Fetal Dysmorphology: An Indispensable Tool for Synthesis of Perinatal Diagnosis
Shagun Aggarwal Department of Medical Genetics, Nizam’s Institute of Medical Sciences, Hyderabad & Centre for DNA Fingerprinting and Diagnostics, Hyderabad Email:shagun.genetics@gmail.com
1 Introduction
Dysmorphology is the science (and art!) of studying abnormal form, with special emphasis on subtle findings which
provide clue to an underlying diagnosis, mostly a genetic syndrome. It has been the prime tool of the geneticist enabling a
syndromic diagnosis on basis of patient’s gestalt with findings like a white forelock, heterochromia iridis, broad thumb,
asymmetric crying facies and many other subtle features acting as decisive tools in the genetics clinic. Most individuals
with dysmorphism are affected with genetic syndromes, which can be due to chromosomal abnormalities, copy number
variations or single gene defects. However, various environmental factors can also lead to dysmorphism,
many times mimicking specific genetic syndromes due to involvement of a common biological pathway. A
dysmorphological evaluation typically involves a head to toe examination looking for malformations, and minor
features showing deviation from the expected norm as per sex, age, family background and ethnicity. This
often forms the first and most crucial step in establishing a genetic diagnosis and is subsequently followed
by relevant genetic testing for confirmation. In the era of next generation sequencing when the rate of
gene discovery has surpassed the clinical recognition of a new genetic syndrome and reverse phenotyping
has become commonplace, dysmorphology still remains an important tool in the hands of an experienced
geneticist.
Although as a discipline dysmorphology evolved in the paediatrics setting, it can be extended to the fetal life to enable
the diagnosis of a genetic syndrome in the fetus. The recognition of a genetic syndrome in particular, has
important implications for pregnancy management as it aids in accurate prognostication and communicating
the possibility of intellectual disability and other co-morbidities in such children, helps in decision-making
regarding termination or continuation of pregnancy, facilitates appropriate postnatal management and also
provides recurrence risk estimates for subsequent conceptions. In the postnatal scenario, such a diagnosis
facilitates emotional closure, recurrence risk counseling and early, definitive prenatal diagnosis in subsequent
pregnancies.
Any morphological or growth abnormality in the fetal life can be an isolated abnormality of multifactorial origin, the
consequence of environmental etiologies like a teratogenic insult, intrauterine factors, maternal illness, etc. or a component
of a genetic syndrome. In such a scenario, it is important to be aware of these possibilities, and perform a
complete dysmorphological evaluation with an aim to distinguish between these different situations with
varied prognosis and recurrence risks. Figure 1 shows some common fetal abnormalities and respective
etiologies.
Figure 1: Common fetal abnormalities and their etiologies.
2 Setting of fetal dysmorphology
There are two main settings where syndromic diagnosis in the fetus is a possibility and should be actively looked
for:
a.
Abnormal antenatal ultrasound.
b.
Postmortem evaluation of an unexplained fetal demise or morphologically abnormal fetus.
2.1 Abnormal antenatal ultrasound
Abnormalities on antenatal ultrasound can be found in 5-10% of pregnancies. These can vary from growth abnormalities,
major or minor malformations, soft markers and liquor or placental abnormalities. At least 10-30% of prenatally
detected malformations are due to a genetic etiology (Beke et al., 2005). This figure is much higher for
specific abnormalities like omphalocele, holoprosencephaly and cystic hygroma where 50-90% cases can be
attributed to genetic abnormalities involving the chromosomes. In each of these scenarios, the antenatal
ultrasonography should be performed by a fetal medicine specialist with a dysmorphology or clinical genetics
knowledge. Alternatively, a clinical geneticist consultation should be sought, along with relevant images to enable
recognition of dysmorphic facies, recognize the pattern of abnormalities and elicit a detailed family history,
which would help in synthesis of a syndromic diagnosis. The advent of 3D ultrasound technology provides
opportunity for facial dysmorphism recognition, and can be used as an adjunct to the conventional 2D
ultrasonography.
