行政院國家科學委員會專題研究計畫 成果報告
台灣家族性及早發型(年輕型)巴金森氏病之臨床與基因研
究(2/2)
計畫類別： 個別型計畫
計畫編號： NSC92-2314-B-002-131-
執行期間： 92 年 08 月 01 日至 93 年 07 月 31 日
執行單位： 國立臺灣大學醫學院神經科
計畫主持人： 吳瑞美
計畫參與人員： 吳瑞美、胡務亮、林靜嫻
報告類型： 完整報告
處理方式： 本計畫可公開查詢
中 華 民 國 93 年 11 月 8 日
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- i r r l oParkin Mutations and Earry-onset parkinsonism
. h ^ l t - - - /
rn a laiwanese Cohort
Ruey-MeeiWu,
MD, phD; Rebecca
Bounds
Wuh-Liang
Hwu, MD, phD; ludy Chen, M
Bockground: Loss of function of the parkin gene (pRICV) is the predominant genetic cause of iu.,reniie and early_ onset parkinsonism in Japan, Europe, and the United States.
Obiective* To evaluate the frequency of pRKN muta-tions in Taiwanese (ethnic Chineje) paiients with early_ o n s e t p a r k i n s o n i s m a n d t o e x p l o r e g e n o t y p e _ p henotype correlations.
Design: Clinical assessmenr included medical, neuro-logic, aad psychiatric evaluation. Genomic DNA sequenc_ i"nS an$ tla,ntiuriv_e polymerase chain reacdon were per-tormed to identify pRKN mutations. Gene expression was examined in patient lymphoblastoid cell lines, in which PRKN mutations were identified.
Pntienls: Forty-one Taiwanese patients with early-onset parkinsonism (aged <50 years at early-onset). Resulls: Four of 4l probands had pRKN mutations. One ploband had compound heterozygous mutations, with
HE PREDOMINANT GENETIC
cause of early-onset parkin-sonism (aged <50 years at onset) in Japan, Europe, and the United States is re-cessive homozygous or compound het-erozygous mutation of the parkin gene (PRI(N). Many studies suggesr that l8o/o 't"o
49To of early-onset disease can be as-cribed to loss of parkin function in these populations (reviewedby Mata et a|). Ex-onic deletions/duplications of pRKN are generally de novo, whereas many of the missense mutations discovered in Euro-pean and North American populations seem to originate from common Euro-pean founders.2'3
Taiwan's population history encom-passes indigenous Austronesian peoples and early Chinese setrlers, known as the Hakka, originating from the Hunan prov-ince approximately 1500 years ago.
Ben-a PRKN exon 2 deletion Ben-and Ben-an exon 7 G2g4R substitu-tion. The phenotype resembled typical parkinson dis_ ,ease, ]\1 patients were mutarion carriers. One pro_ band had PRKN exon 2 and exon 3 deletions in the same allele. However, this patient's phenotype was that of clas-sic "parkin-prove.n" autosomal receslive juvenile par_ kinsonism, characterized by symmetrical ioot dystonia at onser, gait disturbance, diurnal change, and veiy slow progression. The 2 remaining carriers had novel Lretero_ zygous exon 1l R396G substitutions. parients with pRKN mutations were younger at onset than those without mu-tations, and they required a lower dose of levodopa de_ spite longer disease duration.
Gonclusions: Mutations in pRKN are a rare cause of earh-onset parkinsonism in Taiwanese individuals. The ovei-all mritation-frequcncy, adjusted for age ai onset, lvas com-parable with that reported for white cohorts; however, th-e point murarions identified seem to be population
spe-c l t I spe-c .
