Myofibrillar myopathy (MFM) is a noncommittal term that refers to a group of morphologically homogeneous, but genetically heterogeneous chronic neuromuscular disorders. The morphologic changes in skeletal muscle in MFM result from disintegration of the sarcomeric Z disc and the myofibrils, followed by abnormal ectopic accumulation of multiple proteins involved in the structure of the Z disc, including desmin, alpha-B-crystallin (CRYAB; 123590), dystrophin (300377), and myotilin (TTID; 604103). Genetic Heterogeneity of Myofibrillar Myopathy Other forms of MFM include MFM2 (608810), caused by mutation in the CRYAB gene (123590); MFM3 (609200), caused by mutation in the MYOT gene (604103); MFM4 (609452), caused by mutation in the ZASP gene (LDB3; 605906); MFM5 (609524), caused by mutation in the FLNC gene (102565); MFM6 (612954), caused by mutation in the BAG3 gene (603883); MFM7 (617114), caused by mutation in the KY gene (605739); MFM8 (617258), caused by mutation in the PYROXD1 gene (617220); MFM9 (603689), caused by mutation in the TTN gene (188840); MFM10 (619040), caused by mutation in the SVIL UNC45B gene (611220); MFM11 (619178), caused by mutation in the UNC45B gene (611220); and MFM12 (619424), caused by mutation in the MYL2 gene (160781). 'Desmin-related myopathy' is another term referring to MFM in which there are intrasarcoplasmic aggregates of desmin, usually in addition to other sarcomeric proteins. Rigid spine syndrome (602771), caused by mutation in the SEPN1 gene (606210), is another desmin-related myopathy. Goebel (1995) provided a review of desmin-related myopathy.

Alpha-B crystallin-related myofibrillar myopathy is an autosomal dominant muscular disorder characterized by adult onset of progressive muscle weakness affecting both the proximal and distal muscles and associated with respiratory insufficiency, cardiomyopathy, and cataracts. There is phenotypic variability both within and between families (Fardeau et al., 1978; Selcen and Engel, 2003). A homozygous founder mutation in the CRYAB gene has been identified in Canadian aboriginal infants of Cree origin who have a severe fatal infantile hypertonic form of myofibrillar myopathy; see 613869. For a phenotypic description and a discussion of genetic heterogeneity of myofibrillar myopathy, see MFM1 (601419).

Distal myopathy-3 (MPD3) is an autosomal dominant skeletal muscle disorder characterized by adult onset of slowly progressive distal muscular weakness and atrophy affecting the upper and lower limbs, leading to difficulties using the hands and walking difficulties. Proximal muscle involvement may occur later in the disease, but patients typically remain ambulatory. Muscle biopsy shows myopathic changes with rimmed vacuoles (Hackman et al., 2021).