Mitochondrial damage-associated inflammation highlights biomarkers in PRKN/PINK1 parkinsonism

There is increasing evidence for a role of inflammation in Parkinson's disease. Recent research in murine models suggests that parkin and PINK1 deficiency leads to impaired mitophagy, which causes the release of mitochondrial DNA (mtDNA), thereby triggering inflammation. Specifically, the CGAS (cyclic GMP-AMP synthase)-STING (stimulator of interferon genes) pathway mitigates activation of the innate immune system, quantifiable as increased interleukin-6 (IL6) levels. However, the role of IL6 and circulating cell-free mtDNA in unaffected and affected individuals harbouring mutations in PRKN/PINK1 and idiopathic Parkinson's disease patients remain elusive. We investigated IL6, C-reactive protein, and circulating cell-free mtDNA in serum of 245 participants in two cohorts from tertiary movement disorder centres. We performed a hypothesis-driven rank-based statistical approach adjusting for multiple testing. We detected (i) elevated IL6 levels in patients with biallelic PRKN/PINK1 mutations compared to healthy control subjects in a German cohort, supporting the concept of a role for inflammation in PRKN/PINK1-linked Parkinson's disease. In addition, the comparison of patients with biallelic and heterozygous mutations in PRKN/PINK1 suggests a gene dosage effect. The differences in IL6 levels were validated in a second independent Italian cohort; (ii) a correlation between IL6 levels and disease duration in carriers of PRKN/PINK1 mutations, while no such association was observed for idiopathic Parkinson's disease patients. These results highlight the potential of IL6 as progression marker in Parkinson's disease due to PRKN/PINK1 mutations; (iii) increased circulating cell-free mtDNA serum levels in both patients with biallelic or with heterozygous PRKN/PINK1 mutations compared to idiopathic Parkinson's disease, which is in line with previous findings in murine models. By contrast, circulating cell-free mtDNA concentrations in unaffected heterozygous carriers of PRKN/PINK1 mutations were comparable to control levels; and (iv) that circulating cell-free mtDNA levels have good predictive potential to discriminate between idiopathic Parkinson's disease and Parkinson's disease linked to heterozygous PRKN/PINK1 mutations, providing functional evidence for a role of heterozygous mutations in PRKN or PINK1 as Parkinson's disease risk factor. Taken together, our study further implicates inflammation due to impaired mitophagy and subsequent mtDNA release in the pathogenesis of PRKN/PINK1-linked Parkinson's disease. In individuals carrying mutations in PRKN/PINK1, IL6 and circulating cell-free mtDNA levels may serve as markers of Parkinson's disease state and progression, respectively. Finally, our study suggests that targeting the immune system with anti-inflammatory medication holds the potential to influence the disease course of Parkinson's disease, at least in this subset of patients.

Altered regulation of serum lysosomal acid hydrolase activities in Parkinson's disease: A potential peripheral biomarker?

INTRODUCTION

Recent studies have indicated that lysosomal dysfunction contributes to the development of idiopathic Parkinson's disease (PD). It is uncertain whether dysregulation of serum lysosomal acid hydrolase activity exists in sporadic PD patients compared with normal controls (NCs) and parkinsonian syndrome (PS) patients.

METHODS

Sporadic PD patients without GBA1 mutations (n = 68) were matched with normal controls (n = 45), and parkinsonian syndrome patients (n = 32) in terms of family history, age, and sex. We measured the activities of lysosomal enzymes, α-galactosidase, β-galactosidase, and β-hexosaminidase and examined the possible correlations between lysosomal acid hydrolase activities with age in NCs, PD, and PS patients.

