Dandy-Walker malformation and Wisconsin syndrome: novel cases add further insight into the genotype-phenotype correlations of 3q23q25 deletions

Nanopore long-read sequencing analysis reveals ZIC1 dysregulation caused by a de novo 3q inversion with a breakpoint located 7 kb downstream of ZIC1

Zic family member 1 (ZIC1), a gene located on chromosome 3q24, encodes a transcription factor with zinc finger domains that is essential for the normal development of the cerebellum. Heterozygous loss-of-function of ZIC1 causes Dandy-Walker malformation, while heterozygous gain-of-function leads to a multiple congenital anomaly syndrome characterized by craniosynostosis, brain abnormalities, facial features, and learning disability. In this study, we present the results of genetic analysis of a male patient with clinically suspected Gomez-Lopez-Hernandez syndrome. The patient displayed multiple congenital abnormalities, including bicoronal craniosynostosis, characteristic facial features, cerebellar malformation with rhombencephalosynapsis, and temporal alopecia, and a de novo inversion of chromosome 3q. Breakpoint analysis using a Nanopore long-read sequencer revealed a breakpoint in the distal centromere of 3q24 located 7 kb downstream of the 3' untranslated region of ZIC1. On the basis of the clinical similarities, we concluded that the abnormalities in this patient were caused by the transcriptional dysregulation of ZIC1. We hypothesize the underlying molecular mechanisms of transcriptional dysregulation of ZIC1 such as the abnormalities in topologically associated domains encompassing ZIC1. This study highlights the usefulness of long-read sequencing in the analysis of de novo balanced chromosomal abnormalities.

Dandy-Walker Syndrome: Delayed Acute Presentation With Unusual Symptoms

Dandy-Walker syndrome (DWS) is a rare congenital brain malformation defined by the presence of an expanded posterior fossa, full or partial absence of the cerebellar vermis, and a cystic expansion of the fourth ventricle. We report an 18-month-old girl with DWS presenting with atypical clinical manifestations and unusual symptoms. She initially presented with persistent vomiting and abdominal pain for four days, not responding to antiemetic medication. In addition, she was found to have abnormal postural arching of the back, extension of the lower limbs, and neck extension. MRI and CT head suggested Dandy-Walker syndrome with hydrocephalus (the lateral ventricle, third ventricle, and fourth ventricle are all significantly dilated with evidence of trans-ependymal cerebrospinal fluid permeation, severe compression anterior displacement of the brain stem). The patient underwent urgent, lifesaving right sub-occipital craniotomy, evacuation, and decompression of the posterior fossa cyst and external ventricular drain (EVD) insertion along with left supra-tentorial EVD insertion. A series of brain magnetic imaging and CT brain post-procedure studies showed a significant reduction in the size of the ventricular system and mass effect on the brain stem.

Wisconsin syndrome with brain volume laterality: a case report and review of the literature

Background

Wisconsin syndrome is a congenital anomaly caused by a 3q interstitial deletion. It is associated with characteristic facies and developmental delays. Only 33 cases with a deletion estimated to be in the associated region 3q25 have been reported.

Case report

We present the case of a 5-year-old Japanese girl with a 3q24q25.2 deletion. Her facial features corresponded to the Wisconsin syndrome phenotype, and she exhibited brain volume laterality, which has not been reported previously.

Conclusion

The clinical features of our case may contribute to narrowing down the list of candidate genes of Wisconsin syndrome.

A Rare Case of Dandy-Walker Syndrome

Dandy-Walker syndrome (DWS) is a rare congenital malformation characterized by hypoplasia of the cerebellar vermis and its upward rotation and cystic enlargement of the fourth ventricle. The clinical manifestations include psychomotor retardation, ataxia and hydrocephalus. We report a case of 16-year-old female patient in Ali Abad Teaching Hospital who was suffering from unsteady gait, memory deterioration and urinary incontinence. A brain magnetic resonance imaging revealed enlarged cystic posterior fossa, dilated fourth ventricles and upward rotated cerebellar vermis which were indicating DWS. The patient prepared for planned surgical operation and a written informed consent was obtained from her parents for surgery and general anesthesia. A cystoperitoneal (CP) shunt was placed and then the patient transferred to recovery room. After recovery and hospital stay, the patient discharged with improved clinical symptoms.

