Exploring the Micro-Mosaic Landscape of FGFR3 Mutations in the Ageing Male Germline and Their Potential Implications in Meiotic Differentiation

Advanced paternal age increases the risk of transmitting de novo germline mutations, particularly missense mutations activating the receptor tyrosine kinase (RTK) signalling pathway, as exemplified by the FGFR3 mutation, which is linked to achondroplasia (ACH). This risk is attributed to the expansion of spermatogonial stem cells carrying the mutation, forming sub-clonal clusters in the ageing testis, thereby increasing the frequency of mutant sperm and the number of affected offspring from older fathers. While prior studies proposed a correlation between sub-clonal cluster expansion in the testis and elevated mutant sperm production in older donors, limited data exist on the universality of this phenomenon. Our study addresses this gap by examining the testis-expansion patterns, as well as the increases in mutations in sperm for two FGFR3 variants-c.1138G>A (p.G380R) and c.1948A>G (p.K650E)-which are associated with ACH or thanatophoric dysplasia (TDII), respectively. Unlike the ACH mutation, which showed sub-clonal expansion events in an aged testis and a significant increase in mutant sperm with the donor's age, as also reported in other studies, the TDII mutation showed focal mutation pockets in the testis but exhibited reduced transmission into sperm and no significant age-related increase. The mechanism behind this divergence remains unclear, suggesting potential pleiotropic effects of aberrant RTK signalling in the male germline, possibly hindering differentiation requiring meiosis. This study provides further insights into the transmission risks of micro-mosaics associated with advanced paternal age in the male germline.

Thanatophoric dysplasia in nonadherent to antenatal care in low middle income country: a rare case reports

Introduction and importance

Thanatophoric dysplasia is a rare, fatal, and sporadic form of skeletal dysplasia caused by a mutation in fibroblast growth factor receptor 3 (FGFR3). It is characterized by a conical thorax, platyspondyly (flat vertebral bodies), and macrocephaly. This disorder can be diagnosed antenatally as early as 13 weeks of gestation.

Case presentation

The authors reported a case of thanatophoric dysplasia on USG in a 19 year old young consanguineous female in her second trimester of pregnancy. Ultrasound examination showed a clover leaf-shaped skull, a widened anterior fontanel, a coarse and edematous face, a flattened nasal bridge, a short neck, a low set of ears, shortening of both upper and lower limbs with short fingers, bowed thighs and legs, and a relatively narrow thorax.

Clinical discussion

Lung hypoplasia, polyhydramnios, and hydrops in affected individuals lead to a poor prognosis. Hence, timely intervention should be done to avoid a poor prognosis. However, a mix of sonographic, genetic, histological, and autopsy studies are applied to make the most accurate diagnosis.

Conclusion

The authors reported this case due to the rarity of this condition and the need for a systematic and multidisciplinary approach.

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).

Development of individuals with thanatophoric dysplasia surviving beyond infancy

BACKGROUND

This study aimed to analyze the physical and psychosocial development of long-term survivors (age >1 year) of thanatophoric dysplasia (TD).

METHODS

The participants were 20 long-term survivors recruited from a cohort obtained through a nationwide survey for TD conducted across 147 pediatric departments in Japan between 2012 and 2016. Their guardians consented to participate in this study. Medical and psychosocial information was collected through questionnaires and interviews with primary physicians and guardians.

RESULTS

The participants were 1.2-27.8 years old, and all showed marked growth deficiency. The mean length at birth was 36 cm (-3.4 SD to -7.9 SD). The adult height (age >16 years) was <-15.2 SD. All individuals showed severely delayed psychomotor development. The highest level of psychosocial development was equivalent to that at 2 years of age. Skin disorders (acanthosis nigricans and seborrheic keratoses) were common. Eleven subjects had been hospitalized or institutionalized consistently after birth, and nine had been moved to home care, and four were exclusively orally fed. All individuals required assisted ventilation.

CONCLUSIONS

Long-term survival of TD individuals is common. Some individuals enjoy home-based lives; however, they are severely psychosocially and physically disabled and require meticulous respiratory and nutritional support.

Should We Stop Calling Thanatophoric Dysplasia a Lethal Condition? A Case Report of a Long-Term Survivor

Thanatophoric dysplasia (TD) is a rare skeletal dysplasia commonly thought to be lethal. In this case report, we discuss a nine-year-old male with TD and review his parents' decision making shortly after their son was born, the technology needed to sustain him, and his parents' perception of his quality of life. We also summarize the clinical course of published long-term survivors with TD. Pediatric Palliative Care teams, especially those conducting perinatal palliative care consultations, are often asked to support families in the face of prognostic uncertainty. Our case report and review of the literature adds to the uncertainty of prognosis in TD and suggests that pediatric palliative care providers should be wary of the label “lethal.”

