***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: To assess whether trace elements are involved in Parkinson 's disease ( PD ) we have conducted a prospect i ve study where 19 trace elements have been determined in serum collected from 33 patients before they were diagnosed with the disease , and 99 controls . As a follow-up , serum from 19 of the same patients collected 4 - 12 years after they were diagnosed with PD has been analysed . In the prospect i ve part of the study , the only significant difference was a slightly lower content of Hg in the patient group than in the controls . In the follow-up , significantly higher levels of Hg , Ni , and Y , and lower levels of Ca , Fe , Mg , Mn , Rb and Se were found in the serum sample s collected after the patients were diagnosed with PD compared with pre-diagnostic levels Objective To investigate whether cigarette smoking interacts with genes involved in individual susceptibility to xenobiotics for the risk of Parkinson disease ( PD ) . Methods Two French population -based case-control studies ( 513 patients , 1,147 controls ) were included as a discovery sample to examine gene-smoking interactions based on 3,179 single nucleotide polymorphisms ( SNPs ) in 289 genes involved in individual susceptibility to xenobiotics . SNP – by – cigarette smoking interactions were tested in the discovery sample through an empirical Bayes ( EB ) approach . Nine SNPs were selected for replication in a population -based case-control study from California ( 410 patients , 845 controls ) with st and ard logistic regression and the EB approach . For SNPs that replicated , we performed pooled analyses including the discovery and replication data sets and computed pooled odds ratios and confidence intervals ( CIs ) using r and om-effects meta- analysis . Results Nine SNPs interacted with smoking in the discovery data set and were selected for replication . Interactions of smoking with rs4240705 in the RXRA gene and rs1900586 in the SLC17A6 gene were replicated . In pooled analyses ( logistic regression ) , the interactions between smoking and rs4240705-G and rs1900586-G were 1.66 ( 95 % CI 1.28–2.14 , p = 1.1 × 10−4 , p for heterogeneity = 0.366 ) and 1.61 ( 95 % CI 1.17–2.21 , p = 0.003 , p for heterogeneity = 0.616 ) , respectively . For both SNPs , while smoking was significantly less frequent in patients than controls in AA homozygotes , this inverse association disappeared in G allele carriers . Conclusions We identified and replicated suggestive gene-by-smoking interactions in PD . The inverse association of smoking with PD was less pronounced in carriers of minor alleles of both RXRA-rs4240705 and SLC17A6-rs1900586 . These findings may help identify biological pathways involved in the inverse association between smoking and PD The diagnosis of Parkinson 's disease ( PD ) still lacks objective diagnostic markers independent of clinical criteria . Cerebrospinal fluid ( CSF ) sample s from 36 PD and 42 age-matched control patients were subjected to inductively coupled plasma-sector field mass spectrometry and a total of 28 different elements were quantified . Different machine learning algorithms were applied to the data set to identify a discriminating set of elements yielding a novel biomarker signature . Using 19 stably detected elements , the extreme gradient tree boosting model showed the best performance in the discrimination of PD and control patients with high specificity and sensitivity ( 78.6 % and 83.3 % , respectively ) , re-classifying the training data to 100 % . The 10 times 10-fold cross-validation yielded a good area under the receiver operating characteristic curve of 0.83 . Arsenic , magnesium , and selenium all showed significantly higher mean CSF levels in the PD group compared to the control group ( p = 0.01 , p = 0.04 , and p = 0.03 ) . Reducing the number of elements to a discriminating minimum , we identified an elemental cluster ( Se , Fe , As , Ni , Mg , Sr ) , which most importantly contributed to the sample discrimination . Selenium was identified as the element with the highest impact within this cluster directly followed by iron . After prospect i ve validation , this elemental fingerprint in the CSF could have the potential to be used as independent biomarker for the diagnosis of PD . Next to their value as a biomarker , these data also argue for a prominent role of these highly discriminating six elements in the pathogenesis of PD Background Little is known about factors influencing progression from mild cognitive impairment to Alzheimer ’s dementia . A potential role of environmental chemicals and specifically of selenium , a trace element of nutritional and toxicological relevance , has been suggested . Epidemiologic studies of selenium are lacking , however , with the exception of a recent r and omized trial based on an organic selenium form . Methods We determined concentrations of selenium species in cerebrospinal fluid sample d at diagnosis in 56 participants with mild cognitive impairment of nonvascular origin . We then investigated the relation of these concentrations to subsequent conversion from mild cognitive impairment to Alzheimer ’s dementia . Results Twenty-one out of the 56 subjects developed Alzheimer ’s dementia during a median follow-up of 42 months ; four subjects developed frontotemporal dementia and two patients Lewy body dementia . In a Cox proportional hazards model adjusting for age , sex , duration of sample storage , and education , an inorganic selenium form , selenate , showed a strong association with Alzheimer ’s dementia risk , with an adjusted hazard ratio of 3.1 ( 95 % confidence interval 1.0–9.5 ) in subjects having a cerebrospinal fluid content above the median level , compared with those with lower concentration . The hazard ratio of Alzheimer ’s dementia showed little departure from unity for all other inorganic and organic selenium species . These associations were similar in analyses that measured exposure on a continuous scale , and also after excluding individuals who converted to Alzheimer ’s dementia at the beginning of the follow-up . Conclusions These results indicate that higher amounts of a potentially toxic inorganic selenium form in cerebrospinal fluid may predict conversion from mild cognitive impairment to Alzheimer ’s dementia BACKGROUND Parkinson 's disease ( PD ) is a progressive neurodegenerative disorder . The etiology of this disease is still not fully clear , but free radicals have been proposed to cause neuronal injury . Metals play a key role in the intracellular oxidative balance . However their implication in the degeneration process remains unknown . AIM To assess Cu , Zn and Se concentrations in serum of a group of PD patients in order to determinate , in comparison with age-matched controls , whether alteration in their levels could be involved in PD . METHODS A serum level of 3 trace elements ( Cu , Zn and Se )  was investigated in 48 patients with PD and 36 matched controls using plasma atomic absorption spectrometry .  