Discussion

CHARGE syndrome is an acronym for [1]:

• Coloboma
• Heart defect
• Choanal Atresia
• Postnatal growth Restriction
• Genitourinary abnormality and/or hypogonadism
• Ear anomalies and/or deafness

CHARGE syndrome was originally described in 1979 [2,3] with an incidence of approximately 1 in 8,500 live births [4]. There is a broad phenotype and variable expression of a number of different features [5].

CHARGE syndrome is caused most commonly by a de novo mutation in the CHD7 gene [6]. These mutations are found in approximately 60-80% of patients with a clinical diagnosis [6,7]. Most of these are small, truncating or missense mutations that cause a milder phenotype, which may not be diagnosed prenatally. These mutations are not identified by microarray, but may be identified by whole exome sequencing. Larger truncating lesions are associated with a more severe phenotype with multiple congenital abnormalities which may be diagnosed prenatally. Many of these cases lead to pregnancy loss or termination of pregnancy.

CHARGE syndrome can be diagnosed prenatally, though rare [8,9]. Often it is suspected prenatally and confirmed with molecular testing postnatally [9,10,11]. Isolated or multiple congenital abnormalities are identified prenatally in approximately 45-60% of cases where CHARGE syndrome is confirmed postnatally [7,10]. Prenatal features that may be detectable on imaging include:

• Cleft lip and/or palate which occurs in 33-50% of patients [5,7].
• External ear abnormalities, which are present in over 85% of cases and can be assessed on 3D ultrasound [7].
• Middle ear abnormalities are present in 95% of cases [7]. Hypoplasia of the semi-circular canals may be detected with ultrasound between 20 and 25 weeks of gestation [8,10]. On fetal MRI the semi-circular canal can be evaluated on an axial T2 image in which the main anatomical landmarks include the lower part of the cerebellum in the axis of the cochlea. Due to the limited spatial resolution of fetal MRI, identifying a triangular shaped petrous bone is more straightforward, and this finding is associated with semicircular canal agenesis [12].
• Arhinencephaly is present in approximately 80% of cases and describes the congenital absence of the olfactory bulbs and olfactory tracts [7]. It can be detected on ultrasound after 30 weeks gestation [8]. On fetal brain MRI, a coronal T2 image allows for the best visualization of these structures [12].
• Posterior fossa abnormalities occur in approximately 70% of cases and include vermian hypoplasia, partial agenesis of the corpus callosum and ventriculomegaly [7]
• Congenital heart defects, present in 65-80%, most commonly include atrial septal defects, ventricular septal defects and Tetralogy of Fallot [5,7].
• Thymic hypoplasia occurs in over 40% of cases [7].
• Genital abnormalities occur in approximately 90% of males and 15% of females, most often genital hypoplasia including micropenis, hypoplastic testicles, and hypoplastic ovaries [7].
• Tracheo-oesophageal abnormalities occur in 20% of patients [5,7].

Additional features which are usually only detectable postnatally include:

• Ocular coloboma, which are present in approximately 70-80% of cases [5,7]. Large ocular coloboma can sometimes be seen on prenatal ultrasound [13,14] and MRI [12]. Often, ocular asymmetry leads to the suspicion of an ocular anomaly. Coloboma can be suspected on fetal MRI when asymmetry of the orbits and distortion of the papilla display a posterior focal bulging of the eyeball on an axial T2 image [12].
• Choanal atresia is present in approximately 40-50% of cases [5,7]. This can be suspected on prenatal ultrasound [15], and MRI [12]. In the early second-trimester, ultrasound findings may include a transient fluid collection within the obstructed nasal cavity [15]. In the late second and third trimester, the patency of the nasopharyngeal pathway can be shown by using Doppler Color ultrasound in either a coronal or longitudinal sagittal plane of the face during fetal breathing movements [16].
• Postnatal growth restriction
• Deafness
• Developmental delay
• Growth hormone deficiency
• Cranial nerve dysfunction
• Patent ductus arteriosus

According to 2016 diagnostic criteria established by Hale et al, diagnosis of CHARGE syndrome requires the presence of at least 2 major criteria, and any number of other criteria. Major criteria include coloboma, choanal atresia and/or facial cleft, abnormal external, middle, or inner ears, (including hypoplastic semicircular canals), and confirmation of a pathogenic CHD7 mutation on genetic testing [17]. As major criteria are not usually detectable antenatally, prenatal diagnosis is rare.

Legendre et al describe 40 fetuses with CHARGE syndrome and argue that clinical features leading to the diagnosis in fetuses and living affected patients are not the same [18]. Developmental delay, growth retardation and patent ductus arteriosus are only detected postnatally.  “Fetal CHARGE” is more likely to present with anomalies of the external ear, hypoplasia of the semi-circular canals, and arhinencephaly [8]. Arhinencephaly and semi-circular canal hypoplasia are highly suggestive of CHARGE syndrome and were present together in 80% of fetal cases [18]. In cases where CHARGE syndrome is suspected, subsequent fetal brain MRI can be pursued starting from the 28^th week of gestation to further delineate the anomalies and search for arhinencephaly. The molecular analysis of CHD7 can be used to confirm the diagnosis [7,8,9,10]. It may be postulated that a larger truncating mutation may account for the more severe phenotype which allows prenatal diagnosis.

Differential diagnosis includes 22q11.2 deletion syndrome, Kabuki Syndrome, VACTERL association, Smith-Lemli-Opitz Syndrome and Joubert Syndrome [11].

Neonates with CHARGE syndrome may have several life-limiting medical comorbidities, including congenital heart defects and brainstem dysfunction. In patients who survive beyond the first year of life, blindness and deafness is a major cause of disability [10]. Early diagnosis and coordination of multidisciplinary care is essential.

References

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