Lumpers, splitters, and FGFRs

Advances in the molecular pathogenesis of craniofacial conditions

The impact that the understanding of fibroblast growth factor receptor (FGFR) biology and its relevance to the pathogenesis of the craniosynostoses has made cannot be underestimated. As the genetic and molecular pathology of other conditions become increasingly understood, there is much hope that robust and relevant animal models of these conditions may be generated. From these models-and in conjunction with laboratory studies in vitro-comes a real hope of improved therapeutic strategies. The future lies in increased cooperation between clinicians working in high-volume centers and basic scientists. This article decribes the results of a decade of research in which the molecular pathology of the craniosynostoses was unravelled. The understanding of the importance of FGFR mutations to the genetic etiology of craniosynostosis opened up novel studies in developmental biology in various tissues. Such studies describe the functional effects of FGFR mutations. Investigations of FGFR expression in human craniofacial development have related functional molecular studies to human craniosynostosis syndromes, which provides a link between the gene mutation and the affected child.

Presence of the Apert canonical S252W FGFR2 mutation in a patient without severe syndactyly

Apert syndrome, characterised by craniosynostosis, craniofacial anomalies, and symmetrical syndactyly of the digits (cutaneous and bony fusion), has been associated with two canonical mutations in the FGFR2 gene (S252W, P253R) in the great majority of cases. Since these two alterations have been observed exclusively among these patients, it has been suggested that the S252W and P253R changes may play an important role in the occurrence of syndactyly. In order to verify whether the mutations S252W and P253R could also cause a milder phenotype, without involvement of the limbs, we have screened 22 patients with clinical characteristics compatible with Crouzon or Pfeiffer syndrome for these two particular changes. Surprisingly, we identified a Pfeiffer-like patient with the mutation S252W, and therefore we have shown for the first time the occurrence of one of the canonical Apert mutations without severe abnormalities of the upper and lower extremities.

Craniosynostosis associated with FGFR3 pro250arg mutation results in a range of clinical presentations including unisutural sporadic craniosynostosis

Several mutations involving the fibroblast growth factor receptor (FGFR) gene family have been identified in association with phenotypically distinct forms of craniosynostosis. One such point mutation, resulting in the substitution of proline by arginine in a critical region of the linker region between the first and second immunoglobulin-like domains, is associated with highly specific phenotypic consequences in that mutation at this point in FGFR1 results in Pfeiffer syndrome and analogous mutation in FGFR2 results in Apert syndrome. We now show that a much more variable clinical presentation accompanies analogous mutation in the FGFR3 gene. Specifically, mental retardation, apparently unrelated to the management of the craniosynostosis, appears to be a variable clinical consequence of this FGFR3 mutation.