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The first genetic biomarker for dementia with Lewy bodies “Although all patients fulfill diagnostic criteria fitting within a certain spectrum of symptoms and disease course, the primary cause of dementia with Lewy bodies may not be the same in all cases.”
KEYWORDS: b-synuclein n butyrylcholinesterase n dementia with Lewy bodies n diagnostic biomarkers n genetic biomarkers n genotype combinations
Biomarkers have become powerful tools for dis ease diagnosis, estimation of disease prognosis and response to specific treatments. For neuro degenerative disorders, such as Alzheimer’s dis ease (AD), frontotemporal dementia, Parkinson’s disease (PD) with dementia (PDD) or dementia with Lewy bodies (DLB), their use is of special importance because these diseases are hetero geneous and show partially overlapping features. Neuropathological changes start to appear long before the disease becomes symptomatic. These changes, including neuron and synaptic loss, the formation of toxic protein oligomers and inclu sion bodies, can be observed only histopatho logically post-mortem, making correct clinical diagnosis difficult. Nevertheless, treatments spe cifically indicated for each of these disorders can be applied only after precise clinical diagnosis and, for this purpose, diagnostic biomarkers are required. Important advances in the search for biomarkers include the discovery of CSF bio markers for AD and PD [1,2], the implementation of amyloid [3] and dopamine transporter imaging [4] techniques, and the description of the ApoE- e4 allele as a possible genetic marker for response to immunotherapy [5]. Although genetic research has seen spectacular advances during recent years and some new risk factors have been established, only the ApoE- e4 allele has been confirmed as a biomarker for outcome monitoring. However, the advantage of genetic biomarkers is their use by noninvasive, inexpensive and easy-to-perform methodologies. Furthermore, a main goal of biomarker search in neurodegenerative disorders is the discovery of early diagnostic markers, which even before the appearance of first symptoms permit the applica tion of specific treatments to brake the progres sion of disease-specific changes and to prevent disease onset [6,7].
Importance of biomarker discovery for the diagnosis of DLB DLB is a common form of dementia and the second most frequent cause of dementia after AD. It is very heterogeneous and shows over lapping features with both AD as well as PDD. However, DLB has a more malignant disease course and is more complicated to manage than AD. In 2008 Aarsland and colleagues asked two main questions with answers that underline the need of specific DLB markers [8]: Question: why is DLB difficult to diagnose? Answer: whereas at early stages, attention, motor or psychiatric changes prevail on reduced memory function, in the later stages of DLB its presentation resembles that of other late-stage dementia types [8];
10.2217/BMM.13.107 © 2013 Future Medicine Ltd
Biomarkers Med. (2013) 7(6), 909–911
Katrin Beyer Department of Pathology, Health Sciences Research Institute of the ‘Germans Trias i Pujol’ Foundation (IGTP), Badalona, Barcelona, Spain [email protected]
Question: why is early discrimination of DLB important? Answer: a correct early diagnosis of DLB is crucial to assess the prognosis of the patient and make informed decisions on the best course of management. Since evidence points to differences in treat ment response between DLB and AD, only early differentiation between both assures effective and safe management. Most importantly, DLB patients are at high risk of severe reactions to antipsychotic drugs [9], have more functional impairment owing to many different symptoms and suffer from greater impairment of quality of life than AD patients [8].
