Vol.:(0123456789)
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Jou nal o Neu ology (2023) 270:477–485
h ps://doi.o g/10.1007/s00415-022-11361-y
ORIGINAL COMMUNICATION
Homocys eine le els, gene ic backg ound, andcogni i e impai men
inPa kinson’s disease
Ma íaTe esaPe iñán1,2· DanielMacías‑Ga cía1,2· Sil iaJesús1,2· JuanF anciscoMa ín‑Rod íguez1,2,3·
Lau aMuñoz‑Delgado1,2· Ma iaValleJimenez‑Ja aba1· Dolo esBuiza‑Rueda1,2· Ma aBonilla‑To ibio1,2·
As idDanielaAda mes‑Gómez1,2· Pila Gómez‑Ga e1,2· PabloMi 1,2,4
Recei ed: 22 Ma ch 2022 / Re ised: 26 July 2022 / Accep ed: 30 Augus 2022 / Published online: 28 Sep embe 2022
© The Au ho (s) 2022
Abs ac
Backg ound Hype homocys einemia is conside ed an independen isk ac o o cogni i e impai men .
Objec i e To s udy he co ela ion be ween homocys eine le els and cogni i e impai men in pa ien s wi h PD.
Me hods We conduc ed a case–con ol s udy ha included 246 pa ien s wi h PD, o whom 32 we e cogni i ely impai ed. The
le els o homocys eine, ola e, and i amin B12 we e measu ed in pe iphe al blood. Mul i a ia e logis ic eg ession analysis
was applied o de e mine di e ences in homocys eine le els be ween PD pa ien s wi h and wi hou cogni i e impai men .
A me a-analysis was pe o med o cla i y he ole o Hcy le els in PD wi h cogni i e decline. Fi e polymo phisms in genes
in ol ed in Hcy me abolism, including MTHFR s1801133 and s1801131, COMT s4680, MTRR s1801394, and TCN2
s1801198, we e geno yped.
Resul s Ou case–con ol s udy showed ha homocys eine le els we e associa ed wi h cogni i e impai men in PD a e
adjus ing o possible con ounding ac o s such as le odopa equi alen daily dose. The esul s o ou me a-analysis u he
suppo ed he posi i e associa ion be ween homocys eine le els and cogni ion in PD. We ound ha he MTHFR s1801133
TT geno ype led o highe homocys eine le els in PD pa ien s, whe eas he MTHFR s1801131 CC geno ype esul ed in
highe ola e le els. Howe e , he polymo phisms s udied we e no associa ed wi h cogni i e impai men in PD.
Conclusions Inc eased homocys eine le els we e a isk ac o o cogni i e decline in PD. Howe e , no associa ion was
ound be ween polymo phisms in genes in ol ed in homocys eine me abolism and cogni i e impai men in PD. La ge-scale
s udies o e hnically di e se popula ions a e equi ed o de ini i ely assess he ela ionship be ween MTHFR and cogni i e
impai men in PD.
Keywo ds Pa kinson’s disease· Homocys eine· Cogni i e impai men · Me a-analysis· MTHFR
In oduc ion
Pa kinson’s disease (PD) is a p og essi e neu odegene a-
i e diso de ha encompasses mo o , cogni i e, beha io al,
and au onomic ea u es [1]. The e is g owing e idence ha
oxida i e s ess is in ol ed in he pa hophysiology, disease
p og ession, and de elopmen o cogni i e impai men in
PD [2].
In ecen yea s, se e al s udies ha e shown ha nea ly
30% o PD pa ien s ha e inc eased plasma homocys eine
(Hcy) le els [3]. Hcy is an amino acid gene a ed h ough
he deme hyla ion o me hionine. The Hcy p oduced in he
human body is mainly elimina ed h ough (1) eme hyla ion,
in which Hcy is eme hyla ed o me hionine wi h i amins
B2 and B12 as co ac o s; (2) anssul u a ion, in which Hcy
* Pila Gómez-Ga e
[email p o ec ed]
* Pablo Mi
[email p o ec ed]
1 Se icio de Neu ología y Neu o isiología Clínica, Unidad
de T as o nos del Mo imien o, Ins i u o de Biomedicina de
Se illa, (IBiS), Hospi al Uni e si a io Vi gen del Rocío/
CSIC/Uni e sidad de Se illa, A da. Manuel Siu o s/n,
41013Se ille, Spain
2 Cen o de In es igación Biomédica en Red sob e
En e medades Neu odegene a i as (CIBERNED), Mad id,
Spain
3 Depa amen o de Psicología Expe imen al, Facul ad de
Psicología, Uni e sidad de Se illa, Se ille, Spain
4 Depa amen o de Medicina, Facul ad de Medicina,
Uni e sidad de Se illa, Se ille, Spain
478 Jou nal o Neu ology (2023) 270:477–485
1 3
is i s ans o med in o cys a hionine (wi h i amin B6 as
co ac o ) o be me abolized in o cys eine and α-ke obu y ic
acid, which a e ul ima ely exc e ed om he body; and (3)
eleased in o he ex acellula luid [4]. Ele a ed plasma Hcy
le els migh be due o impai ed me abolism due o gene ic
a ian s in genes ha encode enzymes in ol ed in Hcy
me abolism. Se e al unc ional polymo phisms wi hin he
me hylene e ahyd o ola e educ ase (MTHFR), me hionine
syn hase educ ase (MTRR ), ca echol-O-me hyl ans e ase
(COMT), and anscobalamin II (TCN2) genesha e been
shown o a ec Hcy me abolism [5–7].
