PINK1 mutation heterozygosity and the risk of Parkinson’s
M Toft, R Myhre, L Pielsticker, L R White, J O Aasly, M J Farrer
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J Neurol Neurosurg Psychiatry 2007;78:82–84. doi: 10.1136/jnnp.2006.097840
Background: Mutations in the PTEN-induced kinase 1 (PINK1)
gene have been identified in recessively inherited and sporadic
early-onset parkinsonism (EOP).
Methods: A total of 131 Norwegian patients diagnosed with
Parkinson’s disease were included. Of them, 89 participants
had EOP (onset (50 years); the remaining had familial late-
onset disease (mean age at onset 64 years). PINK1 analysis
included sequencing and gene dose assessment. Mutations
were examined in 350 controls .
Results: Heterozygous missense mutations in PINK1 were
found in 3 of 131 patients; none of the patients carried
homozygous or compound heterozygous mutations. One of
these three patients had a father affected by Parkinson’s
disease, and he carried the mutation. Three new and seven
known polymorphic variants were identified, although none
seemed to be associated with disease risk.
Conclusions: PINK1 mutations are rare in Norwegian patients
with EOP and familial Parkinson’s disease. However, the data
suggest that some heterozygous mutations might increase the
risk of developing Parkinson’s disease.
Familial parkinsonism can be inherited as an autosomal
dominant or recessive trait. Mutations in three genes have
been associated with recessively inherited early-onset parkin-
sonism (EOP): parkin, DJ-1 and PTEN-induced kinase 1 (PINK1).
Mutations in the parkin gene may account for nearly 50% of
familial and a considerable proportion of apparently sporadic
EOP (with age of onset (45 years).2Pathogenic mutations in
the DJ-1 gene seem to be rare, causing ,1% of EOP cases.3
Missense mutations in the PINK1 gene were first identified in
three consanguineous Italian and Spanish kindreds affected
with EOP.4Mutations in this gene have now been found in
families originating from several European and Asian popula-
tions, making PINK1 the second most common genetic known
cause of EOP.5–9PINK1 mutations have also been identified in
patients with sporadic disease, including heterozygous muta-
tions of unknown pathogenicity.10 11To further evaluate the
pathogenic role of PINK1 mutations in familial and sporadic
Parkinson’s disease, we performed a comprehensive mutation
analysis of this gene in a series of Norwegian patients with
he causes of Parkinson’s disease are still largely unknown.
Evidence suggests that both environmental factors and
genetic susceptibility contribute to disease aetiology.1
In all, 89 patients with EOP (age at onset (50 years) were
recruited from a study of the genetics of Parkinson’s disease in
Central Norway. Mean (standard deviation (SD)) age at disease
onset in this group was 44 (5) years (range 31–50 years); 27 of
them had a family history of Parkinson’s disease. We also
included 42 patients with familial late-onset Parkinson’s disease
(mean (SD) age at onset 64 (6) years, range 51–75 years). Of
them, 20 patients had a family history consistent with recessive
siblings or first-degree cousins, without evidence of affected
parents or offspring. The remaining 22 patients had familial
disease without a clear pattern of Mendelian inheritance. Of the
131 patients, 77 were men and 54 were women.Inall, 350 healthy
Norwegian controls were drawn from the same population (mean
(SD) age 66 (13) years, range 49–100 years).
Patients were diagnosed with Parkinson’s disease in accor-
dance with the Gelb criteria.12Known carriers of homozygous
or compound heterozygous mutations in the parkin gene were
not included. All patients were previously screened for the
presence of seven mutations in the LRRK2 gene, and mutation
carriers were not included.13Mutations in the DJ-1 gene have
not been completely examined; several Norwegian patients
with EOP were included in a previous study and no DJ-1
mutations were found.14Informed consent was obtained from
all participants, and the study was approved by the regional
committee for medical research ethics in Central Norway and
the Mayo Clinic Institutional Review Board.
All eight PINK1 exons were amplified by polymerase chain
reaction, with primers flanking intronic sequences (primer
sequences and assay conditions are available on request).
Sequencing was performed using BigDye Terminator V.3.1.
Sequence variations identified in patients were genotyped in
350 Norwegian control samples using designed TaqMan single-
Biosystems, Foster City, CA, USA) or by direct sequencing.
