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FB2026_01
,
released March 12, 2026
This report describes a fly model of congenital myopathy 7B, myosin storage, autosomal recessive (CMYP7B), also described as the autosomal recessive form of myosin storage myopathy or as autosomal recessive hyaline body myopathy. The human gene implicated in this disease (and also in the dominant form) is MYH7, which encodes a cardiac muscle myosin class II heavy chain. There are multiple forms of myopathy, cardiomyopathy, and related diseases associated with MYH7 (see MIM:160760). In flies there is one gene, Mhc, orthologous to the ten genes that encode forms of muscle myosin class II heavy chain in humans; MYH7 is a reciprocal best hit of Dmel\Mhc. Classical amorphic and hypomorphic alleles, RNAi targeting constructs, and alleles caused by insertional mutagenesis have been generated for the Mhc gene.
The human MYH7 gene has not been introduced into flies.
Work in flies has made use of a transgenic construct with a variant introduced into the Mhc gene that is analogous to a specific variant of MYH7 associated with CMYP7B. Variant(s) implicated in human disease tested (as analogous mutation in fly gene): E1881K in the fly Mhc gene (corresponds to E1883K in the human MYH7 gene). Two variants implicated in the dominant form of myosin storage myopathy have also been characterized; see the human disease model report 'myopathy, myosin storage, autosomal dominant' (FBhh0000814).
No difference was found in the phenotypes of flies carrying this recessive variant (E1881K) vs. those carrying either of the two dominant variants (L1793P, R1845W). Flies expressing exclusively one of the mutant myosins exhibit severe impairment of flight and jump ability, progressively disrupted muscle ultrastructure, and myosin aggregates.
See also the human disease model report 'myopathy, MYH-class-II-related' (FBhh0000423).
[updated Jul. 2023 by FlyBase; FBrf0222196]
Congenital myopathy is a term for any genetic muscle disorder that is typically noticed at birth and includes weakness and lack of muscle tone. Some congenital myopathies may not show symptoms until infancy or childhood. There are many types of congenital myopathy with varying severity. Some symptoms may remain stable or progress slowly. The following is a range of symptoms: lack of muscle control and weakness; difficulty breathing; difficulty eating; slow to reach developmental goals; delayed motor skills; skeletal problems. (https://www.ninds.nih.gov/health-information/disorders/congenital-myopathy#:~:text=Congenital%20myopathy)
[CONGENITAL MYOPATHY 7B, MYOSIN STORAGE, AUTOSOMAL RECESSIVE; CMYO7B](https://omim.org/entry/255160)
[MYOSIN, HEAVY CHAIN 7, CARDIAC MUSCLE, BETA; MYH7](https://omim.org/entry/160760)
Myosin storage myopathy is a condition that causes muscle weakness that does not progress or progresses very slowly over time. This condition is characterized by the formation of myosin protein aggregates within certain muscle fibers. Onset is usually during childhood, although it may be later. Because of muscle weakness, affected individuals may start walking later than usual and have a waddling gait, trouble climbing stairs, and difficulty lifting the arms above shoulder level. Muscle weakness also causes some affected individuals to have trouble breathing. [Genetics Home Reference, Myosin storage myopathy; 2018.05.24]
Autosomal recessive myosin storage congenital myopathy-7B (CMYP7B) is a skeletal muscle disorder characterized by the onset of scapuloperoneal muscle weakness in early childhood or young adulthood. Affected individuals have difficulty walking, steppage gait, and scapular winging due to shoulder girdle involvement. The severity and progression of the disorder is highly variable, even within families. Most patients develop respiratory insufficiency, nocturnal hypoventilation, and restrictive lung disease; some develop hypertrophic cardiomyopathy. Additional features include myopathic facies, high-arched palate, scoliosis, and muscle wasting with thin body habitus. Serum creatine kinase may be normal or elevated. (Onengut et al., 2004; pubmed:14659406; Tajsharghi et al., 2007; pubmed:17372140; Beecroft et al., 2019; pubmed:31130376). [from MIM:255160; 2023.07.18]
Autosomal recessive myosin storage congenital myopathy-7B (CMYP7B) is caused by homozygous or compound heterozygous mutation in the MYH7 gene on chromosome 14q11. Autosomal dominant myosin storage congenital myopathy-7A (FBhh0000814) is caused by heterozygous mutation in the MYH7 gene. [from MIM:255160; 2023.07.18]
Skeletal muscle biopsy can show different abnormalities, including hyaline bodies, type 1 fiber predominance, congenital fiber-type disproportion (CFTD), and nonspecific myopathic changes with myofibrillar disarray (Beecroft et al., 2019; pubmed:31130376). [from MIM:255160; 2023.07.18]
The MYH7 gene encodes the beta-cardiac/slow skeletal myosin heavy chain (MyHC-slow), expressed predominantly in the cardiac ventricles and slow skeletal (type 1) myofibers. Myosin acts as a molecular motor through its interaction with actin of the thin filament, which is vital for skeletal muscle force generation (summary by Beecroft et al., 2019; pubmed:31130376). [from MIM:160760; 2023.07.18]
Many to one: 10 human to 1 Drosophila; MYH7 is a reciprocal best hit to Dmel\Mhc.