The enzymes in ol ed in he me abolism o me hionine
depend on B i amins: i amin B12, i amin B6, and olic
acid. A de iciency o ola e and i amin B12 leads o he
a ophy o CA1 neu ons in he hippocampus and he dis up-
ion o cogni i e p ocesses wi h inc eased Hcy [8]. The e
is e idence ha ele a ed Hcy le els a e associa ed wi h a
decline in cogni i e unc ioning [9, 10]. Samped o e al.
desc ibed an associa ion be ween highe Hcy le els wi h
on al co ical hinning and inc eased in aco ical di usi -
i y in on al and empo o-occipi al egions. The obse ed
mic os uc u al al e a ions in hese egions co ela ed, in
u n, wi h cogni i e pe o mance. Howe e , he li e a u e
on Hcy le els and cogni i e impai men in PD is mixed.
Some epo s ha e ound impai ed cogni ion in PD pa ien s
wi h hype homocys einemia [7, 11–18], while o he s ound
no ela ionship be ween Hcy le els and cogni i e impai -
men in PD [19, 20]. The disc epancies in he li e a u e can
be a ibu ed o he sample size, he comp ehensi eness o
cogni i e es s, o he in e indi idual gene ic a iabili y.
Consequen ly, he p esen s udy aimed o examine
whe he ele a ed Hcy le els we e associa ed wi h cogni-
i e impai men in PD. We i s in es iga ed di e ences in
Hcy le els be ween PD pa ien s wi h and wi hou cogni i e
impai men h ough a case–con ol s udy. Subsequen ly, we
pe o med a me a-analysis o cla i y he ole o Hcy le els
in PD wi h cogni i e decline. Then, we analyzed whe he
single nucleo ide polymo phisms (SNPs) in he MTHFR,
MTRR, COMT and TCN2 genes co ela e wi h hype homo-
cys einemia and con ibu e o cogni i e dys unc ion in PD.
Ma e ials andme hods
Pa icipan s ands udy design
We included 246 pa ien s wi h PD om he Mo emen
Diso de s Clinic o he Hospi al Uni e si a io Vi gen del
Rocio in Se ille (Spain), diagnosed ollowing he Mo e-
men Diso de s Socie y (MDS)clinical diagnos ic c i e ia
o PD [21].
All subjec s unde wen a medical assessmen by mo e-
men diso de s specialis s. PD pa ien s we e e alua ed in
he “on” mo o s a e and good dopamine gic esponse.
The diagnosis o cogni i e impai men in PD was de ined
acco ding o he MDSclinical diagnos ic c i e ia [22, 23].
Global cogni i e unc ion was e alua ed using he esul s
o he neu opsychological assessmen and he sco es on
s anda d scales (wi h he cu -o sco es o cogni i e impai -
men ) such as he Ma is Demen ia Ra ing Scale (
≤
139),
Pa kinson’s Disease Cogni i e Ra ing Scale (
≤
81), Mini
Men al S a e Examina ion (MMSE) (
≤
24), Mon eal Cogni-
i e Assessmen (
≤
26), Scales o Ou comes in Pa kinson’s
Disease-Cogni ion (
≤
22), and Pa kinson’s Disease Demen-
ia Sho Sc een (
≤
11) [24–29] as sc eening ools. Conse-
quen ly, we iden i ied PD pa ien s who me he diagnos ic
c i e ia o mild cogni i e impai men o demen ia in a long-
e m e iew o medical eco ds. All pa ien s wi h PD wi h
cogni i e impai men unde wen b ain magne ic esonance
as well as biochemical analyses o exclude non-degene a i e/
me abolic causes o cogni i e impai men . Fu he mo e, all
pa icipan s we e examined o exclusion c i e ia ha could
in luence Hcy le els a he ime o blood ex ac ion o any
o he ele an neu ological disease.
