Validation of the first quality-of-life measurement for patients with Huntington's disease: the Huntington Quality of Life Instrument.

Health-related quality-of-life instruments are critical for assessing disease burdens. Generic tools allow comparison between diseases but do not discriminate between disease severities. Specific tools also tend to be more sensitive. No specific tool is available to assess quality of life in patients with Huntington's disease (HD). In the context of the European study on HD burden, a specific tool was created: the Huntington Quality of Life Instrument (H-QoL-I). The aim of this study was to optimize the content and validate the H-QoL-I. After a semistructured interview with patients, caregivers and HD specialists, we conducted a patient focus group. A self-reported questionnaire was then developed in French and Italian. A total of 252 patients were recruited to answer the questionnaire. Face, internal and external validities were examined using a variety of methods. The shortened H-QoL-I that resulted from the successive analyses comprises 11 items, which are divided into three dimensions: motor functioning (four items), psychology (four items) and socializing (three items). These three domains were identified as being essential to cover the full domain of the quality of life for patients affected by HD. The H-QoL-I showed an acceptable reliability (Cronbach's α>0.84). Factor analyses demonstrated satisfactory construct validity. Moreover, the item internal consistency and item discriminant validity criteria were fulfilled. No differential item functioning was detected. External validity supported the scale's robustness. These data support the validity of the H-QoL-I in patients with HD.