Utility of the Rett syndrome behavior questionnaire (RSBQ) for Japanese patients with Rett syndrome: A pilot study

Rett syndrome (RTT) is a neurodevelopmental disorder caused by MECP2 gene mutations. It mainly affects females and is characterized by age-dependent neurological and behavioral abnormalities. The Rett Syndrome Behavior Questionnaire (RSBQ) is a caregiver-completed tool accepted by the US Food and Drug Administration as a primary outcome measure in RTT clinical trials. However, its reliability remains uncertain, and few Japanese studies have used it.

In this study, 18 female RTT patients aged 4-44 years who regularly visited our hospital were assessed using the 45-item RSBQ through physician-guided, face-to-face caregiver interviews to ensure accurate understanding of each question. RSBQ scores were analyzed across nine behavioral domains and compared between patients aged <15 years (n = 8) and those aged ≥15 years (n = 10). Correlations between age and domain scores were examined using Spearman's rank test. Multiple regression was conducted to identify independent predictors of RTT-characteristic domains, which we defined as Domain 2 (breathing abnormalities) and Domain 3 (hand stereotypies) total scores.

Among patients aged ≥15 years, Domain 2 scores showed a strong negative correlation with age (r = -0.936, p < 0.001). Multiple regression showed that age was an independent factor associated with lower total scores on Domains 2 and 3.

Breathing abnormalities and hand stereotypies tended to decrease with age. The RSBQ appears useful for evaluating symptom profiles in Japanese RTT patients. Future comparative and multicenter validation studies including female patients with intellectual disabilities are warranted. (242 words).