National survey of prevalence and prognosis of thanatophoric dysplasia in Japan

BACKGROUND

Thanatophoric dysplasia (TD) is a rare congenital disease of the skeletal system, with an incidence of 1.68-8.3 per 100 000 births, but statistical data on the estimated number of TD patients across Japan are not available. The aim of this study was therefore to investigate the prevalence and prognosis of TD in Japan.

METHODS

A nationwide primary questionnaire survey was conducted.

RESULTS

A total of 127 obstetric, 186 pediatric, and 115 orthopedic facilities provided responses. Excluding duplications, we identified 73 patients with TD. Of the 73 cases, 15 were abortions, four were stillbirths, 51 were live births, and three had unknown details. Of the 51 live newborns, 27 died ≤7 days after birth, with an early neonatal mortality rate of 56%. Of the 24 newborns who survived the early neonatal period, 16 survived for ≥1 year. All of the 24 newborns received respiratory management and survived during the early neonatal period. Of the 51 live newborns, 25 did not receive respiratory management and died ≤2 days after birth.

CONCLUSIONS

The prevalence of TD in Japan is estimated to be at 1.1 (95%CI: 0.84-1.37) per 100 000 births, but the actual incidence is expected to be higher. To our knowledge, we have confirmed for the first time that newborns with TD may not always die during the early neonatal period but can survive the early neonatal period with appropriate respiratory management. Therefore, the term "thanatophoric dysplasia" does not accurately reflect the nature of the disease.

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.

Achondroplasia: Development, pathogenesis, and therapy

Autosomal dominant mutations in fibroblast growth factor receptor 3 (FGFR3) cause achondroplasia (Ach), the most common form of dwarfism in humans, and related chondrodysplasia syndromes that include hypochondroplasia (Hch), severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN), and thanatophoric dysplasia (TD). FGFR3 is expressed in chondrocytes and mature osteoblasts where it functions to regulate bone growth. Analysis of the mutations in FGFR3 revealed increased signaling through a combination of mechanisms that include stabilization of the receptor, enhanced dimerization, and enhanced tyrosine kinase activity. Paradoxically, increased FGFR3 signaling profoundly suppresses proliferation and maturation of growth plate chondrocytes resulting in decreased growth plate size, reduced trabecular bone volume, and resulting decreased bone elongation. In this review, we discuss the molecular mechanisms that regulate growth plate chondrocytes, the pathogenesis of Ach, and therapeutic approaches that are being evaluated to improve endochondral bone growth in people with Ach and related conditions. Developmental Dynamics 246:291-309, 2017. © 2016 Wiley Periodicals, Inc.

A case of thanatophoric dysplasia type 2: a novel mutation

Thanatophoric dysplasia (TD) is a lethal form of skeletal dysplasia with short-limb dwarfism. Two types distinguished with their radiological characteristics have been defined clinically. The femur is curved in type 1, while it is straight in type 2. TD is known to be due to a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene. We report a male patient who showed clinical findings congruent with TD type 2 and a new mutation in the FGFR3 gene, a finding which has not been reported previously.

Temporal lobe dysplasia: a characteristic sonographic finding in thanatophoric dysplasia

OBJECTIVE

To determine the incidence of temporal lobe dysplasia (TLD) detected on prenatal ultrasound in thanatophoric dysplasia (TD) over an 11-year period in a tertiary referral center.

METHODS

An 11-year retrospective review of perinatal autopsies from 2002 to 2013 was performed to identify cases of TD. The ultrasound images and corresponding reports of all TD cases were examined for the presence of TLD. The same set of images subsequently underwent a retrospective review by a perinatal radiologist with knowledge of the features of TLD to determine whether they could be identified.

RESULTS

Thirty-one cases of TD underwent perinatal autopsy, and prenatal ultrasound imaging was available for review in 24 (77%). Mean gestational age at diagnosis of TD was 21.3 (range, 18-36) weeks. TLD was identified and reported in 6/24 (25%) cases; all six cases occurred after 2007. Retrospective interpretation of the ultrasound images identified features of TLD in 10 additional cases. In total, 16/24 (67%) cases displayed sonographic evidence of TLD. Temporal trends showed that TLD features were present in 50% (5/10) of all TD cases between 2002 and 2006 and in 79% (11/14) of those detected between 2007 and 2013.

CONCLUSIONS

At present, the detection rate of TLD by ultrasound is low but may be increased by modified brain images that enhance visualization of the temporal lobes. Prenatal identification of TLD may help in the prenatal diagnosis of TD and thus provide more accurate prenatal counseling and guide molecular investigations to confirm the specific diagnosis of TD.

Thanatophoric dysplasia type I: a rare case report at fetal autopsy

Thanatophoric dysplasia type 1 is a lethal congenital anomaly with skeletal dysplasia. It is characterized by short limb dwarfism, enlarged head with frontal bossing, short neck, protuberant abdomen. It is detected in early gestational period by ultrasonography. The other associated anatomical abnormalities and characteristic laboratory findings aid in the early diagnosis and further work-up.

