Clinical Description
PINK1 type of young-onset Parkinson disease is characterized by typically early-onset Parkinson disease that is often clinically indistinguishable from other genetic causes of Parkinson disease or idiopathic Parkinson disease. Typical features include bradykinesia, rigidity, dyskinesia, motor fluctuations, and dystonia. Some individuals have cognitive decline and psychiatric manifestations. The following information is based on a systematic review of published reports including 205 individuals with PINK1 type of young-onset Parkinson disease from 136 families (see www.mdsgene.org and references therein).
Table 2.
PINK1 Type of Young-Onset Parkinson Disease: Frequency of Select Features
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Feature | % of Persons w/Feature 1 | Comment |
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Bradykinesia
| 95% | |
Rigidity
| 90% | |
Resting tremor
| 78% | |
Dyskinesia
| 67% | |
Motor fluctuations
| 79% | |
Dystonia
| 48% | Often of the lower limbs |
Cognitive decline
| 29% | Including mild cognitive impairment & dementia |
Autonomic dysfunction
| 48% | Most commonly including urinary urgency or urge incontinence & orthostatic hypotension |
Psychiatric manifestations
| 33%-56% | Depression in 51%, anxiety in 56%, psychotic symptoms in 33% |
- 1.
Data is based on 205 reported individuals identified through the MDSGene PINK1 Review, previously published by Kasten et al [2018] and updated on the MDSGene website in February 2024 (from www.mdsgene.org; last accessed 2-29-24). Note: Clinical information was often incomplete (e.g., missing data ranged from 7%-79% for the items reported above). Numbers displayed indicate the percentages of individuals with the respective clinical feature out of all individuals for whom this feature was reported (valid percentages); missing data was not taken into account for calculation.
Onset. The majority of individuals (57%) have early onset (age at onset <40 years), 27% have late onset, and 16% have juvenile onset (age at onset <21 years). Note: The age of onset was not specified in 10% of individuals. The median age of onset is 32 years (interquartile range: age 24-40 years; range: age 9-67 years) (see www.mdsgene.org).
Parkinsonian features are usually asymmetric; in some individuals the manifestations at onset are symmetric. PINK1 type of Parkinson disease clinically resembles other monogenic causes of Parkinson disease, especially those with recessive inheritance, and Parkinson disease of unknown cause. Individuals frequently present with all the typical features of Parkinson disease, including bradykinesia, rigidity, tremor, and postural instability. Tremor and bradykinesia are the most common presenting signs. The disease is slowly progressive. Rigidity and postural instability (60%) frequently occur with disease progression. Sleep benefit was reported for 40% of individuals (see www.mdsgene.org). A clinical presentation resembling atypical parkinsonism is very rare.
Non-motor Parkinson features are frequently reported (92%) in individuals with PINK1 type of young-onset Parkinson disease and commonly include psychiatric involvement, cognitive impairment, and autonomic dysfunction.
Psychiatric involvement. Abnormal behavior and/or psychiatric manifestations – in particular, depression (51%), anxiety (56%), and psychotic symptoms (33%) (see www.mdsgene.org) – can occur in affected individuals. Related sleep impairment (e.g., falling and staying asleep) is also common in individuals with PINK1 type of young-onset Parkinson disease [Ricciardi et al 2014].
Cognitive decline, ranging from mild cognitive impairment to dementia, has been reported for a subset of individuals.
Information on the occurrence of hyposmia is scarce (www.mdsgene.org; only available for 24 individuals in total and present in ten).
Autonomic dysfunction was reported for 48% of individuals (see www.mdsgene.org) and most commonly include urinary urgency, urge incontinence, constipation, and orthostatic hypotension.
Other additional neurologic manifestations. Dystonia (often of the lower limbs) and hyperreflexia may also be present or develop as the disease progresses [Bonifati et al 2005]. Dystonia has also been reported as the initial sign in a subset of individuals (18% of individuals with available data).
Neuroimaging. CT and MRI neuroimaging of individuals with PINK1 type of young-onset Parkinson disease is usually normal. Imaging of dopamine function (using DaTscan) generally demonstrated relatively symmetric loss of radioligand uptake in the striatum, similar to the pattern seen in the Parkin type of young-onset Parkinson disease, LRRK2 (Gly2019Ser) type of Parkinson disease, and SNCA type of Parkinson disease [McNeill et al 2013].
