title: Composite biomarkers for assessing Duchenne muscular dystrophy: an initial assessment.
abstract: BACKGROUND
  Compared with individual parameters, composite biomarkers may provide a more effective means for monitoring disease progression and the effects of therapy in clinical trials than single measures. In this study, we built composite biomarkers for use in Duchenne muscular dystrophy by combining values from two objective measures of disease severity: electrical impedance myography and quantitative ultrasound and evaluating how well they correlated to standard functional measures.
  
  
  METHODS
  Using data from an ongoing study of electrical impedance myography and quantitative ultrasound in 31 Duchenne muscular dystrophy and 26 healthy boys aged 2-14 years, we combined data sets by first creating z scores based on the normal subject data and then using simple mathematical operations (addition and multiplication) to create composite measures. These composite scores were then correlated to age and standard measures of function including the 6-minute walk test, the North Star Ambulatory Assessment, and handheld dynamometry.
  
  
  RESULTS
  Combining data sets resulted in stronger correlations with all four outcomes than for either electrical impedance myography or quantitative ultrasound alone in six of eight instances. These improvements reached statistical significance (P < 0.05) in several cases. For example, the correlation coefficient for the composite measure with the North Star Ambulatory Assessment was 0.79 but was only 0.66 and 0.67 (respectively) for gray scale level and electrical impedance myography separately.
  
  
  CONCLUSIONS
  Arithmetically derived composite scores can provide stronger correlations to functional measures than isolated biomarkers. Longitudinal study of such composite markers in Duchenne muscular dystrophy clinical trials is warranted.
authors.affiliation: Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts.
authors.forename: Irina
authors.initials: I
authors.lastname: Shklyar
authors.affiliation: Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts.
authors.forename: Amy
authors.initials: A
authors.lastname: Pasternak
authors.affiliation: Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts.
authors.forename: Kush
authors.initials: K
authors.lastname: Kapur
authors.affiliation: Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts.
authors.forename: Basil T
authors.initials: BT
authors.lastname: Darras
authors.affiliation: Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts. Electronic address: srutkove@bidmc.harvard.edu.
authors.forename: Seward B
authors.initials: SB
authors.lastname: Rutkove
mesh_terms: D000293:Adolescent; D015415:Biomarkers / Q000378:metabolism*; D002648:Child; D002675:Child, Preschool; D018450:Disease Progression; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D053581:Muscle Strength Dynamometer; D018482:Muscle, Skeletal / Q000503:physiopathology*; D020388:Muscular Dystrophy, Duchenne / Q000150:complications* / Q000175:diagnosis*; D009213:Myography / Q000379:methods; D017063:Outcome Assessment, Health Care; D013223:Statistics as Topic
chemical_list: D015415:Biomarkers
keywords: Duchenne muscular dystrophy; biomarker; composite; electrical impedance myography; outcome measure; quantitative ultrasound