We compared these parameters in PD patients with controls , and we also compared the variations within the PD group according to age , illness duration , stage of the disease and levodopa intake . RESULTS Patients with PD had significantly lower Cu levels compared to controls . The mean Zn and Se levels in PD patients did not differ significantly from those of controls . Levodopa therapy , age , stage , and illness duration did not significantly influence the measured parameters . CONCLUSION These results suggest that a disturbance of the plasmatic rate of Cu could be a marker of PD or at least , a risk factor for the development of this disease . Although zinc participates to the reduction of oxidative stress and the antioxidant role of the selenium , their implication in the onset of PD is not clearly established . Perspectives for the future could include antioxidant therapy . For this reason , other prospect i ve studies should be conducted on this subject to eluci date the implication of trace elements in PD UNLABELLED Reactive oxygen species ( ROS ) are well known to contribute to the pathophysiology of Parkinson 's disease ( PD ) . Clinical trials of antioxidants are currently underway in PD patients , however , antioxidant research has been hindered by a lack of peripheral biomarkers . METHODS Twenty-two patients with PD elected to have a novel antioxidant assessment ( Functional Intracellular Assay ( FIA ) , SpectraCell Lab , Houston , TX ) performed between 2004 and 2008 . Each PD case was compared to four age- and gender-matched controls ( n=88 ) in four separate , r and om iterations using laboratory data su bmi tted during the same time period . Logistic regression was used to determine the odds of functional deficiency in antioxidant nutrients ( i.e. , glutathione , coenzyme Q10 , selenium , vitamin E and alpha-lipoic acid ) by case-control status . The proportion of cases with functional deficiency was also compared to that for controls by chi(2 ) test . RESULTS Compared to cases , PD patients had a significantly greater odds of deficiency in coenzyme Q10 status ( OR : 4.7 - 5.4 ; 95 % CI : 1.5 - 17.7 ; P=0.003 - 0.009 ) based on FIA results , but not of vitamin E , selenium , lipoic acid , or glutathione ( all P>0.05 ) . The proportion of cases with coenzyme Q10 deficiency was also significantly greater in cases than in controls ( 32 - 36 % vs. 8 - 9 % ; P=0.0012 - 0.006 ) . CONCLUSIONS Deficiency of coenzyme Q10 assessed via FIA should be explored as a potential peripheral biomarker of antioxidant status in PD This study aims to examine the effect of zinc supplementation on free-radical formation and antioxidant system in individuals who are actively engaged in wrestling as a sport . The study registered a total of 40 male subjects , of whom 20 were wrestlers and 20 were sedentary individuals . The subjects were equally allocated to four groups : group 1 , zinc-supplemented sportsmen group ; group 2 , sportsmen group without supplementation ; group 3 , zinc-supplemented sedentary group ; group 4 , sedentary group without supplementation . Blood sample s were collected from all subjects twice , once at the beginning of the study and once again at the end of 8-week procedures . The blood sample s collected were analyzed to determine the levels of malondialdehyde ( MDA ) , serum glutathione ( GSH ) , serum glutathione peroxidase ( GPx ) activity , serum superoxide dismutase ( SOD ) activity ( ELISA colorimetric method ) and zinc ( colorimetric method ) . No difference was found between MDA levels of the study groups in the beginning of the study . The highest MDA value at the end of the study was obtained in group 4 ( p < 0.01 ) . MDA levels in group 2 were established to be significantly higher than those in groups 1 and 3 ( p < 0.01 ) . GSH level , GPx , and SOD activities and zinc level measured in the beginning of the study were not different between groups . Measurements performed at the end of the study showed that groups 1 and 3 ( zinc-supplemented groups ) had the highest GSH level , GPx , and SOD activities and zinc level ( p < 0.01 ) . These parameters were not different in the groups without supplementation ( groups 2 and 4 ) . Results obtained at the end of the study indicate that zinc supplementation prevents production of free radicals by activating the antioxidant system . In conclusion , physiologic doses of zinc supplementation to athletes may beneficially contribute to their health and performance Parkinson 's disease ( PD ) is a degenerative process affecting the striato nigral system ( SN ) . Its etiology , although obscure , may involve oxidative damage . Selenium , an antioxidant , was shown to protect the SN in animal models . In the current study , we investigate the association between plasma selenium concentrations and the presence of " soft " neurological signs related to the SN .  Plasma selenium concentration was assessed in participants of age ≥65 years in the InCHIANTI study , a population -based cohort study in Tuscany , Italy . PD was defined based on st and ard criteria . " Soft " neurological signs were ascertained by physical examination . A total of 1,012 participants were included . No association was found between the presence of PD and plasma selenium . There was , however , a strong association between plasma selenium and timed performance-based assessment s. Lower levels of selenium were significantly associated withdecreased performance in neurological tests of coordination among older adults . Prospect i ve studies are needed to further investigate the effects of selenium on SN dysfunction 
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A longer duration of the disease tends to be associated with overall lower trace element levels in either CSF or blood .
Conclusions : Due to the study findings and the greater relevance of the CSF compartment compared with the circulating peripheral ones , this meta- analysis suggests that overexposure in the central nervous system to selenium , and possibly to copper and iron , may be a risk factor of the disease , while zinc might have a protective effect