2.2 Postmortem evaluation/ Fetal autopsy
Post-mortem evaluation is an important modality for establishing the cause of unexplained fetal deaths as well as a
medically terminated morphologically abnormal fetus. At least 15-30% of stillbirths are reported to be due to genetic
causes (Reddy et al., 2012). Besides the histopathological examination of the placenta which provides evidence of acquired
insults like utero-placental insufficiency and perinatal infections, dysmorphological evaluation by a geneticist or perinatal
pathologist with expertise in dysmorphology is essential for syndrome recognition. Various studies indicate that
autopsy provides additional findings or modifies the antenatal diagnosis in 20-50% cases (Rodriguez et al.,
2014). Antenatal series have also shown that at least 50% syndromic diagnoses are possible only after an
autopsy (Stoll et al., 2003). Hence, all cases with abnormal ultrasound findings should undergo a post-mortem
evaluation.
3 Practical approach to fetal dysmorphology
The evaluation of the fetus in-utero and/or post-mortem for syndrome recognition involves the following steps (depicted
in figure 2):
Antenatal and medical history
Family history
Ultrasonographic findings
Reports of serum aneuploidy screen
Postmortem evaluation
Genetic testing
Figure 2: Practical approach to fetal syndrome diagnosis.
3.1 Antenatal history
The woman should be asked about history of potential teratogenic exposure in the form of prescription drugs,
high grade fever, exposure to environmental toxins and infection with teratogenic pathogens like rubella,
cytomegalovirus, etc. History of decreased fetal movement perception and malpresentations is important
in cases with arthrogryposis, polyhydramnios and small stomach bubble, where these finds can provide
a clue regarding a primary neuromuscular disorder in the fetus. History of previous pregnancies is also
important, as previous pregnancy losses, pregnancy terminations due to similar or overlapping findings, neonatal
deaths or previous live abnormal offspring all indicate possible segregation of a genetic disorder in the
family.
3.2 Medical history
History of maternal illness like uncontrolled diabetes, phenylketonuria, thyroid disorders, etc. needs to be elicited as they
can play an important role in fetal growth and development. Maternal drug use especially antiepileptic drugs, coumarin
derivatives, ACE inhibitors and some rarer drugs like retinoic acid derivatives, thalidomide, etc. needs to be ascertained
as these are known to be potent fetal teratogens. Some of these can result in fetal malformations which
mimic genetic disorders involving defects in the common biological pathway. An example is fetal warfarin
syndrome, arising due to exposure to warfarin in the first half of pregnancy. Warfarin inhibits the activity
of Vitamin K, and its fetal effects are similar to a genetic disorder brachytelephalangic chondrodysplasia
punctata which is caused by a mutation in the ARSE gene, important for Vitamin K metabolism in the
body.
3.3 Family history
A three-generation family pedigree forms the cornerstone of the family history ascertainment. This can provide important
information like consanguinity, which increases the risk of autosomal recessive disorders; previous fetus or child with
similar or overlapping phenotype; other family members with pregnancy losses, infertility or abnormal offspring indicating
possibility of a chromosomal rearrangement or single gene etiology; and at times a parent with milder manifestation of the
same condition as the fetus.
3.4 Ultrasonographic findings
Various ultrasonographic findings may be a manifestation of an underlying genetic syndrome in the fetus and a
high degree of suspicion as well as careful search for associated abnormality(ies) is important to recognise
these.
a. Structural/ morphological abnormality: These most commonly are malformations i.e. intrinsic defects in the
formation of a structure, but can also be deformations due to compressive effects on a normally formed structure e.g.
varus deformity in oligohydramnios, or disruptions due to sudden insult, traumatic or vascular on a normally formed
structure e.g. amputation due to amniotic band. Malformations or intrinsic defects are likely to be of genetic etiology.
They may be isolated or may be associated with other malformations and/or growth problems which indicate an
underlying genetic syndrome. A specific spectrum of abnormalities may be characteristic of a specific genetic syndrome
e.g. Meckel Gruber syndrome presents with encephalocele, polydactyly and multicystic dysplastic kidneys; trisomy 13
presents with holoprosencephaly, midline cleft, polydactyly and multicystic dysplastic kidneys; and similarly many
other patterns of malformations indicating a particular diagnosis. As a rule, multiple abnormalities per se
indicate possibility of a genetic syndrome, whereas a single malformation may or may not be genetic in
etiology.
b. Soft markers: These are ultrasound findings, which may be seen in many normal fetuses, but are also indicators of
underlying syndromic etiology, primarily chromosomal disorders in some fetuses. Many soft markers have been
described and the risk of chromosomal disorders associated with each has been statistically quantified.
