MOLECULAR ANALYSIS OF FIBROBLAST-GROWTH-FACTOR-RECEPTOR-3-GENE (FGFR3) 279 PATIENTS WITH ACHONDROPLASIA, HYPOCHONDROPLASIA AND THANATOPHORIC DYSPLASIA AND A NOVEL MUTATION IN HYPOCHONDROPLASIA

M. Hilbert. K. Hilbert, J. Spranger, A. Winterpacht, B. Zabel

Universitäts-Kinderklinik Mainz, Germany

OBJECTIVE: In 1994, achondroplasia (ACH), the most commen form of chondrodysplasia, was shown to be caused by one specific mutation in the fibroblast-growth-factor-receptor-3-gene (FGFR3). Subsequently characteristic FGFR3 mutations have been identified in other members of this chondrodysplasia family. These are the thanatophoric dysplasia (TD type I and II), the most frequent form of neonatal lethal skeletal dysplasia, the severe SADDAN dysplasia and the hypochondroplasia (HCH), the mildest form of this clinical spectrum.

METHODS: Here we report the molecular analysis of 279 patients (132 ACH, 127 HCH, 18 TD type I, 2 TD type II). DNA extraction from peripheral blood leucocytes or cultered fibroblasts was followed by PCR amplification of specific exons of FGFR3. The sequencing of PCR products was carried out on ABI automatic sequencing apparatus.

RESULTS: We show that characteristic mutations could be ascertained in only 65 % of HCH cases. Remaining cases may be caused by defects in yet unidentified genes or other FGFR3 gene regions. We screened the complete coding sequence of FGFR3 gene for mutation in three patients with typical features of HCH. In one patient we could identify a novel A to T transversion in exon 9 that results in a amino acid conversion from asparagine to isoleucin at position 328. About 90 % of ACH were caused by Gly380Arg exchange in the transmembrane domain of FGFR3. Evaluation of remaining cases showed that these patient didn't present the typical clinical findings and radiological features of ACH. The rate of identified mutations in TD (I and II) was 100 %. CONCLUSIONS: Our report is the first characterisation of a mutation located in the extracellular, ligand binding domain of FGFR3 in a patient with hypochondroplasia. It affects a putative N-glycosylation site witch is highly conserved between different FGFRs and species. The phenotype could be a result of altered receptor glycosylation, a pathophysiological consequence that couldn't be described for FGFRS so far. HCH is a heterogeneous condition with difficult clinical and radiological diagnostic so that molecular analysis of FGFR3 is an important diagnostic tool. Beside clinical features and radiological datas the molecular analyses of FGFR3 gene in patients with ACH and TD I and II is an established method. For a more detailed understanding of biological consequences of FGFR3 gene mutations and their pathological changes additional studies are necessary.