CME Evaluation of 50 probands with early-onset Parkinson’s disease for Parkin mutations K. Hedrich, MS; K. Marder, MD, MPH; J. Harris, MS, PhD; M. Kann, BS; T. Lynch, MD; H. Meija–Santana, MS; P.P. Pramstaller, MD; E. Schwinger, MD; S.B. Bressman, MD; S. Fahn, MD; and C. Klein, MD Abstract—Background: Early onset PD has been associated with different mutations in the Parkin gene, including exon deletions and duplications. Methods: The authors performed an extensive mutational analysis on 50 probands with onset of PD at younger than 50 years of age. Thirteen probands were ascertained from a registry of familial PD and 37 probands by age at onset at younger than 50 years, blind to family history. Mutational analysis was undertaken on the probands and available family members and included conventional techniques (single strand conformation polymorphism analysis and sequencing) and a newly developed method of quantitative duplex PCR to detect alterations of gene dosage (exon deletions and duplications) in Parkin. Results: Using this new technique, the authors detected eight alterations of gene dosage in the probands, whereas 12 mutations were found by conventional methods among the probands and another different mutation in an affected family member. In total, the authors identified compound heterozygous mutations in 14%, heterozygous mutations in 12%, and no Parkin mutation in 74% of the 50 probands. We expanded the occurrence of Parkin mutations to another ethnic group (African-American). Conclusion: The authors systematically screened all 12 Parkin exons by quantitative PCR and conventional methods in 50 probands. Eight mutations were newly reported, 2 of which are localized in exon 1, and 38% of the mutations were gene dosage alterations. These results underline the need to screen all exons and to undertake gene dosage studies. Furthermore, this study reveals a frequency of heterozygous mutation carriers that may signify a unique mode of inheritance and expression of the Parkin gene. NEUROLOGY 2002;58:1239 –1246 PD is the second most common neurodegenerative dis- order with a prevalence of about 2% in persons older than 65 years of age. 1 However, PD also can manifest earlier in life, which is referred to as early onset PD (EOPD). Age at onset in EOPD usually is considered to be below 40 2 to 50 years. 3-5 PD is characterized clini- cally by tremor, rigidity, bradykinesia, and postural instability. In the last few years, three genes and four gene loci have been associated with PD (alpha- synculein, 6 Parkin, 7 UCH-L1, 8 and gene loci on chromo- somes 2p13, 9 4p14 –16, 10 1p35–36, 11 and 1p36 12 ). Whereas mutations in alpha-synculein and UCH-L1 are rare, mutations in the Parkin gene have been found in many patients with early onset autosomal recessive PD. 4,5,7,13 The phenotype associated with Par- kin mutations is variable but usually is characterized by an early age at onset, even presenting itself in child- hood. 4 In addition, disease progression usually is slow, patients respond well to levodopa therapy, and various additional signs may be observed such as diurnal fluc- tuation of symptoms, sleep benefit, dystonia, early levodopa-induced dyskinesia, and hyperreflexia. 4,14 All proteins currently associated with monogenic forms of parkinsonism appear to be involved in the ubiquitin-mediated pathway of protein degradation. It has been shown recently that Parkin acts as an E3– ubiquitin ligase that ubiquitinates itself and promotes its own degradation. 15-17 In addition, it is involved in the ubiquitin-dependent degradation of several sub- strates, for example, O-glycosylated alpha-synuclein, 18 the parkin-related endothelin receptor–like receptor (Pael-R), 19 the synaptic vesicle-associated protein called CDCrel-1, 17 and synphilin-1, a protein interacting with alpha-synuclein. 20 From the Departments of Neurology (K. Hedrich, M. Kann, and Dr. Klein) and Human Genetics (K. Hedrich, M. Kann, and Drs. Schwinger and Klein), Medical University of Lübeck, Germany; Department of Neurology (Drs. Marder, Harris, Lynch, and Fahn, and H. Meija–Santana), Columbia University, Gertrude H. Sergievsky Center (Drs. Marder and Meija–Santana), and Taub Institute for Research on Alzheimer’s disease and the Aging Brain (Dr. Marder), New York, NY; University College (Dr. Lynch), Dublin, Ireland; Department of Neurology (Dr. Pramstaller), Regional General Hospital, Bolzano, Italy; and Department of Neurology (Dr. Bressman), Albert Einstein College of Medicine, Bronx, NY. Supported by the Deutsche Forschungsgemeinschaft (Kl-1134/2-1 - K.H., C.K.), the Parkinson’s Disease Foundation (C.K., T.L., K.M., S.F., H.M.), NIH (K08 to T.L., NS36630 to K.M., RR00645 to K.M.), the Irving Scholarship (T.L.), the Lowenstein Foundation (T.L.), ARDAD (T.L.), NARSAD (T.L.), and a Galen Fellowship (T.L.). Received September 4, 2001. Accepted in final form January 2, 2002. Address correspondence and reprint requests to Dr. Christine Klein, Department of Neurology, Medical University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany; e-mail: klein_ch@neuro.mu-luebeck.de Copyright © 2002 by AAN Enterprises, Inc. 1239