Diagnosis of thanatophoric dysplasia using clinical exome screening.

Bone dysplasias are a broad, heterogeneous group of diseases. Thanatophoric dysplasia is a rare bone dysplasia, but it is the most common lethal skeletal dysplasias. The major role in diagnostics plays a high-quality ultrasound examination in the 2nd trimester and the latest methods of genetic testing, including clinical exome testing. Knowing the correct diagnosis is crucial for the future of the fetus and the couple.

De novo variants of dominant monogenic disorders in Vietnam detected by a noninvasive prenatal test: a case series.

Background: Noninvasive prenatal tests for monogenic diseases (NIPT-SGG) have recently been reported as helpful in early-stage antenatal screening. Our study describes the clinical and genetic features of cases identified by NIPT-SGG. Materials & methods: In a cohort pregnancy with abnormal sonograms, affected cases were confirmed by invasive diagnostic tests concurrently, with NIPT-SGG targeting 25 common dominant single-gene diseases. Results: A total of 13 single-gene fetuses were confirmed, including Noonan and Costello syndromes, thanatophoric dysplasia, achondroplasia, osteogenesis imperfecta and Apert syndrome. Two novel variants seen were tuberous sclerosis complex (TSC2 c.4154G>A) and Alagille syndrome (JAG1 c.3452del). Conclusion: NIPT-SGG and standard tests agree on the results for 13 fetuses with monogenic disorders. This panel method of screening can benefit high-risk Vietnamese pregnancies, but further research is encouraged to expand on the causative gene panel.

Orthopaedic Manifestations of Thanatophoric Dwarfism: A Case Report.

CASE: We report the rare case of a 3-year-old male patient with thanatophoric dwarfism, a fatal skeletal dysplasia that arises from an autosomal dominant mutation in the fibroblast growth factor receptor 3 gene. The role of the orthopaedic surgeon in the in the management of this disease is discussed. CONCLUSION: We advocate for the close monitoring of disease progression by the orthopaedic surgery team and offer a potential surgical intervention that may help prevent cardiorespiratory demise.

Skeletal dysplasias of the fetus and infant: comprehensive review and our experience over a 10-year period.

We present a comprehensive review dealing with rare genetic skeletal disorders. More than 400 entities are included in the latest classification. The most severe or lethal phenotypes are identifiable in the prenatal period and the pregnancy can be terminated. Perinatal autopsy and posmortem X-rays are crucial in providing a definitive diagnosis. The number of cases confirmed by genetic testing is increasing. We report our own experience with genetic skeletal disorders based on 41 illustrative fetal and neonatal cases which we encountered over a 10-year period. Thanatophoric dysplasia and osteogenesis imperfecta represent approximately half of the cases coming to autopsy. Achondrogenesis type 2 and hypochondrogenesis, short-rib dysplasia, chondrodysplasia punctata, campomelic dysplasia and achondroplasia are less common. Skeletal dysplasias with autosomal recessive inheritance are the least frequent, e.g. perinatally lethal hypophophatasia, achondrogenesis type 1A, diastrophic dysplasia/atelosteogenesis type 2 or mucolipidosis type 2 (I cell disease).

Early prenatal presentation of the cartilage-hair hypoplasia / anauxetic dysplasia spectrum of disorders mimicking recurrent thanatophoric dysplasia.

Three sibling fetuses identified with limb shortening and thoracic narrowing at twelve weeks' gestation on first trimester ultrasound examination are presented. The parents were non-consanguineous, Caucasian, healthy, of normal stature and had a healthy normal daughter. The radiographic abnormalities were highly suggestive of thanatophoric dysplasia, but molecular analysis failed to identify a pathogenic variant in FGFR3. The three fetuses were found to have identical compound heterozygous mutations in RMRP in trans, one inherited from the mother and one from the father. This represents the early prenatal presentation and fetal findings of metaphyseal dysplasia type McKusick (Cartilage-hair hypoplasia; CHH)/anauxetic dysplasia spectrum of disorders.

Thanatophoric Skeletal Dysplasia: A Case Report.