Hcy, ola e, and i amin B12 le els we e measu ed in
pe iphe al blood. The s udy was app o ed by he local e hics
commi ee in acco dance wi h he Decla a ion o Helsinki,
and w i en consen was ob ained om all pa icipan s p io
o blood wi hd awal.
Gene ics
Genomic DNA was isola ed om pe iphe al blood samples
acco ding o es ablished p o ocols using s anda d o au o-
ma ed me hods (DNA Isola ion Ki o Mammalian Blood,
Roche Diagnos ics, Indianapolis, IN, USA; MagNA Pu e
LC, Roche Diagnos ics, Indianapolis, IN, USA). DNA quan-
i ica ion was de e mined by a NanoD op2000 spec opho-
ome e (The mo Fishe Scien i ic, Wal ham, MA, USA).
All pa icipan s we e geno yped o s1801133 and
s1801131 (MTHFR), s4680 (COMT), s1801394 (MTRR
) and s1801198 (TCN2). Geno yping was pe o med using
Taqman SNP Geno yping Assays (Applied Biosys ems, Fos-
e Ci y, CA, USA) in a Ligh Cycle 480-II (Roche Applied
Science, Penzbe g, Ge many).
S a is ical analysis
All analyses we e pe o med using he s a is ical so wa e
R 4.0.4 and he PLINK so wa e 1.07. Demog aphic and
clinical a iables we e examined o no mali y using Shap-
i o–Wilk es ing. Compa isons o means we e made using
independen - es o he K uskal–Wallis es . Chi-squa e es
was used o assess he bina y ou come a iables. To exam-
ine he associa ion be ween cogni i e impai men and Hcy
le els in PD, mul i a ia e logis ic eg ession analysis was
479Jou nal o Neu ology (2023) 270:477–485
1 3
used con olling o age, sex, le odopa equi alen daily dose
(LEDD), disease du a ion, ola e, and i amin B12 le els.
The signi icance le el o all s a is ical es s was se a 0.05.
The associa ion be ween polymo phisms and Hcy le -
els in PD was assessed using mul i a ia e linea logis ic
eg ession models adjus ed o sex, age, LEDD, ola e, and
i amin B12 le els. Fu he mo e, he associa ion o hese
SNPs wi h ola e and i amin B12 le els in PD was e alu-
a ed using mul iple linea eg ession models adjus ed o
sex and age. We u he assessed he associa ion be ween
cogni i e impai men in PD and hese SNPs using logis ic
eg ession analyses adjus ed o sex, age, LEDD, disease
du a ion, ola e, and i amin B12 le els. All esul s we e
co ec ed o mul iple es ing using he Bon e oni co ec-
ion me hod. A P < 0.01 in he Ha dy–Weinbe g equilib ium
es and a mino allele equency o 1% we e es ablished as
quali y con ols.
Me a‑analysis
We pe o med his me a-analysis acco ding o he P e e ed
Repo ing I ems o Sys ema ic Re iews and Me a-analyses
(PRISMA) s a emen . De ailed in o ma ion on me a-analysis
me hods can be ound in he Supplemen a y Ma e ial.
Resul s
Obse a ional case–con ol s udy
A e applying inclusion and exclusion c i e ia, a o al o
246 PD pa ien s we e included. Demog aphic and clini-
cal da a o he s udy pa icipan s a e shown in Table1. PD
pa ien s wi h cogni i e impai men showed signi ican ly
highe Hcy le els compa ed o PD pa ien s wi hou cogni-
i e decline (21.8 ± 7.9 s. 17.5 ± 6.3μmol/L, P = 0.040).
We also obse ed ha PD pa ien s wi h cogni i e impai -
men we e olde , hey p esen ed an olde age a he onse
o he disease, and showed a longe du a ion o he disease
han PD pa ien s wi hou cogni i e decline. Fu he mo e, he
le odopa equi emen s acco ding o LEDD we e highe in
pa ien s wi h PD wi h cogni i e impai men .
Me a‑analysis
A e applying inclusion and exclusion c i e ia, 12 a icles
we e selec ed o his me a-analysis. Along wi h ou s udy,
13 Hcy le els mean di e ences we e included, comp ising
568 PD pa ien s wi h cogni i e impai men and 1241 PD
pa ien s wi hou cogni i e decline (TableS1).
The s anda dized mean di e ence (SMD) o each indi-
idual s udy and he pooled e ec size (ES) a e shown in
Fig.1. PD pa ien s wi h cogni i e impai men had highe
Hcy le els compa ed o PD pa ien s wi hou cogni i e
decline (SMD = 0.67; 95% CI 0.42–0.92,
X
212 = 40.54,
I2 = 70.4%, P < 0.001).
