The QOLA study: psychometric validation of the Quality of Life of Parents of Children with Achondroplasia (QOLA) questionnaire - a multinational study in Germany, Italy, and Portugal.

BACKGROUND: Parents of children with achondroplasia experience multidimensional impacts on quality of life (QoL), yet validated condition-specific instruments for assessing these outcomes across countries are scarce. This study evaluated the psychometric properties of the Quality of Life of Parents of Children with Achondroplasia (QOLA) questionnaire in three European settings. METHODS: A multinational, multicentre observational psychometric validation study was conducted in Germany, Italy, and Portugal. Parents/primary caregivers (N = 149) completed the 43-item QOLA (eight conceptual domains) and the EUROHIS-QOL-8 at baseline (T1); a subsample completed follow-up assessments (T2; n = 77) for test-retest analyses. Data quality (missingness, floor/ceiling effects), internal consistency (Cronbach's α; composite reliability), temporal stability (Pearson correlations; intraclass correlation coefficients), and convergent validity (correlations with EUROHIS-QOL-8) were examined. Exploratory factor analysis informed item reduction and domain aggregation, followed by confirmatory factor analysis of the reduced model. RESULTS: Item-level missingness was minimal, and no substantial floor/ceiling effects were observed. Eight-domain scores showed acceptable to excellent internal consistency (α = 0.706-0.905) and moderate-to-good temporal stability (single-measure ICCs = 0.64-0.75). Convergent validity was supported by negative associations between QOLA domains and generic QoL (r = .15-0.69). Exploratory and confirmatory analyses supported a parsimonious three-factor, 20-item model, comprising Healthcare System Trust, Caregiving Burden and Daily Impact, and Worries About the Future and Social Relationships, with acceptable fit (CFI = 0.935, TLI = 0.925, RMSEA = 0.066), strong reliability (α = 0.852-0.918; CR = 0.864-0.914), and good test-retest stability (r = .670-0.782; average-measure ICCs = 0.801-0.877). CONCLUSIONS: The QOLA demonstrates robust reliability and validity across three countries and offers both an eight-domain profile and a three-factor summary for assessing parental QoL in achondroplasia.