Thanatophoric skeletal dysplasiais the most lethal, rare, sporadic birth defect due to de novo mutation in the fibroblast growth factor receptor-3. Clinically this is characterized by shortening of the limbs (micromelia), small conical thorax, flat vertebral bodies and macrocephaly at birth. We encountered a similar case with ultrasonographic findings suggestive of Thanatophoric Skeletal Dysplasia which resulted in the death of the baby within an hour of birth. Almost all cases of this condition have been reported to have died interuterinally or a few days after birth.

Rapid prenatal diagnosis of skeletal dysplasia using medical trio exome sequencing: Benefit for prenatal counseling and pregnancy management.

OBJECTIVE: The aim of this study is to explore the utility of rapid medical trio exome sequencing (ES) for prenatal diagnosis using the skeletal dysplasia as an exemplar. METHOD: Pregnant women who were referred for genetic testing because of ultrasound detection of fetal abnormalities suggestive of a skeletal dysplasia were identified prospectively. Fetal samples (amniocytes or cord blood), along with parental blood, were send for rapid copy number variations testing and medical trio ES in parallel. RESULTS: Definitive molecular diagnosis was made in 24/27 (88.9%) cases. Chromosomal abnormality (partial trisomy 18) was detected in one case. Sequencing results had explained the prenatal phenotype enabling definitive diagnoses to be made in 23 cases. There were 16 de novo dominant pathogenic variants, four dominant pathogenic variants inherited maternally or paternally, two recessive conditions with pathogenic variants inherited from unaffected parents, and one X-linked condition. The turnaround time from receipt of samples in the laboratory to reporting sequencing results was within 2 weeks. CONCLUSION: Medical trio ES can yield very timely and high diagnostic rates in fetuses presenting with suspected skeletal dysplasia. These definite diagnoses aided parental counseling and decision making in most of cases.

Thanatophoric dysplasia: a case report.

A case of thanatophoric dysplasia with sudden death at term is hereby presented. Thanatophoric dysplasia is an uncommon, lethal skeletal dysplasia which is associated with mutation in the extracellular region of fibroblast growth factor receptor 3 (FGFR3). It is an autosommal dominant condition that has sporadic occurrence and early ultrasound scan has not been of great benefit in its detection. Diagnosis is mostly made in the third trimester. The fetal death is usually due to severe respiratory insufficiency from a reduced thoracic capacity and hypoplastic lungs and/or respiratory failure due to brainstem compression. In view of the autosomal dominance of TD, it will be advisable for a woman with previous history to have prenatal screening to relieve parental anxiety and prevent late detection.

Clinical features and molecular genetic analysis of thanatophoric dysplasia type I in a neonate with a de novo c.2419 T > C (p. Ter807Arg) (X807R) mutation in FGFR3.

We present a case report that entails prenatal ultrasonography, postnatal characteristics, and molecular genetic analysis of a newborn who presented with thanatophoric dysplasia type I (TDI) with a mutation in the fibroblast growth factor receptor 3 gene (FGFR3). A malformed newborn with tachypnea, delivered by caesarean at the gestational age of 39 weeks, was the first child of nonconsanguineous parents by a spontaneous pregnancy. Features in prenatal ultrasonography and postnatal radiography were consistent with the diagnosis of TDI, presenting with short body length (38 cm, <3rd percentile), redundant skin folds, a narrow thorax with a bust of 29.5 cm (3-5th percentile), and macrocephaly with a head circumference of 36 cm (>97th percentile). The proposita had postnatal dyspnea and unfortunately died of respiratory failure at the age of 13 days. Molecular genetic analysis revealed a mutation of c.2419 T > C (p. Ter807Arg) (X807R) in FGFR3. Live-born infants with TDI are exceedingly rare, and we hereby report a newborn with a c.2419 T > C mutation in FGFR3, emphasizing phenotype with clinical characteristics and ultrasonographic and X-ray findings, to raise awareness about the heterogeneous patterns of TD.

Non-invasive prenatal sequencing for multiple Mendelian monogenic disorders using circulating cell-free fetal DNA.

