title: Next-generation phenotyping using the parkin example: time to catch up with genetics.
abstract: OBJECTIVE
  Two decades of intense research have led to important insights into the pathophysiology of neurodegenerative diseases, with limited direct clinical impact. While next-generation sequencing has emerged as a powerful research tool, we hypothesized that systematic exploitation of phenotypic data are lagging behind genetic advances.
  
  
  OBJECTIVE
  To use the 15-year experience with parkin-associated Parkinson disease (PD) to evaluate type, quality, and quantity of genetic and phenotypic data and to elucidate clinical or genetic features impacting genetic testing and counseling.
  
  
  METHODS
  We searched MEDLINE: (1998-2012) using the term parkin AND mutation for English publications about proved parkin-associated PD and at least minimal, individual clinical information excluding digenic cases, and redundant articles. This approach identified 877 articles, of which 196 described patients with PD with confirmed parkin mutations and 127 articles fulfilled our inclusion criteria. Information was extracted using predefined criteria and a consensus approach for questionable details. To evaluate study method differences, we devised a quality score representing the completeness of clinical, demographic, and genetic information.
  
  
  RESULTS
  In the data about 1184 patients, the quality score increased steadily and was driven exclusively by improvements in genetic analyses. By contrast, demographic and clinical content stagnated. The mean age at onset was 9 years lower in index patients with 2 mutant parkin alleles than in heterozygotes. Genotype-phenotype correlation was observed for the number of mutated alleles and dystonia. By contrast, dementia was rare in all parkin-mutation carriers (<3%), despite long disease duration.
  
  
  CONCLUSIONS
  Notwithstanding large gaps in phenotypic information content, we identified dystonia and the absence of dementia as "red flags" to be incorporated in counseling guidelines. We propose mandatory minimal criteria for genotype-phenotype studies to facilitate the next breakthrough-following genetics-toward more personalized medicine for genetic conditions, extending well beyond the parkin example.
authors.affiliation: Insitute of Neurogenetics, University of Lübeck, Lübeck, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Grünewald
authors.forename: Meike
authors.initials: M
authors.lastname: Kasten
authors.forename: Andreas
authors.initials: A
authors.lastname: Ziegler
authors.forename: Christine
authors.initials: C
authors.lastname: Klein
mesh_terms: D056726:Genetic Association Studies / Q000639:trends; D020022:Genetic Predisposition to Disease; D005820:Genetic Testing; D006801:Humans; D009154:Mutation / Q000235:genetics*; D010300:Parkinson Disease / Q000235:genetics*; D010641:Phenotype