Subgroups of DLB DLB is thought to result from complex interac tions among different susceptibility genes and environmental risk factors with a particular impact for each individual. Although all patients fulfill diagnostic criteria fitting within a certain
part of
ISSN 1752-0363
909
Editorial
Beyer
spectrum of symptoms and disease course, the primary cause of DLB may not be the same in all cases. So far, a-synuclein pathology [10] and cholinergic deficit [11] have been unequivocally involved in the pathogenesis of DLB. Whereas pathological a-synuclein oligomerization and its further aggregation are key events during DLB development, cholinergic deficit found in DLB brains is more pronounced than in AD [11]. However, even these main patho logical events reach different degrees of severity in each patient. Similar degrees of severity of the various pathological processes involved in DLB development define molecular subgroups of the disease, each one detectable independently by its own biomarkers. This concept agrees with the observation that more than one biomarker will be needed to identify all DLB patients [8]. In this context, we have recently described the first molecular subgroup of DLB, compris ing between 15 and 20% of all DLB patients [12]. It is characterized by the drastic diminu tion of b-synuclein expression in cortical areas in patients, who in addition to presenting pure Lewy body pathology show a short disease course and the clinical phenotype of DLB, but not of PDD. Since it has been demonstrated that b-synuclein interacts directly with and regulates the functionality of a-synuclein, patients with low cortical b-synuclein levels could develop faster a-synuclein-related pathological changes and present increased synaptic dysfunction. Early and severe cholinergic deficit is partly due to the overexpression of either acetylcho linesterase or butyrylcholinesterase (BChE), or both, varying significantly between patients. Very recently, we found that BChE expression in the frontal cortex of DLB and AD patients is increased in comparison with controls. Never theless, approximately 15% of all DLB brains showed similar BChE expression as control brains, and may therefore constitute another molecular subgroup of DLB.
DLB subgroup-specific biomarkers Since expression changes may be caused by mutations within the promoter region of a gene, we have analyzed the sequences of both the b-synuclein and BChE promoter regions. For the moment we have not found any adequate marker for the identification of the b-synu clein-lacking DLB subgroup, but we have detected four variable single-nucleotide poly morphisms in the BChE promoter in our sam ple. Together with the well-described K-variant in BChE exon 4, these four single-nucleotide 910
Biomarkers Med. (2013) 7(6)
polymorphisms constitute genotype combina tions with variable frequencies in DLB, AD and controls. Two of these genotype combi nations are associated with unchanged BChE expression with sensitivity of 98%, thus repre senting the first genetic biomarker to identify a subset of patients suffering from DLB [101]. This first genetic biomarker may have various applications. On one hand, it can be used as a diagnostic tool offering differential diagnosis for one of the DLB subgroups. In a diagnos tic algorithm, when the clinical diagnosis for a patient is possible or probable AD, PDD, or DLB, the determination of the BChE promoter genotype combination will help to establish the diagnosis of DLB and to dismiss other neurode generative dementias. Moreover, DLB patients who carry these genotype combinations do not overexpress BChE in the cerebral cortex and will therefore need a specific adjustment of their treatment with cholinesterase inhibitors. On the other hand, use of the genetic BChE biomarker is also suitable for the characteriza tion of patients to be included in a clinical trial, providing precise clinical diagnosis of the trial’s participants.
“Similar degrees of severity of the various pathological processes involved in dementia with Lewy bodies development define molecular subgroups of the disease, each one detectable independently by its own biomarkers.” Between 15 and 20% of all DLB patients carry one of the two identified BChE genotype combinations belonging to the corresponding DLB subgroup. Since none of the carriers of these genotype combinations show diminished b-synuclein expression, it is possible to affirm that we have identified two nonoverlapping molecular subgroups of DLB. Each of these sub groups comprise approximately 15% of all DLB patients, leaving approximately 70% of all DLB patients yet to be exhaustively characterized. However, there is another important question to be answered: is the percentage of 15% too low to consider the genetic BChE biomarker a valid DLB marker? At this point it is important to take into account that, in personalized medi cine, it is acceptable to deal with small patient groups presenting different markers, even those belonging to the same disease [13]. Therefore, if the sensitivity of a biomarker is even as low as 15% for a disease but identifies patients with similar molecular alterations reaching up to 90% future science group
The first genetic biomarker for dementia with Lewy bodies
for this specific subgroup, it should be considered as adequate.
