Rapid detection of K650E mutation in FGFR3 using uncultured amniocytes in a pregnancy affected with fetal cloverleaf skull, occipital pseudoencephalocele, ventriculomegaly, straight short femurs, and thanatophoric dysplasia type II

Perinatal imaging findings of a fetus with Pfeiffer syndrome and a heterozygous c.1019A>G, p.Tyr340Cys (Y340C) mutation in FGFR2 presenting a cloverleaf skull, craniosynostosis and short limbs on prenatal ultrasound mimicking thanatophoric dysplasia type II

OBJECTIVE

We present perinatal imaging findings of a fetus with Pfeiffer syndrome and a heterozygous c.1019A>G, p.Tyr340Cys (Y340C) mutation in FGFR2 presenting a cloverleaf skull, craniosynostosis and short limbs on prenatal ultrasound mimicking thanatophoric dysplasia type II (TD2).

CASE REPORT

A 37-year-old, gravida 2, para 1, woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 46,XY. However, craniofacial anomaly was found on prenatal ultrasound at 21 weeks of gestation, which showed a cloverleaf skull with severe craniosynostosis and relatively short straight long bones. Fetal magnetic resonance imaging (MRI) analysis at 22 weeks of gestation showed a cloverleaf skull, proptosis and relatively shallowing of the sylvian fissures. Prenatal ultrasound at 24 weeks of gestation showed a fetus with a cloverleaf skull with a biparietal diameter (BPD) of 6.16 cm (equivalent to 24 weeks), an abdominal circumference (AC) of 18.89 cm (equivalent to 24 weeks) and a femur length (FL) of 3.65 cm (equivalent to 21 weeks). A tentative diagnosis of TD2 was made. The pregnancy was subsequently terminated, and a 928-g malformed fetus was delivered with severe craniosynostosis, proptosis, midface retrusion, a cloverleaf skull, broad thumbs and broad big toes. The broad thumbs were medially deviated. Whole body X-ray showed a cloverleaf skull and straight long bones. However, molecular analysis of FGFR3 on the fetus revealed no mutation in the target regions. Subsequent whole exome sequencing (WES) on the DNA extracted from umbilical cord revealed a heterozygous c.1019A>G, p.Tyr340Cys (Y340C) mutation in the FGFR2 gene.

CONCLUSION

Fetuses with a Y340C mutation in FGFR2 may present a cloverleaf skull on prenatal ultrasound, and WES is useful for a rapid differential diagnosis of Pfeiffer syndrome from TD2 under such a circumstance.

Cranial Base Synchondrosis: Chondrocytes at the Hub

The cranial base is formed by endochondral ossification and functions as a driver of anteroposterior cranial elongation and overall craniofacial growth. The cranial base contains the synchondroses that are composed of opposite-facing layers of resting, proliferating and hypertrophic chondrocytes with unique developmental origins, both in the neural crest and mesoderm. In humans, premature ossification of the synchondroses causes midfacial hypoplasia, which commonly presents in patients with syndromic craniosynostoses and skeletal Class III malocclusion. Major signaling pathways and transcription factors that regulate the long bone growth plate-PTHrP-Ihh, FGF, Wnt, BMP signaling and Runx2-are also involved in the cranial base synchondrosis. Here, we provide an updated overview of the cranial base synchondrosis and the cell population within, as well as its molecular regulation, and further discuss future research opportunities to understand the unique function of this craniofacial skeletal structure.

A new biometric: In utero growth curves for metacarpal and phalangeal lengths reveal an embryonic patterning ratio

OBJECTIVES

The objectives of this study are to develop gestational age-specific growth curves for fetal third metacarpal and phalangeal lengths and to determine if fetal hand proportion is established in utero.

METHODS

This prospective cross-sectional study used 2D ultrasound across gestational ages 12 to 39 weeks to evaluate the third fetal metacarpal and phalangeal measurements. Gestational age-specific reference growth curves were developed. Associations between continuous variables were assessed using Spearman correlations (r_s ) and restricted cubic splines. A nonlinear biologic regression model was used to predict metacarpal and phalangeal lengths as a function of gestational age. Measurements derived from five cases of thanatophoric dysplasia were used to determine if brachydactyly could be objectified.

RESULTS

Fetal metacarpal and phalangeal lengths are highly correlated across gestational age (r_s  = 0.96, P < 0.001). The mean fetal metacarpal to phalangeal ratio is constant from gestational age 15 to 39 weeks (r_s  = -0.07, P = 0.49). Third-digit metacarpal and phalangeal lengths in thanatophoric dysplasia showed brachydactyly in all cases (5/5), and none of the cases (0/5) demonstrated a normal metacarpal to phalangeal ratio of 0.49.

CONCLUSION

We present gestational age-specific reference growth curves for fetal third metacarpal and phalangeal lengths, which may be used to detect brachydactyly. We demonstrate a prenatal metacarpal to phalangeal ratio of 1:2.

Prenatal diagnosis of hydrancephaly and enlarged cerebellum and cisterna magna in a fetus with thanatophoric dysplasia type II and a review of prenatal diagnosis of brain anomalies associated with thanatophoric dysplasia

OBJECTIVE

We present prenatal diagnosis of hydrancephaly and enlarged cerebellum and cisterna magna in a fetus with thanatophoric dysplasia type II (TD2) and a review of prenatal diagnosis of brain anomalies associated with TD.

CASE REPORT

A 33-year-old woman was referred for genetic counseling at 25 weeks of gestation because of fetal ultrasound abnormalities. Prenatal ultrasound at 14 weeks of gestation revealed an increased nuchal translucency (NT) and hydrocephalus. Level II ultrasound examination at 25 weeks of gestation revealed hydrancephaly, macrocephaly, a cloverleaf skull, frontal bossing, enlarged cerebellum and cisterna magna, a narrow chest, small ribs, short straight limbs. Amniocentesis revealed a karyotype of 46,XX. FGFR3 mutation analysis using the DNA extracted from uncultured amniocytes revealed a genotype of WT/c.1948A>G (p.Lys650Glu). The result was consistent with a K650E mutation in FGFR3 and TD2. The pregnancy was subsequently terminated.

CONCLUSION

Fetuses with TD2 may present increased NT, early onset hydrocephalus, enlarged cerebellum and cisterna magna, and hydrancephaly on prenatal ultrasound.