Sarah Lincoln; Gwinn-Ha
Mary Hulihan, MS
; Chin-Hsien
Lin, MD ;
MD; MattFarrer, PhD
aA ArchNeurol.2005
Author Affiliations: Departments of Neurology, Pediatrics, and Medical
Genetics, National Taiwan
University Hospital and College of Medicine, National Thiwan University, Taipei (Drs Wu, Lin, and Hwu); Department of Medicine, University of Califomia at Los Angeles (Dr Chen); Division of
Neurogenetics, National
Institute of Neurological
Disease and Stroke, Bethesda,
Md (Dr Gwinn-Hardy); and
Laboratories of Neurogenetics,
Department of Neuroscience, Mayo Clinic, Jaclisonville, Fla (Dr Farrer and Mss Bounds. Lincoln, and Hulihan).
shengren settlers originated frorn the-Fu-jlan province during the Ming dynasty (L366-I64+). During the tTth century, the Portuguese, Dutch, and Spanish main-tained colonial interests in Taiwan for sev-eral decades. However, ethnic Chinese im-migration increased 7-fold during the subsgquent 150 years of Manchu rule on the Chinese mainland. More recent his-tory includes the Treary of Shimonoseki, which ceded Taiwan to Japan from 1895 to 1945. Most recently, ethnic Chinese Waishengren immigrants settled. in Tai. wan starting in 1949.4 Taiwan's diverse population history suggesrs that known and novel PRKN mutations may be preva-lent in patienrs with early-onset parkin-sonism. Herein, we report the first com-prehensive evaluation of the clinical features and frequency of pRKN muta-tions in Taiwanese patients wirh early-onset parkinsonism iiving on the island.
: !-44__ .
o z
40-44 45.50 25-29 30-34 35-39
Age at oisease onset, y
Figure 1. Distribution of 41 faiwanese patients with early-onset parkinsonism by age at disease onset.
Taiwanese (ethnic Chinese) patients with early-onset parkin-sonism (s;mptomatic onset at age <50 years) were recruited lrom the Movemenr Disorder Clinics of the National Taiwan University Hospital (Figure l). Informed consent was ob_ tarnect accordin€ to an ethically approved protocol before the
?lud,y;,1, l*.ologist who sp"iialires in m'ovement disorders
\K.-M.w.) evaluated all patients in Taiwan, where they cur_
I1-T]Y.Tid. Allpatients met the criteria forpossible orirob_
aDle rarklnson disease (pD), including the presence of ai least 2 (possible PD) or 3 (probable pD) oithe 4 cardinal fearures
lresdng rremor, bradykinesia, rigidity, and postural instabil_
rty with asymmetrical onset), with a substantial and sustained
response to treatment withlevcdopa or a dopanine agcnist.5
Clinical evnluations included a hisory oi the preient ill-ness, a family history, a medical history, and a review of sys-tems, with an emphasis on movement dlorder, psychiatric ill_
1-ess^, a1d cognitive function. parient evaluations included the
Unified Parkiruon's Disease Rating Scale, the Hoehn and yahr ,
{u9., the Folstein Mini-Mental State Examination, aird a stan--dard neurologic examinarion.6 patienb with arypical fearures or evidence of secondary parkinsonism .urlr"d by other neu_
rologic diseases or kno#n'drugs or toxins weie eicluded.
As-:eT--e"-r of possible secondary parkinsonism or atypicai pD
included neuroimaging (head iomputed romography or mag_ n€tic resonance
_imaging) and additional laboritory
-tests (ii_ cluding rests for Wilson disease and for trinucleotide repear ex_ pansions in the ataxin-2 and ataxin-3 genes).
,. . For each proband identified as having a pRIO/ murarion, the
nvlng relatives were contacted according to an approved proto-col, and informed consenr was obtained"for further clinical and genedc srudies. Follow-up was performed for the nuclear fami-nes ot probands ll:2 and II:5 (Flgure 2); 2 additional family A members were included. Neither family C nor family D hah a family history of PD or psychiatric disorder. Fony-5srr"r, f.i wanese parients with rypical late-onset pD and 50 control
sub-Jects witholt signs of neurologic disease were also recruited to
assess the frequency of any pIiI(N poinr mutarion identified.
- For_geneilc analysis, a 10-mL venous blood sample was col_
Iected lor Epstein-Barr vi-rus transformation, providing a source ot lymphoblasroid cells from which m"rr"rrge. RNAind DNA were isolated. Spectrophotometry and electrof,horesis were used
lo_Tr^._s rhe quality of DNA extracred. A generic marker,
D6S305, in PRKN inrron 6 underwenr g.notJping for tamily members as previously described (Figure 2).t ln addltion, quan_ titative polymerase chain reaction and sequencing of genomic
SUMMARY OF CLINICAL FINDINGS
DNA were carried out to assay for pRKN exonic deletion/ duplication For patients in whom pRKN muudons were iden-tified, total RNA was exrracred from Epstein_Barr virus_ transformed lymphoblastoid cell lines using TRlzol reagenr z ^ G.
