Background: Phenylketonuria (PKU) is a rare genetic disorder caused by a defect in the metabolism of phenylalanine (PHE) resulting in elevated blood and brain PHE levels, and leading to cognitive, emotional, and psychosocial problems. The phenylketonuria - quality of life (PKU-QOL) questionnaire was the first self-administered disease-specific instrument developed to assess the impact of PKU and its treatment on the health-related quality of life (HRQL) of patients and their caregivers. Available in four versions (child, adolescent, adult and parent), the PKU-QOL was simultaneously developed and validated in seven countries [i.e., France, Germany, Italy, The Netherlands, Spain, Turkey and the United Kingdom (UK)]. The objectives of our study were to develop and linguistically validate the PKU-QOL questionnaire for use in the United States (US).
Methods: The UK versions served as a basis for the development of the US English PKU-QOL questionnaire. The linguistic validation process consisted of 4 steps: 1) adaptation of the UK versions into US English by a translator native of US English and living in the US; 2) a clinician review; 3) cognitive interviews with patients and caregivers to test the appropriateness, understandability and clarity of the US translations; and 4) two proof-readings.
Results: The adaptation from UK to US English revealed the usual syntactic and idiomatic differences between the two languages, such as differences in: 1) Spelling, e.g., "dietician" (UK) vs. "dietitian" (US), or "mum" (UK) vs. "mom" (US); 2) Syntax or punctuation; and 3) Words/expressions use, e.g., "holidays" (UK) vs. "vacation" (US), or "biscuits" (UK) vs. "crackers" (US). The major issue was cultural, and consisted of using a different terminology to describe PKU treatment throughout the questionnaires. The clinician, with the patients and the caregivers, during the interviews suggested to replace "supplement and amino-acid mixture" or "supplements" with "medical formula." This wording was later changed to "medical food" to be consistent with the terminology used in current US published guidelines.
Conclusions: The translation of the UK English PKU-QOL questionnaire into US English did not raise critical semantic and cultural issues. The PKU-QOL will be valuable for US healthcare providers in individualizing treatment and managing patients with PKU.
Keywords: Health-related quality of life; Linguistic validation; PKU-QOL questionnaire; Phenylketonuria; Translation.