Clinical insight meets scientific innovation to develop a next generation ERT for Pompe disease.

Years of research into the structure, processing, and function of acid alpha-glucosidase led to the development and 2006 approval of alglucosidase alfa (recombinant human acid alpha-glucosidase, Myozyme®/Lumizyme®), an enzyme replacement therapy and the first approved treatment for Pompe disease. Alglucosidase alfa has been a lifesaving treatment for patients with infantile-onset Pompe disease and radically improved daily life for patients with late-onset Pompe disease; however, long-term experience with alglucosidase alfa unraveled key unmet needs in these populations. Despite treatment, Pompe disease continues to progress, especially from a skeletal muscle perspective, resulting in a multitude of functional limitations. Strong collaboration between the scientific and patient communities led to increased awareness of Pompe disease, a better understanding of disease pathophysiology, knowledge of the clinical course of the disease as patients surpassed the first decade of life, and the strengths and limitations of enzyme replacement therapy. Taken together, these advancements spurred the need for development of a next generation of enzyme replacement therapy and provided a framework for progress toward other novel treatments. This review provides an overview of the development of avalglucosidase alfa as a model to highlight the interaction between clinical experience with existing treatments, the role of the clinician scientist, translational research at both system and cellular levels, and the iterative and collaborative process that optimizes the development of therapeutics.

Whole exome sequencing reveals a dual diagnosis of BCAP31-related syndrome and glutaric aciduria III.

Background: Biochemical testing is a common first-tier approach in the setting of genetic evaluation of patients with unexplained developmental delay. However, results can be unclear, and a plan for second-tier analysis must be determined based on the patient's biochemical results and clinical presentation - in many cases, triggering a diagnostic odyssey. Case presentation: A male patient from the United States presenting with unexplained developmental delay, microcephaly, hypotonia, and feeding difficulties was referred for clinical genetic evaluation at age 8 months. Biochemical testing revealed an isolated marked elevation of glutaric acid on urine organic acid profile, without elevations of related metabolites. Further testing included GCDH sequencing, a neurometabolic gene panel, chromosomal microarray, Prader Willi/Angelman testing, and lysosomal disease enzyme panel, all of which were non-diagnostic. The patient had persistent developmental delay and hypotonia, dystonia, sensorineural hearing loss, and abnormal brain myelination on magnetic resonance imaging. Whole exome sequencing (WES) was performed and revealed a dual diagnosis of glutaric aciduria III (GA III) and BCAP31-related disorder, an X-linked intellectual disability syndrome, caused by a novel pathogenic variant. Conclusions: GA III has historically been considered clinically benign, with few reported cases. This patient's presenting symptoms were similar to those commonly seen in GA I and GA II, however the biochemical abnormalities were not consistent with these disorders, prompting additional molecular and biochemical testing. Ultimately, WES confirmed a diagnosis of BCAP31-related syndrome, a rare neurological disorder, which explained the patient's presenting symptoms. WES also identified a secondary diagnosis of GA III. We present a patient with two rare genetic conditions, highlighting the importance of deep phenotyping and the utility of WES in the setting of a patient with dual genetic diagnoses.

New insights into the landscape of ALPL gene variants in patients with hypophosphatasia from the Global HPP Registry.

Hypophosphatasia (HPP) is a rare, inherited metabolic disease characterized by low tissue-nonspecific alkaline phosphatase activity due to ALPL gene variants. We describe ALPL variants from the observational, prospective, multinational Global HPP Registry. Inclusion in the analysis required a diagnosis of HPP, low serum ALP activity, and ≥1 ALPL variant. Of 1176 patients enrolled as of September 2022, 814 met inclusion criteria in Europe (48.9%), North America (36.7%), Japan (10.2%), Australia (2.6%), and elsewhere (1.6%). Most patients (74.7%) had 1 ALPL variant; 25.3% had ≥2 variants. Nearly all patients (95.6%) had known disease-causing variants; 4.4% had variants of uncertain significance. Disease-causing variants were predominantly missense (770/1556 alleles). The most common variants were c.571G>A (102/1628 alleles), c.1250A>G (66/1628 alleles), and c.1559del (61/1628 alleles). Variant profiles were generally consistent, except in Japan, where a higher proportion of patients (68.7%) had ≥2 ALPL variants, likely because more had disease onset before age 6 months (53.0% vs. 10.1%-23.1% elsewhere). Frameshift mutations (61/164 alleles) and inframe deletions (7/164 alleles) were more common in Japan. Twenty-three novel variants were discovered, each in a single geographic region, predominantly Europe. Analyses confirmed previously known ALPL variants, identified novel variants, and characterized geographic variation in frequency and type of ALPL variants in a large population.

