Apolipoprotein E Genotypes in Parhnson's Disease with and without Dementia

William C. Koller, MD, PhD," Sander L. Glatt, MD," Jean P. Hubble, MD," Anthony Paolo, PhD," Alexander I. Troster, PhD," Michael S. Handler, MD,? Rebecca T. Horvat, PhD,t Coleman Martin, BS,t

Karen Schmidt, BS," Annette Karst, RN," Ellen M. Wijsman, PhD,$ Chang-En Yu, PhD,S: and Gerard D. Schellenberg, PhD#

The apolipoprotein E gene (Apo E) type 4 allele is a genetic risk factor influencing the development and age of onset of Alzheimer's disease. Because Parkinson's disease shares many characteristics of Alzheimer's disease, we studied the frequencies of Apo E genotypes in a cohort of 52 Parkinson's disease patients with dementia and 61 patients without dementia. Dementia was determined per National Institute of Neurological and Communicative Disorders and Stroke criteria and Mattis Dementia Rating Scale (DRS) < 126. Normal cognition was defined as DRS > 132. Apo E genotype and allele frequencies did not differ between demented and nondemented parkinsonian patients. Neither group's genotype and allele frequencies differed from that of a nondemented population of 78 controls. We conclude that the Apo E ~4 allele influences neither the development of Parkinson's disease nor the dementia associated with Parkinson's disease.

Koller WC, Glatt SL, Hubble JP, Paolo A, Troster AI, Handler MS, Horvat RT, Martin C, Schmidt K, Karst A, Wijsman EM, Yu C-E, Schellenberg GD. Apolipoprotein E genotypes in Parkinson's

disease with and without dementia. Ann Neurol 1995;37:242-245

The ~4 allele of apolipoprotein E gene (Apo E) is asso- ciated with late-onset Alzheimer's disease (AD) [ 1-41. Furthermore the ~4 dosage has been found to correlate with both increased risk and earlier age of onset of A D C4). Thus Apo E appears to be a susceptibility gene or risk factor that affects the rate of disease expressivity of late-onset familial and sporadic AD. Suggested mechanisms underlying Apo E ~4 effects in A D in- clude enhancement of amyloid deposition in plaques [5, 6 } and increased neurofibrillary protein deposition in neuronal tangles 171.

Parkinson's disease (PD), like AD, is a neurodegen- erative process. The two diseases share many common characteristics and may have common determinants [S]. Both conditions are age related and have some common risk factors [9, lo}. A higher frequency of secondary cases of P D among first-degree relatives of A D cases [ 111 and similarly of secondary cases of AD among first-degree relatives of P D [12} has been re- ported. Dementia frequently occurs in P D [13, 141 and, conversely, A D patients can exhibit parkinsonian features 15, 161. Neuropathological features of the two diseases overlap [17, IS} and cholinergic and do- paminergic deficiencies occur in both conditions [ 19, 20).

We determined Apo E genotypes in P D patients with and without dementia to assess the role of this genetic risk factor in PD.

Methods Subjects with PI) were recruited from the PD Center at the University of Kansas Medical Center, either from a longitudi- nal research study (AD Center) or from the PD clinic. Only whites were studied because of reports of racial differences in allele frequencies [ 3 ] . PD was defined by the presence of two of the three cardinal features including tremor, rigidity and bradykinesia, and sustained responsiveness to levodopa therapy. Patients who developed clinically obvious cognitive deficits prior to the motor deficits of P D and patients with clinical features of progressive supranuclear palsy, Shy- Drager syndrome, or olivopontocerebellar degeneration were excluded. Controls were volunteers participating in a longitudinal study of aging ( A D Center).

Clinical evaluation included the Unified Parkinson's Dis- ease Rating Scale (UPDRS) and neurological examination. Functional disability was assessed by the Blessed Dementia Rating [2 I]. Neuropsychological evaluation included the Mattis Dementia Rating Scale (DRS). Subjects were consid- ered demented per National Institute of Neurological and Communicative Disorders and Stroke (NINCDS) criteria with total DKS score below 126 and cognitively related func-

From the Departments of "Neurology and tPathology, University of Kansas Medical Center, Kansas City, KS, and Departments of $Medicine and Biostaristics and $Neurology. University of Washing- ton, Seattle, WA.

Received Apr 28, 1904, and in revised form Jul 15. Accepted for publication Aug 2 5 , 1994.

Department of Neurologs, University of Kanhas Medical Center. 390 I Rainbow Blvd, Kansas City, KS 66100-73 Id.

correspondence to Dr

242 Copyright 6 1995 by the American Neurological Association

tional disability. Subjects were considered to be cognitively intact if their DRS score was above 132. Control subjects were not included unless their DRS was above 132.