RESULTS

β-Galactosidase activity was significantly higher in the PD and PS than in the NC group (P < 0.001). The β-galactosidase to α-galactosidase and β-hexosaminidase to β-galactosidase activity ratios were more useful for distinguishing PD and PS patients from NCs (P < 0.0001). Furthermore, α-galactosidase activity was significantly higher in PS patients than both PD and NC groups (p = 0.04). β-Galactosidase and α-galactosidase activities exhibited a statistically significant negative correlation with age in NCs, and β-hexosaminidase activity showed a positive correlation with age in PS. However, PD patients did not show any of these correlations.

CONCLUSION

Our results suggest the presence of an unknown regulatory mechanism(s) of serum acid hydrolase activities with aging in the normal population and abnormalities in their regulation in PD and PS patients. However, the pattern of dysregulation in these two groups is different. Thus, serum lysosomal acid hydrolase activity can be used as a peripheral biomarker for PD.

A Patient with the GLA p.E66Q Mutation Exhibiting Vascular Parkinsonism and Bilateral Pulvinar Lesions

A 76-year-old man was admitted to our hospital due to gait difficulty. Brain imaging indicated bilateral pulvinar lesions and moderate white matter lesions. The serum α-galactosidase A levels were measured for the differential diagnosis of bilateral pulvinar lesions and were found to be abnormally low. Therefore, the patient was suspected to have variant Fabry disease. A GLA mutation analysis showed the p.E66Q mutation, which is speculated to be a functional polymorphism rather than a disease-causing mutation of Fabry disease. Enzyme replacement therapy did not result in a marked improvement, however, the disease progression stopped.

Manganese efflux in Parkinsonism: insights from newly characterized SLC30A10 mutations

Although manganese (Mn) is required for normal cellular function, overexposure to this metal may cause an extrapyramidal syndrome resembling Parkinson's disease (PD). Notably, high whole-blood Mn levels have been reported in patients with idiopathic PD. Because Mn is both essential at low dose and toxic at higher dose; its transport and homeostasis are tightly regulated. Previously, the only protein known to be operant in cellular Mn export was the iron-regulating transporter, ferroportin (Fpn). The causal role for Mn in PD has yet to be fully understood, but evidence of a familial predisposition to PD associated with Mn toxicity is mounting. A recently discovered mutation in SLC30A10 identified its gene product as putatively involved in Mn efflux. Patients with the SLC30A10 mutation display Parkinsonian-like gate disturbances and hypermanganesemia. This review will address Mn transport proteins, the newly discovered SLC30A10 mutations and their implications to Parkinsonism and Mn regulation.

Postoperative parkinsonism and lupus anticoagulant: A model of autoantibody-mediated neurotoxicity in stress

PRIMARY OBJECTIVE

Nigrostriatal hypodopaminergism is the fundamental basis in parkinsonism. It may arise secondarily from a variety of disorders but is rarely mentioned shortly after surgery.

METHODS AND PROCEDURES

To report the clinical course of five patients who had had symptomatic parkinsonism developed shortly after surgery (lumbar laminectomy, prostatectomy and cholestectomy). Appropriate investigations were done to elucidate their pathogenesis.

MAIN OUTCOMES AND RESULTS

There was no remarkable finding of their anesthetic agents, duration of surgery, type of surgery, medical conditions or preoperative screening test. Extensive investigations did not reveal consistent abnormality. However, an abnormal presence of lupus anticoagulant was detected in four patients; primary antiphospholipid antibody syndrome was fulfilled in two of them. The lupus anticoagulant restored to the reference range in another two patients later. Catastrophic antiphospholipid antibody syndrome was not seen. Initially, their parkinsonian symptoms rapidly progressed but slowed down after six months.

CONCLUSION

Lupus anticoagulant possesses neurotoxic property and has been found in cases of movement disorder involving with the central dopaminergism. Surgery, a form of traumatic stress, has been reported to bring on lupus anticoagulant and catastrophic antiphospholipid antibody syndrome. These relationships remind a generation or an enhancement of pathognomic autoantibody vulnerable for dopaminergic toxicity, such as lupus anticoagulant or other antiphospholipid antibody.

