Two journeys, one diagnosis: exploring the clinical outcomes of twins with congenital myopathy.

Mutations in the RYR1 gene, responsible for encoding the skeletal muscle calcium release channel, are linked to conditions such as malignant hyperthermia and central core disease. These mutations can severely affect calcium handling and excitation-contraction coupling, leading to different clinical manifestations including muscle fiber abnormalities. We present two siblings diagnosed with congenital myopathy due to a homozygous variant c.14,928 C > G (p.Phe4976Leu) in the RYR1 gene, inherited in an autosomal recessive pattern. Both twins, born prematurely via cesarean section, exhibited hypotonia and arthrogryposis. Clinical exome sequencing confirmed the RYR1 mutation, and an antioxidant supplement, idebenone, was introduced. Despite sharing the same variant, the twins presented discordant clinical phenotypes with varying degrees of muscle impairment and other complications. This case highlights the critical role of epigenetic in modulating disease expression, suggesting personalized therapeutic strategies are paramount even in siblings sharing the same homozygous variant.