What is Myofibrillar Myopathy type 13 with Rimmed Vacuoles (MFM13)?
MFM13 is an ultra-rare, incurable genetic disorder marked by muscle wasting and progressive weakness, typically manifesting in young adults between their 20s and 40s. This slowly progressing, autosomal dominant condition is caused by a mutation in the HSPB8 gene. HSPB8 is involved in normal skeletal muscule function and repair. Muscle weakness usually, but not always, begins distally. To date, eight publications describing around 60 patients have been published.
Cure MFM13 (previously Cure HSPB8)
We are the only charitable project dedicated to addressing the challenges of MFM13, with a vision of life free from this burden and a mission to find a cure for this debilitating condition. Our collaboration with healthcare professionals and researchers aims to unravel the complexities of MFM13. We are determined to find effective treatments and a cure, bringing hope to those affected. Equally important is our commitment to building a vibrant community for patients and families, providing a supportive space to share experiences, learn from each other, and stay informed about medical advancements.
Join us in our endeavor. Your involvement, whether as a patient living with MFM13, a family member, or a healthcare professional, is a step towards change. Together, we are stronger and can create a future where MFM13 no longer defines lives.
Myofibrillar Myopathies
To date, at least thirteen genetically distinct forms of MFM (MFM1–MFM13) have been described (Table 1). These subtypes are caused by mutations in genes encoding proteins that play essential roles in maintaining muscle structure, protein quality control, and cellular stress responses. Despite their genetic diversity, the disease mechanisms often converge on common pathways involving protein misfolding, protein aggregation, impaired autophagy, and disruption of the muscle fiber architecture (Wannarong et al., 2025, Ziemian et al., 2025, Zhou et al., 2026).
Myofibrillar myopathies (MFMs) are a group of rare inherited neuromuscular disorders characterized by progressive muscle weakness and the abnormal accumulation of proteins within muscle fibers. Although the different forms of MFM are caused by mutations in different genes, they share a common pathological hallmark: the breakdown of myofibrils, the structures responsible for muscle contraction, beginning at the Z-disk, followed by the accumulation of protein aggregates within muscle cells. These changes can be observed in muscle biopsies and are a defining feature of the disease group (Schröder et al., 2009, Selcen 2008 and 2011, Fichna et al., 2018, Inoue et al., 2025)
Individuals with MFM may experience muscle weakness affecting the arms, legs, trunk, or respiratory muscles. Some forms can also involve the heart, leading to cardiomyopathy or cardiac conduction abnormalities. The age of onset, disease severity, and pattern of muscle involvement vary considerably depending on the underlying genetic cause (Schröder et al., 2009, Selcen 2008 and 2011).
Cure MFM13 is dedicated to advancing research and therapeutic development for MFM13, a form of myofibrillar myopathy caused by mutations in the HSPB8 gene. While our primary focus is MFM13, many biological mechanisms are shared across the broader MFM family, including protein aggregation, impaired protein quality control, and progressive muscle degeneration (Zhou et al., 2026).
Studying other forms of MFM can provide valuable insights into common disease pathways, potential biomarkers, and therapeutic strategies that may benefit multiple patient communities. Likewise, advances in MFM13 research may contribute to the understanding and treatment of other myofibrillar myopathies.
The following pages provide an overview of each currently recognized MFM subtype (MFM1–MFM13), including the causative gene, clinical features, inheritance patterns, and key research developments.
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