MedGen

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. [from OMIM]

Nemaline myopathy-2 (NEM2) is an autosomal recessive skeletal muscle disorder with a wide range of severity. The most common clinical presentation is early-onset (in infancy or childhood) muscle weakness predominantly affecting proximal limb muscles. Muscle biopsy shows accumulation of Z-disc and thin filament proteins into aggregates named 'nemaline bodies' or 'nemaline rods,' usually accompanied by disorganization of the muscle Z discs. The clinical and histologic spectrum of entities caused by variants in the NEB gene is a continuum, ranging in severity. The distribution of weakness can vary from generalized muscle weakness, more pronounced in proximal limb muscles, to distal-only involvement, although neck flexor weakness appears to be rather consistent. Histologic patterns range from a severe usually nondystrophic disturbance of the myofibrillar pattern to an almost normal pattern, with or without nemaline bodies, sometimes combined with cores (summary by Lehtokari et al., 2014). Genetic Heterogeneity of Nemaline Myopathy See also NEM1 (255310), caused by mutation in the tropomyosin-3 gene (TPM3; 191030) on chromosome 1q22; NEM3 (161800), caused by mutation in the alpha-actin-1 gene (ACTA1; 102610) on chromosome 1q42; NEM4 (609285), caused by mutation in the beta-tropomyosin gene (TPM2; 190990) on chromosome 9p13; NEM5A (605355), also known as Amish nemaline myopathy, NEM5B (620386), and NEM5C (620389), all caused by mutation in the troponin T1 gene (TNNT1; 191041) on chromosome 19q13; NEM6 (609273), caused by mutation in the KBTBD13 gene (613727) on chromosome 15q22; NEM7 (610687), caused by mutation in the cofilin-2 gene (CFL2; 601443) on chromosome 14q13; NEM8 (615348), caused by mutation in the KLHL40 gene (615340), on chromosome 3p22; NEM9 (615731), caused by mutation in the KLHL41 gene (607701) on chromosome 2q31; NEM10 (616165), caused by mutation in the LMOD3 gene (616112) on chromosome 3p14; and NEM11 (617336), caused by mutation in the MYPN gene (608517) on chromosome 10q21. Several of the genes encode components of skeletal muscle sarcomeric thin filaments (Sanoudou and Beggs, 2001). Mutations in the NEB gene are the most common cause of nemaline myopathy (Lehtokari et al., 2006). [from OMIM]

Myofibrillar myopathy refers to a genetically heterogeneous group of muscular disorders characterized by a pathologic morphologic pattern of myofibrillar degradation and abnormal accumulation of proteins involved with the sarcomeric Z disc (summary by Foroud et al., 2005). For a general phenotypic description and a discussion of genetic heterogeneity of myofibrillar myopathy, see MFM1 (601419). [from OMIM]

Protein Z serves as a cofactor for the downregulation of coagulation by forming a complex with the protein Z-dependent protease inhibitor (ZPI; 605271). Evidence also suggests that protein Z may promote the assembly of thrombin with phospholipid surfaces, thus enhancing coagulation. There is a wide variation of protein Z levels in human plasma, and studies have reported conflicting results of the clinical consequences of protein Z deficiency in humans. Most studies have reported an association between decreased protein Z levels and thrombosis, including stroke, venous thrombosis, and obstetric complications, although early reports suggested an association between protein Z deficiency and bleeding tendency (Kemkes-Matthes and Matthes, 1995). Overall, a role for protein Z in the pathogenesis of hemostatic disorders in humans is controversial and remains unclear (review by Broze, 2001 and Vasse, 2008). Protein Z deficiency has been shown to exacerbate the thrombotic phenotype in patients with thrombophilia due to factor V Leiden (see 188055). [from OMIM]

Myofibrillar myopathy-6 is an autosomal dominant severe neuromuscular disorder characterized by onset in the first decade of rapidly progressive generalized and proximal muscle weakness, respiratory insufficiency, cardiomyopathy, and skeletal deformities related to muscle weakness. Muscle biopsy shows fiber-type grouping, disruption of the Z lines, and filamentous inclusions, and sural nerve biopsy shows a neuropathy, often with giant axonal neurons. Most patients are severely affected by the second decade and need cardiac transplant, ventilation, and/or a wheelchair (summary by Jaffer et al., 2012). For a phenotypic description and a discussion of genetic heterogeneity of myofibrillar myopathy (MFM), see MFM1 (601419). [from OMIM]

A disruption of the structure of the sarcomeres of cardiomyocytes. The sarcomere is the repeating unit between two Z lines comprised largely of myosin and actin that mediates contractility, and normally sarcomeres are aligned with the long axis of cells, with the Z bands being in register throughout the length of the cardiac myocytes. [from HPO]

A condition in which there is increased production of gastrin by a gastrin-secreting tumor (usually located in the pancreas, duodenum, or abdominal lymph nodes) that stimulates the gastric mucosa to maximal activity, with consequent gastrointestinal mucosal ulceration. [from HPO]

Developmental and epileptic encephalopathy-71 (DEE71) is characterized by early neonatal refractory seizures, respiratory failure, structural brain abnormalities and cerebral edema, with death within weeks after birth. Glutamine levels are significantly increased (z score 3.2-11.7). Three patients have been described (summary by Rumping et al., 2019). [from OMIM]

A rare primary bone dysplasia with characteristics of reduced bone mineral density (defined as a Z score below -2.0), vertebral compression fractures, and recurrent peripheral fractures caused by low-impact trauma, leading to bone pain and impaired mobility. Patients typically become symptomatic in childhood or adolescence. [from SNOMEDCT_US]

A rare congenital bleeding disorder resulting from variably decreased levels of coagulation factors II, VII, IX and X, as well as natural anticoagulants protein C, protein S and protein Z. Other symptoms are often present, including developmental and skeletal anomalies (stippling of the long bones, shortness of the distal phalanges of the fingers, osteoporosis) and pseudoxanthoma elasticum-like syndrome. This disease is an autosomal recessive disorder caused by mutations in the genes encoding either gamma-glutamyl carboxylase (GGCX; 2p12) or the vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1; 16p11.2). These two proteins are necessary for gamma-carboxylation, a postsynthetic modification that allows coagulation proteins to display their proper function. [from SNOMEDCT_US]

A reduction of bone mineral density, that is, of the amount of matter per cubic centimeter of bones. [from HPO]

An anomaly of the small joints located between and behind adjacent vertebrae. [from HPO]

Increased bone density affecting the bones of the spine (vertebral column). [from HPO]

Congenital myopathy-8 (CMYO8) is an autosomal dominant disorder of the skeletal muscle characterized by hypotonia and delayed motor development apparent from infancy or childhood, resulting in difficulties walking or loss of ambulation within the first few decades. Affected individuals show respiratory insufficiency, high-arched palate, and scoliosis; external ophthalmoplegia may also be present. Skeletal muscle biopsy shows cores and myofibrillar disorganization (Lornage et al., 2019). For a discussion of genetic heterogeneity of congenital myopathy, see CMYO1A (117000). [from OMIM]