Symptoms and impact of aromatic l-amino acid decarboxylase (AADC) deficiency: a qualitative study and the development of a patient-centred conceptual model

Abstract

Background Aromatic l-amino acid decarboxylase (AADC) deficiency is a rare neurological condition, with an estimated global prevalence of 1:32,000 to 1:90,000 live births. AADC deficiency is associated with a range of symptoms and functional impairments, but these have not previously been explored qualitatively. This study aimed to understand the symptoms of AADC deficiency and its impact on individuals’ health-related quality of life. Methods Qualitative interviews were conducted with caregivers of individuals with AADC deficiency in Italy, Spain, Portugal and the United States. An interview guide was developed with input from clinical experts and caregivers, and explored the symptoms and impacts of AADC deficiency. Interviews were conducted by telephone and were recorded and transcribed. Data were analysed using thematic analysis and saturation was recorded. Results Fourteen caregivers took part, who provided care to 13 individuals with AADC deficiency aged 1–15 years. All individuals had impaired motor function, which was attributed to low muscle tone and muscle weakness. The level of motor function varied considerably, ranging from no motor function (no head control) to being able to take a few steps without support. Other impairments included cognitive impairment, communication difficulties, movement disorders (e.g. oculogyric crises), gastrointestinal symptoms, eating difficulties, fatigue and sleep disruption. Most individuals were completely dependent on their caregivers for all aspects of their lives. This limited function had a negative impact on their ability to socialise with their peers and on their emotional wellbeing. These concepts and relationships are illustrated in a conceptual model, and moderating factors (e.g. physiotherapy and medication) are discussed. Conclusion This is the first qualitative study to report on the experience of living with AADC deficiency. Caregivers report individuals with AADC deficiency experience a wide range of symptoms and functional impairments, which have a substantial impact on their health-related quality of life.