Current non-invasive prenatal screening is targeted toward the detection of chromosomal abnormalities in the fetus1,2. However, screening for many dominant monogenic disorders associated with de novo mutations is not available, despite their relatively high incidence3. Here we report on the development and validation of, and early clinical experience with, a new approach for non-invasive prenatal sequencing for a panel of causative genes for frequent dominant monogenic diseases. Cell-free DNA (cfDNA) extracted from maternal plasma was barcoded, enriched, and then analyzed by next-generation sequencing (NGS) for targeted regions. Low-level fetal variants were identified by a statistical analysis adjusted for NGS read count and fetal fraction. Pathogenic or likely pathogenic variants were confirmed by a secondary amplicon-based test on cfDNA. Clinical tests were performed on 422 pregnancies with or without abnormal ultrasound findings or family history. Follow-up studies on cases with available outcome results confirmed 20 true-positive, 127 true-negative, zero false-positive, and zero-false negative results. The initial clinical study demonstrated that this non-invasive test can provide valuable molecular information for the detection of a wide spectrum of dominant monogenic diseases, complementing current screening for aneuploidies or carrier screening for recessive disorders.

Multiplex PCR in noninvasive prenatal diagnosis for FGFR3-related disorders.

Thanatophoric dysplasia and achondroplasia are allelic disorders caused by a constitutively active mutation in the FGFR3 gene. Because thanatophoric dysplasia is a lethal disorder and achondroplasia is non-lethal, they need to be distinguished after ultrasound identification of fetal growth retardation with short limbs. Accordingly, we have developed a noninvasive prenatal test using cell-free fetal DNA in the maternal circulation to distinguish thanatophoric dysplasia and achondroplasia. A multiplex PCR system encompassing five mutation hotspots in the FGFR3 gene allowed us to efficiently identify the responsible mutation in cell-free DNA in all examined pregnancies with a suspected thanatophoric dysplasia or achondroplasia fetus. This system will be helpful in the differential diagnosis of thanatophoric dysplasia and achondroplasia in early gestation and in couples concerned about the recurrence of thanatophoric dysplasia due to germinal mosaicism.

Chylous Ascites in an Infant with Thanatophoric Dysplasia Type I with FGFR3 Mutation Surviving Five Months.

BACKGROUND: Thanatophoric dysplasia (TD) results from sporadic de novo mutations in the FGFR3 gene. Upon confirming intrauterine diagnosis of this perinatal disease, pregnancy termination is recommended. There is limited information on the natural history of longer-term survivors with type 1 TD. CASE REPORT: A full-term neonate was confirmed via postnatal genetic testing to have type 1 TD. At 28 days, chylous ascites developed. Medium-chain triglyceride use improved the ascites. Cerebral ventriculomegaly worsened throughout life. Death due to respiratory failure occurred at age 5 months. CONCLUSION: The chylous ascites in this child with type 1 TD and survival past the neonatal stage suggests that type 1 TD may be accompanied by abnormalities of the lymphatic channels. Moreover, ventriculomegaly can be progressive.

Noninvasive prenatal test for FGFR3-related skeletal dysplasia based on next-generation sequencing and plasma cell-free DNA: Test performance analysis and feasibility exploration.

OBJECTIVE: To explore the feasibility and accuracy of a noninvasive prenatal test for fibroblast growth factor receptor 3 (FGFR3)-related skeletal dysplasia based on next-generation sequencing (NGS) of plasma cell-free DNA. METHOD: Fragmented genome DNA (gDNA) of fetuses with achondroplasia (ACH) and thanatophoric dysplasia type I (TD I) was mixed with postdelivery maternal plasma cell-free DNA to generate spiked samples of different modeled fetal fractions. Multiplex polymerase chain reaction was used to amplify the 19 FGFR3 loci, and the amplification products were then sequenced by NGS to detect the fetal mutant alleles. Then, maternal plasma samples of pregnant women carrying ACH (n = 4) and TD I fetuses (n = 2), as well as healthy controls (n = 15), were tested by NGS, and the test performance was evaluated. RESULTS: Fetal FGFR3 mutations were detected in all artificial mixtures with fetal gDNA concentrations above 3%. In clinical validation, our method identified all fetal FGFR3 mutant alleles from maternal plasma, with no false positive results. The sensitivity and specificity of our method were 100% (95% CI, 54.1%-100%) and 100% (78.2%-100%), respectively. CONCLUSION: Our method had a favorable performance for noninvasively detecting fetal FGFR3 mutations in maternal plasma, highlighting its promising value in developing a noninvasive prenatal test for de novo and paternally inherited disorders.