Chromosomal Microarray Analysis Has a Poor Diagnostic Yield in Children with Developmental Delay/Intellectual Disability When Concurrent Cerebellar Anomalies Are Present

Chromosomal microarray analysis is commonly used as screening test for children with neurodevelopmental issues, also in case of complex neurological phenotypes. Developmental delay/intellectual disability is a common presentation sign in pediatric ataxias, diseases with high clinical and genetic heterogeneity. In order to determine the diagnostic yield of Array-CGH in such conditions, all the tests performed in the last 10-year activity of a single referral center in children who present, besides the neurodevelopmental impairment, cerebellar abnormalities have been systematically gathered. The study demonstrates that, except for Dandy-Walker malformation or poly-malformative phenotypes, chromosomal microarray analysis should be discouraged as first-line diagnostic test in pediatric ataxias with neurodevelopmental disability.

Diagnostic Approach to Cerebellar Hypoplasia

Cerebellar hypoplasia (CH) refers to a cerebellum of reduced volume with preserved shape. CH is associated with a broad heterogeneity in neuroradiologic features, etiologies, clinical characteristics, and neurodevelopmental outcomes, challenging physicians evaluating children with CH. Traditionally, neuroimaging has been a key tool to categorize CH based on the pattern of cerebellar involvement (e.g., hypoplasia of cerebellar vermis only vs. hypoplasia of both the vermis and cerebellar hemispheres) and the presence of associated brainstem and cerebral anomalies. With the advances in genetic technologies of the recent decade, many novel CH genes have been identified, and consequently, a constant updating of the literature and revision of the classification of cerebellar malformations are needed. Here, we review the current literature on CH. We propose a systematic approach to recognize specific neuroimaging patterns associated with CH, based on whether the CH is isolated or associated with posterior cerebrospinal fluid anomalies, specific brainstem or cerebellar malformations, brainstem hypoplasia with or without cortical migration anomalies, or dysplasia. The CH radiologic pattern and clinical assessment will allow the clinician to guide his investigations and genetic testing, give a more precise diagnosis, screen for associated comorbidities, and improve prognostication of associated neurodevelopmental outcomes.

Deciphering the complexity of simple chromosomal insertions by genome sequencing

Chromosomal insertions are thought to be rare structural rearrangements. The current understanding of the underlying mechanisms of their origin is still limited. In this study, we sequenced 16 cases with apparent simple insertions previously identified by karyotyping and/or chromosomal microarray analysis. Using mate-pair genome sequencing (GS), we identified all 16 insertions and revised previously designated karyotypes in 75.0% (12/16) of the cases. Additional cryptic rearrangements were identified in 68.8% of the cases (11/16). The incidence of additional cryptic rearrangements in chromosomal insertions was significantly higher compared to balanced translocations and inversions reported in other studies by GS. We characterized and classified the cryptic insertion rearrangements into four groups, which were not mutually exclusive: (1) insertion segments were fragmented and their subsegments rearranged and clustered at the insertion site (10/16, 62.5%); (2) one or more cryptic subsegments were not inserted into the insertion site (5/16, 31.3%); (3) segments of the acceptor chromosome were scattered and rejoined with the insertion segments (2/16, 12.5%); and (4) copy number gains were identified in the flanking regions of the insertion site (2/16, 12.5%). In addition to the observation of these chromothripsis- or chromoanasynthesis-like events, breakpoint sequence analysis revealed microhomology to be the predominant feature. However, no significant correlation was found between the number of cryptic rearrangements and the size of the insertion. Overall, our study provide molecular characterization of karyotypically apparent simple insertions, demonstrate previously underappreciated complexities, and evidence that chromosomal insertions are likely formed by nonhomologous end joining and/or microhomology-mediated replication-based DNA repair.

