title: Individualized Prediction of Changes in 6-Minute Walk Distance for Patients with Duchenne Muscular Dystrophy.
abstract: BACKGROUND
  Deficits in ambulatory function progress at heterogeneous rates among individuals with Duchenne muscular dystrophy (DMD). The resulting inherent variability in ambulatory outcomes has complicated the design of drug efficacy trials and clouded the interpretation of trial results. We developed a prediction model for 1-year change in the six minute walk distance (6MWD) among DMD patients, and compared its predictive value to that of commonly used prognostic factors (age, baseline 6MWD, and steroid use).
  
  
  METHODS
  Natural history data were collected from DMD patients at routine follow up visits approximately every 6 months over the course of 2-5 years. Assessments included ambulatory function and steroid use. The annualized change in 6MWD (Δ6MWD) was studied between all pairs of visits separated by 8-16 months. Prediction models were developed using multivariable regression for repeated measures, and evaluated using cross-validation.
  
  
  RESULTS
  Among n = 191 follow-up intervals (n = 39 boys), mean starting age was 9.4 years, mean starting 6MWD was 351.8 meters, and 75% had received steroids for at least one year. Over the subsequent 8-16 months, mean Δ6MWD was -37.0 meters with a standard deviation (SD) of 93.7 meters. Predictions based on a composite of age, baseline 6MWD, and steroid use explained 28% of variation in Δ6MWD (R2 = 0.28, residual SD = 79.4 meters). A broadened prognostic model, adding timed 10-meter walk/run, 4-stair climb, and rise from supine, as well as height and weight, significantly improved prediction, explaining 59% of variation in Δ6MWD after cross-validation (R2 = 0.59, residual SD = 59.7 meters).
  
  
  CONCLUSIONS
  A prognostic model incorporating timed function tests significantly improved prediction of 1-year changes in 6MWD. Explained variation was more than doubled compared to predictions based only on age, baseline 6MWD, and steroid use. There is significant potential for composite prognostic models to inform DMD clinical trials and clinical practice.
authors.affiliation: University Hospitals Leuven, Child Neurology, Leuven, Belgium.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Goemans
authors.affiliation: University Hospitals Leuven, Child Neurology, Leuven, Belgium.
authors.forename: Marleen
authors.initials: M
authors.lastname: Vanden Hauwe
authors.affiliation: Analysis Group, Inc., 111 Huntington Ave, 14th floor, Boston, Massachusetts, United States of America.|The Trajectory Analysis Project (TAP) Collaboration, One Broadway, 14th floor, Cambridge, Massachusetts, United States of America.
authors.forename: James
authors.initials: J
authors.lastname: Signorovitch
authors.affiliation: Analysis Group, Inc., 111 Huntington Ave, 14th floor, Boston, Massachusetts, United States of America.
authors.forename: Elyse
authors.initials: E
authors.lastname: Swallow
authors.affiliation: Analysis Group, Inc., 111 Huntington Ave, 14th floor, Boston, Massachusetts, United States of America.
authors.forename: Jinlin
authors.initials: J
authors.lastname: Song
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D005080:Exercise Test; D005500:Follow-Up Studies; D005838:Genotype; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D020388:Muscular Dystrophy, Duchenne / Q000188:drug therapy / Q000503:physiopathology*; D011379:Prognosis; D013256:Steroids / Q000627:therapeutic use
chemical_list: D013256:Steroids