(lnvitrogen Corp, Carlsbad, Calif), and comllemerrtrry drue/ \f\ \
f ,?[fl
::il]:?;i:$Rl^'il:'::,':ffi
:l:il!tiffi""il;ll_(!9
ers and established methods (Figure 3).7 BasJvariants aie la_
beled from the ATG start of protein tanslarion (GenBank Accession No. 4.8009973).
lncluded in this study were 4 I probands of Taiwanese (eth-nic Chinese) descent, with a meantSD age at onset of .40.0+6.4 years (range, 19-48 years)-and a meantSD dis_
ease duration of8.0.r5.3 years (range, l-19 years). ln the ovelall sarnple,T (I7Yo) of 4l patients had a family history of PD. Of the 7 probands with lamilial parkinsonism, 3 had affected siblings *ith disease onset before age 40 years , con-sistent with autosomal recessive inheritanie. ln I patient, disease onset was consistent with autosomal dominant in-heritance, with a parent affected by parkinsonism. The re-maining 3 index patients had 3 relatives diagnosed as hav_ lng PD. Of the 4l p-atients with parkinsonism, consanguinity was noted for only I patienr, who was initially sJen for hemiparkinsonism (rigidity and bradykinesia without tremor) at age 30 years, but without a familv historv of pD. ln the affected cohort, there were 25 men and 16 women (male-female ratio, 1.6:l). Regarding clinical manifestations, most patients (39 t93%l of 4D had an SsynT.netric.al onset of symptoms. Dystonic features, sleep benefit, and diurnal variation in symptoms were notei in 44o/o (18/+l), 28Vo (II/39), and i6o/o (6/38) of pa_ tients with early onset, respectively. Resting tremor was less common than rigidity and bradykineJia either ini-tially (4lo/o II7 /4ll vs 73o/o 130/4LD or as a cardinal symp_ tom during the disease course (49"/o [ZO/4I] vs SSy" [:bf 4l l). Psychiatric symptoms of depression and anxiety were seen in 24o/o (Lj/+I) and 27o/" (LI/4I) of the index
pa-L/tJ Ex2 devExTh2B4R Lql
Heterozysous Ex2-3 d€t
- 7{.o
204/228-204t228
[ fr4ale O tr{Probabte parkinsonism fr }eaO
O Female G
lossible parkinsonism O Concomitant Dystonia
Figure 2. Pedigrees of probands
Age at symptom onset is shown
alle.le sizes are shown for D6S30s;the exon 2ieletion [ixioeil ;.g;il;t;; with the 228-base pairailete, whereas the G28aR missinse mititidn dan ne
(99-TcTRODAT-l [a specific ligandJ single_photon emis_ sion computed tomography) in familyAiproband II:2 in_ drcated severe degen_eration of the nigrostriatal path_ w.ay, most pronounced in the putamen an-d consisteni*ith :h1"g:: observed in sporadii pD. Family n pr"U""a f i,i la: a Trst?ry ot..major depression and was inirially con_ :t.,",1.* ro hav-e "dopa^-responsive dystonia" owing to di-urnal llucruation in foot dystonia and remarkafle im-provement in- gait when taking low doses of levodopa (50 mg-twice daily). The clinical presentarions of proiands C Il:7 and D II:2 resembled sporadic pD, but with ear_ lier-onset. The meantSD age at onset in'rh;4 parienrs urifi I or more PRKN muutions was 33.7t lI.0 years !y"g", 19-44 years) , which was younger than ih^, ;f ,h; 37 patients without PRKN -rrtutLrr, (meanrSD. 40.6t5.5 years; range,- 29-48 years; plgefl*Jt,.){WSrJ meantSD duration of parkinsonism was I i.5r5:f;e;Ei. \ .i-(range,5-20 years; n=4), which was lonqer than that in * _ Kj, patienrs without PRKN mutarions (meairSD, 7.6t5.1
y € a r s ; r a n g e , I- 1 9 y e a r s ; n = 3 7 : p 5 . 0 0 7 ) , suggesringXtqoS9 stower clrcease progression. However, despite 1biigEi-dt3-l f-i ease duration, the mean+SD dose of levodopa rJqlri."d -- 'U by these individuals for benefir was trricaliy less than
that prescribed to patiens with early onset witirout pRI(N
mutations
(287t 103 mg/d vs 532t35zmsra;
r.*{13}
_
eg
SUMMARY OF GENETIC FINDINGS (S The PRKN gene was comprehensively evaluated for 4l pa_ tients with early-onser parkinsonism. All 12 exons of ihe
^ -.;^
v a v
i. -+3
?n 4in
\. --+'
Figlf re,3, Seguencing. and comptementary DNA (cDNA) anatysis A, Nucreouoe sequence for the exon 7 (Ex7) 951 G;C trahsveriion leZAAnl tor llr_!r-r9fir9 in family A. primers and meinoos aiiiraoie on rJquest. a, An agarose get of pciymerase chain ieaction (p0R)_amplified cDi{n products
lg^?^.::t.':lilg
jlg lgliq A and
B probairds.