[Dandy-Walker malformation. The CRIT protocol. A propos of a case]

Dandy-Walker malformation is characterised by hypoplasia of the cerebellar vermis and cystic dilation of the fourth ventricle. Some of the clinical manifestations of this malformation are hydrocephalus, delayed motor development, hypotonia, and ataxia. Treatment aims to improve the individual's overall functioning and enhance quality of life through a multidisciplinary team. This case report describes the outcome of a patient diagnosed with Dandy-Walker malformation, after the intervention of the medical model at Centro de Rehabilitación e Inclusión Infantil Teletón Guanajuato (CRIT), which focuses on rehabilitating the patient and the family, covering each of the areas encompassing the patient.

Biallelic mutations in EXOC3L2 cause a novel syndrome that affects the brain, kidney and blood

BACKGROUND

Dandy-Walker malformation features agenesis/hypoplasia of the cerebellar vermis, cystic dilatation of the fourth ventricle and enlargement of posterior fossa. Although Dandy-Walker malformation is relatively common and several genes were linked to the syndrome, the genetic cause in the majority of cases is unknown.

OBJECTIVE

To identify the mutated gene responsible for Dandy-Walker malformation, kidney disease and bone marrow failure in four patients from two unrelated families.

METHODS

Medical assessment, sonographic, MRI and pathological studies were used to define phenotype. Chromosomal microarray analysis and whole-exome sequence were performed to unravel the genotype.

RESULTS

We report four subjects from two unrelated families with homozygous mutations in the Exocyst Complex Component 3-Like-2 gene (EXOC3L2).EXOC3L2 functions in trafficking of post-Golgi vesicles to the plasma membrane. In the first family a missense mutation in a highly conserved amino acid, p.Leu41Gln, was found in three fetuses; all had severe forms of Dandy-Walker malformation that was detectable by prenatal ultrasonography and confirmed by autopsy. In the second family, the affected child carried a nonsense mutation, p.Arg72*, and no detected protein. He had peritrigonal and cerebellar white matter abnormalities with enlargement of the ventricular trigones, developmental delay, pituitary hypoplasia, severe renal dysplasia and bone marrow failure.

CONCLUSION

We propose that biallelic EXOC3L2 mutations lead to a novel syndrome that affects hindbrain development, kidney and possibly the bone marrow.

ZIC1 Function in Normal Cerebellar Development and Human Developmental Pathology

Zic genes are strongly expressed in the cerebellum. This feature leads to their initial identification and their name "zic," as the abbreviation of "zinc finger protein of the cerebellum." Zic gene function in cerebellar development has been investigated mainly in mice. However, association of heterozygous loss of ZIC1 and ZIC4 with Dandy-Walker malformation, a structural birth defect of the human cerebellum, highlights the clinical relevance of these studies. Two proposed mechanisms for Zic-mediated cerebellar developmental control have been documented: regulation of neuronal progenitor proliferation-differentiation and the patterning of the cerebellar primordium. Clinical studies have also revealed that ZIC1 gain of function mutations contribute to coronal craniosynostosis, a rare skull malformation. The molecular pathways contributing to these phenotypes are not fully explored; however, embryonic interactions with sonic hedgehog signaling, retinoic acid signaling, and TGFβ signaling have been described during mouse cerebellar development. Further, Zic1/2 target a multitude of genes associated with cerebellar granule cell maturation during postnatal mouse cerebellar development.

Genetics of cerebellar disorders

The approach to identifying a genetic cause in patients with cerebellar disorders relies on history, examination, consultation, and testing, combined with specialized expertise because they are rare and genetically diverse. Cerebellar disorders can be caused by a variety of DNA alterations including single-nucleotide changes, small insertions or deletions, larger copy number variants, and nucleotide repeat expansions, exhibiting autosomal-recessive, autosomal-dominant (inherited and de novo), X-linked, and mitochondrial modes of inheritance. Imaging findings and a variety of neurologic and nonneurologic clinical features can help direct genetic testing and choose the most appropriate strategy. Clinical and genetic diagnoses are complementary, each providing distinct information for the care of the patient. In this chapter, we provide an overview of inheritance modes for different cerebellar disorders and the variety of genetic testing and tools that are currently available to reach a genetic diagnosis, including conventional and next-generation sequencing, classic, molecular and virtual cytogenetics, testing for repeat expansions, and other techniques. Practical examples are presented in both the text and accompanying vignettes.