G-enotyping Genomic D N A was prepared from white cell pellets and extracted with phenol and chloroform. Apo E genotypes were determined without knowledge of subject's clinical sta- tus using primers, polymerase chain reaction (PCR) condi- tions, and dot-blot methods previously described 122). The frequency of Apo E genotypes for whites in the general pop- ulation taken from a previous report [23] was compared with our control popularion.

t tests were used to test for potential differences in quanti- tative trait levels between groups. x' tests were used for initial tests of potential differences in Apo E allele and geno- type frequencies between groups categorized as demented versus normal. Regression analysis was used to determine whether the Apo E genotype was predictive of DRS in the presence of sex and age effects. This latter analysis was neces- sary to adjust for the age differences in cases and controls because Apo E ~4 frequency is known to decline in older populations 124, 251. This raised concerns that an elevated ~4 frequency would not be detected in this population be- cause the cases were older than the controls. In addition, because men and women may show a different rate of decline in ~4 frequency as a function of age [26], sex was also in- cluded in the regression analysis. The model fit was y = (Y

+ P,a + P1.r + Pig + E , where y = DRS, a = age, s = sex (0 = female, 1 = male), and g = Apo E genotype (indicated as 1 = f4 present, 0 = ~4 absent), F is random error. and a, PI . P2, and pi are the regression coefficients. This analysis was done on actual DRS score, rather than the recoded affectation status. This increases the power of the analysis since it does not require artificial dichotomization of the data. Analyses were also done with g coded as the number of ~4 alleles.

Results Fifty-two P D patients met the criteria for the diagnosis of dementia while 61 were identified as cognitively intact (Table 1). There were 78 nondemented controls. The demented patients were significantly older, had a higher frequency of males, and had more advanced disease as indicated by higher Hoehn-Yahr and UPDRS scores than nondemented PD patients. Dis- ease duration did not differ between the two groups. There was no statistical difference in the distribution of Apo E genotypes between the PD patients with and without dementia (Table 2 ) . The genotypes of both groups also did not differ from that of the control population (Table 2). Comparison of Apo E allele fre- quencies also showed no difference between PD with dementia, PD without dementia, and the control population (Table 3). The genotypes and allele fre- quencies in our control population were similar to that reported for the general population [ 2 3 ] . The regres- sion analysis of DRS on Apo E genotype, age, and sex identified age and sex, but not Apo E genotype, as significant predictors of DRS (Table 4) . The results obtained with Apo E genotype coded as presencelab- sence of ~4 were virtually identifical to those obtained with Apo E genotype coded as number of e4 alleles, so only the former are presented.

Discussion Apo E is well studied because of its role in plasma cholesterol and triglyceride homeostasis [24] . It medi- ates the endocytosis of cholesterol, triglyceride, and phospholipid-rich particles into hepatocytes and other cells by binding to low-density lipoprotein receptors and Apo E-specific receptors [24]. Apo E is also in- volved in the repair response to tissue injury, immuno-

Table. I . Denzogvupbio of- Parkitzsoti's Dikase Putleiits atid Controls

(1 ) PD with Normal (2 I (-3) Post Hoc

Characteristic Cognition P D with Dementia Controls Comparisons

Number Age (mean yr) Sex (male) Disease duration (mean yr) Mattis DRS score Hoehn-Yahr score UPDRS (total ADL) UPDRS (total motor) Blessed DRS

61 67.4 f 7.7 62.30;

6.5 f 5.3 139.5 f 2.6

9.9 ? 5.1 18.6 t 11.4 0.1 2 0.9

1.7 f 0.6

52 74.7 f 7.6 82.0%

7.2 f 5.4a 107.2 2 19.0

2.7 f 0.0"

28.0 ? 1 3 . 1 3.5 f 3.3

17.1 f 7.6

' 8 69.9 f 6.5 2 > 1 . 3 47.4"; 2 > 1 , 3

NIA 138.7 ? 3:4 2 < 1 , 3 NIA

0.3 f 0.8 2 > 1 > J 0.8 ? 1.8 2 > 1 > 3 0.2 f 0.4 2 > 1 , 3

Posr hoc comparisons are Tukey HSD following a significant F at p < 0.01, except for sex. Proportional analyses were used for sex follow- ing a significant ~ ' a r p < 0.01. 'Independent PD = Parkinson's disease; N/A = not applicable; DRS = Dementia Racing Scale; UPDRS = Unified Parkinson's Disease Raring Scale; ADL = activities of daily living; HSD = honestly significant difference (test)

tests significant a r p < 0.01.