Strategies for genetic biomarker discovery in DLB During the last few years, we have been using a three-step protocol to identify new genetic bio markers for DLB. First, candidate genes were analyzed in a cohort of post-mortem human brain samples from individuals with both the pure and common forms of Lewy body pathol ogy, Alzheimer pathology and of brain samples without significant pathological changes. The basics for success in this first phase of the study was the correlation of clinical and neuropatho logical data that permit the grouping of patients with neuropathological diagnosis of Lewy body pathology into the following three groups: DLB, PD and PDD. By this means, the first analysis was carried out within four disease groups, AD, DLB, PD and PDD, as well as the control group. Only those alleles, genotypes, genotype combi nations or haplotypes specifically found in only one of the disease groups were accepted as valid to further establish the marker. The second phase of
1
2
3
4
5
Hu WT, Chen-Plotkin A, Arnold SE et al. Biomarker discovery for Alzheimer’s disease, frontotemporal lobar degeneration, and Parkinson’s disease. Acta Neuropathol. 120(3), 385–399 (2010).
6
Kang JH, Irwin DJ, Chen-Plotkin AS et al. Association of cerebrospinal fluid b-amyloid 1–42, T-tau, P-tau181, and a-synuclein levels with clinical features of drug-naive patients with early Parkinson disease. JAMA Neurol. doi:10.1001/jamaneurol.2013.3861 (2013) (Epub ahead of print).
7
8
Frisoni GB, Bocchetta M, Chételat G et al. Imaging markers for Alzheimer disease: which vs how. Neurology 81(5), 487–500 (2013). de la Fuente-Fernández R. Role of DaTSCAN and clinical diagnosis in Parkinson disease. Neurology 78(10), 696–701 (2012). Liu CC, Kanekiyo T, Xu H, Bu G. Apolipoprotein E and Alzheimer disease: risk,
future science group
the study was carried out in a cohort of clinically diagnosed patients and in corresponding control individuals. The final validation of the genetic biomarker was carried out in a multicenter study.
“...in personalized medicine, it is acceptable to deal with small patient groups presenting different markers, even those belonging to the same disease.” Only if our findings are replicated by others, or if new DLB subgroups and their correspon dent markers are described, will the detection of molecular subgroups become a challenge to advance in the DLB biomarker search. Financial & competing interests disclosure This work was supported by Spain’s Ministry of Health grants CP09/00102 and PI12/1702. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. No writing assistance was utilized in the production of this manuscript. mechanisms and therapy. Nat. Rev. Neurol. 9(2), 106–118 (2013).
References
9
Editorial
10 Kalia LV, Kalia SK, McLean PJ, Lozano AM,
Lang AE. a-synuclein oligomers and clinical implications for Parkinson disease. Ann. Neurol. 73(2), 155–169 (2013).
Reiman EM, Langbaum JB, Tariot PN. Alzheimer’s prevention initiative: a proposal to evaluate presymptomatic treatments as quickly as possible. Biomark. Med. 4(1), 3–14 (2010).
11 Tiraboschi P, Hansen LA, Alford M et al.
Carrillo MC, Brashear HR, Logovinsky V et al. Can we prevent Alzheimer’s disease? Secondary “prevention” trials in Alzheimer’s disease. Alzheimers Dement. 9(2), 123–131 (2013).
12 Beyer K, Domingo-Sàbat M, Santos C et al.
Aarsland D, Kurz M, Beyer M, Bronnick K, Piepenstock Nore S, Ballard C. Early discriminatory diagnosis of dementia with Lewy bodies. The emerging role of CSF and imaging biomarkers. Dement. Geriatr. Cogn. Disord. 25(3), 195–205 (2008). McKeith I, Fairbairn A, Perry R, Thompson P, Perry E. Neuroleptic sensitivity in patients with senile dementia of Lewy body type. BMJ 305(6855), 673–678 (1992).
www.futuremedicine.com
Early and widespread cholinergic losses differentiate dementia with Lewy bodies from Alzheimer disease. Arch. Gen. Psychiatry 59(10), 946–951 (2002). The decrease of b-synuclein in cortical brain areas defines a molecular subgroup of dementia with Lewy bodies. Brain 133(Pt 12), 3724–3733 (2010). 13 Jørgensen JT. A challenging drug
development process in the era of personalized medicine. Drug Discov. Today 16(19–20), 891–897 (2011).
Patent 101 Grifols SA: WO2011/104023 (2010).