fu
esiiiisii
riNA'tilnruni
ano
uurrA were 00ratne0 lrom lymphoblastoid cell lines; pCR used Ei.l lorward
p:'p,'j:il!9]lc-ggl,cJgc_clr,q{T{G(an,,.rriilaoii.enitiEx2)and-bxb reverse pflmer 5/AATTCTGCACTAGICCCAG (anneais _14_bp S,bt gxO spanning the Ex5-6 sbtice lunction) to amptify a O'iA_Op tasmerit. Faint a.mptification is nored for a 474_op'exz ueietdo piJouil iniimil-v n p,ouano ll3: Ll,rgntrq91,a 283-bp band, correspondinsio jn Eii-s ;eio:teo msrun, lo^lu"tly_TllJi" from tamity B proband tt:s.ine ioenw oiOo$r proOucti nas Deen coniirD,ed bv seouencing. C, Nucleotide sequence for thC &1 t .-1]90 nf q transition (nssbol toriamir1l c. rnt-Jolil waiimpririeo ano :9.9111!,rg Jlgr prob?nds C_and 0 Assay Cetairs avairaoti on iequest. The nucreortoe sequence for the Ex1 1 1 196 AIG transition (R396G) is shown; the chromatogram AIG indicates that mltant anO wilO-tyoe oe;r, ure expresseo. Assay methods available on request.
tients, respectively. The meantSD Unified parkinson,s Disease Rating Scale moror score was 10.5 t 5.5 in the on state and 20.8t8.2 in the off state, and the mean Hoehn and Yahr stage was 1.8 in the on srate and 2.9 in the off state. Dyskinesia and wearing-off phenomenon, related to levodopa therapy and possi-bly dir.ur" d.uration, were observed in 59o/o (24/4I) and 561" (23/4I) of patients. respectively. Similar clinical observations harre been noted tor early-onset parkinsonism in Western populations.B,e
A summary of the clinical features of t^he 4 probands with earlponset parkinsonism, identified as having pRKN muta[ions, and their affecred siblings is given in the toble. Disease transmission was consistent vrith autosomal re_ cessive inheritance in 2 probands (Figure 2). The clini cai features of proband Ii:2 and his sib'ling Ii:3 in family A were that of idiopathic pD, but wlth allow progres_ sive course. Brain imaging for dopamine transponers
gene were asse-ssed for genomic copy number, and find-ings were verified using appropriati controls who tested positive fcr specific deletions-or duplications of the par_ kil gene. Complete delerion of exoni (ExZ a.t) was
iden-chromosome band 6q25-27 inheritance us-lng OOS:dS, a microsatellite marker in intron 6, andwere assessed for the presence of PRKN Ex2 deUExT G284R mutations. The Ex2
tified in proband II:2 in revealed anEx7 951
expressed (Figure 3C type genes are del mutation was contributed by the father, and the Ex7 G?941lb:|t"tion segre-gated with the matemal allele along with.the
.2!+-bge pay allele of D6S305, as seen in the proi band and his affected sibling (Figure 2A).