Koller et al: Apo E Genotypes in PD 243

Table 2. Coinpari.ron of the Distribution of Apolipoprotein E Genotypes in Parki~t~oni Disease Patients With and #‘fitbout Denietitia arid the Control Population

PD with Normal PD with

Cognit ion Dement ia Controls

N u m b e r N u m b e r N u m b e r A p o E of of of Genotypes (2 Patients c/; Patients Cf Patients

212 0 0 2 1 3 2 312 10 6 12 6 1 3 10 31 3 62 38 56 29 59 46 412 3 2 6 3 0 0 413 23 14 23 12 24 19 414 2 1 2 1 1 1

Apo E = apolipoprotein E; PD = Parkinson’s disease

regulation, and modulation of cell growth and cell dif- ferentiation. I t has been identihed in both plaques and neurtcic tangles { 2 7 ) and binds tightly to P-amyloid (1, 28) . Three alleles, e3, ~ 3 , and e4, arising from single amino acid substitutions, occur in the general popula- tion. The most common allele, e3 , is present across a variety of different ethnic groups with a frequency of approximately 7 5%. [231. Patients homozygous for the e2 allele may develop type 111 hyperlipidemia. The €4 homozygote patient has elevated cholesterol and triglyceride levels and is predisposed to coronary artery disease.

An association between the e4 allele and late-onset A D is established [ l -4 , 29-3 I ) . For the € 4 homozy- gote, the odds ratio for the risk of A D ranges from 3 to I j (323. Corder and co-workers [41 recently re- ported that gene dosage affects both risk of A D and age of onset in the late-onset familial AD. k s k of A D ranged from 205;’ without an ~4 allele to 90%. in the e4 homozygote. Age of onset ranged from a mean age of 84.3 years without an e4 to 75 .5 years with one ~4 allele and 68.4 years with two e4 copies. Apo E &4/4 A D patients have more senile plaques than e 3 / 3 pa- tients {333. The strong effect of gene dosage suggests a possible direct biologic link to disease pathogenesis.

Table 1. Contpari.rorz of Apohpoprotrin E Al& Frrquenrir~ in Parkimon’.r Dijease Pu’cltiriits With dnd Without Dementid and tbe Control Population

PD with PD with N o r m a l Cognit ion Dement ia Controls

Apo E Allele i(‘i ) i(7 ) (? i ) ~ ~

€ 2 6 6 F 3 78.7 € 4 14.8

11.5 8.9 73. I 77.5 15.4 13.4

Apo E = apolipoprotein; PD = Parkinson’s disease

Table 4. RegresJion AnalyJiJ of Demeniia Rating Scale on Age. Sex, and Apolipoprotein E Genotype

Coefficient Variable Estimates p

a Constant 192.25 < 0.0001 PI Age -0.85 0.0002 P? Sex - 9.60 0.0222 Pi A p o E -2.59 0.5276

Apo E = apolipoprotein E.

Strittmatter and colleagues E71 hypothesized that the lack of ~3 allele may result in disordered microtubular aggregation and the development of neuronal tangles. I t has also been suggested that the role of e4 allele is to exacerbate amyloid deposition in senile plaques [ 5 , 61.

P D like A D is an age-related neurodegenerative dis- ease. The etiology of P D is unknown; however, it is thought that both genetic and environmental influ- ences are important 1341. PD has epidemiologic, clini- cal, and neuropathologic characteristics similar to AD. Dementia is common in PD, occurring in up to 4 0 9 of patients 1141. Several pathologic substrates appear to be responsible for dementia in PD, i.e., coincident A D (neuritic plaques and neurofibrillary tangles), Lewy bodies (in cortical and subcortical structures), and pri- mary nigral degeneration El?, 18, 35, 363. Thus it is possible that an Apo E allele could be a risk factor either for P D or P D with dementia. However, our data indicate that Apo E is not a susceptibility gene or risk factor in PD, even when age and sex are accounted for in the analysis. Marder and co-workers {377 also found no difference in Apo E e4 allele frequency in 22 P D patients with dementia, 57 PD patients without de- mentia, and 44 nondemented controls. These results suggest that amyloid deposition observed in nonneu- ritic plaques of PD and the neurohbrillary changes re- ported in PD dementia are not related to a mechanism associated with Apo E. The dementia of P D most likely has a differenc mechanism than AD. Thal and associ- ates [ 381 in a preliminary report of pathologically con- firmed cases concluded that Apo E ~4 allele is over- represented in A D and the Lewy body variant of A D ( A D pathology and Lewy bodies) but not in diffuse Lewy body disease (DLBD). The entity of DLBD may be more related to PD and AD.

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