Exercise improves efficacy of levodopa in patients with Parkinson's disease

The objective was to investigate the impact of exercise on absorption and efficacy of levodopa (LD) in patients with Parkinson's disease (PD). A soluble, immediate release LD formulation was given followed by exercise near the aerobic limit on one day to PD patients, who underwent the same procedure only at rest on the second day. LD plasma behavior did not significantly differ between both conditions, but the motor response was significantly better 120 and 150 min after LD intake on the day with exercise than on the day with rest. Moderate exercise increases clinical efficacy of LD.

Increased 8-OHdG levels in the urine, serum, and substantia nigra of hemiparkinsonian rats

8-Hydroxy-2'-deoxyguanosine (8-OHdG), the predominant marker of oxidative DNA damage, may be a good biomarker for monitoring the progression of Parkinson's disease (PD). Unfortunately, there are no basic laboratory data examining 8-OHdG levels in animal models of PD. In this study, we demonstrate that rats lesioned with 6-hydroxydopamine (6-OHDA) in the medial forebrain bundle display significantly elevated 8-OHdG levels in urine, serum, and substantia nigra, but not cerebrospinal fluid and striatum, compared to sham controls. These increments in 8-OHdG levels were detected at 2 days, but not at 7 days after the lesion suggesting that oxidative stress is restricted to the acute phase of 6-OHDA neurotoxicity. The present results support 8-OHdG as a biomarker that may aid both in the diagnosis and in the documentation of progression in PD.

Metal changes in CSF and peripheral compartments of parkinsonian patients

BACKGROUND

Involvement of metals in the risk of developing Parkinson's disease (PD) has been suggested. In the present study, concentration of metals in cerebrospinal fluid (CSF), blood, serum, urine and hair of 91 PD patients and 18 controls were compared.

METHODS

Blood and hair were microwave digested, while CSF, serum and urine were water-diluted. Elements quantification was achieved by Inductively Coupled Plasma Atomic Emission Spectrometry and Sector Field Inductively Coupled Plasma Mass Spectrometry.

RESULTS

Some metal imbalances in PD were observed: i), in CSF, lower Fe and Si; ii), in blood, higher Ca, Cu, Fe, Mg and Zn; iii), in serum, lower Al and Cu; iv), in urine, lower Al and Mn, higher Ca and Fe; and v), in hair, lower Fe. The ROC analysis suggested that blood Ca, Fe, Mg and Zn were the best discriminators between PD and controls. In addition, hair Ca and Mg were at least 1.5 times higher in females than in males of patients and controls. A decrement with age of patients in hair and urine Ca and, with less extent, in urine Si was observed. Magnesium concentration in CSF decreased with the duration and severity of the disease. Elements were not influenced by the type of antiparkinsonian therapy.

CONCLUSIONS

Variation in elements with the disease do not exclude their involvement in the neurodegeneration of PD.

Follow-up of patients affected by manganese-induced Parkinsonism after treatment with CaNa2EDTA

In the period of 1998-2004, seven workers affected by manganese-induced Parkinsonism were diagnosed, studied and treated with CaNa2EDTA at our Occupational Health Ward. Biological markers, as well as magnetic resonance imaging and clinical examinations, were used to assess the disease trend. Those workers still employed were immediately removed from exposure. Our results seem to confirm that very good clinical, biological and neuroradiological results can be obtained by timely removal from exposure and chelating treatment, and that amelioration can persist in time. Manganism is, however, a severe condition that can also progress independent of further exposure. Therefore, chelating treatment can be a great aid in overt manganism, but particular attention must be paid to primary prevention, as this disease should now be totally preventable and definitely merits eradication.