These risks are integrated with the maternal demographics and serum screening risks to provide a final
aneuploidy risk, which is then used for decision-making regarding invasive testing and fetal karyotyping.
Similar to malformations, presence of multiple markers increases the risk of chromosomal aneuploidy more
significantly.
c. Growth abnormalities: Both fetal growth restriction as well as fetal overgrowth can be due to maternal and
utero-placental factors or due to an intrinsic fetal abnormality. Besides chromosomal disorders, various single gene
disorders like microcephalic osteodysplastic dwarfism, Seckel syndrome, Smith-Lemli Opitz syndrome (SLOS),
Russel-Silver syndrome, etc. can present with intrauterine growth restriction (IUGR). Another important group of
disorders presenting with short bones and mimicking IUGR is the skeletal dysplasia group, which includes at least 100
different single gene conditions presenting in the prenatal period. Fetal overgrowth may also be due to primary overgrowth
disorders like Beckwith-Wiedemann syndrome(BWS), Pallister-Killian syndrome and Weaver syndrome, among others.
Hence, it is important to look for additional findings like facial dysmorphism and malformations in all cases of fetal
growth abnormalities, where no acquired etiology is apparent. At times, maternal serum screen results can provide
clues to the underlying genetic etiology, such as low estriol levels in SLOS and high alfa-fetoprotein in
BWS.
d. Liquor abnormalities: Both excess and scanty liquor can be due to underlying genetic etiologies, eg Bartter
syndrome in polyhydramnios and autosomal recessive polycystic kidney disease in oligohydramnios. At
times, these could be indicators of other underlying morphological abnormalities, indicating a syndromic
diagnosis.
Figure 3 depicts some common ultrasound abnormalities and associated genetic syndromes.
Figure 3: Common ultrasound abnormalities and associated genetic syndromes.
3.5 Maternal serum screen
These are biomarkers in the maternal serum which are assayed with the primary aim to screen for common fetal
chromosomal abnormalities. Both first and second trimester screening protocols are available, which in combination with
ultrasonic soft markers aid in screening of low risk women for fetal chromosomal disorders with high sensitivity and
low false positive rates. However, these markers are primarily useful for a few specific conditions, and the
detection of most fetal genetic syndromes are on basis of ultrasound findings and historical data as detailed
above.
3.6 Postmortem evaluation/fetal autopsy
This involves a comprehensive and step-wise evaluation of the fetus in a post-mortem setting and forms the single most
important modality for diagnosis of a genetic syndrome. Typically, autopsy encompasses an external examination or
dysmorphological evaluation of the fetus, similar to the approach in a clinical genetics clinic; internal dissection to look for
gross morphological abnormalities of fetal organs and structures; whole body radiogram, both antero-posterior and lateral
views; and histopathological evaluation of fetal organs and placenta. A standard autopsy proforma helps in maintaining
record of the findings. Briefly, the following are the steps, relevant findings and implications during an
autopsy:
a. Radiographs: A complete fetal radiograph is essential for diagnosis of a skeletal dysplasia and in distinguishing the
various types from each other. Cardinal features like platyspondyly, flaring of ends of femur, bent femur, fractures, absent
ossification, epiphyseal stippling, etc. all help in providing diagnosis of a specific condition. A radiograph can also provide
ancillary information like joint dislocations, spine deformities, missing or supernumerary bones, etc., which may help in
diagnosis of a specific genetic syndrome.
b. External/Dysmorphological examination: This involves assessment of anthropometric parameters like crown rump
length, crown heel length, head circumference, chest circumference and foot length. Other parameters like inter-orbital
distance, hand length, philtrum length, phallus length, and limb segment length may also be assessed as
required. All the parameters should be compared to available centile charts and recorded. This is followed by a
head to toe examination with special attention to dysmorphic features. The head, face, neck, spine, chest,
abdomen, external genitalia, extremities, joints and skin are assessed for shape, size and appearance, and
any deviation from normal searched for and noted. The placenta, membranes and umbilical cord are also
examined for appearance and any abnormality. The weight of the placenta and number of cord vessels are
recorded. Figure 4 provides some dysmorphic features and the corresponding genetic syndromes associated with
these.
