Challenges and strategies for clinical trials in propionic and methylmalonic acidemias

Clinical trial development in rare diseases poses significant study design and methodology challenges, such as disease heterogeneity and appropriate patient selection, identification and selection of key endpoints, decisions on study duration, choice of control groups, selection of appropriate statistical analyses, and patient recruitment. Therapeutic development in organic acidemias (OAs) shares many challenges with other inborn errors of metabolism, such as incomplete understanding of natural history, heterogenous disease presentations, requirement for sensitive outcome measures and difficulties recruiting a small sample of participants. Here, we review strategies for the successful development of a clinical trial to evaluate treatment response in propionic and methylmalonic acidemias. Specifically, we discuss crucial decisions that may significantly impact success of the study, including patient selection, identification and selection of endpoints, determination of the study duration, consideration of control groups including natural history controls, and selection of appropriate statistical analyses. The significant challenges associated with designing a clinical trial in rare disease can sometimes be successfully met through strategic engagement with experts in the rare disease, seeking regulatory and biostatistical guidance, and early involvement of patients and families.

Lifelong impact of ENPP1 Deficiency and the early onset form of ABCC6 Deficiency from patient or caregiver perspective

The ectonucleotide pyrophosphatase/phosphodiesterase family member 1 (ENPP1) and ATP-binding cassette subfamily C member 6 (ABCC6) proteins play a prominent role in inhibiting ectopic calcification and arterial stenosis. Patients with ENPP1 Deficiency or infant onset ABCC6 Deficiency often present with pathological calcification, narrowed blood vessels, multiorgan dysfunction and high infant mortality. The heterogenous presentation and progression is well documented. Our objective was to characterize how these morbidities lead to burden of illness and poor quality of life across ages from the patient/caregiver perspective. Patients/caregivers were interviewed via phone using Institutional Review Board–approved questionnaires. Patient-reported outcomes were collected via validated instruments. Thirty-one caregivers and 7 patients participated: infant onset ABCC6 Deficiency, n = 6 (infants/children); ENPP1 Deficiency, n = 32 (13 infants, 12 children, 7 adults). ENPP1 and ABCC6-deficient children aged <8 years and aged 8–18 years reported poor school functioning (0.69 vs 0.72 effect size, respectively) and poor physical health (0.88 vs 1, respectively). In the total ENPP1 cohort, 72% (23/32) reported bone/joint pain and/or mobility/fatigue issues. Three of seven ENPP1-deficient adults reported moderate to severe pain (>4), as measured by the Brief Pain Inventory (BPI), that interfered with daily activities despite pain medication. Top reported burdens for caregivers of infants with ABCC6/ENPP1 Deficiencies included heart-related issues and hospitalizations. Treatment/medications, and hearing loss were the highest burdens reported by caregivers/families of the pediatric ENPP1 Deficiency cohort, whereas adults reported bone/joint pain and mobility impairment as the greatest burdens. Individuals with ENPP1 Deficiency or infant onset ABCC6 Deficiency experience lifelong morbidity causing substantial physical and emotional burden to patients/caregivers.

Mucopolysaccharidosis type VI (Maroteaux-Lamy syndrome): defining and measuring functional impacts in pediatric patients

BACKGROUND

Research about pediatric patients' perspective on mucopolysaccharidosis type VI (MPS VI) and its impact on daily life is limited. We aimed to identify the disease concepts of interest that most impact function and day-to-day life of pediatric patients with MPS VI, and to consider clinical outcome assessments (COAs) that may potentially measure meaningful improvements in these concepts.

METHODS

Potential focus group participants were identified by the National MPS Society (USA) and invited to participate if they self-reported a clinician-provided diagnosis of MPS VI and were 4 to 18 years, receiving enzyme replacement therapy (ERT), and available to attend a 1-day focus group with their caregiver in Dallas, TX, USA. The focus group consisted of a series of polling and open-ended concept elicitation questions and a cognitive debriefing session. The discussion was audio recorded, transcribed verbatim, and analyzed to identify disease concepts of interest and functional impacts most relevant to participants.

