Research Letters 410 www.thelancet.com Vol 365 January 29, 2005 Parkinson’s disease is the second most common neurodegenerative disorder, affecting more than 1% of individuals aged 55 years and 3% of those aged over 75 years. It is characterised by resting tremor, bradykinesia, muscular rigidity, postural instability, and a clinically significant response to treatment with levodopa. 1 Mutations in -synuclein, parkin, PINK1, and DJ1 have already been identified in families segregating Parkinson’s disease. Genetic analyses have detected linkage to several other chromosomal regions, although the genes have not yet been identified. 2 Autosomal dominant families showing linkage to chromosome 12p11.2-q13.1 (PARK8) have been identified with mutations in the leucine-rich repeat kinase 2 (LRRK2) gene that codes for the protein dardarin. 3,4 To ascertain the frequency of a Gly2019Ser mutation of dardarin that was previously identified in two families, 5 we screened patients with familial Parkinson’s disease. As part of our ongoing study to identify susceptibility genes of Parkinson’s disease (PROGENI), we recruited 358 multiplex families with at least one pair of living siblings diagnosed with the disease. Only those members of multiplex families reported to be affected with the disease were recruited for the study, with the exception of a few parents, who were recruited when available irrespective of their disease status. Movement disorder specialists at 59 participating sites for the Parkinson Study Group located throughout North America assessed 767 patients. Mean age at onset of these patients was 60·6 years (SD 13·12; median 63, range 18–87) whereas mean age at time of study participation was 70·5 years (9·85 72, 25–93). The patients were mainly white (720 individuals, 94%), although hispanic people (35, 5%) also participated. After written informed consent approved by every institution’s independent review board was obtained, a standardised clinical assessment (unified Parkinson’s disease rating scale; UPDRS) and a diagnostic checklist were completed and peripheral blood taken from all study participants. We used responses on the diagnostic checklist to classify individuals as having verified or non- verified Parkinson’s disease. 6 To verify the role of the Gly2019Ser mutation in the susceptibility of Parkinson’s disease, we screened for this mutation in two different control samples. Controls included in this study consisted of 262 healthy men from 177 unique, white, twin families (85 dizygotic twins, 84 monozygotic twins, eight singlets), ascertained as part of an ongoing study to identify genes contributing to healthy aging. These men were from the National Academy of Sciences–National Research Council (NAS–NRC) twin panel of World War II veterans born between 1917 and 1927. They completed health screens in 1998 and, at that time, with a median age of 74 years (range 71–82), had not been diagnosed with Parkinson’s disease. 7 Another control sample included 965 North American white individuals. All were examined by a neurologist but did not show any signs of the disease. At assessment, mean age of control individuals was 66·7 years (SD 15·0; median 70·7, range 42–93). 30 ng of genomic DNA from every patient with Parkinson’s disease and twin controls were genotyped for a Gly2019Ser mutation in LRRK2 in a 25 L reaction by use of a TaqMan single-nucleotide-polymorphism assay (Applied Biosystems, Foster City, CA, USA) and an ABI PRISM 7000 sequence detection system (Applied Bio- systems). The panel of 965 controls was genotyped by either direct sequencing (188) or restriction endonuclease digestion with Sfc I and agarose gel electrophoresis (777). We did a statistical comparison of affected patients with and without the Gly2019Ser mutation using either linear or logistic regression for basic characteristics, Blessed functional activity scale, Schwab and England activities of daily living score, Hoehn and Yahr score, and clinical findings. Of patients with Parkinson’s disease who inherited at least one copy of the Gly2019Ser mutant allele, 34 were heterozygous and one homozygous for this mutation (table). Thus, in our large sample of 767 affected patients, 5% carried the same LRRK2 mutation (95% CI 3·1%–6·1%). Of 358 families, we identified a LRRK2 mutation in at least one member of 20 families (6%, 3·2%–8·0%). No other single mutation identified so far in this or any other gene associated with Parkinson’s Lancet 2005; 365: 410–12 See Comment page 363 Published online January 18, 2005 http://image.thelancet.com/ extras/04let12014web.pdf *Members listed at http://image.thelancet.com/ extras/04let12014webappendix. pdf Division of Human Genetics, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA (W C Nichols PhD, V E Michaels BS); Department of Medical and Molecular Genetics, Indiana University Medical Center, Indianapolis, IN, USA (N Pankratz PhD, C A Halter MS, T Reed PhD, T Foroud PhD); Molecular Genetics Unit, National Institute on Aging, National Institutes of Health, Bethesda, MD, USA (D Hernandez MS, C Paisán-Ruíz BSc, S Jain BSc, A Singleton PhD); Unitat de Genètica Molecular, Departament de Genòmica i Proteòmica, Institut de Biomedicina de València- Consejo Superior de Investigaciones Científicas (CSIC), València, Spain (C Paisán-Ruíz); Department of Molecular Neuroscience, Institute of Neurology, London, UK (S Jain); Department of Neurology, University of Rochester, Rochester, NY, USA (A Rudolph PhD); Department of Neurosciences, University of California, La Jolla, CA, USA (Prof C W Shults MD); and Veterans Affairs San Diego Healthcare System, San Diego, CA, USA (Prof C W Shults) Correspondence to: Dr William C Nichols, Division of Human Genetics, Cincinnati Children’s Hospital Medical Center, 3333 Burnet Avenue, 1469 TCHRF, Cincinnati, OH 45229, USA Bill.nichols@cchmc.org Genetic screening for a single common LRRK2 mutation in familial Parkinson’s disease William C Nichols, Nathan Pankratz, Dena Hernandez, Coro Paisán-Ruíz, Shushant Jain, Cheryl A Halter, Veronika E Michaels, Terry Reed, Alice Rudolph, Clifford W Shults, Andrew Singleton, Tatiana Foroud, for the Parkinson Study Group-PROGENI investigators* Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene cause some forms of autosomal dominant Parkinson’s disease. We measured the frequency of a novel mutation (Gly2019Ser) in familial Parkinson’s disease by screening genomic DNA of patients and controls. Of 767 affected individuals from 358 multiplex families, 35 (5%) individuals were either heterozygous (34) or homozygous (one) for the mutation, and had typical clinical findings of idiopathic Parkinson’s disease. Thus, our results suggest that a single LRRK2 mutation causes Parkinson’s disease in 5% of individuals with familial disease. Screening for this mutation should be a component of genetic testing for Parkinson’s disease.