Figure 4: Common postmortem dysmorphic findings and associated genetic syndromes.
c. Internal examination: This involves the examination of the intra-abdominal, intra-thoracic and intra-cranial
structures for any abnormalities, in size, shape or morphology. Incision is made on the anterior aspect of the trunk and
the skull following standard techniques. It is important to be aware of some normal gestation-dependent findings, like the
lobulated appearance of fetal kidney, the relative large size of adrenals, thymus and liver, the developing internal genitalia
and lung fissures and the smooth brain surface in early gestation among others. Gestation-specific photographs
should be used for comparison before concluding a structure as abnormal. Figure 5 provides some normal
gestation-dependent findings. Figure 4 depicts some internal organ abnormalities and respective associated genetic
syndromes.
Figure 5: Some gestation-dependent normal morphological findings in fetal life a: Blake pouch cyst with normal
cerebellum (inset) at 19 weeks; b: Smooth brain at 19 weeks gestation; c: Low set and poorly formed ear placode
in a first trimester fetus; d: Lobulated fetal kidneys similar in size to fetal adrenals at mid-trimester.
d. Gross examination and histopathology of fetal organs: All fetal organs are weighed and compared with
gestation-dependent percentiles. A detailed histopathological evaluation is performed, using H&E staining, and if
necessary special stains and immunohistochemistry. Many renal and brain pathologies can be well delineated following
histopathology and in many instances this forms the sole basis for diagnosis. An example being cystic diseases of kidney,
where histopathology can distinguish between autosomal recessive, dominant polycystic kidneys, multicystic dysplastic
kidneys and glomerulocystic kidney disease, all of which can have a similar gross appearance and clinical
presentation. Similarly, brain pathologies like neuronal migration disorders can be well delineated and classified
on histopathology. Placental histopathology can provide evidence of uteroplacental insufficiency and fetal
infections.
This comprehensive approach to an abnormal fetus, using historical, imaging and postmortem findings provides
important diagnostic information and often leads to the diagnosis of a specific dysmorphic syndrome or identification of
an acquired etiology. However, final confirmation of a genetic etiology depends on laboratory testing and identification of
the underlying genetic aberration.
4 Genetic testing for the dysmorphic fetus
Genetic disorders can broadly be classified into three different types, and each of these require a specific laboratory
diagnostic approach.
a. Chromosomal disorders: These are disorders arising due to numerical or structural abnormalities in
chromosomes. The common ones with well described prenatal phenotypes are Down syndrome (Trisomy 21), Patau
syndrome(Trisomy 13), Edward syndrome (Trisomy 18), Turner syndrome and triploidy. A karyotype from the amniotic
fluid (following amniocentesis), cord blood (following cordocentesis or at birth), intra-cardiac blood (post
mortem) or skin fibroblasts, is the gold standard for the diagnosis of this group of disorders. These on average
constitute 10-30% of fetuses with an antenatal malformation (Beke et al., 2005). Since karyotyping requires the
presence of viable cells, it is essential to obtain suitable samples antenatally or soon after birth for this
investigation.
b. Single gene disorders/ Mendelian disorders: These are diseases arising due to mutations in individual genes. At
least 6000 single gene disorders have been described and for 4500 of them the molecular basis is known. Many of these
disorders present in the prenatal period with fetal abnormalities, some common examples being Meckel-Gruber syndrome,
Noonan syndrome, short rib polydactyly syndromes, lysosomal storage disorders, etc. The exact estimate of such disorders
in the prenatal period is not known, however some recent studies employing Next generation sequencing-based novel
technologies have found single gene defects in 20-30% of fetuses with antenatal malformations (Drury et al., 2015). The
diagnosis of these disorders is challenging in the laboratory as many conditions have overlapping features and genetic
heterogeneity is common. Conventionally, most often the diagnosis was made following a post-mortem
evaluation, and then subsequent targeted testing was done by Sanger sequencing of the causative gene in
the fetal DNA. However, availability of the Next generation sequencing technology has made it easier to
provide molecular testing, as this enables the parallel sequencing of multiple genes enabling interrogation of
overlapping phenotypes as well as genetically heterogeneous conditions. An example would be the skeletal
dysplasias, with at least 100 different single gene disorders presenting with short bones on antenatal ultrasound.