Increased plasma levels of TNF-α but not of IL1-β in MPTP-treated monkeys one year after the MPTP administration

The cause of Parkinson's disease remains unknown although some evidence suggests that an inflammatory reaction, mediated by cytokines such as TNF-alpha and IL-1beta, is related with dopaminergic degeneration in the brain. In the present work we measured the plasma levels of TNF-alpha and IL-1beta in parkinsonian monkeys one year after MPTP administration. TNF-alpha levels were seen to have increased in parkinsonian monkeys reflecting the clinical symptoms observed, while IL-1beta levels remained unchanged. These results suggest that TNF-alpha plays a role in sustaining of dopaminergic degeneration in chronic parkinsonism.

Unaltered α-synuclein blood levels in juvenile Parkinsonism with a parkin exon 4 deletion

We recently reported here that SNCA triplication results in a doubling in the amount of alpha-synuclein protein in blood from cases with hereditary Lewy body disease. This observation shows that alpha-synuclein levels in blood accurately reflect gene dosage, which we assume drives pathogenesis in these individuals. A previous report has suggested that parkin can affect alpha-synuclein metabolism in human brain. Here we have tested whether there is also an increase of alpha-synuclein in autosomal recessive juvenile Parkinsonism (ARJP). We find there is not and discuss this result in terms of the putative relationships between alpha-synuclein and parkin.

Kinetics of the uptake and distribution of the dopamine D(2,3) agonist (R)-N-[1-(11)C]n-propylnorapomorphine in brain of healthy and MPTP-treated Göttingen miniature pigs

The binding of radioligand agonists to dopamine receptors in living brain can be informative about the abundance of receptors which are coupled to intracellular second messenger systems. Therefore, we developed a radiosynthesis for the dopamine D(2,3) partial agonist (R)-N- [1-(11)C]n-propylnorapomorphine ([(11)C]NPA). The uptake of this tracer in brain of anesthetized Göttingen miniature pigs was recorded by positron emission tomography (PET) and analyzed by compartmental analysis using the metabolite-corrected arterial input, and using reference tissue methods. [(11)C]NPA had a blood-brain unidirectional clearance of approximately 0.35 ml g(-1) min(-1) and an apparent distribution volume of 6 ml g(-1) in cerebellum. The ligand had a binding potential of 1.5 in striatum, comparable to that reported previously for the receptor antagonist [(11)C]raclopride in the same strain of animals. Significant binding was detected in the hypophysis, thalamus, and medial forebrain bundle. The binding in striatum was of comparable magnitude in normal pigs and in pigs with a documented 50% dopamine depletion produced by MPTP-intoxication. Deep brain stimulation of the subthalamus was without conspicuous effect on the binding of [(11)C]NPA in vivo. Results of this preliminary study indicate that this tracer meets many requirements for assaying dopamine agonist binding sites by PET.

Nerve growth factor levels in Parkinson disease and experimental parkinsonian rats

Nerve growth factor (NGF) is well established for its ability to promote growth and survival for specific neuronal populations. However, its participation in the pathogenesis of human nervous system disorders such as Parkinson's disease (PD) remains to be resolved. This study examined NGF levels in the serum of healthy persons, in patients with PD and in parkinsonian rats using a double site immune-enzymatic assay (EIA) with the murine 27/21 anti-beta-NGF monoclonal antibody. PD patients were divided in two groups according to the stages of the disease (Grade: I-II and Grade: III-IV of Hoenh and Yahr scale). NGF levels in parkinsonian rats showed significant (P<0.01) reductions when compared with serum from normal animals. The NGF levels in early states of the disease (Grade I-II) showed greater reductions (P<0.01) in comparison to those with advanced stages (Grade III-IV). We consider that alterations in NGF levels may reflect ongoing neurodegenerative processes in PD.