Changes in forced vital capacity over ≤ 13 years among patients with late-onset Pompe disease treated with alglucosidase alfa: new modeling of real-world data from the Pompe Registry.

BACKGROUND: Chronic respiratory insufficiency from progressive muscle weakness causes morbidity and mortality in late-onset Pompe disease (LOPD). Previous Pompe Registry (NCT00231400) analyses for ≤ 5 years' alglucosidase alfa treatment showed a single linear time trend of stable forced vital capacity (FVC) % predicted. METHODS: To assess longer term Pompe Registry data, piecewise linear mixed model regression analyses estimated FVC% predicted trajectories in invasive-ventilator-free patients with LOPD aged ≥ 5 years. We estimated annual FVC change 0-6 months, > 6 months-5 years, and > 5-13 years from treatment initiation, adjusting for baseline age, sex, and non-invasive ventilation. FINDINGS: Among 485 patients (4612 FVC measurements; 8.3 years median follow-up), median ages at symptom onset, diagnosis, and alglucosidase alfa initiation were 34.3, 41.1, and 44.9 years, respectively. FVC% increased during the first 6 months' treatment (slope 1.83%/year; 95% confidence interval: 0.66, 3.01; P = 0.0023), then modestly declined -0.54%/year (-0.79, -0.30; P < 0.0001) during > 6 months-5 years, and -1.00%/year (-1.36, -0.63; P < 0.0001) during > 5-13 years. The latter two periods' slopes were not significantly different from each other (Pdifference = 0.0654) and were less steep than published natural history slopes (-1% to -4.6%/year). Estimated individual slopes were ≥ 0%/year in 96.1%, 30.3%, and 13.2% of patients during the 0-6 month, > 6 month-5 year, and > 5-13 year periods, respectively. CONCLUSION: These real-world data indicate an alglucosidase alfa benefit on FVC trajectory that persists at least 13 years compared with published natural history data. Nevertheless, unmet need remains since most individuals demonstrate lung function decline 5 years after initiating treatment. Whether altered FVC trajectory impacts respiratory failure incidence remains undetermined. TRIAL REGISTRATION: This study was registered (NCT00231400) on ClinicalTrials.gov on September 30, 2005, retrospectively registered.

Natural history study of hepatic glycogen storage disease type IV and comparison to Gbe1ys/ys model.

BackgroundGlycogen storage disease type IV (GSD IV) is an ultrarare autosomal recessive disorder that causes deficiency of functional glycogen branching enzyme and formation of abnormally structured glycogen termed polyglucosan. GSD IV has traditionally been categorized based on primary hepatic or neuromuscular involvement, with hepatic GSD IV subclassified as discrete subtypes: classic (progressive) and nonprogressive.MethodsTo better understand the progression of liver disease in GSD IV, we present clinical and histopathology data from 23 patients from around the world and characterized the liver involvement in the Gbe1ys/ys knockin mouse model.ResultsWe propose an alternative to the established subtype-based terminology for characterizing liver disease in GSD IV and recognize 3 tiers of disease severity: (i) "severe progressive" liver disease, (ii) "intermediate progressive" liver disease, and (iii) "attenuated" liver disease. Analysis of liver pathology revealed that risk for liver failure cannot be predicted from liver biopsy findings alone in individuals affected by GSD IV. Moreover, analysis of postmortem liver pathology from an individual who died over 40 years after being diagnosed with nonprogressive hepatic GSD IV in childhood verified that liver fibrosis did not regress. Last, characterization of the liver involvement in a mouse model known to recapitulate the adult-onset neurodegenerative form of GSD IV (Gbe1ys/ys mouse model) demonstrated hepatic disease.ConclusionOur findings challenge the established subtype-based view of GSD IV and suggest that liver disease severity among patients with GSD IV represents a disease continuum.Trial registrationClinicalTrials.gov NCT02683512FundingNone.

Optimizing treatment outcomes: immune tolerance induction in Pompe disease patients undergoing enzyme replacement therapy.