911
The first genetic biomarker for dementia with Lewy bodies “Although all patients fulfill diagnostic criteria fitting within a certain spectrum of symptoms and disease course, the primary cause of dementia with Lewy bodies may not be the same in all cases.”
KEYWORDS: b-synuclein n butyrylcholinesterase n dementia with Lewy bodies n diagnostic biomarkers n genetic biomarkers n genotype combinations
Biomarkers have become powerful tools for dis ease diagnosis, estimation of disease prognosis and response to specific treatments. For neuro degenerative disorders, such as Alzheimer’s dis ease (AD), frontotemporal dementia, Parkinson’s disease (PD) with dementia (PDD) or dementia with Lewy bodies (DLB), their use is of special importance because these diseases are hetero geneous and show partially overlapping features. Neuropathological changes start to appear long before the disease becomes symptomatic. These changes, including neuron and synaptic loss, the formation of toxic protein oligomers and inclu sion bodies, can be observed only histopatho logically post-mortem, making correct clinical diagnosis difficult. Nevertheless, treatments spe cifically indicated for each of these disorders can be applied only after precise clinical diagnosis and, for this purpose, diagnostic biomarkers are required. Important advances in the search for biomarkers include the discovery of CSF bio markers for AD and PD [1,2], the implementation of amyloid [3] and dopamine transporter imaging [4] techniques, and the description of the ApoE- e4 allele as a possible genetic marker for response to immunotherapy [5]. Although genetic research has seen spectacular advances during recent years and some new risk factors have been established, only the ApoE- e4 allele has been confirmed as a biomarker for outcome monitoring. However, the advantage of genetic biomarkers is their use by noninvasive, inexpensive and easy-to-perform methodologies. Furthermore, a main goal of biomarker search in neurodegenerative disorders is the discovery of early diagnostic markers, which even before the appearance of first symptoms permit the applica tion of specific treatments to brake the progres sion of disease-specific changes and to prevent disease onset [6,7].
Importance of biomarker discovery for the diagnosis of DLB DLB is a common form of dementia and the second most frequent cause of dementia after AD. It is very heterogeneous and shows over lapping features with both AD as well as PDD. However, DLB has a more malignant disease course and is more complicated to manage than AD. In 2008 Aarsland and colleagues asked two main questions with answers that underline the need of specific DLB markers [8]: Question: why is DLB difficult to diagnose? Answer: whereas at early stages, attention, motor or psychiatric changes prevail on reduced memory function, in the later stages of DLB its presentation resembles that of other late-stage dementia types [8];
10.2217/BMM.13.107 © 2013 Future Medicine Ltd
Biomarkers Med. (2013) 7(6), 909–911
Katrin Beyer Department of Pathology, Health Sciences Research Institute of the ‘Germans Trias i Pujol’ Foundation (IGTP), Badalona, Barcelona, Spain [email protected]
Question: why is early discrimination of DLB important? Answer: a correct early diagnosis of DLB is crucial to assess the prognosis of the patient and make informed decisions on the best course of management. Since evidence points to differences in treat ment response between DLB and AD, only early differentiation between both assures effective and safe management. Most importantly, DLB patients are at high risk of severe reactions to antipsychotic drugs [9], have more functional impairment owing to many different symptoms and suffer from greater impairment of quality of life than AD patients [8].