RESULTS

Overall, caregivers (n = 9) and patients with MPS VI (n = 9) endorsed that although their children/they receive ERT, residual symptoms exist and impact health-related quality of life. The key disease concepts of interest identified were impaired mobility, upper extremity and fine motor deficits, pain, and fatigue. Pain was unanimously reported by all patients across many areas of the body and impacted daily activity. Key disease concepts were mapped to a selection of pediatric COAs including generic measures such as PROMIS®, PODCI, CHAQ, and PedsQL™. Caregivers endorsed the relevance of PODCI and PROMIS Upper Extremity, Mobility, and Pain items and all patients completed the NIH Toolbox Pegboard Dexterity Test. Additional COAs that aligned with the disease concepts included range of motion, the 2- and 6-min walk tests, timed stair climbs, Bruininks-Oseretsky Test of Motor Proficiency, 2nd edition, grip strength, pain visual analog scale, and the Faces Pain Scale-Revised.

CONCLUSION

An MPS VI focus group of pediatric patients and their caregivers identified impaired mobility, upper extremity and fine motor deficits, pain, and fatigue as key disease concepts of interest. These disease concepts were mapped to existing pediatric COAs, which were provided to the group for endorsement of their relevance.

Clinical Outcome Assessments: Use of Normative Data in a Pediatric Rare Disease

Pediatric rare diseases present unique challenges in clinical trial design and in selection of clinical outcome assessments (COAs) used to support claims in medical product labeling. COAs that discriminate level of function relative to a normative sample are particularly important in the pediatric rare disease setting because the literature is often void of natural history data. Pediatric rare disease clinical trials will often include a wide age distribution. Gross and fine motor skills, communication, cognition, and independence in activities of daily living vary by age, and it may be difficult to distinguish between treatment effect and change due to developmental maturation. Asfotase alfa was granted breakthrough therapy designation and subsequently approved for the treatment of hypophosphatasia (HPP; a genetic metabolic musculoskeletal disorder) and is used in this discussion to illustrate COA selection in a pediatric rare disease. Multiple COAs with normative data in HPP clinical trials for asfotase alfa are presented. The assessment instruments included the Bayley Scales of Infant and Toddler Development-Third Edition, the Bruininks-Oseretsky Test of Motor Proficiency, Second Edition, the Childhood Health Assessment Questionnaire, the Pediatric Outcomes Data Collection Instrument, handheld dynamometry, the 6-minute walk test, and the Modified Performance-Oriented Mobility Assessment-Gait scale. Multiple end points were required to adequately capture the impact of asfotase alfa treatment on the multiple systems affected in HPP. These data illustrate the importance of using multiple COAs that provide normative data and to use COAs early in the drug development process for rare pediatric disease.

Physical therapy management of infants and children with hypophosphatasia

Hypophosphatasia (HPP) is a rare inborn error of metabolism resulting in undermineralization of bone and subsequent skeletal abnormalities. The natural history of HPP is characterized by rickets and osteomalacia, increased propensity for bone fracture, early loss of teeth in childhood, and muscle weakness. There is a wide heterogeneity in disease presentation, and the functional impact of the disease can vary from perinatal death to gait abnormalities. Recent clinical trials of enzyme replacement therapy have begun to offer an opportunity for improvement in survival and function. The role of physical therapy in the treatment of the underlying musculoskeletal dysfunction in HPP is underrecognized. It is important for physical therapists to understand the disease characteristics of the natural history of a rare disease like HPP and how the impairment and activity limitations may change in response to medical interventions. An understanding of when and how to intervene is also important in order to optimally impact body function, lessen structural impairment, and facilitate increased functional independence in mobility and activities of daily living. Individualizing treatment to the child's needs, medical fragility, and setting (home/school/hospital), while educating parents, caregivers, and school staff regarding approved activities and therapy frequency, may improve function and development in children with HPP.