Enzyme-replacement therapy in life-threatening hypophosphatasia.

BACKGROUND: Hypophosphatasia results from mutations in the gene for the tissue-nonspecific isozyme of alkaline phosphatase (TNSALP). Inorganic pyrophosphate accumulates extracellularly, leading to rickets or osteomalacia. Severely affected babies often die from respiratory insufficiency due to progressive chest deformity or have persistent bone disease. There is no approved medical therapy. ENB-0040 is a bone-targeted, recombinant human TNSALP that prevents the manifestations of hypophosphatasia in Tnsalp knockout mice. METHODS: We enrolled infants and young children with life-threatening or debilitating perinatal or infantile hypophosphatasia in a multinational, open-label study of treatment with ENB-0040. The primary objective was the healing of rickets, as assessed by means of radiographic scales. Motor and cognitive development, respiratory function, and safety were evaluated, as well as the pharmacokinetics and pharmacodynamics of ENB-0040. RESULTS: Of the 11 patients recruited, 10 completed 6 months of therapy; 9 completed 1 year. Healing of rickets at 6 months in 9 patients was accompanied by improvement in developmental milestones and pulmonary function. Elevated plasma levels of the TNSALP substrates inorganic pyrophosphate and pyridoxal 5'-phosphate diminished. Increases in serum parathyroid hormone accompanied skeletal healing, often necessitating dietary calcium supplementation. There was no evidence of hypocalcemia, ectopic calcification, or definite drug-related serious adverse events. Low titers of anti-ENB-0040 antibodies developed in four patients, with no evident clinical, biochemical, or autoimmune abnormalities at 48 weeks of treatment. CONCLUSIONS: ENB-0040, an enzyme-replacement therapy, was associated with improved findings on skeletal radiographs and improved pulmonary and physical function in infants and young children with life-threatening hypophosphatasia. (Funded by Enobia Pharma and Shriners Hospitals for Children; ClinicalTrials.gov number, NCT00744042.).

Characterization of Strength and Function in Ambulatory Adults With GNE Myopathy.

OBJECTIVE: To characterize the pattern and extent of muscle weakness and impact on physical functioning in adults with GNEM. METHODS: Strength and function were assessed in GNEM subjects (n = 47) using hand-held dynamometry, manual muscle testing, upper and lower extremity functional capacity tests, and the GNEM-Functional Activity Scale (GNEM-FAS). RESULTS: Profound upper and lower muscle weakness was measured using hand-held dynamometry in a characteristic pattern, previously described. Functional tests and clinician-reported outcomes demonstrated the consequence of muscle weakness on physical functioning. CONCLUSIONS: The characteristic pattern of upper and lower muscle weakness associated with GNEM and the resulting functional limitations can be reliably measured using these clinical outcome assessments of muscle strength and function.

Pediatric physical functioning reference curves.

We developed normative profiles of physical functioning (mobility and self-care) in infancy up through 14 years of age with an expanded version of the Pediatric Evaluation of Disability Inventory. Mobility and self-care reference curves were based on the original Pediatric Evaluation of Disability Inventory standardization data (n = 412) and data from an additional cross-sectional, convenience sample (n = 373) via web-based survey, telephone or in-person interviews of parents. This new sample, which included children up through 14 years-of-age, was stratified for race, age, and sex, but was primarily limited geographically to the Northeast region of the United States. Goodness of fit of male, female, and combined sex (male and female) reference curves was examined. The mobility and self-care reference curves produced efficient and well-fitting estimates of conventional percentiles (3rd, 10th, 25th, 50th, 75th, 97th). Differences between males' and females' reference curves were negligible. This study highlights the use of these reference curves for determining the functional impact of Pompe disease, a lysosomal storage disorder that affects skeletal and cardiac muscle, restricting normal expression of mobility and self-care activities. This physical functioning instrument could also be used to evaluate the impact of muscle weakness in other neuromuscular disorders.

A physical performance measure for individuals with mucopolysaccharidosis type I.

The purpose of this article is threefold: (1) to describe the development, reliability, and validity of a revised physical performance measure for individuals with mucopolysaccharidosis type I (MPS I); (2) to standardize the test on a normal sample; and (3) to compare results from a selected sample of individuals with MPS I with age-based centiles. The MPS Physical Performance Measure (MPS-PPM) is composed of eight timed functional tasks (FT-8) and two endurance tasks with a modified Energy Expenditure Index for comfortable walking (CW) and fast walking (FW) speeds. Age norms were derived from a convenience sample of 150 typically developing children and adolescents (75 males, 75 females; mean age 11y 2mo [SD 4y 5mo]; range 5-22y). Using a Rasch model for speed tests and confirmatory factor analysis, we established the unidimensionality of the FT-8. Interrater reliability of the FT-8 (intraclass correlation [ICC]=0.98) and test-retest reliability of the FT-8 (ICC=0.96), CW (ICC=0.91), and FW (ICC=0.83) were good. Results of the age-based profiles in 10 individuals with MPS I (five males, five females; mean age 14y 2mo [SD 7y 6mo]; range 6-29y) indicate that the amount of time needed to perform functional tasks is severely affected by the disease, and most individuals were at or below the fifth centile for their age. The patterns of limitations in endurance were more varied. These results suggest the utility of using this revised MPS-PPM to identify the extent of limitation in age-expected physical performance. Implications for using the MPS-PPM for monitoring physical performance changes during clinical interventions are discussed.