Subgroups of DLB DLB is thought to result from complex interac tions among different susceptibility genes and environmental risk factors with a particular impact for each individual. Although all patients fulfill diagnostic criteria fitting within a certain
part of
ISSN 1752-0363
909
Editorial
Beyer
spectrum of symptoms and disease course, the primary cause of DLB may not be the same in all cases. So far, a-synuclein pathology [10] and cholinergic deficit [11] have been unequivocally involved in the pathogenesis of DLB. Whereas pathological a-synuclein oligomerization and its further aggregation are key events during DLB development, cholinergic deficit found in DLB brains is more pronounced than in AD [11]. However, even these main patho logical events reach different degrees of severity in each patient. Similar degrees of severity of the various pathological processes involved in DLB development define molecular subgroups of the disease, each one detectable independently by its own biomarkers. This concept agrees with the observation that more than one biomarker will be needed to identify all DLB patients [8]. In this context, we have recently described the first molecular subgroup of DLB, compris ing between 15 and 20% of all DLB patients [12]. It is characterized by the drastic diminu tion of b-synuclein expression in cortical areas in patients, who in addition to presenting pure Lewy body pathology show a short disease course and the clinical phenotype of DLB, but not of PDD. Since it has been demonstrated that b-synuclein interacts directly with and regulates the functionality of a-synuclein, patients with low cortical b-synuclein levels could develop faster a-synuclein-related pathological changes and present increased synaptic dysfunction. Early and severe cholinergic deficit is partly due to the overexpression of either acetylcho linesterase or butyrylcholinesterase (BChE), or both, varying significantly between patients. Very recently, we found that BChE expression in the frontal cortex of DLB and AD patients is increased in comparison with controls. Never theless, approximately 15% of all DLB brains showed similar BChE expression as control brains, and may therefore constitute another molecular subgroup of DLB.
DLB subgroup-specific biomarkers Since expression changes may be caused by mutations within the promoter region of a gene, we have analyzed the sequences of both the b-synuclein and BChE promoter regions. For the moment we have not found any adequate marker for the identification of the b-synu clein-lacking DLB subgroup, but we have detected four variable single-nucleotide poly morphisms in the BChE promoter in our sam ple. Together with the well-described K-variant in BChE exon 4, these four single-nucleotide 910
Biomarkers Med. (2013) 7(6)
polymorphisms constitute genotype combina tions with variable frequencies in DLB, AD and controls. Two of these genotype combi nations are associated with unchanged BChE expression with sensitivity of 98%, thus repre senting the first genetic biomarker to identify a subset of patients suffering from DLB [101]. This first genetic biomarker may have various applications. On one hand, it can be used as a diagnostic tool offering differential diagnosis for one of the DLB subgroups. In a diagnos tic algorithm, when the clinical diagnosis for a patient is possible or probable AD, PDD, or DLB, the determination of the BChE promoter genotype combination will help to establish the diagnosis of DLB and to dismiss other neurode generative dementias. Moreover, DLB patients who carry these genotype combinations do not overexpress BChE in the cerebral cortex and will therefore need a specific adjustment of their treatment with cholinesterase inhibitors. On the other hand, use of the genetic BChE biomarker is also suitable for the characteriza tion of patients to be included in a clinical trial, providing precise clinical diagnosis of the trial’s participants.
“Similar degrees of severity of the various pathological processes involved in dementia with Lewy bodies development define molecular subgroups of the disease, each one detectable independently by its own biomarkers.” Between 15 and 20% of all DLB patients carry one of the two identified BChE genotype combinations belonging to the corresponding DLB subgroup. Since none of the carriers of these genotype combinations show diminished b-synuclein expression, it is possible to affirm that we have identified two nonoverlapping molecular subgroups of DLB. Each of these sub groups comprise approximately 15% of all DLB patients, leaving approximately 70% of all DLB patients yet to be exhaustively characterized. However, there is another important question to be answered: is the percentage of 15% too low to consider the genetic BChE biomarker a valid DLB marker? At this point it is important to take into account that, in personalized medi cine, it is acceptable to deal with small patient groups presenting different markers, even those belonging to the same disease [13]. Therefore, if the sensitivity of a biomarker is even as low as 15% for a disease but identifies patients with similar molecular alterations reaching up to 90% future science group
The first genetic biomarker for dementia with Lewy bodies
for this specific subgroup, it should be considered as adequate.