Regulation of ciliary function by fibroblast growth factor signaling identifies FGFR3-related disorders achondroplasia and thanatophoric dysplasia as ciliopathies.

Cilia project from almost every cell integrating extracellular cues with signaling pathways. Constitutive activation of FGFR3 signaling produces the skeletal disorders achondroplasia (ACH) and thanatophoric dysplasia (TD), but many of the molecular mechanisms underlying these phenotypes remain unresolved. Here, we report in vivo evidence for significantly shortened primary cilia in ACH and TD cartilage growth plates. Using in vivo and in vitro methodologies, our data demonstrate that transient versus sustained activation of FGF signaling correlated with different cilia consequences. Transient FGF pathway activation elongated cilia, while sustained activity shortened cilia. FGF signaling extended primary cilia via ERK MAP kinase and mTORC2 signaling, but not through mTORC1. Employing a GFP-tagged IFT20 construct to measure intraflagellar (IFT) speed in cilia, we showed that FGF signaling affected IFT velocities, as well as modulating cilia-based Hedgehog signaling. Our data integrate primary cilia into canonical FGF signal transduction and uncover a FGF-cilia pathway that needs consideration when elucidating the mechanisms of physiological and pathological FGFR function, or in the development of FGFR therapeutics.

Mutant FGFR3 associated with SADDAN disease causes cytoskeleton disorganization through PLCγ1/Src-mediated paxillin hyperphosphorylation.

K650M/E substitutions in the Fibroblast growth factor receptor 3 (FGFR3) are associated with Severe Achondroplasia with Developmental Delay and Acanthosis Nigricans (SADDAN) and Thanatophoric Dysplasia type II (TDII), respectively. Both SADDAN and TDII present with affected endochondral ossification marked by impaired chondrocyte functions and growth plate disorganization. In vitro, K650M/E substitutions confer FGFR3 constitutive kinase activity leading to impaired biosynthesis and accumulation of immature receptors in endoplasmic reticulum (ER)/Golgi. From those compartments, both SADDAN-FGFR3 and TDII-FGFR3 receptors engender uncontrolled signalling, activating PLCγ1, signal transducer and activator of transcription 1, 3 and 5 (STAT1/3/5) and ERK1/2 effectors. Here, we investigated the impact of SADDAN-FGFR3 and TDII-FGFR3 signalling on cytoskeletal organization. We report that SADDAN-FGFR3, but not TDII-FGFR3, affects F-actin organization by inducing tyrosine hyperphosphorylation of paxillin, a key regulator of focal adhesions and actin dynamics. Paxillin phosphorylation was upregulated at tyrosine 118, a functional target of Src and FAK kinases. By using Src-deficient cells and a Src kinase inhibitor, we established a role played by Src activation in paxillin hyperphosphorylation. Moreover, we found that SADDAN-FGFR3 induced FAK phosphorylation at tyrosines 576/577, suggesting its involvement as a Src co-activator in paxillin phosphorylation. Interestingly, paxillin hyperphosphorylation by SADDAN-FGFR3 caused paxillin mislocalization and partial co-localization with the mutant receptor. Finally, the SADDAN-FGFR3 double mutant unable to bind PLCγ1 failed to promote paxillin hyperphosphorylation, pointing to PLCγ1 as an early player in mediating paxillin alterations. Overall, our findings contribute to elucidate the molecular mechanism leading to cell dysfunctions caused by SADDAN-FGFR3 signalling.

Identification and in silico characterization of p.G380R substitution in FGFR3, associated with achondroplasia in a non-consanguineous Pakistani family.

BACKGROUND: 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. 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. METHODS: PCR-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. RESULTS: Genetic 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. CONCLUSIONS: Mutation 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.

Comparative X-ray morphometry of prenatal osteogenesis imperfecta type 2 and thanatophoric dysplasia: a contribution to prenatal differential diagnosis.