A signi ican isk o publica ion bias was de ec ed as
demons a ed by he p esence o asymme ies in he unnel
plo and con i med by he Egge ’s es (P = 0.023) (Fig.
S2). Sensi i i y analysis showed ha he Chen e al. s udy
had a majo in luence on o e all he e ogenei y wi h li -
le impac on he pooled ES, while he Ma inez-Ho a
e al. s udy was he mos in luen ial on he pooled ES (Fig.
S3). In he “lea e-one-ou ” analysis, he pooled ES as well
as he he e ogenei y dec eased when excluding he Chen
Table 1 Demog aphic and clinical da a in PD pa ien s wi h cogni i e impai men and PD pa ien s wi hou cogni i e impai men
PD Pa kinson’s disease, N o al numbe o subjec s, SD s anda d de ia ion, Hcy homocys eine, Vi B12 i amin B12, LEDD le odopa equi alen
daily dose
a Based on chi-squa ed es
b Based on K uskal–Wallis es
c Based on T-S uden es
d Mul i a ia e logis ic eg ession adjus ed o age, sex, LEDD, disease du a ion, ola e and i amin B12 le els
Pa ame e To al PD (N = 246) PD wi hou cogni i e impai -
men (N = 214)
PD wi h cogni i e impai -
men (N = 32) P alue
Sex (% men) 144 (58.5) 129 (60.3) 15 (46.9) 0.15a
Age (y), mean ± SD 62.7 ± 11.4 61.7 ± 11.5 69.3 ± 7.8 < 0.001b
Age a onse (y), mean ± SD 52.9 ± 12.3 52.3 ± 12.6 56.9 ± 9.6 0.043c
Disease du a ion (y), mean ± SD 9.9 ± 6.8 9.4 ± 6.9 12.8 ± 6.0 0.005c
Hcy (μmol/L), mean ± SD 18.1 ± 6.7 17.5 ± 6.3 21.8 ± 7.9 0.040d
Fola e (ng/mL), mean ± SD 8.3 ± 4.2 8.3 ± 4.1 8.1 ± 4.7 0.821c
Vi B12 (pg/mL), mean ± SD 399.0 ± 200.1 396.9 ± 200.5 413.1 ± 200.5 0.672c
LEDD, mean ± SD 793.2 ± 479.1 766.8 ± 488.1 969.5 ± 374.5 0.009c
480 Jou nal o Neu ology (2023) 270:477–485
1 3
e al. s udy (SMD = 0.59, 95% CI 0.38–0.79, I2 = 59%)
(Fig. S4).
A subg oup analysis was pe o med o explo e his he -
e ogenei y. This analysis was based on he s udy design and
showed no impac o his po en ial mode a o on he pooled
ES (
X
21 = 2.58, P = 0.110). The impac o po en ial con inu-
ous mode a o s (yea o publica ion, age, pe cen age o men
in he samples s udied, ola e, and i amin B12 le els) on he
pooled ES was assessed wi h me a- eg ession. This analysis
did no p oduce a signi ican associa ion be ween po en ial
mode a o s and pooled ES (TableS2).
In luence o gene ic ac o s onbiochemical
pa ame e s
We in es iga ed whe he he selec ed polymo phisms we e
associa ed wi h Hcy le els in PD and ound an associa ion
be ween he MTHFR s1801133 TT geno ype and inc eased
Hcy le els in PD a e co ec ion o mul iple es ing (TT
s. CC: β = 3.79; 95% CI 1.76–5.82; co ec ed P = 0.026)
(Table2). Fu he mo e, we assessed whe he hese polymo -
phisms in luenced i amin B12 le els. In his sense, no a i-
an s we e signi ican ly associa ed wi h i amin B12 le els
a e adjus ing o sex and age. Rega ding ola e le els, he
MTHFR s1801131 CC geno ype was ound o be signi i-
can ly associa ed a e co ec ion o mul iple es ing (CC
s. AA: β = 3.03; 95% CI 1.38–4.69; co ec ed P = 0.031).
Compa ison o PD pa ien s
wi handwi hou cogni i e impai men
None o he SNPs we e signi ican ly associa ed wi h cog-
ni i e impai men in PD a e co ec ion o mul iple es s
(Table3).