Absolute quantitative polymerase chain reactions of PINK1
were performed using the iQ SYBR Green Supermix kit
(BioRad, Hercules, CA, USA). Absolute quantification of
template was obtained from a standard curve using the MJ
Opticom Monitor V.3.1. For this assay the concentrations of
PINK1 exon 4 and 7 were individually analysed and compared
with concentrations of the external control gene, human serum
Each sample was run in a triplicate reaction. Relative gene
dosage ratios with SDs were calculated by dividing the
normalised mean PINK1 quantity by the mean albumin
quantity. Positive controls for deletion and multiplication
mutations were designed by using other amounts of DNA
(fig 1A). A relative ratio with SDs between 0.75 and 1.25 was
considered normal, a heterozygous deletion was expected at a
ratio between 0.25 and 0.75, and a duplication was expected
between 1.25 and 1.75. Ambiguous samples were re-run in
triplicate with DNA from a separate tube.
Abbreviations: EOP, early-onset parkinsonism; PINK1, PTEN-induced
We identified two missense mutations in the PINK1 gene:
c.1231GRA (Gly411Ser) and a novel c.1493CRT (Pro498Leu)
mutation (fig 1C). Of the 131 patients, two were heterozygous
for the Gly411Ser substitution and one carried Pro498Leu.
These mutations were not found in any of the 350 controls.
We also identified three new and seven previously published
polymorphic variants in PINK1 (table 1). None of the common
polymorphisms were associated with Parkinson’s disease
(p.0.05). Distributions of genotypes were in Hardy–Weinberg
equilibrium. We identified one as yet undescribed exonic
c.1745GRT mutation removing the stop codon (Stop582Leu),
leading to the translation of nine additional amino acids until
the next stop codon occurred. This variant was found in one
patient and two controls and has unknown pathogenic
significance. Two novel exonic variants were silent mutations.
Both were found only in one patient each and were not present
in control chromosomes. Deletions or multiplications of the
PINK1 gene were not identified in any of the patients.
Patient P392 is a 45-year-old man carrying a heterozygous
Gly411Ser mutation. His parkinsonian syndrome started at age
43 years, with bradykinesia, mild rigidity, resting tremor and a
marked hypomimia. The bradykinesia on the left side is now
severe. Dopaminergic treatment has so far not been started. The
patient’s father has also recently been diagnosed with
Parkinson’s disease at the age of 63 years, and sequencing of
PINK1 exon 6 confirmed that he is also carrying the same
mutation. Two of the father’s uncles had received a diagnosis of
Parkinson’s disease (fig 1B).
Patient P371 is a 60-year-old woman who is heterozygous for
the same Gly411Ser mutation. Age at onset in this patient was
50 years. She presented with typical asymmetric parkinsonism,
withan excellent response
However, she developed severe levodopa-induced fluctuations,
and subthalamic deep brain stimulators were introduced 1 year
ago with a very good effect. There is no history of neurode-
generative disorders in her family.
Finally, patient P266 was diagnosed with Parkinson’s disease
4 years ago at the age of 58 years. He has a slowly progressive
parkinsonian syndrome of mild bradykinesia, action tremor
and rigidity. He carries a Pro498Leu mutation and has not yet
been introduced to dopaminergic treatment. A paternal uncle
was diagnosed with Parkinson’s disease, but he was not
available for examination. The patient has a brother with an
atypical action tremor without other signs of parkinsonism.
to dopaminergic treatment.
Normalized ratio PINK1/albumin
PINK1 gene dosage
Exon 6 1231G>A (Gly411Ser) Exon 8 1493C>T (Pro498Leu)
analyses in Norwegian patients with
Parkinson’s disease. (A) Relative ratios of
gene dosage of PINK1 compared with
albumin for 17 patients with early-onset
parkinsonism (dark grey); the bars represent
standard deviations. The ratios for two
deletion controls and two triplication controls
are shown in light grey. (B) Pedigree for the
family of patient P392. The patient and his
father are affected and have been tested for
mutations in the PINK1 gene (denoted by *).
Two paternal uncles of P392 were affected
by Parkinson’s disease, but were deceased
and thus not available for genetic testing. (C)
Chromatograms showing the two potentially
pathogenic mutations identified in this study.
Results of PINK1 mutation
Polymorphisms and mutations in the PTEN-induced kinase 1 gene
Exon Nucleotide change*
Amino acid change
PD (n=133) Controls (n=350)
het (%) hom (%)het (%)hom (%)
IVS1 –7 ARG
IVS4 –5 GRA
IVS6 +43 CRT
het, heterozygotic; hom, homozygotic; PD, Parkinson’s disease.
