Abstract
BackgroundThe dimerization efficiency of FGFR3 transmembrane domain plays a critical role in the formation of a normal skeleton through the negative regulation of bone development. Recently, gain-of-function mutations in the transmembrane domain of FGFR3 has been described associated with an aberrant negative regulation, leading to the development of achondroplasia-group disorders, including achondroplasia (ACH), hypochondroplasia (HCH) and thanatophoric dysplasia (TD). Here, we describe a non-consanguineous Pakistani family with achondroplasia to explain hereditary basis of the disease.MethodsPCR-based linkage analysis using microsatellite markers was employed to localize the disease gene. Gene specific intronic primers were used to amplify the genomic DNA from all affected as well as phenotypically healthy individuals. Amplified PCR products were then subjected to Sanger sequencing and RFLP analysis to identify a potentially pathogenic mutation. The impact of identified mutation on FGFR3 protein’s structure and stability was highlighted through different bioinformatics tools.ResultsGenetic screening of the family revealed a previously reported heterozygous c.1138 G > A (p.G380R) mutation in the coding exon 8 of FGFR3 gene. Identified genetic variation was confirmed in all affected individuals while healthy individuals and controls were found genotypically normal. The results were further validated by RFLP analysis as c.1138 G > A substitution generates a unique recognition site for SfcI endonuclease. Following SfcI digestion, the electrophoretic pattern of three bands/DNA fragments for each patient is indicative of heterozygous status of the disease allele. In silico studies of the mutant FGFR3 protein predicted to adversely affect the stability of FGFR3 protein.ConclusionsMutation in the transmembrane domain may adversely affect the dimerization efficiency and overall stability of the FGFR3, leading to a constitutively active protein. As a result, an uncontrolled intracellular signaling or negative bone growth regulation leads to achondroplasia. Our findings support the fact that p.G380R is a common mutation among diverse population of the world and like other countries, can be used as a molecular diagnosis marker for achondroplasia in Pakistan.
Highlights
The dimerization efficiency of fibroblast growth factor receptor 3 (FGFR3) transmembrane domain plays a critical role in the formation of a normal skeleton through the negative regulation of bone development
The FGFR3 is one of the four members of fibroblast growth factor receptor (FGFR) family, but differs from other FGFRs in its affinity for ligands and tissue distribution as it is mainly expressed in cartilage and brain [11, 12]
Genotyping Genomic DNA from six family members was genotyped by using FGFR3 linked microsatellite markers; D4S412, D4S2366, D4S394, D4S403, D4S419, D4S391, D4S405, and D4S1627
Summary
The dimerization efficiency of FGFR3 transmembrane domain plays a critical role in the formation of a normal skeleton through the negative regulation of bone development. Gain-of-function mutations in the transmembrane domain of FGFR3 has been described associated with an aberrant negative regulation, leading to the development of achondroplasia-group disorders, including achondroplasia (ACH), hypochondroplasia (HCH) and thanatophoric dysplasia (TD). Hypotonia is the most prominent characteristic caused by delayed and abnormal development of motor milestone [8] Despite all these clinical manifestations, individuals with ACH have normal life span and intelligence factor [9]. Over the last two decades, dominant gain-of-function mutations of the specific site in fibroblast growth factor receptor 3 (FGFR3) have been shown implicated in human skeletal dysplasias, including achondroplasia (ACH), hypochondroplasia (HCH), thanatophoric dysplasia (TD) and severe achondroplasia, with developmental delay and acanthosis nigricans (SADDAN) [4, 10]. The FGFR3 is one of the four members of fibroblast growth factor receptor (FGFR) family, but differs from other FGFRs in its affinity for ligands and tissue distribution as it is mainly expressed in cartilage and brain [11, 12]
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