Proband II:5 in familyB had complete deletion of Ex2 and Ex3 (Ex2-3 del). Analysis of messenger RNA and cDNA revealed that both exonic deletio.rs -er" in cis, af_ fecting only I allele (Figure 3B). Sequencing of cDNA and genomic DNA, and quanritative ulr""mJrrt of copy number, showed that the wild-type allele was,rorm"ilv expressed. Two other patien@
heterozygous
Exl I I 166 Hftrdriti";J""di"g@5
I
giningloplycine amino acid substitutions at position 336 (ExII R396G). the ldTG transition is shown in rhe
-+
= l
ARCH NEUROL/VOL 6l,JAN 200) 3
S E E E E I I g E E E
Control lt:2 in A ll;S in B Wt 638 bp _y
Ex2 del 474 bp --4,
The Ex7 95I Gfr (G284R)
and Extl r1S6 AbG
(R396G) missense murations were not present in 50
9
wanese controls. However, I of the 47 subjecs with id_ iopathic PD with late-onset disease was iientified as a carrier of the Ex7 G284R murarion. This individual also had a neighboring inrron 6 D6S305 204-base pair al_ lele, indicative of linkage disequilibrium and suggesting that the variant may originate from a common founder (Figure 2). There are no published microsatellite mark-ers adjacent to Exl l. Common, polymorphic amino acid substitutions were also identified in 4 patients with early gl!9!t including heterozygous and iromozygous Ex4 S167N substiturions inprobands II:2 in familyLand Il:5 in family B, respectivelf.
To our knowledge, this is the first comprehensive evalu-ation of the PRKN gene in a Taiwanese (ethnic Chinese) series with early-onset parkinsonism; moreover, this is
the first detailed description of the phenotype associ-ated with "parkin-proven" disease in the Taiwanese popu-lation. Three complemenrary merhods, including (uan-titative polymerase chain reaction for pRKN genomic deletion/duplication and sequencing in genomic ONA and cDNA, ensured that all variants were identified. Screen-ing for PRKN mutations has previously been reported. in clinic-based populations of Chinese patienrs with earlv-onset parkinsonism (aged <50 years ai earlv-onset). One scudy'o identified a PRKN muration rate of I4o/o in 35 patients (aged <50 years at onset), and another srudyrr found no homozygous deletions or point mutations in 25 samples (aged <49 yearc at onset). However, the methods used. would have overlooked heterozygous pRKN deletions or duplications in these Chinese patients.
The overall frequency of PRKN murarions in this Tai-wanese cohort of patients with early-onset parkinsonism was 6Yo (5 of 82 alleles): 2o/o (I/41) were compound
het-ARCH NEUROL/VOL 61,JAN 2005 4 Palienl* Clinical Fealure Sex Family {tl:2 Age at onsevexamination/ levodopa treatment, y Disease duration, y Farnily history of PD Cardinal symptoms of earty-onset parkinsonism Tremor, resvposture Htgtotty + Eradykinesia + Posturat instability Dystonia
Hoehn and Yahr stage (orvoff) 2/g
UPDRS lll (on/oft) Initial symptoms Asymmetrical onset Resting tremor Riqidity Bradykinesia 9n6 r l l o n \' \ L v v , t + M 32/44t40 t a + 36/41/NA + F 1 9/39/33 20 f M 40t50t49
1o
+/-+ : 1/3 13t21 +t- -/-t + + + i t 1 2/3 NP/4 11/NP + + t 4 \ t , c 13t26 M 44/49t48 + (Leg) + + - a * \ +t-Remarkable Levodopa,400 mg/d; ropinirole I m0/d -/+ Foot dystonia Hyperreflexia/Babinski sign +l-Psychiatric symptoms Depression/anxiety-/-Sleep benefiVdiurnal change q+
Response to levodopa therapy Remarkable
Antiparkinsoniantreatment Levodopa,lS0mg/d;
atthetimeofstudy
:ffirrr'rlr,,;;,
hydrochloride; selegiline itydrochJoride; biperiden Levodopa therapy complications 0yskinesia/motor lluctuation+ (Leg) - (Legs) + (Leg)
+ -+ + r + + + - + +/- +/-+ + -l+ +/+ (Committed suicide) -l-4- +/+
-l-Untreated Remarkable Good
None Levodopa,300 mgld; Levodopa,300 mgld; carbidopa benseruide; ropinirole +/+ Levodopa, mg/d; amantadine hydrochloride
-/-induced chorei-in the
legs at initial
treatment
Table.