New variants in bold.
*Numbers denote the PINK1 reference sequence, accession NM032409.
PINK1 mutation heterozygosity and Parkinson’s disease 83
DISCUSSION Download full-text
In this study, we performed a comprehensive mutation analysis
of the PINK1 gene in a series of 131 patients. Mutations in the
PINK1 gene seem to be rare in Norwegian patients diagnosed
with Parkinson’s disease. We identified three heterozygous
mutation carriers; none of the patients had homozygous or
compound heterozygous PINK1 mutations. Deletions and
multiplications of the PINK1 gene are uncommon, as only one
exonic deletion has been reported.8Also, our quantitative
analysis failed to detect any such mutations.
Two patients were heterozygous carriers of a PINK1
Gly411Ser substitution. One of them (P392) has a family
history of Parkinson’s disease, and his affected father carries
the mutation, indicating a possible pathogenic role of this
variant. Recently, a male patient with EOP starting at the age of
13 years was also found to be a heterozygous carrier of this
Parkinson’s disease with a familial history of parkinsonism,
but DNA from family members was not available for segrega-
The clinical presentation of our three patients with PINK1-
associated EOPwas indistinguishable
Parkinson’s disease and similar to that found in most other
families and sporadic cases with PINK1 mutations.5 11All
patients had a slowly progressive parkinsonian syndrome; none
of them showed signs of early dementia, had psychiatric
symptoms or had dystonia at disease onset. Only one of our
patients has received dopaminergic treatment and showed an
excellent effect of levodopa treatment. She developed severe
dyskinesias, which have been successfully treated with
implantation of bilateral stimulators in the subthalamic nuclei.
The pathogenic significance of a single heterozygous PINK1
mutation is unclear. In most autosomal recessive disorders
heterozygous carriers are clinically unaffected. However, there
is evidence that heterozygous PINK1 mutation carriers might be
at increased risk of developing parkinsonism. The two muta-
tions found in this study were absent in a large number of
Norwegian control chromosomes, making it less likely that they
are rare polymorphisms. Both mutations are located in the
PINK1 kinase domain and replace evolutionary conserved
amino acids, and may thus affect the kinase activity.
A positron emission tomography study of unaffected hetero-
zygous PINK1 mutation carriers indicated a reduction in F-dopa
uptake in comparison with controls.16Hence, PINK1 dysfunc-
tion might reduce striatal dopamine storage capacity and
increase susceptibility to parkinsonism. Similarly, positron
emission studies of mutation carriers in the parkin gene have
shown a decreased F-dopa uptake compared with controls.17
Several studies have reported high frequencies of single-allele
mutations in the parkin gene of patients with EOP, suggesting
that single parkin mutations might be a risk factor for
Parkinson’s disease.18Interestingly, PINK1 has recently been
shown to genetically interact with parkin in model systems,
indicating that the two proteins act in a common pathway.19
PINK1 mutation screening of sporadic EOP cohorts from
other European populations have identified findings similar to
those in our Norwegian sample, with heterozygous mutations
in patients that are absent in controls.10 11 20In addition, six
carriers of PINK1 mutations in a large German family with
Parkinson’s disease presented with slight or mild symptoms of
disease.21Although it remains unclear to what degree a single
PINK1 mutation is a risk factor for parkinsonism, our findings
support the possibility.
We thank the patients who participated in this study. We also thank
Mary Hulihan, Sarah Lincoln and Minnie Schreiber for technical
M Toft, L R White, Department of Neuroscience, Norwegian University of
Science and Technology, Trondheim, Norway
L Pielsticker, M J Farrer, Department of Neuroscience, Mayo Clinic College
of Medicine, Jacksonville, Florida, USA
R Myhre, Department of Laboratory Medicine, Children’s and Women’s
Health, Norwegian University of Science and Technology, Trondheim,
J O Aasly, Department of Neurology, St Olav’s University Hospital,
Funding: This study was supported by the Research Council of Norway
(grant 153487/V50), the Udall Center at Mayo Clinic Jacksonville (NINDS
NS40256), Reberg’s legacy and the Norwegian Parkinson Foundation.
Competing interests: None declared.
Correspondence to: Dr M Toft, Department of Neuroscience, Norwegian
University of Science and Technology (NTNU), N-7489 Trondheim,
Received 16 May 2006
Revised 28 August 2006
Accepted 31 August 2006
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