Response to treatment. In general, the vast majority of individuals with PINK1 type of young-onset Parkinson disease have a good response to L-dopa therapy [Over et al 2021]; it was suggested to be even better than in Parkinson disease of unknown cause [Valente & Ferraris 2010]. Usually, this positive response persists over time, although no systematic longitudinal assessment is available. L-dopa primarily addresses motor features of the disease; additional medication might be needed to address non-motor features, especially psychiatric involvement. Side effects of L-dopa are common and most frequently include L-dopa-induced dyskinesias; motor fluctuations are also reported, and rarely dystonia. Response to non-L-dopa therapies including dopamine agonists, catechol-O-methyltransferase (COMT) inhibitors, monoamine oxidase-B (MAO-B) inhibitors, anticholinergics, and/or amantadine is also good, but information is limited [Over et al 2021]. Surgical therapies, including deep brain stimulation and thalamotomy, have only been reported in a small number of individuals with usually a moderate-to-good response; however, the sample size is too small to draw meaningful conclusions.
Prognosis. Progression is slower compared to Parkinson disease of unknown cause [Kasten et al 2018]. However, detailed and systematic data on disease progression is limited [Kasten et al 2018]. Large, multicenter studies with longitudinal and systematic data collection are needed. In general, the expected life span in individuals with PINK1 type of young-onset Parkinson disease is similar to Parkinson disease of unknown cause. Common causes of an earlier death include complications related to Parkinson disease (e.g., pneumonia due to severe dysphagia and aspiration, falls resulting in serious injuries due to gait difficulties, or immobility).
Heterozygotes
The evidence of heterozygous PINK1 variants causing or acting as a risk factor for Parkinson disease remains controversial. Individuals with a heterozygous PINK1 pathogenic variant usually remain asymptomatic but may show subtle subclinical alterations (e.g., a latent nigrostriatal dopaminergic deficit on functional imaging, premotor-motor excitability changes detected by transcranial magnetic stimulation, reduced arm swing, hyposmia, and/or diminished color discrimination) [Eggers et al 2010, Nürnberger et al 2015, Weissbach et al 2017]. In asymptomatic heterozygotes, voxel-based morphometry revealed an increase of putaminal and pallidal gray matter volume, findings similar to those in the Parkin type of young-onset Parkinson disease [Binkofski et al 2007, Reetz et al 2010].
Several individuals with Parkinson disease and a heterozygous PINK1 pathogenic variant have been identified, including individuals with young-onset Parkinson disease [Bonifati et al 2005, Abou-Sleiman et al 2006, Hayashida et al 2021]. These studies suggest that age at onset might differ between individuals with biallelic and heterozygous PINK1 pathogenic variants, with the age at onset of biallelic individuals being slightly younger. The clinical phenotype was similar in both groups, except some features (e.g., dystonia, hyperreflexia, and sleep benefit) seemed to be less common in heterozygous individuals. In one case-control study, heterozygous PINK1 variant p.Gly411Ser was significantly associated with a markedly increased risk for Parkinson disease (odds ratio = 2.92, P=0.032), a finding that was supported by functional analyses [Puschmann et al 2017]. However, the results of another more recent large-scale meta-analysis suggested that PINK1 variant p.Gly411Ser is likely benign, that other PINK1 heterozygous pathogenic variants are not likely associated with an increased risk for Parkinson disease, and that heterozygosity for a PINK1 pathogenic variant is not a "robust risk factor" for Parkinson disease [Krohn et al 2020].
Genotype-Phenotype Correlations
No correlation between the type of variant and age at onset, clinical presentation, or disease progression has yet been observed.
Modifiers. Recently, it has been shown that somatic mitochondrial variant load is a disease-onset modifier for PINK1 (and Parkin) type of young-onset Parkinson disease. By investigating mitochondrial DNA (mtDNA) integrity in individuals with biallelic (n=84) and heterozygous (n=170) PINK1 or PRKN pathogenic variants compared to individuals with Parkinson disease of unknown cause (n=67) and controls (n=90), it was shown that affected and unaffected individuals with a heterozygous PINK1 or PRKN pathogenic variant can be distinguished by heteroplasmic mtDNA variant load; and individuals with biallelic PINK1 or PRKN pathogenic variants contain more heteroplasmic mtDNA variants in blood than individuals with a heterozygous PINK1 or PRKN variant [Trinh et al 2023].
Further, one individual with biallelic PINK1 pathogenic variants and homoplasmy for pathogenic variants in two mitochondrial genes encoding subunits of complex I (MT-ND5 and MT-ND6) was reported with very early-onset Parkinson disease [Piccoli et al 2008]; thus, it was hypothesized that the combination of pathogenic variants in MT-ND5 and MT-ND6 accelerated the disease onset.