Discussion
Cogni i e decline in PD has been he subjec o inc easing
esea ch in ecen decades. In ou case–con ol s udy, PD
pa ien s wi h cogni i e impai men showed inc eased Hcy
le els compa ed o PD pa ien s wi hou cogni i e impai -
men . The esul s o ou me a-analysis suppo ed he posi i e
associa ion be ween Hcy le els and cogni ion in PD. Fu -
he mo e, we demons a ed ha he MTHFR s1801133 TT
geno ypeled o highe Hcy le els in PD pa ien s, while he
MTHFR s1801131 CC geno ype esul ed in highe le els
o ola e concen a ion. Howe e , he SNPs s udied we e no
associa ed wi h cogni i e impai men in PD.
Ex ensi e clinical da a suppo he ole o hype homo-
cys einemia as a isk ac o o cogni i e impai men . Hcy
can di ec ly exe oxic e ec s on neu ons by oxida i e
s ess inju y, DNA damage, and al e ing he exp ession o
he NMDA ecep o , leading o dys egula ion in calcium
homeos asis, mi ochond ial unc ion, neu onal au ophagy,
and apop osis [30]. Addi ionally, Hcy can cause damage o
ascula endo helial unc ion and al e he pe meabili y o
he blood–b ain ba ie , esul ing in small essel disease
in he b ain [31]. Some s udies ha e ound ha endo helial
in lamma ion unde high Hcy condi ions p omo ed ascula
inju y, which, in u n, led o cogni i e impai men [32].
The inc eased Hcy le els ound in ou coho o PD
pa ien s wi h cogni i e impai men a e consis en wi h he
da a epo ed in he li e a u e [10]. Howe e , some ela i ely
ew s udies ailed o demons a e his ela ionship [19, 20,
33]. The esul s o a s udy in a Spanish coho ound no e i-
dence o an associa ion be ween Hcy plasma le els and cog-
ni i e impai men and demen ia in PD [20]. The di e ences
seen wi h ou s udy could be explained by he sc eening es s
used o he assessmen o cogni i e s a us. Rod iguez-O oz
e al. e alua ed he cogni i e unc ion wi h he MMSE, bu
Fig. 1 Fo es plo displays
andom-e ec s me a-analysis
esul s o he associa ion
be ween homocys eine le els
and cogni i e impai men
in Pa kinson’s disease. The
o e all s anda d mean di e -
ence be ween g oups and i s
95% con idence in e al a e
ep esen ed by he ligh blue
diamond
481Jou nal o Neu ology (2023) 270:477–485
1 3
Table 2 Le els o homocys eine, i amin B12 and ola e co esponding o he di e en geno ypes o he polymo phisms in PD pa ien s
To al PD
Hcy β (95% CI) P alueaAdjus ed
P alue*
Vi B12 β (95% CI) P aluebAdjus ed
P alue*
Fola e β (95% CI) P aluebAdjus ed
P alue*
MTHFR
s1801133
TT 20.6 ± 9.9 3.787 (1.758/5.816) 0.002 0.026 342.4 ± 142.7 −41.441
(−118.149/35.267)
0.373 1.000 7.5 ± 3.8 −1.552
(−3.080/−0.024)
0.095 1.000
CT 17.8 ± 6.3 1.083 (−0.257/2.422) 0.183 1.000 428.8 ± 251.0 44.185
(−6.100/94.469)
0.148 1.000 8.1 ± 3.9 −1.068
(−2.070/−0.067)
0.079 0.874
CC 17.1 ± 5.5 Re . Re . Re . 384.0 ± 137.0 Re . Re . Re . 9.2 ± 4.7 Re . Re . Re .
TT s. CT + CC – 3.136 (0.922/5.349) 0.006 0.030 – −68.240
(−152.000/15.490)
0.112 0.558 – 0.853 (−2.576/0.768) 0.290 1.000
MTHFR
s1801131
CC 18.1 ± 5.5 0.054 (−2.277/2.386) 0.969 1.000 377.5 ± 115.5 −22.336
(−108.143/63.470)
0.668 1.000 11.2 ± 4.4 3.033 (1.376/4.689) 0.003 0.031
AC 17.9 ± 6.2 −0.424
(−1.766/0.919)
0.602 1.000 415.6 ± 275.0 18.236
(32.227/68.700)
0.551 1.000 8.4 ± 4.2 0.352 (−0.622/1.326) 0.551 1.000
AA 17.8 ± 7.1 Re . Re . Re . 398.3 ± 163.2 Re . Re . Re . 8.0 ± 3.9 Re . Re . Re .