Introduction: Pompe disease, a lysosomal storage disorder, is characterized by acid α-glucosidase (GAA) deficiency and categorized into two main subtypes: infantile-onset Pompe disease (IOPD) and late-onset Pompe disease (LOPD). The primary treatment, enzyme replacement therapy (ERT) with recombinant human GAA (rhGAA), faces challenges due to immunogenic responses, including the production of anti-drug antibody (ADA), which can diminish therapeutic efficacy. This study aims to assess the effectiveness of immune tolerance induction (ITI) therapy in cross-reactive immunologic material (CRIM)-positive Pompe disease patients with established high ADA levels. Method: In a single-center, open-label prospective study, we assessed ITI therapy's efficacy in Pompe disease patients, both IOPD and LOPD, with persistently elevated ADA titers (≥1:12,800) and clinical decline. The ITI regimen comprised bortezomib, rituximab, methotrexate, and intravenous immunoglobulin. Biochemical data, biomarkers, ADA titers, immune status, and respiratory and motor function were monitored over six months before and after ITI. Results: This study enrolled eight patients (5 IOPD and 3 LOPD). After a 6-month ITI course, median ADA titers significantly decreased from 1:12,800 (range 1:12,800-1:51,200) to 1:1,600 (range 1:400-1:12,800), with sustained immune tolerance persisting up to 4.5 years in some cases. Serum CK levels were mostly stable or decreased, stable urinary glucose tetrasaccharide levels were maintained in four patients, and no notable deterioration in respiratory or ambulatory status was noted. Adverse events included two treatable infection episodes and transient symptoms like numbness and diarrhea. Conclusion: ITI therapy effectively reduces ADA levels in CRIM-positive Pompe disease patients with established high ADA titers, underscoring the importance of ADA monitoring and timely ITI initiation. The findings advocate for personalized immunogenicity risk assessments to enhance clinical outcomes. In some cases, prolonged immune suppression may be necessary, highlighting the need for further studies to optimize ITI strategies for Pompe disease treatment. ClinicalTrials.gov NCT02525172; https://clinicaltrials.gov/study/NCT02525172.

Long-term effectiveness of eliglustat treatment: A real-world analysis from the International Collaborative Gaucher Group Gaucher Registry.

Gaucher disease type 1 (GD1) is known for phenotypic heterogeneity and varied natural history. Registrational clinical trials enrolled narrowly defined phenotypes, but greater diversity is encountered in clinical practice. We report real-world outcomes with long-term eliglustat treatment in adults with GD1 in the International Collaborative Gaucher Group Gaucher Registry. Among 5985 GD1 patients in the Registry as of January 6, 2023, 872 started eliglustat at ≥18 years old; of these, 469 met inclusion criteria. We compared clinical parameters at eliglustat initiation (i.e., baseline) and follow-up in treatment-naïve patients and used linear mixed models to estimate annual change from baseline in parameters among patients who switched to eliglustat after ≥1 year on enzyme replacement therapy. Over 4 years of follow-up in non-splenectomized treatment-naïve patients, hemoglobin and platelet count increased, liver and spleen volume decreased, and total lumbar spine bone mineral density (BMD) Z-score decreased slightly. Among non-splenectomized switch patients, on average, hemoglobin decreased -0.030 (95% CI: -0.053, -0.008) g/dL (N = 272) and platelet count increased 2.229 (95% CI: 0.751, 3.706) × 103/mm3 (N = 262) annually up to 10 years; liver volume decreased (-0.009 [95% CI: -0.015, -0.003] MN) (N = 102) and spleen volume remained stable (-0.070 [95% CI: -0.150, 0.010] MN) (N = 106) annually up to 7 years; and total lumbar spine BMD Z-score increased 0.041 (95% CI: 0.015, 0.066) (N = 183) annually up to 8 years. Among splenectomized switch patients, clinical parameters were stable over time. These long-term, real-world outcomes are consistent with the eliglustat clinical trials and emerging real-world experience across the GD phenotypic spectrum.

Effectiveness of asfotase alfa for treatment of adults with hypophosphatasia: results from a global registry.

