Discussion
By studying the WES test results of 79 pregnant women from the third
affiliated hospital of Zhengzhou University from August 2018 to April
2020, the overall detection rate of skeletal abnormalities was 31.6%.
This is higher than the previously reported detection rate (15.4%(Lord,
et al., 2019) and 24%(Petrovski, et al., 2019)). This may be due to our
stricter requirements for the ultrasound test results of the enrolled
cases. Interestingly, we find that for different types of skeletal
abnormalities, the detection rate through WES varies greatly. Among
them, WES has a higher detection rate for short limbs. Especially when
FL<-4.0SD or HL<-4.0SD, the detection rate can rise
to 41.6%. However, when the fetal has short limbs with other bone
abnormal phenotypes, the detection rate will be higher. For example,
when the limbs are short with bone curved, the WES detection rate can
reach 100%; when the limbs are short with nasal bone dysplasia, WES
detection rate can reach 80%. On the contrary, if the phenotype of
short limbs is not detected by ultrasound testing and only other
skeletal abnormal phenotypes exists, such as only fetal hand or foot
deformities, the WES detection rate will be very low, only 11.1% . It
may be that achondroplasia is the cause for the most of skeletal
abnormalities (Pauli, 2019), which is also the most common form of
inherited disproportionate short stature(Waller, et al., 2008). In our
study, through ultrasound,46 of 79 fetal skeletal abnormalities had
clinical manifestations of short limbs, accounting for 58.2%,
consistent with previous reports(Georgoulis, et al., 2011). This shows
that the diagnosis of achondroplasia is the key to the diagnosis of
fetal skeletal abnormalities.
Through our research, we find that for the diagnosis of fetalFGFR3 -related achondroplasia, the WES detection rate is highly
correlated with the results of ultrasound testing of the fetal limb
shortness and severity. Through our research, we find that the diagnosis
of fetal FGFR3 -related achondroplasia(Wynn, et al., 2007)
accounts for the highest proportion of all skeletal abnormalities,
reaching 28%. Almost all the ultrasound test results of fetal
achondroplasia have been detected with FL<-4.0SD or
HL<-4.0SD, suggesting that FL<-4.0SD or
HL<-4.0SD is the most critical basis for the diagnosis of
achondroplasia by fetal ultrasound testing. At the same time, the
detection of macrocephaly through ultrasound is also an important
evidence for the diagnosis of fetal achondroplasia. Among the 7 cases ofFGFR3 -related achondroplasia, 6 cases were caused by FGFR3gene c.1138G>A mutation. FGFR3 gene
c.1138G>A mutation is the most common mutation inFGFR3 -related achondroplasia, which accounts for more than 99%
of all FGFR3 -related achondroplasia together with FGFR3gene c.1138G>C mutation(Foldynova-Trantirkova, et al.,
2012; Xue, et al., 2014). At this point, our research is consistent with
these reports. In addition, we have also detected a case of FGFR3gene c.1620C>A mutation through WES, which is related to
hypochondroplasia(Bellus, et al., 1995). FGFR3 gene
c.1620C>A mutation has been reported
extensively(Deutz-Terlouw, et al., 1998) and is considered to account
for 50%-76% of FGFR3-related hypochondroplasia(Tarja, et al., 2012).
Therefore, FGFR3 gene c.1138G>A mutation and
c.1620C>A mutation may be the two most common causes of
skeletal abnormalities in the fetal period and require special clinical
attention.
Osteogenesis imperfecta caused by the COL1A1 gene is also a major
cause of fetal skeletal dysplasia. The main feature of Osteogenesis
imperfecta is multiple fractures usually caused by minor trauma(W, et
al., 1985; Willing, et al., 1990). This may be manifested by the limbs
being curved by ultrasound testing during the prenatal period. In our
study, osteogenesis imperfecta due to COL1A1 gene mutation was
detected in the presence of limbs slightly curved through ultrasound in
the fetal period, which suggests that the presence of this phenotype
during the fetal period may be highly correlated with COL1A1-related
osteogenesis imperfecta. In addition, COL1A1 gene
c.896G>A mutation and c.1301G>A mutation found
in our research have not been reported in other studies before , which
broadens the clinical understanding of this gene mutation. COL1A1gene c.3235G>A mutation, according to previous reports,
shows that it has a highly variable phenotype in the family, and family
members with this gene mutation can only show signs of disease without
fractures(D., et al., 2012; Kaneko, et al., 2011). This may explain why
in our study, the husband of the pregnant woman also has the
heterozygous mutation of the gene but the phenotype was not abnormal.
In our study, 2 cases of cleidocranial dysplasia related to RUNX2gene mutation were detected, which were c.931_946del mutation and
c.568C>T mutation. The main clinical features of
cleidocranial dysplasia include persistently open skull sutures with
bulging calvaria, hypoplasia or aplasia of the clavicles permitting
abnormal facility in apposing the shoulders, wide pubic symphysis, short
middle phalanx of the fifth fingers, dental anomalies, and often
vertebral malformation(Pan, et al., 2017). It has been pointed out in
previous reports that cleidocranial dysplasia can also be related to the
phenotype of nasal bone loss(Pan, et al., 2017), which is consistent
with our case study. In our study, some other genetic variations or
chromosomal aneuploidies related to the nasal bone loss phenotype are
also found, such as the ARSE gene c.331C>T variation
and trisomy 21. ARSE gene mutation is related to X-linked
recessive chondrodysplasia punctata, which is manifested as nasal
dysplasia and distal phalanx dysplasia(Brunetti-Pierri, et al., 2003),
which is consistent with the phenotype observed during fetal ultrasound
testing. Trisomy 21 is the most frequent form of mental retardation
caused by a microscopically demonstrable chromosomal aberration, is
characterized by well-defined and distinctive phenotypic features and
natural history(Zhu, et al., 2013). It has been reported that nasal bone
dysplasia is a common detected phenotype of fetal trisomy 21(De Jong
Pleij, et al., 2012), which is consistent with the phenotype of a
trisomy 21 case found in our study. Therefore, in the diagnosis of fetal
skeletal abnormalities, nasal bone dysplasia may be another typical
indication of ultrasound abnormality in addition to short limbs.
In our study, some gene mutations related to skeletal abnormalities
related to hand and foot abnormalities are also detected. For example,SCN4A gene c.4361G>A mutation(Gay, et al., 2010),NEB gene c.1569+5G>A and c.2278C>T
compound heterozygous mutation(Lehtokari, et al., 2014), FGFR2gene c.755C>G mutation(Miraoui, et al., 2010). Most of the
diseases related to these gene mutations mainly affect the function of
the muscular system as the main cause(Coen A. C. Ottenheijm, 2009;
Matthews, et al., 2011), and their detection rate in fetal skeletal
abnormalities is low (only FGFR2 gene c.755C>G
mutation), but their detection can play an important guiding role in
clinical diagnosis and treatment.