[Criteria of efficiency of transplantation of embryonic nervous tissue preparations in rats with 6-OHDA-impaired dopaminergic nigrostriatal system]

Effectiveness of transplantation of cells from embryonal nervous tissue of the ventral mesencephalon (VM ENT) and striatum (STR ENT) by apomorphin-induced motor asymmetry (APO-test), consolidation of the transplant (the degree of glyal reaction and amount of dopaminergic neurons) and blood serum levels of GFAP was studied for 3 months in Wistar rats with 6-OHDA-impaired dopaminergic nigrostriatal system. Marked therapeutic effectiveness was registered in VM ENT transplantation in the denervated striatum and in combined transplantation of VM ENT into the lateral cerebral ventricle simultaneously with STR ENT transplantation in the striatum. Separate transplantation of VM ENT in the lateral ventricle and STR ENT in the striatum had no positive effect on recovery of the dopaminergic nigrostriatal system. A correlation was found between the degree of glial reaction of ENT transplants, severity of rotation asymmetry and serum levels of gliofibrillary protein (GFAP). GFAP in the serum for lifetime assessment of transplant consolidation and prognosis of neurotransplantation efficiency was assayed.

Maintenance therapy with zuclopenthixol decanoate: associations between plasma concentrations, neurological side effects and CYP2D6 genotype

RATIONALE

Several antipsychotic drugs are metabolised by the polymorphic cytochrome P(450) CYP2D6. The impact of the polymorphism on the plasma levels and the occurrence of side effects have not been clearly established.

OBJECTIVE

To investigate the impact of the CYP2D6 polymorphism on the steady-state plasma concentrations of zuclopenthixol and the occurrence of extrapyramidal side effects (EPS) and tardive dyskinesia (TD) during treatment with zuclopenthixol-decanoate.

METHODS

Fifty-two clinically stable schizophrenic outpatients on monotherapy with zuclopenthixol-decanoate (100-400 mg/4 weeks) were genotyped for the CYP2D6 variants CYP2D6*3 and CYP2D6*4. Steady-state plasma levels of zuclopenthixol were analysed using high-performance liquid chromatography. Assessments of EPS, TD and psychopathology were performed twice with an 8-week interval using the extrapyramidal symptoms rating scale, the abnormal involuntary movement scale and the brief psychiatric rating scale.

RESULTS

Thirty-five patients were homozygous extensive metabolisers (EMs), 13 were heterozygous EMs and 4 were poor metabolisers (PMs). While there were no significant genotype-related differences in the doses of zuclopenthixol decanoate, PMs as well as heterozygous EMs had significantly higher steady-state plasma levels of zuclopenthixol than homozygous EMs (median 9.5 nmol/l; 8.2 nmol/l and 5.9 nmol/l, respectively, P<0.05). The median dose-corrected plasma concentrations were 0.029, 0.038 and 0.048 nmol.l(-1).mg(-1) in homozygous EMs, heterozygous EMs and PMs, respectively, with statistically significant differences between homozygous EMs and heterozygous EMs ( P=0.014) and homozygous EMs and PMs ( P=0.03). Patients with neurological side effects were significantly older than patients without ( P=0.02 in case of parkinsonism and P=0.04 in case of TD). Mutant CYP2D6*3 and *4 alleles tended to occur more frequently in patients with neurological side effects. An odds ratio (OR) of 2.3 (95% confidence interval 0.7-6.9) for development of parkinsonism and an OR of 1.7 (95% confidence interval 0.5-4.9) for TD was calculated in an individual with at least one mutated allele. However, the ORs were not statistically significant.

CONCLUSIONS

The higher zuclopenthixol steady-state plasma concentrations in heterozygous EM and PM schizophrenic patients receiving monotherapy with zuclopenthixol-decanoate than in homozygous EMs indicates a significant role of CYP2D6 in the systemic elimination of zuclopenthixol. The tendencies for patients carrying at least one mutated CYP2D6 gene to have an increased risk of parkinsonism and TD are in accordance with previous studies. Age was a significant risk factor for neurological side effects.

Protective effect and mechanism of Ginkgo biloba leaf extracts for Parkinson disease induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

AIM

To observe the effects of extracts of Ginkgo biloba leaves (EGb) on the Parkinson disease (PD) models induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its ion 1-methyl-4-phenylpyridinium (MPP+).

