Features include always present findings: Low muscle tone (hypotonia), Weakness of facial musculature, Increased endomysial connective tissue, and Respiratory failure and others; and common findings: Hip contracture, Type 1 muscle fiber predominance, High palate, and Proximal muscle weakness and others. 27 total HPO annotations.

MYL1 encodes myosin light chain 1 (194 aa). Non-regulatory myosin light chain required for proper formation and/or maintenance of myofibers, and thus appropriate muscle function Highest expression in Muscle Skeletal (3,011 TPM) and Minor Salivary Gland (6.0 TPM).

Congenital myopathy with reduced type 2 muscle fibers is associated with mutations in the MYL1 gene on chromosome 2.

MYL1 is classified as a druggable target with score 0.0.

Genetic testing for MYL1 is available. Testing is considered confirmatory for diagnosis.

Phenotype severity distribution: 7 always present features, 17 common features.

Estimated prevalence: <1 in 1,000,000 (VERY_RARE).

No clinical trials have been registered for congenital myopathy with reduced type 2 muscle fibers.

3 publications have been identified in PubMed for congenital myopathy with reduced type 2 muscle fibers. Research spans Basic Science / Preclinical (67%) and Clinical Trial Publication (33%).

Recent Publications

• Krüger P (2025). [PMID: 40429989](https://pubmed.ncbi.nlm.nih.gov/40429989/). *Int J Mol Sci*. [Basic Science / Preclinical]

• Liang C (2024). [PMID: 39466056](https://pubmed.ncbi.nlm.nih.gov/39466056/). *FASEB J*. [Basic Science / Preclinical]

• Scaravilli A (2024). [PMID: 38880819](https://pubmed.ncbi.nlm.nih.gov/38880819/). *J Neurol*. [Clinical Trial Publication]