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Distinct missense mutations of the FGFR3 lys650 codon modulate receptor kinase activation and the severity of the skeletal dysplasia phenotype.

ABSTRACT: The fibroblast growth factor-receptor 3 (FGFR3) Lys650 codon is located within a critical region of the tyrosine kinase-domain activation loop. Two missense mutations in this codon are known to result in strong constitutive activation of the FGFR3 tyrosine kinase and cause three different skeletal dysplasia syndromes-thanatophoric dysplasia type II (TD2) (A1948G [Lys650Glu]) and SADDAN (severe achondroplasia with developmental delay and acanthosis nigricans) syndrome and thanatophoric dysplasia type I (TD1) (both due to A1949T [Lys650Met]). Other mutations within the FGFR3 tyrosine kinase domain (e.g., C1620A or C1620G [both resulting in Asn540Lys]) are known to cause hypochondroplasia, a relatively common but milder skeletal dysplasia. In 90 individuals with suspected clinical diagnoses of hypochondroplasia who do not have Asn540Lys mutations, we screened for mutations, in FGFR3 exon 15, that would disrupt a unique BbsI restriction site that includes the Lys650 codon. We report here the discovery of three novel mutations (G1950T and G1950C [both resulting in Lys650Asn] and A1948C [Lys650Gln]) occurring in six individuals from five families. Several physical and radiological features of these individuals were significantly milder than those in individuals with the Asn540Lys mutations. The Lys650Asn/Gln mutations result in constitutive activation of the FGFR3 tyrosine kinase but to a lesser degree than that observed with the Lys540Glu and Lys650Met mutations. These results demonstrate that different amino acid substitutions at the FGFR3 Lys650 codon can result in several different skeletal dysplasia phenotypes.

SUBMITTER: Bellus GA

PROVIDER: S-EPMC1287918 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Prenatal diagnosis of skeletal dysplasia due to FGFR3 gene mutations: a 9-year experience : prenatal diagnosis in FGFR3 gene.

Project description:PURPOSE: Prenatal diagnosis with ultrasound findings compatible with skeletal dysplasia due to FGFR3 mutations over a 9 year period in pregnancies and abortuses. METHODS: 54 samples were studied. Aneuploidy studies were carried out on all samples. By sequencing analysis, we determined mutations for achondroplasia (ACH), hypochondroplasia (HCH), and type I and type II tanathophoric dysplasia (TD). RESULTS: 2 chorionic villi samples had a G380R mutation due to a mother with ACH; 4 amniotic fluid samples with TDs in which the foetuses had micromelia plus hypoplastic thoraces; 5 samples from abortuses with TDs. Neither ACH nor HCH occurred in sporadic cases. CONCLUSIONS: Molecular studies in ongoing pregnancies are indicated in cases with an affected parent, a family history with positive molecular studies (maternal anxiety), and when the US finding demonstrates micromelia with a hypoplastic thorax. A protocol for tissues of abortuses should include an X-ray, pathologic anatomy, and genetic studies.

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Mutations in EXTL3 Cause Neuro-immuno-skeletal Dysplasia Syndrome.

Project description:EXTL3 regulates the biosynthesis of heparan sulfate (HS), important for both skeletal development and hematopoiesis, through the formation of HS proteoglycans (HSPGs). By whole-exome sequencing, we identified homozygous missense mutations c.1382C>T, c.1537C>T, c.1970A>G, and c.2008T>G in EXTL3 in nine affected individuals from five unrelated families. Notably, we found the identical homozygous missense mutation c.1382C>T (p.Pro461Leu) in four affected individuals from two unrelated families. Affected individuals presented with variable skeletal abnormalities and neurodevelopmental defects. Severe combined immunodeficiency (SCID) with a complete absence of T cells was observed in three families. EXTL3 was most abundant in hematopoietic stem cells and early progenitor T cells, which is in line with a SCID phenotype at the level of early T cell development in the thymus. To provide further support for the hypothesis that mutations in EXTL3 cause a neuro-immuno-skeletal dysplasia syndrome, and to gain insight into the pathogenesis of the disorder, we analyzed the localization of EXTL3 in fibroblasts derived from affected individuals and determined glycosaminoglycan concentrations in these cells as well as in urine and blood. We observed abnormal glycosaminoglycan concentrations and increased concentrations of the non-sulfated chondroitin disaccharide D0a0 and the disaccharide D0a4 in serum and urine of all analyzed affected individuals. In summary, we show that biallelic mutations in EXTL3 disturb glycosaminoglycan synthesis and thus lead to a recognizable syndrome characterized by variable expression of skeletal, neurological, and immunological abnormalities.

| S-EPMC5294674 | biostudies-literature

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