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 abno ...