Case of the Week #572

Korkut Daglar (1), Cem Sanhal (2)
1) Mersin Private Clinic, 2) Akdeniz University Perinatology Department

Posting Dates: Nov 30, 2022 - Dec 14, 2022

30-year-old primigravida presented without significant medical or family history. The pregnancy was not a result of consanguineous marriage and prenatal screening for Down syndrome was normal. Third trimester ultrasound at 29 weeks gestation showed polyhydramnios and the following findings:

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Video 1 © 2022 Daglar and Sanhal
Video 2 © 2022 Daglar and Sanhal
Video 3 © 2022 Daglar and Sanhal
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Image 5

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Answer

We present a case of Treacher Collins syndrome (OMIM #154500). Our ultrasound at 29 weeks gestation showed the following findings concerning for Treacher Collins syndrome:

Image 1: Abnormal fetal profile, small mandible, retrognathia.
Video 1: Abnormal fetal profile and malformed maxilla indicating the possibility of cleft palate.
Video 2: Abnormal ears with deficient malpositioned auricles.
Video 3: Zygomatic arch deficiency with malar hypoplasia.
Image 2: No cleft lip.
Image 3: Relatively prominent nose.
Image 4: Normal corpus callosum
Image 5: 3D view of malar hypoplasia with zygomatic arch deficiency.

The patient refused amniocentesis and pregnancy termination. A neonate was delivered at 38 weeks gestation. Genetic testing confirmed Treacher Collins syndrome. Despite respiratory support with tracheostomy, the baby died at 30 days due to respiratory complications.

Typical features of Treacher Collins Syndrome including downslanting palpebral fissures, zygomatic arch and malar hypoplasia, malformed pinnas, small mandible and relative macrostomia.
Image 1 Typical features of Treacher Collins Syndrome including downslanting palpebral fissures, zygomatic arch and malar hypoplasia, malformed pinnas, small mandible and relative macrostomia. © 2022 Daglar and Sanhal
Typical features of Treacher Collins Syndrome including downslanting palpebral fissures, zygomatic arch and malar hypoplasia, malformed pinnas, small mandible and relative macrostomia.
Image 2 Typical features of Treacher Collins Syndrome including downslanting palpebral fissures, zygomatic arch and malar hypoplasia, malformed pinnas, small mandible and relative macrostomia. © 2022 Daglar and Sanhal
Midline cleft of the hard and soft palate with intact premaxilla.
Image 3 Midline cleft of the hard and soft palate with intact premaxilla. © 2022 Daglar and Sanhal

Discussion

Treacher Collins syndrome (TCS), an example of mandibulofacial dysostosis, is a rare genetic disorder of facial dysmorphism that affects structures of the first and second pharyngeal arches. Patients have normal intelligence, but often face social challenges throughout life because of their physical appearance [1].

The clinical characteristics of Treacher Collins syndrome are well described and distinctive, but have variable expression. They include zygomatic arch hypoplasia resulting in malar hypoplasia with or without cleft palate, down-slanting palpebral fissures, coloboma of the outer third of the lower lids, mandible hypoplasia, and an abnormal shape, size, and position of ears.

Although Treacher Collins syndrome is an autosomal dominant disorder, new cases may be the result of spontaneous mutations. A loss of function mutation in the TCOF1 gene on chromosome 5 is the cause of characteristic features. Several exons within this gene have been identified, and there are distinctive patterns resulting in multiple variants of the mutant gene. More than 120 mutations have been identified but no clear relationship between genotype and phenotype has been demonstrated [2].

Facial features of Treacher Collins syndrome can be detected via ultrasound. Polyhydramnios and abnormal ear shape should raise suspicion, and dedicated 2D sonography with 3D planes may be used to search for typical features including down-slanting palpebral fissures, micrognathia, cleft palate and low-set ears/microtia. It should be kept in mind that facial features are highly variable and subtle cases may not be detected in the antenatal period.

Differential diagnoses include Pierre Robin Sequence, Goldenhar syndrome, and Acrofacial dysostoses (Nager, etc.). The findings in Pierre Robin sequence are severe micrognathia with or without cleft palate. Ears may be low lying but they are rarely deficient, and other facial features are typically normal.  In Goldenhar syndrome, there is usually asymmetric facial involvement with only one abnormal ear, together with cardiac, vertebral and brain abnormalities. In Nager syndrome, there is severe micrognathia, malar hypoplasia and a spectrum of radial ray malformations [3].

References

1.      Chang CC, Steinbache DM. Treacher Collins Syndrome. Semin Plast Surg 2012 May;26(2):83-90.
2.      Dixon MJ. Treacher Collins syndrome. J Med Genet 1995 Oct;32(10):806-8.
3.      Woodward, Paula. "Chapter 284: Treacher Collins Syndrome." Diagnostic Imaging: Obstetrics, 4th Edition. Elsevier, 2021. ISBN: 978-0-323-79396-4

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