clinicar
characteristics
or
the
Individuars
wirh
pB(lr/Mutations
do*,
Abbrerriations: *Probands lJA, not applicable; Np, not performed; pD, parkinson disease; UpDRS, Unified parktnson s Disease Rating Scale; +, yes; _, no.
ll:2 and ll:3 in familv A had mutations ioentitiio in iith parkin a|etes; farnily I probano rt:s, tamiry b,
-ano
]i,iiiiioiai i altete murated.
erozygores and7ok (3/41) were carriers. Adjusting forage at onset (Figure I), our dara are in agreement wi.th those
3fl1t ;tuails
oI sporadic
eurly-ons.ipD
in iu.op.u.,
u.,a
North American cohorts.(reviewed by Mata et air). The clinical phenotype of patienis with pRKN gene mutarions was variabie, even for siblings with idenilcal mutations and a shared environmenr. F?r example, dls-ease in family A proband Il:2 expressed asymmetrical
ri_ glolty and bradykinesia but without tremor. ln conrrasr, nrs anected sibling showed a prolonged course of uni-lateral resting tremor of the great and second toes of the lett lorMer extremity. The clinical features of family B pro_ band II:5 closely resemble dopa-responsive dystonia, r,rrith earty-onser symmerrical foot dystonia, shuffling gait, and pfsluJal, instability. In_addition, her symptoms in_ cluded obvious diurnal fluctuations, with marked ben_ efit frqm, sf eep. psychiatric features (malor depression) precedecl the onset of movement disorder and remained prominent; the patient committed suicide after a dis_ ease durarion
.ol 20 years. Similar behavioral and psy_ chiarric manifestations have been highlighted in oiher families with pRKN murarions7,l2 and"in lliopathic pDr3 and warrant careful evaluation and treatmerit.
It is valuable to thoroughly documenr the symproms of parkin-proven disease, eipecially in patienrs with mis-sense mutations because they may have different phe_ notypic consequences_to truncating mutations, depend_ ing-on the domain of the protein affected.l Family A qr:Fld1!? is a compound Leterozygote with pRKN Ex2 deUExT G284R. De novo Ex2 deletions have been widely reported, whereas the Ex7 G2B4R substirution has been reported only once in an ethnic Chinese patient, consis_ tenr with a founder effecr.t,ro The Ex7 C)A+n substitu-tion is the fourth missense mutasubstitu-tion (in addisubstitu-tion to R256C, R275W, and R275y) to be described in the RINGI domain (from amino acids 23g to 293 of the parkin pro_ tein) and provides an additional tool with *hi.h to ur_ sess the function of RING l. previous posrmortem evalu_ ation of compound heterozygous pad;nts with missense mutations in or adjacent to the RINGI domain have dem_ onstraLed alternate pathologic conditions;including Lewy bodies'" and tauopathy, with or without,r"u.ofGillury tangle5.t:'t0 These studies extend original observa_ tionsrT,rs of predominant nigral n.uror,u'i loss, made in patients with homozygous truncaring mutations. Con-sistent with a dominant negative effect, RINGI muta_ tions R275W and R256C have been shown'to alter the localiza-tion of parkin protein in transfected. cells,re and. clinically, F.{. 7 R275W is associated wirh a more severe pnenorFpe.."
