Within the past year, the achondroplasia locus has been mapped to 4p 16.3 (refs 5-7) and mutations in the fibroblast growth factor receptor 3 (FGFR3) gene have been identified in patients with the disorder.
When grouped according to the "International Skeletal Dysplasia Society 2010 classification" the most frequent group is "FGFR3 group" (achondroplasia).
We now report the linkage for the Ellis-van Creveld syndrome gene to markers on the distal short arm of human chromosome 4, with Zmax = 6.91 at theta = 0.02 for marker HOX7, in a region proximal to the FGFR3 gene responsible for the achondroplasia phenotype.
We have now tested this approach for the detection of a fetal point mutation in the fibroblast growth factor receptor 3 (FGFR3) gene that causes achondroplasia.
We developed a quantitative fluorescent-polymerase chain reaction (QF-PCR) method suitable for detection of the FGFR3 mutation (G1138A) causing achondroplasia.
We describe a Klinefelter patient (non-mosaic 47,XXY karyotype) who was heterozygous for the classical 1138G>A mutation in the fibroblast growth factor receptor 3 (FGFR3) gene, which is a gain-of-function mutation resulting in achondroplasia.
Using sperm DNA from donors of different ages, we determined the frequency of the nucleotide substitution in the fibroblast growth factor receptor 3 (FGFR3) gene that causes achondroplasia.
Using our established techniques for single-cell ratiometric real-time calcium image analysis, we defined the nature of the basic fibroblast growth factor (bFGF)-induced calcium signal in human diploid fibroblasts, and, in blinded studies, have analyzed the bFGF-induced signals from 18 independent fibroblast cell lines, including multiple lines from patients with known mutant alleles of FGFR3 and syndromes of Ach or TD.
To determine whether the fetus carries the de novo mis-sense genetic mutation at nucleotide 1138 in FGFR3 gene involved in >99% of achondroplasia cases, we developed two independent methods: digital-droplet PCR combined with minisequencing, which are very sensitive methods allowing detection of rare alleles.
Thus, it appears that recurrent mutations of a single amino acid in the transmembrane domain of the FGFR3 protein account for all cases (23/23) of achondroplasia in our series.
Thus it appears that recurrent mutations of a single amino acid in the transmembrane domain of the FGFR3 protein account for all cases (23/23) of achondroplasia in our series.
This work reveals new information about the molecular events that underlie the achondroplasia phenotype, and highlights differences in FGFR3 activation due to different single amino-acid pathogenic mutations.
This result indicates that pathogenesis in achondroplasiacannot be explained simply by a higher dimerization propensity of the mutant FGFR3 TM domain, thus highlighting the importance of the observed slow downregulation in phenotype induction.
This observation indicates allelic heterogeneity and confirms the role of mutations in the transmembrane domain of FGFR-3 in the pathogenesis of achondroplasia.
This mutation has been reported in two different patients and it is located in the Ig-III domain of the FGFR3 region near other mutations associated with ACH.
This mechanism was present in ACH children carrying the G380R mutation but also in a patient in whom no mutation could be detected in the entire coding region of the FGFR3 gene.
This assay, which is performed on the LightCycler thermocycler, enables the rapid and reliable detection of the two most common FGFR3 mutations associated with ACH (1138G --> A and 1138G --> C; G380R) and HYCH (1620C --> A and 1620 C --> G; N540K) in a single test.
These results together with our earlier observation that achondroplasia results from constitutive activation of the related receptor FGFR3, leads to the prediction that other malformation syndromes attributed to FGFRs, such as Pfeiffer syndrome and Thanatophoric dysplasia, also arise from constitutive receptor activation.
These results suggest that the molecular basis of achondroplasia is unregulated signal transduction through FGFR3, which may result in inappropriate cartilage growth plate differentiation and thus abnormal long bone development.