PTEN-induced putative kinase 1 (PINK1) is a causative gene for autosomal 
recessive early onset parkinsonism. Mutations in PINK1 were identified 
originally in PARK6-linked parkinsonism families from Italy and Spain. PINK1 
contains 8 exons spanning 1.8 kb, and encodes a protein of 581 amino acids with 
a mitochondrial targeting motif and a serine-threonine protein kinase domain. 
Until now PINK1-mutation positive parkinsonism is the second frequent one next 
to parkin among autosomal recessive parkinsonism. Most of reported mutations 
were distributed throughout the serine-threonine protein kinase domain. Thus, 
loss of function of kinase activity of PINK1 is the most probable disease 
mechanism. The clinical phenotype of PINK1 -mutation positive parkinsonism is 
similar to that of parkin mutation positive parkinsonism. Single heterozygous 
mutations of PINK1 have been also identified sporadic Parkinson's disease (PD) 
patients. The presence of dopamine hypometabolism in asymptomatic mutation 
carriers suggests that single heterozygous mutations of PINK1 are risk factors 
for developing parkinsonism. In addition, some functional data have been shown 
that PINK1 protein may function as neuroprotective roles for mitochondria. 
Recent biochemical and morphological studies using drosophila melanogaster 
suggested that Parkin and PINK1 share a common pathway to maintain mitochondrial 
function and that PINK1 functions upstream of Parkin. Moreover, co-expression of 
double mutations of PINK1 and DJ-1 in cultured cells from one family with 
heterozygous mutations, enhanced susceptibility to MPP+ 
(1-methyl-4-phenylpyridinium ion)-induced cell death. These data suggest that 
PINK1, parkin, and/or DJ-1 could play an important role to maintain 
mitochondrial functions. In the other word, the mitochondrion is a good target 
for elucidating the pathogenesis of not only sporadic form but also monogenic 
form of PD.