Agenesis of Corpus Callosum, Malformations of Cortical Development, Duodenal Atresia and Fetal Growth Restriction: Prenatal Markers for Zhu‐Tokita‐Takenouchi‐Kim Syndrome

What's already known about this topic? ZTTK syndrome is associated with poor neurodevelopmental outcomes. Postnatally, ZTTK syndrome is associated with brain abnormalities, including hypoplasia of the corpus callosum. What does this study add? To our knowledge, this is the first case describing the prenatal findings associated with ZTTK syndrome. Our case highlights the importance of TRIO-Whole Exome Sequencing in the context of dysgenesis of the corpus callosum. A 27-year-old Gravida 3 Para 2 was referred at 24 weeks (w) 2 days (d) for suspected agenesis of corpus callosum. Family history showed no consanguinity, developmental delay/intellectual disability, congenital anomalies, inherited conditions, or recurrent pregnancy losses (Table 1A). Anatomy ultrasound and neurosonogram revealed a small gestational age fetus with an estimated fetal weight at the 9th percentile with normal Doppler and amniotic fluid. There was near complete agenesis of the corpus callosum with only a small anterior remnant visualized (Figure 1a) and delay in the right Sylvian sulcation with irregularity along the right perisylvian region (Figure 1b). Fetal MRI performed at 25 weeks 2d confirmed these findings (Figure 1c). At 31 weeks 2d, the fetus was on the 2nd percentile and there was a new finding of a double bubble sign suggestive of duodenal atresia. Brain findings were again noted with better visualization of the cortical abnormality and mild cerebellar hypoplasia (transcerebellar diameter on the 5th percentile [1] for gestational age) (Figure 1d). Transvaginal ultrasound images at 24 + 2 weeks. (a) Near complete absence of the corpus callosum with only a small anterior remnant in a midsagittal plane (white arrow). (b) Irregular appearance of the right perisylvian area (white arrow) and serrated appearance of the left perisylvian cortical mantle (white triangle). MRI Axial T2 sequences at 25 + 2 weeks (c) and 32 + 2 weeks (d) confirmed the absence of the corpus callosum and the altered gyral pattern in the right cerebral hemisphere and perisylvian region (arrow). Amniocentesis revealed a male fetus with normal quantitative fluorescent polymerase chain reaction (QF-PCR) for chromosomes, 13, 18, 21, X, Y and a normal male microarray. At 31w2d, TRIO-WES was initiated due to additional imaging findings (Table 1B). ACMG criteria: PVS1: Frameshift variant predicted to result in protein truncation or nonsense mediated decay in a gene for which loss of function is a known mechanism of disease PS2: De novo variant with confirmed parentage in a proband with features consistent with the disease PM2: Not observed at a significant frequency in large population cohorts De novo Autosomal dominant Heterozygous TRIO-WES was performed on the proband's DNA using a proprietary capture system developed by GeneDx for next-generation sequencing with CNV calling (NGS-CNV). The enriched targets were simultaneously sequenced with paired-end reads on the Illumina platform. Bi-directional sequence reads were assembled and aligned to reference sequences based on NCBI RefSeq transcripts and human genome build GRCh37/UCSC hg19. Using a custom-developed analysis tool (XomeAnalyzer), data were filtered and analyzed to identify sequence variants and most deletions and duplications involving three or more coding exons [2]. A de novo heterozygous frameshift variant in exon 3 of the SON gene (NM_032195.2): c.2787del p.(R929Sfs*9) was identified, which was predicted to result in protein truncation or nonsense-mediated decay in a gene for which loss of function is a known mechanism of disease. This variant was not observed at a significant frequency in large population cohorts (gnomAD). The variant was classified as pathogenic (Table 1B). At 35w2d, the fetus measured below the 1st percentile with oligohydramnios and a biophysical profile (BPP) of 2/8. The patient declined active management for the abnormal BPP and opted for termination of pregnancy and declining autopsy (Table 1A). ZTTK syndrome has only recently been described with 60 postnatal cases in the literature, none of which followed prenatal detection [3]. Nearly all individuals with a loss-of-function variant had intellectual disability, with the majority being on the moderate to severe spectrum (79%) [4]. In a cohort of 15 individuals with the de novo loss-of-function variant, the majority had motor and speech delays, and even the individuals that reached milestones appropriately eventually experienced regression [5]. The majority of affected individuals presented with seizures and hypotonia. Postnatal brain imaging performed in 41 cases described ventriculomegaly (24/41, 59%), cortical dysplasia (7/41, 17%), hypoplasia of the corpus callosum (7/41, 17%), and abnormalities in the cerebral white matter (6/41, 15%) and the cerebellum (6/41, 15%) [3]. These abnormalities can be diagnosed prenatally with a detailed neurosonogram and complemented with fetal brain MRIs. Additionally, low birthweight, genitourinary, cardiac, and gastrointestinal abnormalities have been described postnatally [6]. All these conditions can be detected prenatally. In our case, fetal growth restriction (FGR) was detected early on with the additional finding of duodenal atresia only detected later. Our case suggests that when faced with the constellation of findings of early-onset FGR, brain abnormalities, especially dysgenesis of the corpus callosum and malformations of cortical development and gastrointestinal abnormalities, ZTTK syndrome should be considered and TRIO-WES is therefore indicated. To our knowledge, this is the first case describing the findings of ZTTK syndrome diagnosed prenatally. We would like to acknowledge and thank the clinical staff at the Ontario Fetal Center for the care of this patient. This study was conducted ethically in accordance with the World Medical Association Declaration of Helsinki. The patient has given their written informed consent. This case report was reviewed and approved by the Mount Sinai Hospital Research Ethics Board. The authors declare no conflicts of interest. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.