BACKGROUND: Hypophosphatasia (HPP) is a rare inherited disease caused by deficient activity of tissue-nonspecific alkaline phosphatase. Many adults with HPP have a high burden of disease, experiencing chronic pain, fatigue, limited mobility, and dental issues, contributing to decreased health-related quality of life (HRQoL). HPP may be treated with the enzyme replacement therapy asfotase alfa though real-world data in adults are limited. This analysis was conducted to assess the clinical effectiveness of asfotase alfa among adults in the Global HPP Registry. METHODS: The Global HPP Registry is an observational, prospective, multinational study. Adults ≥ 18 years of age were included in this analysis if they had serum alkaline phosphatase (ALP) activity below the age- and sex-adjusted reference ranges, and/or ALPL variant(s), and received asfotase alfa for ≥ 6 months. Mobility was assessed with the 6-Minute Walk Test (6MWT), and patient-reported outcomes tools were used to assess pain (Brief Pain Inventory-Short Form), quality of life (36-item Short Form Health Survey, version 2 [SF-36v2]), and disability (Health Assessment Questionnaire-Disability Index) at multiple time points from baseline through Month 36. Data were collected as per usual standard of care; patients may not have contributed data at all time points. RESULTS: A total of 190 patients met the inclusion criteria. For patients with ≥ 1 follow-up measurement, the mean distance achieved on 6MWT increased from 404 m (range 60-632 m) at baseline (n = 31) to 484 m at Month 12 (range 240-739 m; n = 18) and remained above baseline through Month 36 (n = 7). Improvements in mean self-reported pain severity scores ranged from - 0.72 (95% CI: - 1.23, - 0.21; n = 38) to - 1.13 (95% CI: - 1.76, - 0.51; n = 26) and were observed at all time points. Improvements in the Physical Component Summary score of SF-36v2 were achieved by Month 6 and sustained throughout follow-up. There was a trend toward improvement in the Mental Component Summary score of SF-36v2 at most time points, with considerable fluctuations from Months 12 (n = 28) through 36 (n = 21). The most frequent adverse events were injection site reactions. CONCLUSIONS: Adults with HPP who received asfotase alfa for ≥ 6 months experienced improvements in mobility, physical function, and HRQoL, which were maintained over 3 years of follow-up. REGISTRATION: NCT02306720; EUPAS13514.

Underrepresentation of Diverse Ancestries Drives Uncertainty in Genetic Variants Found in Cardiomyopathy-Associated Genes.

BACKGROUND: Thousands of genetic variants have been identified in cardiomyopathy-associated genes. Diagnostic genetic testing is key for evaluation of individuals with suspected cardiomyopathy. While accurate variant pathogenicity assignment is important for diagnosis, the frequency of and factors associated with clinically relevant assessment changes are unclear. OBJECTIVES: The authors aimed to characterize pathogenicity assignment change in cardiomyopathy-associated genes and to identify factors associated with this change. METHODS: We identified 10 sarcomeric and 6 desmosomal genetic cardiomyopathy-associated genes along with comparison gene sets. We analyzed clinically meaningful changes in pathogenicity assignment between any of the following: pathogenic/likely pathogenic (P/LP), conflicting interpretations of pathogenicity or variant of unknown significance (C/VUS), and benign/likely benign. We explored association of minor allele frequency (MAF) differences between well, and traditionally poorly, represented ancestries in genetic studies with assessment stability. Analyses were performed using ClinVar and GnomAD data. RESULTS: Of the 30,975 cardiomyopathy-associated gene variants in ClinVar, 2,276 of them (7.3%) had a clinically meaningful change in pathogenicity assignment over the study period, 2011 to 2021. Sixty-seven percent of variants that underwent a clinically significant change moved from P/LP or benign/likely benign to C/VUS. Among cardiomyopathy variants downgraded from P/LP, 35% had a MAF above 1 × 10 -4 in non-Europeans and below 1 × 10 -4 in Europeans. CONCLUSIONS: Over the past 10 years, 7.3% of cardiomyopathy gene variants underwent a clinically meaningful change in pathogenicity assignment. Over 30% of downgrades from P/LP may be attributable to higher MAF in Non-Europeans than Europeans. This finding suggests that low ancestral diversity in genetic studies has increased diagnostic uncertainty in cardiomyopathy gene variants.

An updated management approach of Pompe disease patients with high-sustained anti-rhGAA IgG antibody titers: experience with bortezomib-based immunomodulation.