CC s. AC + AA – 0.234 (−2.443/2.911) 0.864 1.000 – −29.940
(−128.500/68.610)
0.552 1.000 – 2.886 (0.983/4.788) 0.003 0.016
COMT
s4680
AA 19.5 ± 9.1 1.213 (−0.562/2.988) 0.260 1.000 389.9 ± 176.5 −10.800
(−74.551/52.952)
0.780 1.000 7.8 ± 4.2 −0.581
(−1.886/0.725)
0.464 1.000
AG 17.4 ± 6.2 −0.106
(−1.436/1.225)
0.896 1.000 402.1 ± 219.5 1.570
(−46.228/49.369)
0.957 1.000 8.5 ± 4.2 0.237 (−0.742/1.216) 0.690 1.000
GG 18.1 ± 6.0 Re . Re . Re . 398.0 ± 183.2 Re . Re . Re . 8.2 ± 4.2 Re . Re . Re .
AA s. AG + GG – 1.275 (−0.611/3.161) 0.187 0.932 – −11.74
(−79.280/55.800)
0.734 1.000 – −0.722
(−2.106/0.662)
0.308 1.000
TCN2
s1801198
GG 16.2 ± 4.4 −0.879
(−2.667/0.910)
0.418 1.000 467.1 ± 201.4 61.488
(−5.280/128.256)
0.130 1.000 8.3 ± 4.0 0.132 (−1.213/1.476) 0.872 1.000
GC 18.1 ± 7.3 0.342 (−1.025/1.709) 0.680 1.000 374.6 ± 188.6 −30.005
(−81.043/21.033)
0.333 1.000 8.7 ± 4.2 0.512 (−0.516/1.539) 0.412 1.000
CC 18.3 ± 6.5 Re . Re . Re . 406.4 ± 224.7 Re . Re . Re . 8.3 ± 4.3 Re . Re . Re .
GG s. GC + CC – −1.055
(−3.001/0.890)
0.289 1.000 – 77.420
(5.032/149.800)
0.037 0.186 – −0.140
(−1.596/1.317)
0.851 1.000

482 Jou nal o Neu ology (2023) 270:477–485
1 3
also wi h he Blessed Demen ia Ra ing Scale, which was no
included in ou cogni i e e alua ion ba e y o diagnosis o
cogni i e impai men . Annanmaki e al. ound no co ela ion
be ween Hcy le els and neu opsychological pe o mance in
a s udy coho o 40 pa ien s wi h PD [33]. Fu he mo e,
Camicioli e al. showed ha Hcy did no co ela e wi h
global cogni ion measu es in a Canadian popula ion o 51
pa ien s wi h PD [19]. No ably, he s udies ailing o ind a
ela ionship in ol ed ela i ely small sample sizes (N = 40
and N = 51, espec i ely), which would explain he incon-
sis encies seen wi h ou s udy.
The me a-analysis pe o med con i med ha he Hcy
le els we e highe in he PD pa ien s wi h cogni i e impai -
men . The esul s o his me a-analysis may guide powe
analysis and sample size es ima ion o u u e obse a ional
s udies as well as p eclinical and clinical s udies. One majo
limi a ion is ha he subs an ial he e ogenei y obse ed
among all he included s udies could no be cla i ied. Con-
side ing ha some o he s udies analyzed ew PD-speci ic
Signi ican P alues a e ma ked in bold
PD Pa kinson’s disease, Hcy homocys eine, Vi B12 i amin B12, LEDD o al le odopa equi alen daily dose, CI con idence in e al, Re . e e ence
a Linea eg ession model adjus ed o sex, age, LEDD, ola e and i amin B12 le els
b Linea eg ession model adjus ed o sex and age
*Bon e oni P alue adjus men
Table 2 (con inued)
To al PD
Hcy β (95% CI) P alueaAdjus ed
P alue*
Vi B12 β (95% CI) P aluebAdjus ed
P alue*
Fola e β (95% CI) P aluebAdjus ed
P alue*
MTRR
s1801394
GG 18.0 ± 6.0 −0.208
(−2.150/1.005)
0.860 1.000 370.9 ± 137.2 7.107
(−53.024/67.238)
0.0748 0.823 7.6 ± 4.4 1.108 (−0.351/2.567) 0.211 1.000
AG 17.6 ± 6.9 −0.609
(−2.223/1.005)
0.534 1.000 402.8 ± 194.3 Re . 0.1607 1.000 8.7 ± 4.4 1.007 (−0.207/2.221) 0.172 1.000
AA 18.4 ± 6.5 Re . Re . Re . 450.9 ± 285.4 Re . Re . Re . 8.7 ± 4.4 Re . Re . Re .
