Feasibility of quantifying behavior in early progressive MPS II

Hunter syndrome is a rare X-linked lysosomal disorder associated with progressive multisystem involvement. Ages of onset vary, as do disease course and phenotypic severity. The early progressive phenotype involves delayed developmental milestones with worsening intellectual impairment and regression. Disease progression creates dramatic neurobehavioral symptoms, including hyperactivity, inattention, behavior difficulties, sleep disturbance, and others. These behaviors are highly disruptive, distressing to families, and significantly impact quality of life. But these symptoms have been difficult to measure. Existing pediatric behavioral assessment tools do not capture the unique constellation of symptoms, nor variability of expression. To address this problem, we are developing a Hunter-specific caregiver rating scale of neurobehavioral symptoms. The goal is to create a valid, reliable tool that detects change in neurobehavioral profile, informing natural history and therapeutic response. A first step involves drafting a tool using methods of scale development for another MPS type with neurobehavioral impairment, the Sanfilippo Behavior Rating Scale. Item sets are informed by coded video recordings of: 1) semi-structured play in small groups of affected boys and 2) focus groups with caregivers literature review and review of existing tools. Inclusion criteria include: 1) confirmed diagnosis of early progressive Hunter syndrome 2) age 4 to 9 years 3) able to ambulate. Findings aligned with the literature’s descriptions of diverse symptoms, with considerable differences in presentation within-child, dependent upon internal and external factors (e.g., fatigue, hunger, novelty of a setting). Caregiver reports indicated a need for a behaviorally anchored scale that assesses frequency of symptoms and context rather than severity. Next steps will involve piloting the draft scale and soliciting caregiver feedback. Future directions include validating the measure in a larger multi-center study. Support: Shire pharmaceuticals, NIH U54NS065768, National MPS Society, UMN Center for Neurobehavioral Development