Introduction: High sustained anti-rhGAA antibody titers (HSAT; ≥12,800) are directly linked to reduced efficacy of enzyme replacement therapy (ERT) and subsequent clinical deterioration in infantile-onset Pompe disease (IOPD). We have previously demonstrated the safety and effectiveness of a bortezomib-based immune-tolerance induction (ITI) regimen (bortezomib, rituximab, methotrexate, and IVIG) in eliminating HSAT. Methods: Here, we describe two IOPD cases (patients 6 and 8) who developed HSAT at 8 and 10 weeks on ERT despite transient low-dose methotrexate ITI administration in the ERT-naïve setting and were treated with a bortezomib-based ITI regimen, and we compare their courses to a series of six historical patients (patients 1-5, and 7) with a similar presentation who exemplify our evolving approach to treatment. Results: In total, patients 6 and 8 received 16 and 8 doses of bortezomib (4 doses=1 cycle) respectively reducing titers from 25,600 to seronegative, but differences in the course of their therapy were instructive regarding the optimal approach to initial treatment of HSAT; specifically, patient 6 was treated initially with only a single course of bortezomib rescue therapy, while patient 8 received two back-to-back courses. Patient 8 received IVIG therapy throughout the immunosuppression whereas patient 6 received IVIG therapy and was switched to subcutaneous IgG replacement. Patient 6 had a transient reduction in anti-rhGAA antibodies, after receiving a single initial cycle of bortezomib, but had a recurrence of high anti-rhGAA antibody titer after 160 weeks that required 3 additional cycles of bortezomib to ultimately achieve tolerance. In contrast, patient 8 achieved tolerance after being given two consecutive cycles of bortezomib during their initial treatment and had B cell recovery by week 54. Since the reduction in anti-rhGAA antibodies, both patients are doing well clinically, and have decreasing ALT, AST, and CK. No major infections leading to interruption of treatment were observed in either patient. The bortezomib-based ITI was safe and well-tolerated, and patients continue to receive ERT at 40 mg/kg/week. Discussion: These case studies and our previous experience suggest that to achieve an effective reduction of anti-rhGAA antibodies in the setting of HSAT, bortezomib should be initiated at the earliest sign of high anti-rhGAA antibodies with a minimum of two consecutive cycles as shown in the case of patient 8. It is important to note that, despite initiation of ERT at age 2.3 weeks, patient 8 quickly developed HSAT. We recommend close monitoring of anti-rhGAA antibodies and early intervention with ITI as soon as significantly elevated anti-rhGAA antibody titers are noted.

104-week efficacy and safety of cipaglucosidase alfa plus miglustat in adults with late-onset Pompe disease: a phase III open-label extension study (ATB200-07).

The phase III double-blind PROPEL study compared the novel two-component therapy cipaglucosidase alfa + miglustat (cipa + mig) with alglucosidase alfa + placebo (alg + pbo) in adults with late-onset Pompe disease (LOPD). This ongoing open-label extension (OLE; NCT04138277) evaluates long-term safety and efficacy of cipa + mig. Outcomes include 6-min walk distance (6MWD), forced vital capacity (FVC), creatine kinase (CK) and hexose tetrasaccharide (Hex4) levels, patient-reported outcomes and safety. Data are reported as change from PROPEL baseline to OLE week 52 (104 weeks post-PROPEL baseline). Of 118 patients treated in the OLE, 81 continued cipa + mig treatment from PROPEL (cipa + mig group; 61 enzyme replacement therapy [ERT] experienced prior to PROPEL; 20 ERT naïve) and 37 switched from alg + pbo to cipa + mig (switch group; 29 ERT experienced; 8 ERT naive). Mean (standard deviation [SD]) change in % predicted 6MWD from baseline to week 104 was + 3.1 (8.1) for cipa + mig and - 0.5 (7.8) for the ERT-experienced switch group, and + 8.6 (8.6) for cipa + mig and + 8.9 (11.7) for the ERT-naïve switch group. Mean (SD) change in % predicted FVC was - 0.6 (7.5) for cipa + mig and - 3.8 (6.2) for the ERT-experienced switch group, and - 4.8 (6.5) and - 3.1 (6.7), respectively, in ERT-naïve patients. CK and Hex4 levels improved in both treatment groups by week 104 with cipa + mig treatment. Three patients discontinued the OLE due to infusion-associated reactions. No new safety signals were identified. Cipa + mig treatment up to 104 weeks was associated with overall maintained improvements (6MWD, biomarkers) or stabilization (FVC) from baseline with continued durability, and was well tolerated, supporting long-term benefits for patients with LOPD.Trial registration number: NCT04138277; trial start date: December 18, 2019.