GG s. AG + AA – 0.236 (−1.595/2.068) 0.801 1.000 – −41.610
(−110.600/27.430)
0.239 1.000 – 0.384 (−1.006/1.775) 0.589 1.000
Table 3 Gene ic associa ion be ween he gene ic polymo phisms and
he de elopmen o cogni i e impai men in PD
OR odds a io, CI con idence in e al, Re . e e ence
a Logis ic eg ession model adjus ed o sex, age, LEDD, disease
du a ion, ola e and i amin B12 le els
*Bon e oni P alue adjus men
OR (95% CI) P alueaAdjus ed
P alue*
MTHFR
s1801133
TT 1.010 (0.893–1.143) 0.895 1.000
CT 0.956 (0.881–1.037) 0.364 1.000
CC Re . Re . Re .
MTHFR
s1801131
CC 1.021 (0.888–1.174) 0.807 1.000
AC 1.030 (0.950–1.116) 0.544 1.000
AA Re . Re . Re .
COMT
s4680
AA 0.925 (0.833–1.027) 0.221 1.000
AG 1.000 (0.926–1.081) 0.997 1.000
GG Re . Re . Re .
TCN2
s1801198
GG 1.016 (0.912–1.132) 0.809 1.000
GC 1.030 (0.949–1.119) 0.552 1.000
CC Re . Re . Re .
MTRR
s1801394
GG 0.940 (0.856–1.032) 0.877 1.000
AG 0.989 (0.884–1.107) 0.277 1.000
AA Re . Re . Re .
483Jou nal o Neu ology (2023) 270:477–485
1 3
epo ed cha ac e is ics, we we e unable o assess o he ac-
o s ha may ha e con ibu ed o he obse ed he e ogenei y.
Some li es yle ac o s such as die a y habi s and physical
exe cise, migh in luence he me abolism o homocys eine.
Fo his eason, u u e esea ch should add ess he con ibu-
ion o hese ac o s o he obse ed he e ogenei y [34, 35].
Among he gene ic causes o hype homocys einemia,
he MTHFR gene is in ol ed in he me abolism o Hcy and
me hionine, as well as in me hyla ion p ocesses. Al hough
se e al polymo phisms ha e been desc ibed o his gene,
he a ian s1801133 is he mos equen ly in es iga ed
due o i s unc ional impac . Se e al s udies ha e add essed
he associa ion be ween he MTHFR s1801133 a ian and
inc eased Hcy le els in pa ien s wi h PD. Ou obse a ions
a e in line wi h hose o Bialecka e al., in which he MTHFR
s1801133 a ian was he gene ic de e minan o Hcy le els
in pa ien s wi h PD [11]. On he o he hand, we also dem-
ons a ed he impac o he MTHFR s1801131 a ian on
ola e le els in pa ien s wi h PD. To ou knowledge, his is
he i s s udy o link MTHFR s1801131 wi h ola e le els
in PD.
Rela i ely ew s udies ha e in es iga ed he associa ion
be ween gene ic ac o s in ol ed in Hcy me abolism and
cogni i e dys unc ion in PD pa ien s [11, 20, 36]. To da e,
no signi ican associa ion has been shown be ween cogni-
i e impai men in PD and he MTHFR C677T, MTHFR
A1298C, TCN2 G776C, SLC19A1 G80A, COMT G472A,
MTR A2756G, and CBS 844ins68 polymo phisms. In ag ee-
men wi h hese esul s, we ailed o iden i y a ela ionship
be ween he polymo phisms and cogni i e impai men in
PD.
In e es ingly, a case–con ol s udy e ealed ha men om
he Heal h in Men S udy coho wi h he MTHFR C677T TT
geno ype had 46% highe odds o cogni i e impai men han
men wi h he CC geno ype [37]. Fu he mo e, a ecen me a-
analysis has demons a ed he ole o he MTHFR C677T
polymo phism in Alzheime ’s disease in Asians bu no in
Caucasian popula ions [38]. Thus, i would be o in e es o
u he s udy he ole o he MTHFR C677T a ian in la ge
popula ions o PD and, in addi ion, in popula ions wi h di -
e en e hnic backg ounds, o assess whe he he MTHFR
a ian s ha e conside able a ia ion be ween di e en e hnic
g oups.
This s udy has some limi a ions. Fi s , cogni i e impai -
men was no assessed wi h he same s anda d cogni i e
scale du ing ollow-up. Howe e , all he scales used o
assess cogni i e pe o mance we e in e na ionally accep ed
and success ully dis inguished PD pa ien s wi h and wi hou
cogni i e impai men . Fu he mo e, we did no assess cogni-
i e pe o mance in a popula ion o heal hy con ols, which
may ep esen an impo an limi a ion since we could no
elucida e whe he he e ec o Hcy on cogni ion in PD migh
in e ac in a di e en way han in heal hy con ols. Ano he
limi a ion was he sample size o ou case–con ol s udy, bu
he esul s o he me a-analysis ein o ced he associa ion
desc ibed in he case–con ol s udy.
