Introduction

• Definition: A rare developmental disorder characterized by:
  • Developmental delay
  • Hypotonia
  • Distinctive facial dysmorphism (elongated palpebral fissures, arched eyebrows, depressed nasal tip, thickened lower lip, prominent ears)
  • Growth retardation
  • Multisystem involvement (cardiac, gastrointestinal, renal, immunological)
• Epidemiology:
  • Estimated prevalence: 1 in 32,000
  • Initially thought to be specific to East Asians, but occurs across ethnicities
• Genetic Basis:
  • KMT2D mutations (75% of cases, autosomal dominant)
  • KDM6A mutations (5%, X-linked dominant)
  • Unknown etiology in ~20% of cases