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FB2026_01
,
released March 12, 2026
This report describes congenital myopathy 2C, severe infantile, autosomal dominant (CMYP2C), also called myopathy, congenital fiber-type disproportion. One of the genes implicated in CMYP2C is ACTA1, which encodes the alpha actin found in human skeletal muscle. CMYP2C is one of several myopathies associated with defects in the human ACTA1 gene; see the human disease model report 'myopathy, congenital, ACTA1-related' (FBhh0000581).
The human ACTA1 gene has not been introduced into flies.
A specific variant of ACTA1 associated with CMYP2C has been investigated in flies, as the analogous mutation in the fly Act88F gene. Variant(s) implicated in human disease tested (as analogous mutation in fly gene): D293V in the fly Act88F gene [corresponds to D294V (D292V) in the human ACTA1 gene]. See the 'Disease-Implicated Variants' table below.
[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 2C, SEVERE INFANTILE, AUTOSOMAL DOMINANT; CMYO2C](https://omim.org/entry/620278)
[ACTIN, ALPHA-1, SKELETAL MUSCLE; ACTA1](https://omim.org/entry/102610)
Congenital myopathy-2C (CMYP2C) is an autosomal dominant disorder of the skeletal muscle characterized by severe congenital weakness usually resulting in death from respiratory failure in the first year or so of life. [from MIM:620278; 2023.07.07]
Congenital myopathy-2C (CMYP2C) is an autosomal dominant disorder of the skeletal muscle characterized by severe congenital weakness usually resulting in death from respiratory failure in the first year or so of life. Patients present at birth with hypotonia, lack of antigravity movements, poor head control, and difficulties feeding or breathing, often requiring tube-feeding and mechanical ventilation. Decreased fetal movements may be observed in some cases. Of the patients with congenital myopathy caused by mutation in the ACTA1 gene, about 90% carry heterozygous mutations that are usually de novo and cause the severe infantile phenotype. Some patients with heterozygous mutations have a more typical and milder disease course with delayed motor development and proximal muscle weakness, but are able to achieve independent ambulation (CMYP2A; MIM:161800). The severity of the disease most likely depends on the detrimental effect of the mutation, although there are probably additional modifying factors (Ryan et al., 2001; pubmed:11558787; Laing, et al., 2009; pubmed:19562689; Sanoudou and Beggs, 2001; pubmed:11516997; Agrawal et al., 2004; pubmed:15236405; Nowak, et al. 2013; pubmed:22825594; Sewry, et al., 2019; pubmed:31228046; Laitila and Wallgren-Pettersson, 2021; pubmed:34561123). [from MIM:620278; 2016.10.31]
Autosomal dominant severe infantile congenital myopathy-2C (CMYP2C) is caused by heterozygous mutation in the ACTA1 gene. [from MIM:620278; 2023.07.07]
Autosomal dominant severe infantile congenital myopathy-2C (CMYP2C) is caused by heterozygous mutation in the ACTA1 gene on chromosome 1q42. Heterozygous mutation in the ACTA1 gene can also cause autosomal dominant typical congenital myopathy-2A (CMYP2A; MIM:161800). Biallelic mutation in the ACTA1 gene causes autosomal recessive severe infantile congenital myopathy-2B (CMYP2B; MIM:620265). [from MIM:620278; 2023.07.18]
Skeletal muscle biopsy of patients with congenital fiber-type disproportion (CFTD) myopathy exhibits relative hypotrophy of type 1 muscle fibers compared to type 2 fibers. However, these findings are not specific and can be found in many different myopathic and neuropathic conditions; diagnosis is one of exclusion, with the term CFTD used for those cases in which no secondary cause can be found. [from MIM:255310; 2017.07.24]
Alpha, beta and gamma actin isoforms have been identified, with alpha actins being a major constituent of the contractile apparatus, while beta and gamma actins are involved in the regulation of cell motility. [from Gene Cards, ACTA1; 2017.07.24]
The ACTA1 gene encodes skeletal muscle alpha-actin, the principal actin isoform in adult skeletal muscle, which forms the core of the thin filament of the sarcomere where it interacts with a variety of proteins to produce the force for muscle contraction (Laing et al., 2009; pubmed:19562689). [from MIM:102610; 2017.07.24]
Many to many: there are multiple actins in both species.
There are multiple actins in both species (many to many). The actins are very highly conserved; Dmel\Act88F shares 93% identity and 96% similarity with the human ACTA1 gene; it shares a similar level of orthology with human ACTA2 and a slightly higher level with ACTB (96% identity and 99% similarity).