In conclusion, ou case–con ol s udy demons a ed ha
inc eased Hcy le els we e associa ed wi h cogni i e decline
in PD. The esul s o ou me a-analysis u he suppo ed he
posi i e associa ion be ween Hcy le els and cogni ion in PD.
No associa ion was ound be ween polymo phisms in genes
implica ed in Hcy me abolism and cogni i e impai men in
PD pa ien s. La ge-scale s udies in e hnically di e se popu-
la ions will be equi ed o de ini i ely de e mine he ela-
ionship be ween MTHFR and cogni i e impai men in PD.
Supplemen a y In o ma ion The online e sion con ains supplemen-
a y ma e ial a ailable a h ps:// doi. o g/ 10. 1007/ s00415- 022- 11361-y.
Acknowledgemen s The au ho s hank he dono s and he Hospi al
Uni e si a io Vi gen del Rocio-Ins i u o de Biomedicina de Se illa
Biobank (Andalusian Public Heal h Sys em Biobank and ISCIII-Red
de Biobancos PT17/0015/0041) o he human specimens used in his
s udy.
Au ho con ibu ions MTP: concep ion and design o he s udy, analy-
sis and in e p e a ion o da a; w i ing o he i s d a and e iew and
c i ique o he manusc ip . DM-G, SJ, LM-D, and ADA-G: acquisi ion
o da a; e iew and c i ique o he manusc ip . JFM-R, MVJ-J, and
PG-G: analysis and in e p e a ion o da a; e iew and c i ique o he
manusc ip . DB-R and MB-T: analysis o da a; e iew and c i ique o
he manusc ip . PM: concep ion and design o he s udy; in e p e a ion
o da a; e iew and c i ique o he manusc ip . All he lis ed au ho s
ga e hei inal app o al o he inal e sion o he manusc ip .
Funding Open Access unding p o ided hanks o he CRUE-CSIC
ag eemen wi h Sp inge Na u e. This wo k was suppo ed by he
Spanish Minis y o Science and Inno a ion [RTC2019-007150-1], he
Ins i u o de Salud Ca los III-Fondo Eu opeo de Desa ollo Regional
(ISCIII-FEDER) [PI14/01823, PI16/01575, PI18/01898, PI19/01576],
he Conseje ía de Economía, Inno ación, Ciencia y Empleo de la Jun a
de Andalucía [CVI-02526, CTS-7685], he Conseje ía de Salud y Bie-
nes a Social de la Jun a de Andalucía [PI-0471-2013, PE-0210-2018,
PI-0459-2018, PE-0186-2019], and he Fundación Alicia Koplowi z.
Pila Gómez-Ga e was suppo ed by he “Nicolás Mona des” p o-
g am [C-0048-2017] ( om Andalusian Regional Minis y o Heal h).
Sil ia Jesús was suppo ed by he "Acción B Clínicos In es igado es”
p og am om he Conseje ía de Salud y Familias de la Jun a de Anda-
lucía [B-0007-2019]. Daniel Macías-Ga cía was suppo ed by he “Río
Ho ega” p og am [CM18/00142] om he Ins i u o de Salud Ca los
III (ISCIII-FEDER). Juan F ancisco Ma ín-Rod íguez was suppo ed
by he VI-PPIT-US om he Uni e si y o Se ille [USE-18817-A].
Lau a Muñoz-Delgado was suppo ed by he “Río Ho ega” p og am
[CM21/00051] om he Ins i u o de Salud Ca los III (ISCIII-FEDER).
The unde s had no ole in s udy design, da a collec ion and analysis,
decision o publish, o p epa a ion o he manusc ip .
Decla a ions
Con lic s o in e es Pe iñán MT: none. Macías-Ga cía D: has ecei ed
hono a ia om Abb ie and Zambon. Jesús S: has ecei ed hono a ia
om Abb ie, Bial, Me z, UCB, I al a maco and Zambon. Ma ín-Rod-
iguez JF: none. Muñoz-Delgado L: has ecei ed hono a ia om Te a.
Jiménez-Ja aba MV: none. Buiza-Rueda D: none. Bonilla-To ibio M:
484 Jou nal o Neu ology (2023) 270:477–485
1 3
none. Ada mes-Gómez AD: has ecei ed hono a ia om Abb ie and
I al a maco. Goméz-Ga e P: none. Mi P: has ecei ed hono a ia om
Abbo , Alle gan, Abb ie. Bial, B i annia, I al a maco, Me z, UCB,
Te a and Zambon. The au ho s ha e no con lic o in e es o epo .
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