## 1 Introduction  
Pompe disease (Online Mendelian Inheritance in Man (OMIM) 606800) is an autosomal recessive inherited orphan disease caused by mutations in the glucosidase alpha acid (GAA) gene. Resulting in deficient activity of the enzyme alpha-1,4-glucosidase that is located in cellular lysosomes involved in the degradation of glycogen. Consequently, glycogen accumulation occurs not only in skeletal muscle, but also in cardiac and smooth muscles [1].  
The entrapment of lysosomal glycogen results in muscle damage by a number of pathogenic mechanisms, such as defective autophagy, calcium homeostasis, oxidative stress, and mitochondrial abnormalities [2]. Recently, metabolic abnormalities and energy deficits have also been shown to contribute to this pathogenic cascade [3]. The severity of clinical manifestations, tissue impairment and age of onset correlate with the residual enzymatic activity and can be classified into two forms: the Infantile Onset Pompe Disease (IOPD) or classical form has no or very low enzymatic activity levels, leading to severe general muscular weakness with floppy infant syndrome. Cardiomyopathy and respiratory failure usually lead to death within the first year of life. The late-onset Pompe disease (LOPD) or non-classical form has a higher residual enzyme activity. This disease progresses slowly and may start at any age after the first year of life. A common sign of LOPD is weakness of the proximal limbs, predominantly affecting the hip girdle. Axial muscles as well as respiratory muscles may also be impaired due to myopathy [4]. Patients often present clinically with back pain and exercise intolerance and dyspnea [5]. Recently, the systemic characteristics of this primary muscular disorder have been discovered: alteration of smooth muscles of the intestine and vessels, especially ectasia of vertebobrasial arteries, and the involvement of the nervous system (white matter lesions and small fiber neuropathy) widening the Pompe disease phenotype [6].  
Since 2006, a causal treatment is available with enzyme replacement therapy (ERT) using recombinant human \(\alpha\)-glucosidase. This treatment has been shown to improve patient survival and muscle strength to a variable extent [7]. It can also improve the quality of life of LOPD patients due to better mobility and participation in activities of daily life [8]. However, the actual ERT is not a cure for the disease and further therapeutic approaches are necessary. A detailed understanding of LOPD patients' gait patterns and balance may help improve physiotherapeutic strategies in the prevention of falls and preserving the patient's ambulatory status. Additionally, analysis of these features might be a tool for following up on future therapeutic strategies (i.e., next level ERT order gene therapy) [9]. There is a paucity in this research, with one study reporting reduced spatio-temporal parameters during gait in 22 LOPD patients on ERT [10] and another showing deficits in standing postural stability among five LOPD patients [11].  
The aim of this study was to provide a systematic analysis of both gait parameters and postural abilities, as well as their interaction in patients with LOPD. These data were then compared to a group of matched healthy controls.