Whole-exome sequencing recently identified a homozygous truncating mutation in Synaptojanin 1 (SYNJ1, PARK20), p.Arg258Gln, in 2 independent families with autosomal recessive young-onset parkinsonism with seizures and cognitive decline. This mutation's role in typical Parkinson's disease (PD) is unclear. We sequenced all coding exons and exon-intron boundaries of SYNJ1 gene in a total of 700 participants: 250 early-onset PD patients, 100 familial PD patients with family history, and 350 age/sex-matched controls from Taiwan. No patients harbored homozygous or compound heterozygous mutations of SYNJ1 gene in our study population. We observed 1 novel missense substitution, p.Ala551Val, in a single heterozygous state in 1 early-onset PD patient. This variant was not observed in controls with total 700 normal alleles. The clinical phenotype of this genetic variant carrier is similar to that seen in idiopathic PD, with motor fluctuation after 11 years of PD diagnosis and comorbidity with dementia after 13 years of motor symptoms. Our results suggest that mutations in SYNJ1 gene do not play a major role in early-onset or familial PD in our population.