METHODS

MPTP was microinjected into substantia nigra of rats to induce a behavior change of rotation. EGb (ip, 50 or 100 mg.kg(1 . d-1) was pretreated consecutively for 19 d before MPTP administered and 1 d after MPTP administered. The contents of malondialdehyde (MDA), superoxide dismutase (SOD), and dopamine (DA) in substantia nigra of model rats were determined. Apoptosis of PC12 cells was induced by MPP+, and the protective effect of EGb (25, 50, and 100 mg/L) was also observed. The cells of apoptosis were observed under a microscope and counted under a fluoroscope after stained with AO/EB.

RESULTS

EGb (100 mg . kg-1 . d-1) decreased the duration and frequency of the rotation of rats (P < 0.05, n = 10 ) while EGb (50 or 100 mg/L)inhibited the decreases of DA and SOD and the increase of MDA induced by MPTP, (P < 0.05 or P < 0.01, n = 10). MPP+ (10 micromol/L) induced the apoptosis of PC12 cells, and EGb (50 or 100 mg/L) prevented cells from apoptosis at 6 h, 12 h, and 24 h (P < 0.05 or P < 0.01, n = 3).

CONCLUSION

EGb possesses protective effect on the PD models in vivo and in vitro. The anti-oxidation and anti-apoptosis may be one of the mechanisms underlying the neuroprotective effect of EGb.

Analysis of the metabolism of haloperidol and its neurotoxic pyridinium metabolite in patients with drug-induced parkinsonism

The blood levels of the neurotrophic drug haloperidol (HP) and its pyridinium metabolite, HPP(+), have been analyzed by liquid chromatography/electrospray ionization-mass spectrometry in 10 schizophrenic patients treated with HP, without carbamazepine (HP, oral daily dose of 0.3-0.5 mg/kg body weight for more than 1 year, females, aged 41 +/- 8.5 years). There was a significant difference (t-test, d.f. = 8, p (t(0) = 7.2) <0.005) in the blood HPP(+) level between the 5 patients with (18.5 +/- 6.4 ng/ml) and the 5 without (6.3 +/- 2.4 ng/ml) severe side effects such as drug-induced parkinsonism (Extrapyramidal Symptom Rating Scale (ESRS) parkinsonism severity scores 2.8 +/- 1.5 and 1.8 +/- 1.1, respectively). Moreover, it is suggested that vitamin E may be effective for drug-induced parkinsonism through a change in the blood HPP(+) level. It is necessary to investigate the HPP(+) metabolism in psychiatric patients to avoid severe side effects such as drug-induced parkinsonism and cardiac functional disorders.

Analysis of alpha-synuclein, parkin, tau, and UCH-L1 in a Japanese family with autosomal dominant parkinsonism

We examined whether autosomal dominant parkinsonism of a Japanese family, Sagamihara family, was due to the mutations of alpha-synuclein, parkin, tau, and UCH-L1, which have been reported as the causal genes for parkinsonism in other families. Restriction-enzyme digestion of polymerase-chain reaction (PCR) amplified genomic DNA fragments of alpha-synuclein exons 3 and 4 detected no point mutation. PCR-amplification of parkin exons 3, 4, 5, 6 and 7 detected no exon deletion. Direct sequencing of PCR-amplified DNA fragments of tau exons 9, 10, 12, and 13 and intron 10, and of UCH-L1 exon 4 revealed that all these exons and intron were normal including a polymorphic nucleotide substitution. These results indicated that the parkinsonism of the Sagamihara family seems not to be due to previously identified point mutations of alpha-synuclein, tau, or UCH-L1, or to exon deletion of parkin.