Effect of avalglucosidase alfa on disease-specific and general patient-reported outcomes in treatment-naïve adults with late-onset Pompe disease compared with alglucosidase alfa: Meaningful change analyses from the Phase 3 COMET trial.

BACKGROUND: The Phase 3 COMET trial (NCT02782741) comparing avalglucosidase alfa and alglucosidase alfa included health-related quality of life (HRQoL) assessments in treatment-naïve patients with late-onset Pompe disease (LOPD). Here, we further characterize results from disease-specific and general patient-reported outcome (PRO) measures. METHODS: Adults who participated in the COMET trial receiving avalglucosidase alfa or alglucosidase alfa (both 20 mg/kg biweekly) during the 49-week double-blind treatment period were included in the analysis. Proportions of patients exceeding meaningful change thresholds at Week 49 were compared post hoc between treatment groups. PROs and their meaningful change thresholds included: Pompe Disease Severity Scale (PDSS; decrease 1.0-1.5 points), Pompe Disease Impact Scale (PDIS; decrease 1.0-1.5 points), Rasch-built Pompe-specific Activity Scale (R-PAct; change from unable to able to complete activity), 12-item Short Form Health Survey (SF-12; physical component summary [PCS] score: increase ≥6 points, mental component summary [MCS] score: increase ≥7 points), EuroQol 5 Dimension 5 Level (EQ-5D-5L; improvement of ≥1 category), and Patient Global Impression of Change (PGIC; any improvement). RESULTS: The analysis included 99 adult patients (avalglucosidase alfa n = 50; alglucosidase alfa n = 49). Patients who received avalglucosidase alfa had significantly greater odds of achieving a meaningful change versus alglucosidase alfa for the PDSS Shortness of Breath (OR [95% CI] 11.79 [2.24; 62.18]), Fatigue/Pain (6.24 [1.20; 32.54]), Morning Headache (13.98 [1.71; 114.18]), and Overall Fatigue (5.88 [1.37; 25.11]) domains, and were significantly more likely to meet meaningful change thresholds across multiple PDSS domains (all nominal p < 0.05). A numerically greater proportion of patients in the avalglucosidase alfa group were able to complete selected activities of the R-PAct compared with the alglucosidase alfa group. Significantly greater proportions of patients who received avalglucosidase alfa achieved meaningful improvements for EQ-5D-5L usual activities dimension, EQ visual analog scale, and all four PGIC domains. The proportion of patients with improvements in SF-12 PCS and MCS was greater in the avalglucosidase alfa group versus alglucosidase alfa group, but was not significant (p > 0.05). CONCLUSIONS: These analyses show that avalglucosidase alfa improves multiple symptoms and aspects of daily functioning, including breathing and mobility. This supports the clinical relevance of the effects of avalglucosidase alfa on HRQoL for patients with LOPD.

Severe CNS involvement in a subset of long-term treated children with infantile-onset Pompe disease.

INTRODUCTION: The standard of care for patients with infantile-onset Pompe disease (IOPD) is enzyme replacement therapy (ERT), which does not cross the blood brain barrier. While neuromuscular manifestations of IOPD are well-described, central nervous system (CNS) manifestations of this disorder are far less characterized. Here we describe severe CNS-related neurological manifestations including seizures and encephalopathy in six individuals with IOPD. METHOD: We identified six children with IOPD who developed CNS manifestations such as seizures and/or encephalopathy. We studied their brain magnetic resonance imaging scans (MRIs) and graded the severity of white matter hyperintensities (WMHI) using the Fazekas scale scoring system as previously published. Longitudinal cognitive measures were available from 4/6 children. RESULTS: All six IOPD patients (4 males/2 females) had been treated with ERT for 12-15 years. Seizures and/or encephalopathy were noted at a median age at onset of 11.9 years (range 9-15 years). All were noted to have extensive WMHI in the brain MRIs and very high Fazekas scores which preceded the onset of neurological symptoms. Longitudinal IQ scores from four of these children suggested developmental plateauing. DISCUSSION: Among a subset of IOPD patients on long-term ERT, CNS manifestations including hyperreflexia, encephalopathy and seizures may become prominent, and there is likely an association between these symptoms and significant WMHI on MRI. Further study is needed to identify risk factors for CNS deterioration among children with IOPD and develop interventions to prevent neurological decline.

