1. Background

• also called King-Denborough Syndrome
• first described by J.O. King and M.A. Denborough; J. Pediatr. 83: 37-40 (1973).
• reviewed by E.W. McPherson and C.A. Taylor; Am. J. Med. Genet. 8: 159-165 (1981).
• there are at least 5 features which distinguish King Syndrome from Noonan Syndrome: the former is associated with muscle weakness and is sporadic in occurence but there is no congenital heart disease, mental retardation, or webbed neck

2. Pathogenesis

• unknown etiology
• there may be elevated serum creatine kinase (CK) levels in relatives of those with King Syndrome (which may increase the risk of malignant hyperthermia in these relatives)
• see file on Malignant Hyperthermia for pathogenesis of this disorder

1. King Syndrome Phenotype

• 100% - malignant hyperthermia
• 100% - micrognathia*
• 100% - kyphoscoliosis and/or lordosis
• 100% - normal intelligence
• 91% - pectus carinatum*
• 89% - cryptorchidism*
• 82% - short stature*
• 82% - midfacial hypoplasia
• 73% - transient gross motor delay*
• 64% - downward slanting palpebral fissures*
• 64% - muscle weakness (mild and non-progressive)
• 64% - low-set ears*
• 55% - ptosis*
• 27% - contractures

1. Muscle Biopsy

• areas of degeneration and fatty infiltration in certain muscle groups
• elevated phospholipase A activity

1. Supportive

• Paediatrics, Orthopedics, Metabolics
• physiotherapy for muscle weakness

2. Medical

• prompt administration of dantrolene for malignant hyperthermia

3. Prognosis

• normal life span if malignant hyperthermia is avoided

1. Mary-Louise Buyse, Birth Defects Encyclopedia (1994). p. 1013-1014.