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Background: The C749G (Pro250Arg) mutation in the gene for fibroblast growth factor receptor 3 (FGFR3) has been found in patients with various types of craniosynostosis. We aimed to find out the proportion of cases of apparently non-syndromic coronal craniosynostosis attributable to this mutation., Methods: We studied 26 patients with coronal craniosynostosis but no syndromic diagnosis, who were referred to a supra-regional specialist centre. Genomic DNA was analysed by PCR and restriction-enzyme digestion to identify the C749G mutation in FGFR3. Family members of patients found to have the mutation were also tested., Findings: Eight (31%) of the 26 probands were heterozygous for the C749G mutation. In two cases, the mutation showed autosomal dominant transmission with evidence of variable expressivity; the remaining six cases were sporadic. We demonstrated in six families that the mutation had arisen de novo from clinically unaffected parents., Interpretation: The C749G mutation in FGFR3 is a frequent cause of apparently non-syndromic coronal craniosynostosis. Our finding will aid genetic counselling and prenatal diagnosis. The mutation rate at this nucleotide is one of the highest described in the human genome.

The underlying basis of many forms of syndromic craniosynostosis has been defined on a molecular level. However, many patients with familial or sporadic craniosynostosis do not have the classical findings of those craniosynostosis syndromes. Here we present 61 individuals from 20 unrelated families where coronal synostosis is due to an amino acid substitution (Pro250Arg) that results from a single point mutation in the fibroblast growth factor receptor 3 gene on chromosome 4p. In this instance, a new clinical syndrome is being defined on the basis of the molecular finding. In addition to the skull findings, some patients had abnormalities on radiographs of hands and feet, including thimble-like middle phalanges, coned epiphyses, and carpal and tarsal fusions. Brachydactyly was seen in some cases; none had clinically significant syndactyly or deviation of the great toe. Sensorineural hearing loss was present in some, and developmental delay was seen in a minority. While the radiological findings of hands and feet can be very helpful in diagnosing this syndrome, it is not in all cases clearly distinguishable on a clinical basis from other craniosynostosis syndromes. Therefore, this mutation should be tested for in patients with coronal synostosis.

Dominantly acting, allelic mutations of the fibroblast growth factor receptor 2 (FGFR2) gene have been described in five craniosynostosis syndromes. In Apert syndrome, characterised by syndactyly of the hands and feet, recurrent mutations of a serine-proline dipeptide (either Ser252Trp or Pro253Arg) in the linker between the IgII and IgIII extracellular immunoglobulin-like domains, have been documented in more than 160 unrelated individuals. We have identified three novel mutations of this dipeptide, associated with distinct phenotypes. A C-->T mutation that predicts a Ser252Leu substitution, ascertained in a boy with mild Crouzon syndrome (craniosynostosis with normal limbs) is also present in three clinically normal members of his family. A CG-->TT mutation that predicts a Ser252Phe substitution results in a phenotype consistent with Apert syndrome. Finally, a CGC-->TCT mutation that predicts a double amino acid substitution (Ser252Phe and Pro253Ser) causes a Pfeiffer syndrome variant with mild craniosynostosis, broad thumbs and big toes, fixed extension of several digits, and only minimal cutaneous syndactyly. The observation that the Ser252Phe mutation causes Apert syndrome, whereas the other single or double substitutions are associated with milder or normal phenotypes, highlights the exquisitely specific molecular pathogenesis of the limb and craniofacial abnormalities associated with Apert syndrome. Ser252Phe is the first noncanonical mutation to be identified in this disorder, its rarity being explained by the requirement for two residues of the serine codon to be mutated. The description of independent, complex nucleotide substitutions involving identical nucleotides is unprecedented, and we speculate that this may result from functional selection of FGFR mutations in sperm.

Apert syndrome results from one or other of two specific nucleotide substitutions, both C-->G transversions, in the fibroblast growth factor receptor 2 (FGFR2) gene. The frequency of new mutations, estimated as 1 per 65,000 live births, implies germline transversion rates at these two positions are currently the highest known in the human genome. Using a novel application of the amplification refractory mutation system (ARMS), we have determined the parental origin of the new mutation in 57 Apert families: in every case, the mutation arose from the father. This identifies the biological basis of the paternal age effect for new mutations previously suggested for this disorder.