Validation of the Patient-Reported Outcomes Measurement Information System (PROMIS®) physical function questionnaire in late-onset Pompe disease using PROPEL phase 3 data.

BACKGROUND: The construct validity and interpretation of the Patient-Reported Outcome Measurement Information System (PROMIS®) Physical Function short form 20a (PF20a) questionnaire were evaluated for patients with late-onset Pompe disease (LOPD), a rare, autosomal recessive, progressive neuromuscular disorder treatable by enzyme replacement therapy (ERT). METHODS: In the phase 3 PROPEL study, adults with LOPD underwent testing of physical functioning and had PRO measurements at baseline and at weeks 12, 26, 38, and 52 while receiving experimental or standard-of-care ERT. All patients were pooled for analyses, without comparisons between treatment groups. Associations and correlations between PROMIS PF20a scores and the 6-minute walk distance (6MWD), % predicted forced vital capacity (FVC), manual muscle test (MMT) of the lower extremities, Gait, Stairs, Gowers' maneuver, Chair (GSGC) score, and Rasch-built Pompe-specific Activity (R-PAct) scale were evaluated by calculating regression coefficients in linear regression models and Pearson correlation coefficients (R); patients' age, sex, race, ERT prior to study, body mass index, and study treatment were included as covariables. The minimal clinically important difference (MCID) of PROMIS PF20a was determined using distribution- and anchor-based methods. RESULTS: 123 patients received at least 1 dose of ERT. In multivariable analyses, PROMIS PF20a scores had strong correlations with R-PAct scores (R = 0.83 at baseline and R = 0.67 when evaluating changes between baseline and 52 weeks) and moderate correlations with the 6MWD (R = 0.57 at baseline and R = 0.48 when evaluating changes between baseline and 52 weeks). Moderate correlations were also observed between PROMIS PF20a and MMT (R = 0.54), GSGC (R=-0.51), and FVC (R = 0.48) at baseline. In multivariable linear regression models, associations were significant between PROMIS PF20a and 6MWD (P = 0.0006), MMT (P = 0.0034), GSGC (P = 0.0278), and R-PAct (P < 0.0001) at baseline, between PROMIS PF20a and 6MWD (P < 0.0001), FVC (P = 0.0490), and R-PAct (P < 0.0001) when combining all measurements, and between PF20a and 6MWD (P = 0.0016) and R-PAct (P = 0.0001) when evaluating changes in scores between baseline and 52 weeks. The anchor-based and distribution-based MCID for a clinically important improvement for PROMIS PF20a were 2.4 and 4.2, respectively. CONCLUSIONS: PROMIS PF20a has validity as an instrument both to measure and to longitudinally follow physical function in patients with LOPD. TRIAL REGISTRATION: ClinicalTrials.gov, NCT03729362. Registered 2 November 2018, https://www. CLINICALTRIALS: gov/search?term=NCT03729362 .

The Global ALPL gene variant classification project: Dedicated to deciphering variants.

BACKGROUND: Hypophosphatasia (HPP) is an inherited multisystem disorder predominantly affecting the mineralization of bones and teeth. HPP is caused by pathogenic variants in ALPL, which encodes tissue non-specific alkaline phosphatase (TNSALP). Variants of uncertain significance (VUS) cause diagnostic delay and uncertainty amongst patients and health care providers. RESULTS: The ALPL gene variant database (https://alplmutationdatabase.jku.at/) is an open-access archive for interpretation of the clinical significance of variants reported in ALPL. The database contains coding and non-coding variants, including single nucleotide variants, insertions/deletions and structural variants affecting coding or non-coding sequences of ALPL. Each variant in the database is displayed with details explaining the corresponding pathogenicity, and all reported genotypes and phenotypes, including references. In 2021, the ALPL gene variant classification project was established to reclassify VUS and continuously assess and update genetic, phenotypic, and functional variant information in the database. For this purpose, the database provides a unique submission system for clinicians, geneticists, genetic counselors, and researchers to submit VUS within ALPL for classification. An international, multidisciplinary consortium of HPP experts has been established to reclassify the submitted VUS using a multi-step process adhering to the stringent ACMG/AMP variant classification guidelines. These steps include a clinical phenotype assessment, deep literature research including artificial intelligence technology, molecular genetic assessment, and in-vitro functional testing of variants in a co-transfection model to measure ALP residual activity. CONCLUSION: This classification project and the ALPL gene variant database will serve the global medical community, widen the genotypic and phenotypic HPP spectrum by reporting and characterizing new ALPL variants based on ACMG/AMP criteria and thus facilitate improved genetic counseling and medical decision-making for affected patients and families. The project may also serve as a gold standard framework for multidisciplinary collaboration for variant interpretation in other rare diseases.

