The aim of this study was to elucidate whether sensory abnormalities are present and may precede motor symptoms in familial parkinsonism by characterizing sensory function in symptomatic and asymptomatic PINK1 mutation carriers.
Mutations associated with early-onset autosomal recessive parkinsonism have been identified in the Parkin gene, and recently a second gene, PARK6, involved in early-onset recessive parkinsonism was localized on chromosome 1p35-36.
Recent evidence from studies on the genetic forms of parkinsonism with particular stress on DJ-1, parkin, and PINK-1 also suggest the involvement of mitochondria and oxidative stress.
Mutations in seven genes are robustly associated with autosomal dominant (SNCA, LRRK2, EIF4G1, VPS35) or recessive (parkin/PARK2, PINK1, DJ1/PARK7) Parkinson's disease (PD) or parkinsonism.
Mutations in PINK1 (PTEN-induced putative kinase 1) are causal for early onset recessive parkinsonism in humans, characterized by damage to the nigrostriatal system.
The identification of a higher number of patients (5%) than controls (1%) carrying a single heterozygous mutation, along with previous positron emission tomography studies demonstrating a preclinical nigrostriatal dysfunction in PARK6 carriers, supports the hypothesis that haploinsufficiency of PINK1, as well as of other EOP genes, may represent a susceptibility factor toward parkinsonism.
The recessive Parkinsonism-linked genes PTEN-induced kinase 1 (PINK1) and Parkin maintain mitochondrial integrity by regulating diverse aspects of mitochondrial function, including membrane potential, calcium homeostasis, cristae structure, respiratory activity, and mtDNA integrity.
Other entities entailing dystonia-parkinsonism include dopamine transporter deficiency syndrome (SLC63 mutations); dopa-responsive dystonias; young-onset parkinsonism (PARKIN, PINK1 and DJ-1 mutations); PRKRA mutations; and X-linked TAF1 mutations, which rarely can also manifest in women.
This review highlights the role of the mitochondrial kinase, PINK1, in protection against mitochondrial dysfunction and how this might relate to loss of substantia nigra neurons in recessive parkinsonism.
Loss-of-function mutations in the PTEN-induced kinase 1 (PINK1) or parkin genes, which encode a mitochondrially localized serine/threonine kinase and a ubiquitin-protein ligase, respectively, result in recessive familial forms of Parkinsonism.