In family B proband II:5, the pRKN Ex2-3 del was in cis, affecting only I allele ofthe gene. The other allele was expressed normally, and no additional nmutionswere iden_ tified. The Ex2-3 deleted messenger RNA is abundantly expressed in lymphoblastoid tissue, may be translated in_ lram€, to produce a 330-amino acid parkin isoform, and would lack the N-terminal ubiquitin-like domain rhar me-diates parkin binding to the Rpnl0 subunit of the 265 pro-teasome.zr Consequently, a 330-amino acid parkin iso-lo* T3y conceivably be more deleterious than a simple Ioss-ot-Iuncr.ion murarion. Family B proband II:5 was also anEx4 NI67 homozygore, a genorype that may contrib_
:,..,9-h-"j-gnse.r of parkinsonism ar age 19 years. parkin Ex4 Sl67N substirurions have previiusly'been associ_ ated with risk of idiopathic pD.21 Howevei, the evid.ence geAlils eguivocal even in fuian popularions.B,2a The Exl l R396G substitutions in familles e and O are norrel and may be specific to the Taiwanese population; d.espite compre_ hensive anaiysis of the gene, no-other -ut"tion *"s iden-tified.in these patients with earhonset disease. egui", "*_ pression of the wild-rype allele seems to be normal=in these sporadic cases. At this time, it is unclear whether the Exl I R396G substitution is pathogenic or a rare but harmless variant. Given the lack of family history, we postulate the latter; functional analysis mayhelp clarify ihe pathoge-niciry of PRKN point mutatior6.te
-. Findings from twin studies suggest that susceptibil_ ity.to early-onset parkinsonism (i[ed (50 years at on_ set) is consistent with a genetic eti-ology,25 and the inci /i:---h dence of PD in the Tiiwanese poiulation closelyltl0\5!/ approximates that reported in Western nations.26 In Eu_ rope, in hospital referral series, pRKN mutations ac-count for 187o of sporadic pD and +9o/o of familial dis, ease.(aged (45 ye_ars at onset).r'27 ln the present study, we show that the lrequency of pRKN murations is simi-Iar across Asian and white populations. We are confi_ dent that no exo,nic point mutations, splice mutations, or deletions/duplications have been oveilooked because genomic DNA, messenger RNA, and cDNA were exam_ ined for each case. Our screening methods were suffi_ ciently sensitive to identify known-and novel parkin mu_ tations Ex7 G284R and Exl l R396G, both of which may be specific to the Taiwanese population. However, re-ferral bias and the small sample iize remain limitations of this and many previous srudies.
Given the wide range of clinical symptoms inparkin-proven disease, a genetic diagnosis of pRKN mutations should be considered as part ofan evaluation for early-onset or familial parkinsonism. Because mutations in the PRKN gene explain only a small proportion of disease in this cohort, additional risk factors musr now be identi-fied.
Accepted for Publication: March 31,2004.
Correspondence: Ruey-Meei Wu, MD, phD, Depart-*..1! olN:yrology, Narional Taiwan University Hospi-tal, No 7, Chung-Shan South Road, Taipei, tOO, taiwin ([email protected]).
Author Contributions: Study conceptord design: Wu, Lin-coln, Gwinn-Hardy, and Farrer. A-cquisition of data:Wu, Bounds, Lincoln, Lin, Hwu, Chen, and Farrer. Analysis and interpretation of data: Wu, Bounds, Lincoln, Huli-han, Lin, Hwu, Gwinn-Hardy, and Farrer. DraftingoJthe manuscript: Wu, Gwinn-Hardy, and Farrer. Cntiral re-,,,ision oJ the manuscriptfor important intellectual contenti Wu, Lin, Hwu, Chen, and Farrer. Statisttcalanalysis: Lin-coln, Hulihan, and Farrer. Obtatnedfunding: Wu, Bounds, Lincoln, and Farrer. Administrative, techiical, and mate-rial support: Bounds, Lincoln, Lin, and Farrer. Study su-pemision: Wu and Farrer.
Iunding/Support: This study was funded in part by the Morris K. Udall Parkinson's Disease Research Cenier of Excellence, Mayo Clinic, Jacksonville, Fla; by research grants NSC 91-2314-8-002-188 and NSC
92-23I4-B-ARCH NEUROL/VOL 61,JAN 2005 5
JUbNAME: Ne_urology
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{.kryy}agenr: We thank Alexis drice, VtO, phD, and the EU Consortium on parkinson's Disease for provid-ing control DNA from individuals with hererozygous par_ kin exonic deletions and duplications; MlnniJichreiber and Shu-Chuan Chiang foi their technical assisrance; ...:,nll-song. Lu tor perlbrming ee.TcTRoDAT_ I single. photon emission computed tomographic examinations; anct the patients.
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