved tests for odor threshold, discrimination, and identification. Results from the present study revealed that Wilson's disease patients with neurological symptoms show a significant olfactory dysfunction compared to hepatic-type patients. Individuals who are more severely neurologically affected also present with a more pronounced olfactory deficit. Of interest, there was no significant effect of long-term treatment with penicillamine on olfactory function. Olfactory function did not correlate significantly with the presence of MRI visible lesions in the basal ganglia or with any regional glucose metabolism as measured by [18]F-FDG-PET. In conclusion, these findings indicate that the underlying pathological alterations with degeneration in the basal ganglia and neuronal loss in association with a marked increase of the copper content in this brain region play a role in the olfactory deficit.

Dopamine transporter binding in Wilson's disease

INTRODUCTION

In Wilson's disease (WD), brain magnetic resonance images (MRI) show increased signal intensity in T2 weighted images in the lenticular nuclei, thalamus and brainstem, including the substantia nigra. A poor therapeutic response to levodopa in WD suggests the mechanism of a postsynaptic abnormality. However positron emission tomography studies show an involvement of the nigrostriatal presynaptic dopaminergic pathway.

CASE REPORT

We report the clinical manifestations in a case of WD with akinetic-rigid syndrome and initial hesitation. The brain MRI showed an increased signal intensity lesion in the substantia nigra region, in addition to basal ganglion and thalamic lesions. However, dopamine transporter (DAT) imaging with 99mTc-TRODAT-1 revealed a nonsignificantly increased DAT uptake, suggesting a normal presynaptic nigrostriatal dopaminergic terminal.

CONCLUSION

We suggest that significant heterogeneity can be found in WD patients and a normal presynaptic dopaminergic pathway may occur in some patients, even those with typical akinetic-rigid syndrome and evidence of substantia nigra involvement in the brain on MRI.

Neurological impairment and recovery in Wilson's disease: evidence from PET and MRI

We studied the relationship of regional cerebral glucose consumption (rCMRGlc) and striatal dopamine D2 receptor binding as assessed with positron emission tomography (PET) with the structural abnormalities of the brain in magnetic resonance images (MR), and the degree of neurological impairment in 18 patients with Wilson's disease (WD). The rCMRGlc was determined in the basal ganglia, the thalamus, the cerebral cortex, and the cerebellar hemispheres. The severity of neurological signs, defined by semiquantitative motor impairment scores, correlated highly (r = -0.80) with the reduction of striatal rCMRGlc. Clinical scores, striatal rCMRGlc, and the degree of MRI abnormalities showed no correlation with different indices of dopamine D2 receptor binding. Sequential PET measurements in three patients during treatment with chelating agents revealed a moderate increase of striatal rCMRGlc (in two patients) and a moderate to marked increase of striatal D2 receptor binding (in three patients) in association with clinical improvement. Our data suggest that the rCMRGlc represents a sensitive and objective measure for assessing and monitoring striatal and extrastriatal involvement in WD. The lack of correlation between the dopamine D2 receptor binding and striatal rCMRGlc and structural abnormalities may be explained by the wide spectrum of clinical manifestations and different responses to treatment in WD patients.