title: The curious case of phenocopies in families with genetic Parkinson's disease.
abstract: Monogenic forms of Parkinson's disease account for ∼3% of all "idiopathic" Parkinson's disease. With reduced penetrance in dominant forms and manifesting heterozygotes in recessive forms of Parkinson's disease, it has been well recognized that inheritance patterns do not always follow classic Mendelian genetics. A novel twist to the puzzle is the presence of phenocopies (i.e., family members with the same clinical syndrome as the mutation carriers, but lacking the familial mutation). We reviewed all pedigrees published between 1997 and 2009 with α-synuclein, leucine-rich repeat kinase 2, Parkin, or PTEN-induced kinase 1 mutations with at least 2 affected individuals and known genetic status for the possible presence of phenocopies. Of 537 patients with clinical Parkinson's disease in 160 families meeting our inclusion criteria, 27 patients (5.0%) from 23 families (14.4%) were phenocopies. Phenocopies represented 3.8% of all blood relatives reported in the pedigrees containing phenocopies and an estimated 1.3% of all blood relatives in all pedigrees included. Both of these rates exceeded age-specific prevalences of Parkinson's disease. In 4 families, the phenocopy was explained by another known mutation: In 2 pedigrees, a monogenic cause was likely; in another 2, secondary parkinsonism was suspected; and in the remaining 15 families, "sporadic Parkinson's disease" was suggested as the cause of disease in the phenocopy. The unexpectedly high number of phenocopies of mostly unknown origin within families with a seemingly known etiology of Parkinson's disease adds another level of complexity to genetic research of Parkinson's disease, as well as to the interpretation of genetic testing results in the clinical diagnostic setting.
authors: Morton and Gloria Shulman Movement Disorders Center and the Edmond J. Safra Program in Parkinson's Disease, Toronto Western Hospital, University of Toronto, Toronto, Ontario, Canada.
authors: Christine
authors: C
authors: Klein
authors: Rosalind
authors: R
authors: Chuang
authors: Connie
authors: C
authors: Marras
authors: Anthony E
authors: AE
authors: Lang
mesh_terms: D005192:Family Health; D020022:Genetic Predisposition to Disease; D005820:Genetic Testing; D006801:Humans; D000071158:Leucine-Rich Repeat Serine-Threonine Protein Kinase-2; D009154:Mutation / Q000235:genetics; D010300:Parkinson Disease / Q000235:genetics*; D010641:Phenotype; D011494:Protein Kinases / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D044767:Ubiquitin-Protein Ligases / Q000235:genetics; D051844:alpha-Synuclein / Q000235:genetics; D000099202:PTEN-Induced Putative Kinase
chemical_list: D000071158:Leucine-Rich Repeat Serine-Threonine Protein Kinase-2; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D044767:Ubiquitin-Protein Ligases; D051844:alpha-Synuclein; D000099202:PTEN-Induced Putative Kinase; C111567:parkin protein; C495280:LRRK2 protein, human