The emerging role of the pediatric physical therapist in evaluation and intervention for individuals with lysosomal storage diseases.

PURPOSE: The purposes of this article are to describe the pathology, medical implications, and typical impairments of individuals with various lysosomal storage diseases (LSDs), summarize results of recent clinical trials on medical interventions relevant to physical therapy practice, report new advances in functional measurement, and suggest a framework for physical therapy management and intervention. SUMMARY OF KEY POINTS: Medical and surgical interventions are enabling individuals with LSDs to not only survive but to improve their daily functioning and quality of life. This is likely to become an increasing area of emphasis in pediatric physical therapy, as the intervention emphasis for some individuals will shift from maintenance to restorative programs. RECOMMENDATIONS: We recommend that pediatric physical therapists become familiar with new LSD therapeutics, play a major role in evaluating impairment and functional limitation changes in individuals with LSDs, and become knowledgeable about the indications and precautions for restorative physical therapy programs.

A computer adaptive testing approach for assessing physical functioning in children and adolescents.

The purpose of this article is to demonstrate: (1) the accuracy and (2) the reduction in amount of time and effort in assessing physical functioning (self-care and mobility domains) of children and adolescents using computer-adaptive testing (CAT). A CAT algorithm selects questions directly tailored to the child's ability level, based on previous responses. Using a CAT algorithm, a simulation study was used to determine the number of items necessary to approximate the score of a full-length assessment. We built simulated CAT (5-, 10-, 15-, and 20-item versions) for self-care and mobility domains and tested their accuracy in a normative sample (n=373; 190 males, 183 females; mean age 6y 11mo [SD 4y 2m], range 4mo to 14y 11mo) and a sample of children and adolescents with Pompe disease (n=26; 21 males, 5 females; mean age 6y 1mo [SD 3y 10mo], range 5mo to 14y 10mo). Results indicated that comparable score estimates (based on computer simulations) to the full-length tests can be achieved in a 20-item CAT version for all age ranges and for normative and clinical samples. No more than 13 to 16% of the items in the full-length tests were needed for any one administration. These results support further consideration of using CAT programs for accurate and efficient clinical assessments of physical functioning.

Pompe disease and physical disability.

This study describes the physical disability of 30 children and adolescents with Pompe disease (23 males, 7 females; mean age 7 years 7 months, SD 5 years 6 months; range 6 months to 22 years 1 month) using a disease-specific functional instrument. Data were collected by telephone interview with parents using a modified version of the Pediatric Evaluation of Disability Inventory. The sample included mostly males of Caucasian origin, recruited from several countries. Disability profiles in mobility and self-care skills were heterogeneous because functional status was not related to chronological age. Most children had severe functional deficits: nearly two-thirds of the sample was non-ambulatory and could not perform age-expected self-care skills. Three-quarters of the children used a ventilator. Two children were able to participate in age-appropriate sports and peer activities. Although the mean chronological age of the sample was 7 years 7 months, the mean age-performance for self-care skills was under 2 years 6 months and under 1 year 6 months for mobility. Implications of physical disability findings for individuals with Pompe disease are discussed.

Development of a disease-specific disability instrument for Pompe disease.

PURPOSE: The purpose of this study was to modify the Paediatric Evaluation of Disability Inventory (PEDI) to create a Pompe disease-specific disability instrument for use in clinical trials and natural history studies. METHODS: PEDI item content was revised to include self-care and mobility items appropriate for children and youth with Pompe disease. Data were collected on 30 individuals with Pompe disease (mean age 7.7+/-5.6 years; range 0.4-22.1 years) by parent proxy through telephone interviews. New items were merged with original PEDI items using Rasch rating scale methods. RESULTS: The Pompe-PEDI extended the content range and scoring precision of the original PEDI. Construct validity was demonstrated and test-re-test reliability was excellent. CONCLUSIONS: The Pompe-PEDI is a reliable and valid instrument to assess and monitor the functional changes of children and youth with Pompe disease.

Physical performance testing in mucopolysaccharidosis I: a pilot study.

OBJECTIVE: To develop and field-test a physical performance measure (MPS-PPM) for individuals with Mucopolysaccharidosis I (MPS I), a rare genetic disorder. METHODS: Motor performance and endurance items were developed based on literature review, clinician feedback, feasibility, and equipment and training needs. A standardized testing protocol and scoring rules were created. The MPS-PPM includes: Arm Function (7 items), Leg Function (5 items), and Endurance (2 items). Pilot data were collected for 10 subjects (ages 5-29 years). We calculated Spearman's rho correlations between age, severity and summary z-scores on the MPS-PPM. RESULTS: Subjects had variable presentations, as correlations among the three sub-test scores were not significant. Increasing age was related to greater severity in physical performance (r = 0.72, p<0.05) and lower scores on the Leg Function (r = -0.67, p<0.05) and Endurance (r = -0.65, p<0.05) sub-tests. The MPS-PPM was sensitive to detecting physical performance deficits, as six subjects could not complete the full battery of Arm Function items and eight subjects were unable to complete all Leg Function items. Subjects walked more slowly and expended more energy than typically developing peers. CONCLUSIONS: Individuals with MPS I have difficulty with arm and leg function and reduced endurance. The MPS-PPM is a clinically feasible measure that detects limitations in physical performance and may have potential to quantify changes in function following intervention.