Measuring Friedreich ataxia: complementary features of examination and performance measures.
OBJECTIVE
To examine the potential validity of performance measures and examination-based scales in Friedreich ataxia (FA) by examining their correlation with disease characteristics.


METHODS
The authors assessed the properties of a candidate clinical outcome measure, the Friedreich Ataxia Rating Scale (FARS), and simple performance measures (9-hole peg test, the timed 25-foot walk, PATA test, and low-contrast letter acuity) in 155 patients with FA from six institutions, and correlated the scores with disease duration, functional disability, activity of daily living scores, age, and shorter GAA repeat length to assess whether these measures capture the severity of neurologic dysfunction in FA.


RESULTS
Scores for the FARS and performance measures correlated significantly with functional disability, activities of daily living scores, and disease duration, showing that these measures meet essential criteria for construct validity for measuring the progressive nature of FA. In addition, the FARS and transformed performance measures scores were predicted by age and shorter GAA repeat length in linear regression models accounting for sex and testing site. Correlations between performance measures were moderate in magnitude, suggesting that each test captures separate yet related dimensions of neurologic function in FA and that a composite measure might better predict disease status. Composite measures created using cohort means and standard deviations predicted disease status better than or equal to single performance measures or examination-based measures.


CONCLUSIONS
The Friedreich Ataxia Rating Scale, performance measures, and performance measure composites provide valid assessments of disease progression in Friedreich ataxia.
Lynch
D R
DR
Department of Neurology, University of Pennsylvania School of Medicine, and Children's Hospital of Philadelphia, PA 19104-4318, USA. lynch@pharm.med.upenn.edu
Farmer
J M
JM
Tsou
A Y
AY
Perlman
S
S
Subramony
S H
SH
Gomez
C M
CM
Ashizawa
T
T
Wilmot
G R
GR
Wilson
R B
RB
Balcer
L J
LJ
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D004185:Disability Evaluation; D005260:Female; D005621:Friedreich Ataxia / Q000175:diagnosis* / Q000453:epidemiology*; D020234:Gait Ataxia / Q000175:diagnosis* / Q000453:epidemiology*; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care / Q000379:methods*; D010808:Physical Examination / Q000379:methods / Q000706:statistics & numerical data*; D011379:Prognosis; D011597:Psychomotor Performance; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D014481:United States / Q000453:epidemiology