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Andreas Unger, Andreas Roos, Andrea Luise Gangfuß, Andreas Hentschel, Dieter Gläser, Karsten Krause, Kristina Döring, Ulrike Schara, Sabine Hoffjan, Matthias Vorgerd, Anne-Katrin Güttsches

• \(\it BICD2\) variants have been linked to neurodegenerative disorders like spinal muscular atrophy with lower extremity predominance (SMALED2) or hereditary spastic paraplegia (HSP). Recently, mutations in \(\it BICD2\) were implicated in myopathies. Here, we present one patient with a known and six patients with novel \(\it BICD2\) missense variants, further characterizing the molecular landscape of this heterogenous neurological disorder. A total of seven patients were genotyped and phenotyped. Skeletal muscle biopsies were analyzed by histology, electron microscopy, and protein profiling to define pathological hallmarks and pathogenicity markers with consecutive validation using fluorescence microscopy. Clinical and MRI-features revealed a typical pattern of distal paresis of the lower extremities as characteristic features of a \(\it BICD2\)-associated disorder. Histological evaluation showed myopathic features of varying severity including fiber size variation, lipofibromatosis, and fiber splittings. Proteomic analysis with subsequent fluorescence analysis revealed an altered abundance and localization of thrombospondin-4 and biglycan. Our combined clinical, histopathological, and proteomic approaches provide new insights into the pathophysiology of \(\it BICD2\)-associated disorders, confirming a primary muscle cell vulnerability. In this context, biglycan and thrombospondin-4 have been identified, may serve as tissue pathogenicity markers, and might be linked to perturbed protein secretion based on an impaired vesicular transportation.