Parkinson’s disease (PD) is a common neurodegenerative disorder that is caused, in some cases, by mutations in single genes, then referred to as monogenic PD. In the past, genetic forms of PD have been categorized using a PARK designation and consecutive numbering, currently comprising PARK1 to PARK20 (http://omim.org/). However, this system harbours several shortcomings and mistakes and is no longer recommended. Instead, it has been suggested to use the PARK designation for confirmed genes, followed by the gene name [4]. With the advent of next generation sequencing, a rapidly increasing number of novel PD genes has been reported [1] including a specific mutation (c.773G[A, p.Arg258Gln) in the synaptojanin 1 (SYNJ1) gene (PARK20). This mutation was independently identified by two groups via homozygosity mapping followed by exome sequencing in two consanguineous families from Iran and Sicily (Italy), respectively [3, 6]. All four patients (2 siblings per family) presented with autosomal, recessively inherited, earlyonset Parkinsonism with bradykinesia, an only transient response to levodopa, and early development of levodopainduced dyskinesias. Age at onset of motor symptoms was in the 20s, and disease progression was observed. Additional clinical features in some patients included eyelid apraxia, generalized seizures, and dementia [3, 6]. A 3-year follow-up examination in one of the families indicated slowing of the progression in later disease stages [5]. MRI revealed cortical and cerebral atrophy; SPECT and FDG-PET demonstrated metabolic deficits. Screening of all 32 exons in 138 additional patients did not identify any other clear mutation [3, 6]. Functional analysis of the Arg258Gln mutation within the SAC1-like inositol phosphatase domain of SYNJ1 demonstrated reduced phosphatase activity for certain targets of SYNJ1 [3]. With high-throughput methods such as exome sequencing facilitating identification of novel PD genes, the validation of novel genes deserves a high level of attention to evaluate the relevance, clinical spectrum, and frequency of mutations in novel predicted PD genes [4]. For this, independent studies on large patient cohorts are mandatory. In the present study, we tested for the presence of the Arg258Gln mutation in Exon 5 of SYNJ1 by Sanger sequence analysis in a large sample of PD patients and controls. All patients and controls provided written informed consent and the local ethics committee approved the study, which has been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. We included a total of 792 PD patients (748 Germans, 41 other Caucasians, 2 Asians, and 1 African) with an age at onset at 52.9 ± 14.6 years (mean ± standard deviation) (range 10–79 years) and a mean disease duration of 13.3 ± 11.9 years. Fifty patients (6.3 %) had an age of onset \30 years, as was seen in the previously reported mutation carriers [3, 6]. A positive family history was reported for 22 % of the patients, and 60 % were male. In addition, we included 266 populationbased controls from the EPIPARK cohort [2] (age 52–80 years, range 63.9 ± 7.2). We used the following S. Winkler E.-J. Vollstedt M. Kasten D. Alvarez-Fischer C. Klein K. Lohmann (&) Institute of Neurogenetics, University of Lubeck, Ratzeburger Allee 160, 23538 Lubeck, Germany e-mail: katja.lohmann@neuro.uni-luebeck.de