Immunophenotype associated with high sustained antibody titers against enzyme replacement therapy in infantile-onset Pompe disease.

Introduction: The efficacy of enzyme replacement therapy (ERT) with alglucosidase alfa for infantile-onset Pompe disease (IOPD) is limited in some patients due to the development of high and sustained antibody titers (HSAT; ≥12,800). Methods: We carried out detailed immunophenotyping of IOPD patients (n=40), including analysis of circulating cell populations by flow cytometry and plasma cytokines by multiplex array, to determine whether patients with HSAT have unique immunological characteristics compared to those with low titers (LT; <12,800). Results: Compared to patients with LT, patients who develop HSAT were skewed toward a type 2 immune profile, with an increased frequency of Th2 cells that was positively correlated with levels of Th2 (IL-4, IL-5, IL-13) and pro-inflammatory (IL-6, TNF-α, MIP-1α, MIP-1ß) cytokines. B cells were increased in HSAT patients with a decreased fraction of unswitched memory B cells. Plasma GM-CSF concentrations were lower on average in HSAT patients, while CXCL11 was elevated. Finally, using principal components analysis, we derived an HSAT Signature Score that successfully stratified patients according to their antibody titers. Discussion: The immune profiles revealed in this study not only identify potential biomarkers of patients that developed HSAT but also provide insights into the pathophysiology of HSAT that will ultimately lead to improved immunotherapy strategies.

Case report: Expanding the understanding of the adult polyglucosan body disease continuum: novel presentations, diagnostic pitfalls, and clinical pearls.

Introduction: Adult polyglucosan body disease (APBD) has long been regarded as the adult-onset form of glycogen storage disease type IV (GSD IV) and is caused by biallelic pathogenic variants in GBE1. Advances in the understanding of the natural history of APBD published in recent years have led to the use of discrete descriptors ("typical" versus "atypical") based on adherence to traditional symptomatology and homozygosity for the p.Y329S variant. Although these general descriptors are helpful in summarizing common findings and symptoms in APBD, they are inherently limited and may affect disease recognition in diverse populations. Methods: This case series includes three American patients (cases 1-3) and four Brazilian patients (cases 4-7) diagnosed with APBD. Patient-reported outcome (PRO) measures were employed to evaluate pain, fatigue, and quality of life in cases 1-3. Results: We describe the clinical course and diagnostic odyssey of seven cases of APBD that challenge the utility and efficacy of discrete descriptors. Cases 1-3 are compound heterozygotes that harbor the previously identified deep intronic variant in GBE1 and presented with "typical" APBD phenotypically, despite lacking two copies of the pathogenic p.Y329S variant. Patient-reported outcome measures in these three cases revealed the moderate levels of pain and fatigue as well as an impacted quality of life. Cases 4-7 have unique genotypic profiles and emphasize the growing recognition of presentations of APBD in diverse populations with broad neurological manifestations. Conclusion: Collectively, these cases underscore the understanding of APBD as a spectrum disorder existing on the GSD IV phenotypic continuum. We draw attention to the pitfalls of commonly used genetic testing methods when diagnosing APBD and highlight the utility of patient-reported outcome questionnaires in managing this disease.

Pulmonary Arterial Hypertension in Glycogen Storage Disease Type I

Abstract Pulmonary arterial hypertension (PAH) is a rare and highly fatal disease that has been reported in 8 patients with glycogen storage disease type I (GSDI). We describe an additional case of an acute presentation of PAH in a 14-year-old patient with GSDI, which was successfully treated with inhaled nitric oxide and sildenafil. We investigated the incidence of PAH in 28 patients with GSDI on routine echocardiography and found no evidence of PAH and no significant cardiac abnormalities. This study highlights that PAH is a rare disease overall, but our case report and those previously described suggest an increased incidence in patients with GSDI. Should cardiopulmonary symptoms develop, clinicians caring for patients with GSDI should have a high degree of suspicion for acute PAH and recognize that prompt intervention can lead to survival in this otherwise highly fatal disease.