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Introduction Late‐onset Pompe disease (LOPD) is characterized by a progressive myopathy resulting from a deficiency of acid α‐glucosidase enzyme activity. Enzyme replacement therapy has been shown to be effective, but long‐term treatment results vary. Avalglucosidase alfa demonstrated non‐inferiority to alglucosidase alfa in a phase 3 study, allowing in France compassionate access for advanced LOPD patients unresponsive to alglucosidase alfa. Methods Data from the French Pompe registry were analyzed for patients who benefited from a switch to avalglucosidase alfa with at least 1 year of follow‐up. Respiratory (forced vital capacity [FVC]) and motor functions (Six‐Minute Walk Test [6MWT]) were assessed before and 1 year after switching. Individual changes in FVC and 6MWT were expressed as slopes and statistical analyses were performed to compare values. Results Twenty‐nine patients were included (mean age 56 years, 11 years of prior treatment). The FVC and 6MWT values remained stable. The individual analyses showed a stabilization of motor worsening: –1 m/year on the 6MWT after the switch versus –63 m/year the year before the switch (i.e., a worsening of 33%/year before vs. an improvement of 3%/year later). Respiratory data were not statistically different. Discussion At the group level, gait parameters improved slightly with a stabilization of previous worsening, but respiratory parameters showed limited changes. At the individual level, results were discordant, with some patients with a good motor or respiratory response and some with further worsening. Conclusion Switching to avalglucosidase alfa demonstrated varied responses in advanced LOPD patients with failing alglucosidase alfa therapy, with a general improvement in motor stabilization.

Pompe disease (PD) is caused by a deficiency of lysosomal acid α-glucosidase resulting from mutations in the GAA gene. The clinical spectrum ranges from a rapidly fatal multisystemic disorder (classic PD, onset < 1 year) to a milder adult onset myopathy. The aims of this study were to characterize the GAA mutations, to establish the disease epidemiology, and to identify potential genotype-phenotype correlations in French late-onset PD patients (onset ≥ 2 years) diagnosed since the 1970s. Data were collected from the two main laboratories involved in PD diagnosis and from the French Pompe registry. Two hundred forty-six patients (130 females and 116 males) were included, with a mean age at diagnosis of 43 years. Eighty-three different mutations were identified in the GAA gene, among which 28 were novel. These variants were spread all over the sequence and included 42 missense (one affecting start codon), 8 nonsense, 15 frameshift, 14 splice mutations, 3 small in-frame deletions, and one large deletion. The common c.-32-13T>G mutation was detected in 151/170 index cases. Other frequent mutations included the exon 18 deletion, the c.525del, and the missense mutations c.1927G>A (p.Gly643Arg) and c.655G>A (p.Gly219Arg). Patients carrying the c.-32-13T>G mutation had an older mean age at onset than patients non-exhibiting this mutation (36 versus 25 years). Patients with the same genotype had a highly variable age at onset. We estimated the frequency of late-onset PD in France around 1/69,927 newborns. In conclusion, we characterized the French cohort of late-onset PD patients through a nationwide study covering more than 40 years.

Background and purpose The Rasch‐Built Pompe‐Specific Activity (R‐PAct) scale is a patient‐reported outcome measure specifically designed to quantify the effects of Pompe disease on daily life activities, developed for use in Dutch‐ and English‐speaking countries. This study aimed to validate the R‐PAct for use in other countries. Methods Four other language versions (German, French, Italian, and Spanish) of the R‐PAct were created and distributed among Pompe patients (≥16 years old) in Germany, France, Spain, Italy, and Switzerland and pooled with data of newly diagnosed patients from Australia, Belgium, Canada, the Netherlands, New Zealand, the USA, and the UK and the original validation cohort (n = 186). The psychometric properties of the scale were assessed by exploratory factor analysis and Rasch analysis. Results Data for 520 patients were eligible for analysis. Exploratory factor analysis suggested that the items separated into two domains: Activities of Daily Living and Mobility. Both domains independently displayed adequate Rasch model measurement properties, following the removal of one item (\"Are you able to practice a sport?\") from the Mobility domain, and can be added together to form a \"higher order\" factor as well. Differential item functioning (DIF)‐by‐language assessment indicated DIF for several items; however, the impact of accounting for DIF was negligible. We recalibrated the nomogram (raw score interval‐level transformation) for the updated 17‐item R‐PAct scale. The minimal detectable change value was 13.85 for the overall R‐PAct. Conclusions After removing one item, the modified‐R‐PAct scale is a valid disease‐specific patient‐reported outcome measure for patients with Pompe disease across multiple countries.