Strategies for genetic biomarker discovery in DLB During the last few years, we have been using a three-step protocol to identify new genetic bio markers for DLB. First, candidate genes were analyzed in a cohort of post-mortem human brain samples from individuals with both the pure and common forms of Lewy body pathol ogy, Alzheimer pathology and of brain samples without significant pathological changes. The basics for success in this first phase of the study was the correlation of clinical and neuropatho logical data that permit the grouping of patients with neuropathological diagnosis of Lewy body pathology into the following three groups: DLB, PD and PDD. By this means, the first analysis was carried out within four disease groups, AD, DLB, PD and PDD, as well as the control group. Only those alleles, genotypes, genotype combi nations or haplotypes specifically found in only one of the disease groups were accepted as valid to further establish the marker. The second phase of
1
2
3
4
5
Hu WT, Chen-Plotkin A, Arnold SE et al. Biomarker discovery for Alzheimer’s disease, frontotemporal lobar degeneration, and Parkinson’s disease. Acta Neuropathol. 120(3), 385–399 (2010).
6
Kang JH, Irwin DJ, Chen-Plotkin AS et al. Association of cerebrospinal fluid b-amyloid 1–42, T-tau, P-tau181, and a-synuclein levels with clinical features of drug-naive patients with early Parkinson disease. JAMA Neurol. doi:10.1001/jamaneurol.2013.3861 (2013) (Epub ahead of print).
7
8
Frisoni GB, Bocchetta M, Chételat G et al. Imaging markers for Alzheimer disease: which vs how. Neurology 81(5), 487–500 (2013). de la Fuente-Fernández R. Role of DaTSCAN and clinical diagnosis in Parkinson disease. Neurology 78(10), 696–701 (2012). Liu CC, Kanekiyo T, Xu H, Bu G. Apolipoprotein E and Alzheimer disease: risk,
future science group
the study was carried out in a cohort of clinically diagnosed patients and in corresponding control individuals. The final validation of the genetic biomarker was carried out in a multicenter study.
“...in personalized medicine, it is acceptable to deal with small patient groups presenting different markers, even those belonging to the same disease.” Only if our findings are replicated by others, or if new DLB subgroups and their correspon dent markers are described, will the detection of molecular subgroups become a challenge to advance in the DLB biomarker search. Financial & competing interests disclosure This work was supported by Spain’s Ministry of Health grants CP09/00102 and PI12/1702. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. No writing assistance was utilized in the production of this manuscript. mechanisms and therapy. Nat. Rev. Neurol. 9(2), 106–118 (2013).
References
9
Editorial
10 Kalia LV, Kalia SK, McLean PJ, Lozano AM,
Lang AE. a-synuclein oligomers and clinical implications for Parkinson disease. Ann. Neurol. 73(2), 155–169 (2013).
Reiman EM, Langbaum JB, Tariot PN. Alzheimer’s prevention initiative: a proposal to evaluate presymptomatic treatments as quickly as possible. Biomark. Med. 4(1), 3–14 (2010).
11 Tiraboschi P, Hansen LA, Alford M et al.
Carrillo MC, Brashear HR, Logovinsky V et al. Can we prevent Alzheimer’s disease? Secondary “prevention” trials in Alzheimer’s disease. Alzheimers Dement. 9(2), 123–131 (2013).
12 Beyer K, Domingo-Sàbat M, Santos C et al.
Aarsland D, Kurz M, Beyer M, Bronnick K, Piepenstock Nore S, Ballard C. Early discriminatory diagnosis of dementia with Lewy bodies. The emerging role of CSF and imaging biomarkers. Dement. Geriatr. Cogn. Disord. 25(3), 195–205 (2008). McKeith I, Fairbairn A, Perry R, Thompson P, Perry E. Neuroleptic sensitivity in patients with senile dementia of Lewy body type. BMJ 305(6855), 673–678 (1992).
www.futuremedicine.com
Early and widespread cholinergic losses differentiate dementia with Lewy bodies from Alzheimer disease. Arch. Gen. Psychiatry 59(10), 946–951 (2002). The decrease of b-synuclein in cortical brain areas defines a molecular subgroup of dementia with Lewy bodies. Brain 133(Pt 12), 3724–3733 (2010). 13 Jørgensen JT. A challenging drug
development process in the era of personalized medicine. Drug Discov. Today 16(19–20), 891–897 (2011).
Patent 101 Grifols SA: WO2011/104023 (2010).
911