Immunoenzyme assay of glial fibrillary acidic protein for evaluation of functional activity of cell grafts from embryonic ventral mesencephalon in rats with experimental hemiparkinsonism

The relationship between the release of glial fibrillary acidic protein (GFAP) into systemic circulation and the efficacy of transplantation of embryonic nervous tissue was studied on rats with 6-OHDA-induced hemiparkinsonism. It was found that intrastriatal transplantation of cell preparations from embryonic ventral mesencephalon significantly attenuated apomorphine-induced rotation, which points to functional recovery of the dopaminergic nigrostriatal system. The degree of this recovery depends on reactive astrogliosis around the graft and survival of dopaminergic neurons. Analysis of GFAP concentration revealed significant elimination of this antigen into the circulation 7 and 14 days after transplantation. In rats with good consolidation of the graft without pronounced reactive gliosis, the concentration of GFAP reached 253.99+/-79.30 ng/ml on week 4 after transplantation and decreased to 8.2+/-3.3 ng/ml 8-12 weeks after transplantation. In rats with poor graft consolidation associated with death of transplanted neurons and gliosis in the graft and surrounding tissue the concentration GFAP increased to 476.4+/-111.0 ng/ml within 4 weeks after transplantation and remained elevated (235.0+/-44.8 ng/ml) for 12 weeks. Thus, monitoring of serum GFAP concentrations allows in vivo evaluation of the functional state of intracerebral graft and the level of reactive gliosis. This test can be used for the prognosis of transplantation efficacy.

Movement disorder, memory, psychiatric symptoms and serum DHEA levels in schizophrenic and schizoaffective patients

OBJECTIVE

Reports of low levels of dehydroepiandrosterone (DHEA) or its sulphate (DHEA-S) in some schizophrenic patients and in some persons with poorer motoric and cognitive functioning led us to examine clinical correlates of serum DHEA and DHEA-S levels in schizophrenic patients.

METHOD

Ratings of abnormal movements, memory and psychiatric symptoms in 17 medicated chronic schizophrenic or schizoaffective inpatients at a state hospital were correlated with serum DHEA and DHEA-S levels, and their ratios with serum cortisol.

RESULTS

Controlling for age, higher DHEA levels and/or higher DHEA/cortisol ratios were significantly correlated with lower symptom ratings on the Brief Psychiatric Rating Scale, better performance on some measures of memory, and lower ratings of parkinsonian symptoms.

CONCLUSION

Relatively low DHEA levels or DHEA/cortisol ratios may identify a particularly impaired subgroup of medicated patients with chronic schizophrenia. Potential implications are discussed.

Increased growth hormone response to apomorphine in Parkinson disease compared with multiple system atrophy

BACKGROUND

Parkinson disease (PD) is often difficult to distinguish from parkinsonian syndromes of other causes in early stages of the disease. In search of a suitable endocrinologic challenge test, we investigated dopaminergic sensitivity in patients with de novo parkinsonian syndromes.

OBJECTIVE

We measured the growth hormone (GH) response to a subthreshold dose of the dopamine 1-dopamine 2 receptor agonist apomorphine hydrochloride to differentiate parkinsonian syndromes from PD.

PATIENTS AND METHODS

Seventeen patients with a clinical diagnosis of PD, 16 patients with a clinical diagnosis of multiple system atrophy, and 11 healthy controls. The GH response to a subthreshold dosage of apomorphine and to somatorelin (GH-releasing factor) was tested in a randomized order; on the third day the protocol was repeated with a clinically effective dose of apomorphine.

RESULTS

The GH response to the low dose of apomorphine was significantly increased in patients with PD when compared with patients with multiple system atrophy or the control subjects (multivariate analyses of covariance; univariate F test, all P<.05). In contrast, there were no significant group differences with use of the higher dose of apomorphine or in the somatorelin-induced GH release.

CONCLUSIONS

The GH response to a subthreshold dose of apomorphine appears to be a useful tool to identify patients with PD vs multiple system atrophy. The enhanced GH response to a subthreshold dopaminergic stimulus may reflect a hypersensitivity of the extrastriatal dopamine receptors in PD.