A novel mutation p.Ser348Cys in FGFR3 causes achondroplasia

Review of published 467 achondroplasia patients: clinical and mutational spectrum

AIM

Achondroplasia is the most common of the skeletal dysplasias that cause fatal and disabling growth and developmental disorders in children, and is caused by a mutation in the fibroblast growth factor receptor, type 3 gene(FGFR3). This study aims to analyse the clinical characteristics and gene mutations of ACH to accurately determine whether a patient has ACH and to raise public awareness of the disease.

METHODS

The database of Pubmed, Cochrane Library, Wanfang and CNKI were searched with terms of "Achondroplasias" or "Skeleton-Skin-Brain Syndrome" or "Skeleton Skin Brain Syndrome" or "ACH" and "Receptor, Fibroblast Growth Factor, Type 3" or "FGFR3".

RESULTS

Finally, four hundred and sixty-seven patients with different FGFR3 mutations were enrolled. Of the 138 patients with available gender information, 55(55/138, 40%) were female and 83(83/138, 60%) were male. Among the patients with available family history, 47(47/385, 12%) had a family history and 338(338/385, 88%) patients were sporadic. The age of the patients ranged from newborn babies to 36 years old. The mean age of their fathers was 37 ± 7 years (range 31-53 years). Patients came from 12 countries and 2 continents, with the majority being Asian (383/432, 89%), followed by European (49/432, 11%). Short stature with shortened arms and legs was found in 112(112/112) patients, the abnormalities of macrocephaly in 94(94/112) patients, frontal bossing in 89(89/112) patients, genu valgum in 64(64/112) patients and trident hand were found in 51(51/112) patients. The most common mutation was p.Gly380Arg of the FGFR3 gene, which contained two different base changes, c.1138G > A and c.1138G > C. Ten rare pathogenic mutations were found, including c.831A > C, c.1031C > G, c.1043C > G, c.375G > T, c.1133A > G, c.1130T > G, c.833A > G, c.649A > T, c.1180A > T and c.970_971insTCTCCT.

CONCLUSION

ACH was caused by FGFR3 gene mutation, and c.1138G > A was the most common mutation type. This study demonstrates the feasibility of molecular genetic testing for the early detection of ACH in adolescents with short stature, trident hand, frontal bossing, macrocephaly and genu valgum.

Achondroplasia-First Report from India of a Rare FGFR3 Gene Variant

The clinical manifestations of FGFR3 sequence variations can vary from mild unnoticed short stature to neonatal lethal dwarfism and can be causative of phenotypes including achondroplasia, hypochondroplasia, and thanatophoric dysplasia. Clinical data describe an 11 month old girl with restricted growth and preserved intellect. She had rhizomelic short stature with peculiar facies but no Acanthosis nigricans. In view of the absence of the hotspot mutation c.1138 G>A/G>C (p.Gly380Arg), complete gene sequencing was done that revealed a rare sequence variation, NM_000142.4:c.1043C>G (p.Ser348Cys) in FGFR3. This sequence variation has not been reported from India so far. This report emphasizes the benefit of sequencing the whole gene in individuals who are negative for hotspot mutation of achondroplasia with strong clinical suspicion.

Typical achondroplasia secondary to a unique insertional variant of FGFR3 with in vitro demonstration of its effect on FGFR3 function

We describe an individual in whom clinical and radiographic features are typical for achondroplasia, but in whom the common variants of FGFR3 that result in achondroplasia are absent. Whole exome sequencing demonstrated a novel, de novo 6 base pair tandem duplication in FGFR3 that results in the insertion of Ser-Phe after position Leu324. in vitro studies showed that this variant results in aberrant dimerization, excessive spontaneous phosphorylation of FGFR3 dimers and excessive, ligand-independent tyrosine kinase activity. Together, these data suggest that this variant leads to constitutive disulfide bond-mediated dimerization, and that this, surprisingly, occurs to an extent similar to the neonatal lethal thanatophoric dysplasia type I Ser249Cys variant.

p.Ser348Cys mutation in FGFR3 gene leads to "Mild ACH /Severe HCH" phenotype

Achondroplasia (ACH) and hypochondroplasia (HCH) are genetic bone disorders known to be caused by gain-of-function mutations in the fibroblast growth factor receptor 3 (FGFR3) gene. Both conditions share radiographic and phenotypical features. HCH is a milder form of ACH. Most individuals with ACH have the recurrent mutation (p.Gly380Arg) in the transmembrane (TM) domain of the receptor and individuals with HCH show the common mutation (p.Asn540Lys) in the tyrosine kinase 1 (TK1) region. Other rare mutations have been reported, however no additional hot-spot has been identified. We report an 8-month-old infant, with the heterozygous mutation, c.1043C > G, leading to an amino acid change from serine at 348 to cysteine (p.Ser348Cys). Clinical diagnosis of the patient is intertwined with "mild ACH" or "severe HCH". He did not demonstrate acanthosis nigricans (AN). 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. Among the two the 8-year old one also demonstrated AN without evindece of hyperinsulinem. This report emphasizes the benefit of whole gene sequencing for FGFR3 in individuals with suspected "mild ACH/severe HCH". This child will be monitored for future occurrence of AN.