Exact diagnosis is often not possible antenatally, and fetal sampling followed by a NGS-based testing of all
skeletal dysplasia genes can be done to arrive at a final diagnosis and provide accurate prognostication to the
family.
c. Genomic disorders: Another group of genetic diseases are caused by copy number abnormalities in
the genome i.e. small, submicroscopic microdeletions or microduplications involving part of the genome.
These conditions require special molecular cytogenetic techniques for diagnosis, and often in the antenatal
period, where a specific diagnosis is not apparent, a chromosomal microarray is the most common testing
modality used. Various antenatal series have found that chromosomal microarray studies from fetal DNA
of a morphologically abnormal fetus indicate a copy number abnormality in 6-10% (de Wit et al., 2014).
Presently, microarray studies are recommended as first tier test in case of morphological abnormalities on
ultrasound. Postnatal studies have also found 2-10% of stillbirths as having copy number abnormalities,
indicating the significant contribution of this group of genetic aberrations to fetal abnormalities (Reddy et
al.,2012).
d.A relatively rarer type of genetic disorders known as imprinting disorders can also present with fetal abnormalities,
primarily affecting growth. Examples being Beckwith-Wiedemann syndrome presenting with overgrowth, organomegaly,
omphalocele and polyhydramnios; and Russel-Silver syndrome presenting with fetal growth restriction. Testing for these
conditions requires methylation studies on fetal DNA.
Unlike samples for karyotyping, which require viable cells, fetal DNA can be obtained from any fetal sample, including
an umbilical cord segment, either antenatally or post-mortem. The only prerequisite for suitable DNA sample is that the
concerned sample should not be exposed to formalin, which can lead to cross linkage, adduct formation and fragmentation
of DNA, precluding further molecular studies. Hence, to facilitate laboratory testing and confirmation of a genetic
diagnosis, suitable fetal sample should be obtained and stored if immediate testing is not possible. Storage for purpose of
DNA extraction can be done at 2-8°C for few weeks and at -20°C for long term. For karyotyping, sample
can be stored at 2-8°C and be transferred to the laboratory as soon as possible, and at least within 48
hours.
5 Genetic counseling
Appropriate genetic counselling is possible after an accurate diagnosis has been made following the clinical and laboratory
evaluations. Counseling typically addresses the following issues:
1. Prognosis: This is relevant in the antenatal setting when a couple is faced with an ultrasound diagnosis of a fetal
abnormality. Besides the morbidities of the abnormality and outcome of postnatal surgery in structural abnormalities, the
recognition of a syndrome has various implications. Most genetic syndromes are associated with intellectual handicap,
which does not have a satisfactory therapy. Additionally, there can be growth issues, presence of other internal
malformations not detectable by imaging, and occasionally premature lethality. This information needs to be
communicated to the couple as it helps in decision making regarding pregnancy termination, obstetric management as
well as neonatal management.
2. Recurrence risk: There is an increased recurrence risk associated with genetic etiologies, which is 25% for autosomal
recessive disorders, 50% for an autosomal dominant disorder with affected parent and 50% for male offspring of a carrier
female for X-linked recessive disorders. The risk is low for chromosomal disorders, unless they arise due to a parental
chromosomal rearrangement and for autosomal dominant disorders with normal parents. This risk estimate helps the
couple in availing prenatal diagnosis services in subsequent pregnancies, and the need and availability of the same should
be communicated.
3. Prenatal diagnosis: The pre-requisite to definitive prenatal diagnosis in subsequent pregnancies is
identification of the underlying genetic aberration in the affected fetus. Hence, laboratory genetic testing and
confirmation of the clinical diagnosis plays an important role in fetal dysmorphology. Once the exact mutation or
chromosomal abnormality or biochemical defect in the index case is known, early and definitive prenatal
diagnosis is possible by chorionic villus sampling at 11-12 weeks in subsequent conceptions. In absence of a
laboratory diagnosis, prenatal diagnosis can be attempted by ultrasound, however this may not be of utility
till later in pregnancy, and milder or discordant manifestations may not be detected. These issues need
to be discussed with the family prior to pregnancy termination, so that appropriate fetal samples can be
obtained.
6 Conclusion
Feta dysmorphology plays an important role in evaluation of an abnormal fetus with far reaching implications for the
current as well as future pregnancies. A multi-disciplinary approach, with clinical geneticist playing a pivotal role is
integral to optimising the care of these special patients and their families.
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