Using n-of-1 methodology to inform the development of individualised, evidence-based interventions for patients with xeroderma pigmentosum

Introduction: XP is a very rare inherited disease affecting 1 in 250,000
people (~90 UK patients). It involves extreme sensitivity to UV light; the
only treatment is complete avoidance of UV – not going outside during
daylight, fitting UV screens to windows, or ensuring complete skin coverage.
Most patients die by age 35, usually from skin cancers. No research
on the psychological consequences of XP or factors relating to UV protection
currently exists.
Methods: In phase one, an N-of-1 study was conducted in 25 adult XP
patients, as part of a mixed methods approach to intervention development.
Participants wore a UV wristwatch and completed a brief survey,
including adherence behaviors and psychological predictors (e.g., emotions,
self-regulation), for 50 consecutive days. Constructs were selected
from the theory domains framework and a review of behavioral maintenance
theories.
Results: N-of-1 analysis revealed differences in the patterns of predictors of
adherence across participants, supporting the need for an individualized
approach. Following MRC guidelines, phase two involves the development
of a series of individualized interventions to improve adherence, informed
directly by the specific predictors identified for each participant in phase
one (e.g., including BCTs to target motivation, planning, or emotions).
After PPI feedback and piloting, the interventions will be tested in a
waitlist-controlled RCT in a matched sample of non-adherent adults.
Conclusions: The XP study provides a novel example of systematic intervention
development in a rare and unstudied condition, which could be
used as a model for understanding and improving health outcomes in
other rare diseases.