Craniosynostosis, or premature fusion of the cranial sutures, occurs in 
approximately 1 in 2500 live births. The genetic causes and molecular basis of 
these disorders have greatly expanded over the last 2 decades, with numerous 
causative and contributory mutations having been identified. The role of 
fibroblast growth factor receptor (FGFR) mutations in the etiology of certain 
eponymous forms of craniosynostosis is now well elucidated; the most common 
syndromes associated with craniosynostosis are Pfeifer (FGFR1, FGFR2), Apert 
(FGFR2), Crouzon (FGFR2), Saethre-Chotzen (TWIST1), Jackson-Weiss (FGFR2), Greig 
(GL13), and Muenke (FGFR3) syndromes. Although pathological expression of these 
mutations often results in bilateral coronal craniosynostosis, single suture 
fusions (typically unilateral coronal synostosis) or multiple suture 
craniosynostosis are possible.The majority of patients diagnosed with 
craniosynostosis lack an identifiable syndrome or genetic mutation. The 
etiopathogenesis of these "nonsyndromic" forms of craniosynostosis is believed 
to involve a complex interplay of genetics, epigenetics, and environmental 
factors. Evaluation of genes implicated in nonsyndromic craniosynostosis has 
been conflicting; some evidence demonstrates an interplay between genetic and 
epigenetic influences while others do not. Certain environmental factors such as 
teratogenic levels of retinoic acid, maternal metabolic and hematologic 
disorders, and head growth constraint in utero may increase the likelihood of 
developing craniosynostosis, but these associations are again tenuous.The 
authors present 1 of 2 genetically confirmed identical twins discordant for 
metopic craniosynostosis. The implications of this case are clear: epigenetic 
influences, environmental influences, or both played a role in the development 
of this premature suture fusion.