OBJECTIVE: The purpose of the paper was to assess the morphometric parameters to improve the specificity of the ultrasound (US) signs for the early differential diagnosis between two lethal dysplasias, as thanatophoric dysplasia (TD) and osteogenesis imperfecta type 2 (OI-2). METHOD: The diaphyseal length and the bowed shape of long bones associated with vertebral body dimension assessment were investigated in a group of 14 pregnancy terminations carried out in the time period 2007-2013. The definitive diagnosis was established after pregnancy termination by means of skeletal standardized X-rays, histopathology and gene analysis. RESULTS: TD and OI-2 long bones were significantly shorter than controls. No significant differences were observed between the two dysplasias. The bowing angle was higher in OI-2; a true angulation or eventually axial displacement was present only in the latter. Furthermore, they did not show any evidence of vertebral collapse. The thanatophoric dysplasia presented less bowed long bones, and never true angulation. The spine was steadily characterized by flattened anterior vertebral bodies. CONCLUSION: Long bone shortening is not a sufficient and accurate sign for early sonographic differential diagnosis between TD and OI-2. Angled diaphysis, axial diaphyseal displacement and a conserved vertebral body height in the prenatal period support the diagnosis of osteogenesis imperfecta type 2, while moderately regular bowed diaphysis associated with platyspondyly that of thanatophoric dysplasia.

Genetically confirmed thanatophoric dysplasia with fibroblast growth factor receptor 3 mutation.

Thanatophoric dysplasia (TD), the most common lethal skeletal dysplasia, is a de novo genetic disease caused by a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene. "Thanatophoric" means "dead bearing" in Greek. Because FGFR3 is the main modulator of bone maturation, typical features of TD include short extremities, curved femur, clover-leaf skull, small narrow chest, and platyspondyly. TD can be classified into two subgroups according to the morphologic findings, with prominent curved femur suggesting type I TD (TD 1) and with marked clover-leaf skull and relatively straight long bones, favoring type II TD (TD 2). However, considering the genetic profiles, TD 1 and TD 2 could be confidently delineated. Here, we report five genotype-phenotype correlated autopsy cases of TD. Five cases had stigmata of TD on antenatal ultrasonography. Terminations were done at gestational age 16 to 28weeks, after family consultation. In autopsy, all fetuses showed short limbs and clover-leaf skull. The microscopic examination of the bones showed disorganized growth plate, consistent with TD. However, some differences existed in gross and microscopic findings between cases. In genetic analyses, three cases revealed missense mutation of Y373C, while the remaining two cases had missense mutation of S371C and S249C each. They were hot spot mutations of TD 1. A correlation between genotype and phenotype was not apparent due to the limited number of the cases. Therefore, a molecular work up to identify the mutation of FGFR3 is indispensable for TD diagnosis in the era of precision medicine for genetic consultation and future targeted therapy.

Perinatal imaging findings and molecular genetic analysis of thanatophoric dysplasia type 1 in a fetus with a c.2419T>G (p.Ter807Gly) (X807G) mutation in FGFR3.

OBJECTIVE: We present perinatal imaging findings and molecular genetic analysis of thanatophoric dysplasia type I (TD1) in a fetus. CASE REPORT: A 28-year-old woman was referred for genetic counseling at 22 weeks of gestation because of abnormal prenatal ultrasound findings. Level II ultrasound examination revealed a narrow chest, shortened and curved long limbs, protrusion of the abdomen, and macrocephaly. A tentative diagnosis of TD1 was made. After genetic counseling, the pregnancy was terminated and a malformed fetus was delivered. Postnatal radiography findings were consistent with the diagnosis of TD1, with additional findings of short ribs, platyspondyly, and horizontal acetabular roofs. Molecular genetic analysis using umbilical cord tissue revealed a heterozygous mutation of c.2419T>G (p.Ter807Gly) (X807G) in the fibroblast growth factor receptor 3 gene (FGFR3). CONCLUSION: A second-trimester fetus with a heterozygous c.2419T>G mutation in FGFR3 may present characteristic ultrasound and X-ray findings of TD1.