King-Denborough Syndrome-Dysmorphic Features Suggesting Risk of Malignant Hyperthermia

King-Denborough syndrome is a rare disorder within the spectrum of RYR1-related myopathies. It is a congenital myopathy, with characteristic dysmorphic features, and susceptibility to malignant hyperthermia. Early recognition is clinically important because the diagnosis may affect anesthetic management and perioperative safety.

We report a 4.5-year-old boy with delayed motor development, generalized hypotonia, characteristic dysmorphic features, and mildly elevated serum creatine kinase levels. The MRI showed features of asymmetrical atrophy and fatty degeneration in the proximal muscles of the lower limbs.

Molecular testing identified a heterozygous RYR1 variant. In the context of the clinical phenotype and muscle imaging findings, the presentation was considered suggestive of King-Denborough syndrome within the spectrum of RYR1-related disorders.

This case highlights the importance of another RYR1-related myopathy in children presenting with myopathic features, dysmorphism, and muscle MRI abnormalities. Recognition of this phenotype is particularly important because of the potential risk of malignant hyperthermia and the need for appropriate anesthetic precautions.