FGFR3 mutation frequency in 324 cases from the International Skeletal Dysplasia Registry

Fibroblast growth factor receptor 3 (FGFR3) is the only gene known to cause achondroplasia (ACH), hypochondroplasia (HCH), and thanatophoric dysplasia types I and II (TD I and TD II). A second, as yet unidentified, gene also causes HCH. In this study, we used sequencing analysis to determine the frequency of FGFR3 mutations for each phenotype in 324 cases from the International Skeletal Dysplasia Registry (ISDR). Our data suggest that there is a considerable overlap of genotype and phenotype between ACH and HCH. Thus, it is important to test for mutations found in either disorder when ACH or HCH is suspected. Only two of 29 cases with HCH did not have an identified mutation in FGFR3, much less than previously reported. We recommend testing other mutations in FGFR3, instead of just the common HCH mutation, p.Asn540Lys. The mutation frequency for TD I and TD II in the largest series of cases to date are also reported. This study provides valuable information on FGFR3 mutation frequency of four skeletal dysplasias for clinical diagnostic laboratories and clinicians.

Growth and development in thanatophoric dysplasia - an update 25 years later

KEY CLINICAL MESSAGE

Thanatophoric dysplasia is typically a neonatal lethal condition. However, for those rare individuals who do survive, there is the development of seizures, progression of craniocervical stenosis, ventilator dependence, and limitations in motor and cognitive abilities. Families must be made aware of these issues during the discussion of management plans.

Diagnosis of chromosomal abnormalities in a patient with thanatophoric dysplasia (TD) type I: The first report describing an important association between cytogenetic findings and TD

Background:

Thanatophoric dysplasia (TD) is the most lethal and most severe type of dysplasia. It has distinct features, the most important of which is short tubular bones and short ribs with platyspondyly, allowing a precise radiologic and prenatal ultrasonographic diagnosis. It has been reported to be caused by mutations in the FGFR3 gene, but exactly how cytogenetic abnormalities might lead to TD is unclear.

Case Report:

We report a case of TD with different prenatal sonographic features compatible with the classification of type I. In the result of cytogenetic examination, we found de novo CAs in 28% of cells analyzed from the affected infant; 75% of the abnormalities were numerical, and of those, 25% were structural aberrations; 21% of cells revealed predominantly numerical aberrations. Monosomy 18, 21 and 22 was observed in 4% of cells, monosomy 20 in 2%, and monosomy 7, 8, 14, 17 and 19 in 1%. Structural changes were observed in 7% of cells. Conclusions: It appears that these chromosomes may be preferentially involved in and important for TD development.

Prenatal third trimester sonographic behavior of a thanatophoric dwarfs

OBJECTIVES

Thanatophoric dysplasia (TD), the most common of the congenital lethal skeletal dysplasias occurs sporadically in 1/64,000-100,000 live births. To the best of our knowledge, the in utero attitudes and behaviours of such babies with serial ultrasound scans have not been previously described. We present the in utero third trimester sonographic behaviors of TD in a 22-year-old primigravida diagnosed at '32weeks' gestational age along with the clinical and radiographic characteristics.

METHODS

The same radiologists to observe the behavior of a thanatophoric dwarfs did three fortnights serial ultrasound scans.

RESULTS

The baby was found to have short limbs that were constantly in rigid abduction, flexed at both elbows and knees, and demonstrated poverty of synchronous movements. The upper limbs were perpetually in embracing position during all scans. In addition, he was hyperactive, showing "yoyo" body movement and constantly hyper-extended neck. Postmortem radiograph was diagnostic of TD.

CONCLUSION

Though he baby died intra partum, the observed attitudes and behaviors on serial prenatal ultrasonography, which provided us with sufficient information to counsel the family, managed the pregnancy, and direct the postnatal evaluation could possibly add to the in utero diagnostic sonographic features of TD.

Sprouty 2 disturbs FGFR3 degradation in thanatophoric dysplasia type II: a severe form of human achondroplasia

Thanatophoric dysplasia is a member of the achondroplasia family of human skeletal dysplasias, which result from FGFR3 mutations that exaggerate this receptor's inhibitory influence on chondrocyte proliferation and differentiation in the skeletal growth plate. We have previously reported that defective lysosomal degradation of activated receptor contributes to the gain-of-function of the mutant FGFR3. We now provide evidence that this disturbance is mediated by the receptor's kinase activity and involves constitutive induction and activation of Spry2. Our findings suggest that activated Spry2 may interfere with c-Cbl-mediated ubiquitination of FGFR3 by sequestering c-Cbl. They provide novel insight into the pathogenesis of this group of human skeletal dysplasias and identify a mechanism that potentially could be targeted therapeutically.