This podcast discusses the recent publication by Inoue and Weihl (2025) on myofibrillar myopathies (MFMs), focusing on their redefinition as “Z-disk-opathies.” In this episode we explore how new genetic findings challenge the traditional, histopathology-based classification and highlight key disease mechanisms, including Z-disk disruption and impaired protein homeostasis.

The episode also covers the distinction between so called, true MFMs and other myopathies with similar pathology, as well as the implications for diagnosis and future targeted therapies.

In this Journal Club episode, we review the publication by Yang et al., 2024, which presents the first Chinese case of Myofibrillar Myopathy type 13 with Rimmed Vacuoles (MFM13) in a pediatric patient. Unlike previously reported MFM13 cases, this young patient exhibits axial and limb-girdle muscle involvement, highlighting a novel early-onset presentation.

This episode is ideal for researchers, clinicians, and patients interested in MFM13, HSPB8 myopathy, rare pediatric neuromuscular cases, and autophagy-related mechanisms.

Please note that the article refers to the MFM13 disease as HSPB8-related myopathy.

In this episode, we summarize what is known about Myofibrillar Myopathy type 13 (MFM13), previously referred to as HSPB8 Myopathy. Drawing on nine published case studies, we outline the main clinical features — progressive muscle weakness and atrophy, usually starting in the distal lower limbs and leading to foot drop and steppage gait. In some cases, weakness extends to proximal and axial muscles, occasionally affecting breathing or cardiac function.

We also discuss the characteristic pathological findings seen in muscle biopsies: rimmed vacuoles, myofibrillar disorganization, and accumulation of proteins like HSPB8, BAG3, and TDP-43. MRI scans often reveal selective fatty degeneration of paraspinal and leg muscles.

Finally, we highlight the key discovery that frameshift mutations in HSPB8 result in an abnormal C-terminal peptide extension, creating a toxic gain-of-function mechanism that disrupts autophagy and cellular proteostasis — defining the molecular basis of MFM13.

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