Achondroplasia: a comprehensive clinical review

Achondroplasia is the most common of the skeletal dysplasias that result in marked short stature (dwarfism). Although its clinical and radiologic phenotype has been described for more than 50 years, there is still a great deal to be learned about the medical issues that arise secondary to this diagnosis, the manner in which these are best diagnosed and addressed, and whether preventive strategies can ameliorate the problems that can compromise the health and well being of affected individuals. This review provides both an updated discussion of the care needs of those with achondroplasia and an exploration of the limits of evidence that is available regarding care recommendations, controversies that are currently present, and the many areas of ignorance that remain.

Acanthosis nigricans in achondroplasia

Acanthosis nigricans (AN) in those with achondroplasia has been reported occasionally in the literature previously. Other disorders arising from constitutive activation of FGFR3 also manifest AN at various frequencies. We assessed the prevalence of AN in a sequential series of 477 individuals with achondroplasia. Using a REDCap database, we collected and analyzed what other features or medical issues may co-occur with AN in those with achondroplasia. AN arises in approximately 10% of individuals with achondroplasia. It usually first appears in preadolescence or adolescence, is more likely in the non-White population and in those who are obese. It is not severe and generally will need no treatment. It is not associated with any evident risk for neither hyperinsulinemic states nor malignancy, and therefore, no special investigations are warranted when it is recognized. Thus, clinicians should not be surprised or concerned upon discovering this finding in those with achondroplasia. In addition, the mechanisms and genetic causes of AN are detailed.

Quantitative approach to the posterior cranial fossa and craniocervical junction in asymptomatic children with achondroplasia

PURPOSE

We propose an magnetic resonance imaging (MRI)-based quantitative morphovolumetric approach to the posterior cranial fossa (PCF) and craniocervical junction (CCJ) changes in achondroplastic patients investigating possible associations with ventriculomegaly and medullary compression.

METHODS

We analyzed MRI of 13 achondroplastic children not treated by surgery. 3D FSPGR T1-weighted images were used to analyze (1) PCF synchondroses; (2) PCF volume (PCFV), PCF brain volume (PCFBV), PCFV/PCFBV ratio, cerebellar volume, cerebrospinal fluid (CSF) spaces volume, and IV ventricle volume; (3) PCF (clivus, supraocciput, exocciput lengths, tentorial angle) and CCJ (AP and LL diameters of foramen magnum (FM)) morphometry; (4) measurements of FM and jugular foramina (JF) areas; and (5) supratentorial ventricular volume.

RESULTS

All patients showed synostosis of spheno-occipital synchondroses, eight showed synostosis of intra-occipital synchondroses, nine showed CCJ impingement on the cervical cord but only three had cervical myelopathy. Compared to controls, clivus and exocciput lengths, LL and AP diameters of FM, FM area and JF area were significantly reduced, supraocciput length, tentorial angle, PCFV, PCFBV, cerebellar volume, supratentorial ventricular system volume were significantly increased. A correlation was found between clivus length and supratentorial ventricular volume, premature closure of intra-occipital synchondroses and FM area while a trend was found between FM area and supraocciput length.

CONCLUSION

Our analysis demonstrates a relationship between the shortening of the clivus and the ventriculomegaly. On the other hand the premature closure of PCF synchondroses, the shape, and the growth direction of supraocciput bone contribute to reduce the FM area, causing in some patients medullary compression.

Mild achondroplasia/hypochondroplasia with acanthosis nigricans, normal development, and a p.Ser348Cys FGFR3 mutation

Pathogenic allelic variants in the fibroblast growth factor receptor 3 (FGFR3) gene have been associated with a number of phenotypes including achondroplasia, hypochondroplasia, thanatophoric dysplasia, Crouzon syndrome with acanthosis nigricans (Crouzonodermoskeletal syndrome), and SADDAN (severe achondroplasia with developmental delay and acanthosis nigricans). Crouzon syndrome with acanthosis nigricans is caused by the pathogenic variant c.1172C>A (p.Ala391Glu) in the FGFR3 gene. The p.Lys650Thr pathogenic variant in FGFR3 has been linked to acanthosis nigricans without significant craniofacial or skeletal abnormalities. Recently, an infant with achondroplasia and a novel p.Ser348Cys FGFR3 mutation was reported. We describe the clinical history of an 8-year-old child with a skeletal dysplasia in the achondroplasia-hypochondroplasia spectrum, acanthosis nigricans, typical development, and the recently described p.Ser348Cys FGFR3 mutation.