A 6.5 mb deletion at 3q24q25.2 narrows Wisconsin syndrome critical region to a 750 kb interval: A potential role for MBNLI

We report on a patient with a 6.5 Mb interstitial de novo deletion in 3q24q25.2, characterized by array CGH. The patient is a 4-year and 2-month-old girl, who presented to us with mild developmental delay, absence of language, facial dysmorphism, hirsutism, strabismus, and Dandy-Walker Malformation. The main clinical signs typical of WS (Wisconsin syndrome) are evident in the patient. The molecular mapping of WS in 3q23q25 allowed geneticists to define the syndrome more accurately. Comparing the present patient's phenotype with that of cases with a molecular characterization so far reported, it was possible to narrow the critical region for WS to an interval of 750 Kb, where two genes (MBNL1 and TMEM14E) are harbored. The potential role of MBNL1 in causing the WS phenotype is discussed. © 2016 Wiley Periodicals, Inc.

De Novo 3q22.3q24 Microdeletion in a Patient With Blepharophimosis-Ptosis-Epicanthus Inversus Syndrome, Dandy-Walker Malformation, and Wisconsin Syndrome

Interstitial deletions affecting the long arm of chromosome 3 have been associated with a broad phenotype. This has included the features of blepharophimosis–ptosis–epicanthus inversus syndrome, Dandy-Walker malformation, and the rare Wisconsin syndrome. The authors report a young female patient presenting with features consistent with all 3 of these syndromes. This has occurred in the context of a de novo 3q22.3q24 microdeletion including FOXL2, ZIC1, and ZIC4. This patient provides further evidence for the role of ZIC1 and ZIC4 in Dandy-Walker malformation and is the third reported case of Dandy-Walker malformation to have associated corpus callosum thinning. This patient is also only the seventh to be reported with the rare Wisconsin syndrome phenotype.

Gain-of-Function Mutations in ZIC1 Are Associated with Coronal Craniosynostosis and Learning Disability

Human ZIC1 (zinc finger protein of cerebellum 1), one of five homologs of the Drosophila pair-rule gene odd-paired, encodes a transcription factor previously implicated in vertebrate brain development. Heterozygous deletions of ZIC1 and its nearby paralog ZIC4 on chromosome 3q25.1 are associated with Dandy-Walker malformation of the cerebellum, and loss of the orthologous Zic1 gene in the mouse causes cerebellar hypoplasia and vertebral defects. We describe individuals from five families with heterozygous mutations located in the final (third) exon of ZIC1 (encoding four nonsense and one missense change) who have a distinct phenotype in which severe craniosynostosis, specifically involving the coronal sutures, and variable learning disability are the most characteristic features. The location of the nonsense mutations predicts escape of mutant ZIC1 transcripts from nonsense-mediated decay, which was confirmed in a cell line from an affected individual. Both nonsense and missense mutations are associated with altered and/or enhanced expression of a target gene, engrailed-2, in a Xenopus embryo assay. Analysis of mouse embryos revealed a localized domain of Zic1 expression at embryonic days 11.5-12.5 in a region overlapping the supraorbital regulatory center, which patterns the coronal suture. We conclude that the human mutations uncover a previously unsuspected role for Zic1 in early cranial suture development, potentially by regulating engrailed 1, which was previously shown to be critical for positioning of the murine coronal suture. The diagnosis of a ZIC1 mutation has significant implications for prognosis and we recommend genetic testing when common causes of coronal synostosis have been excluded.

Inferior cerebellar hypoplasia resembling a Dandy-Walker-like malformation in purebred Eurasier dogs with familial non-progressive ataxia: a retrospective and prospective clinical cohort study

Cerebellar malformations can be inherited or caused by insults during cerebellar development. To date, only sporadic cases of cerebellar malformations have been reported in dogs, and the genetic background has remained obscure. Therefore, this study`s objective was to describe the clinical characteristics, imaging features and pedigree data of a familial cerebellar hypoplasia in purebred Eurasier dogs. A uniform cerebellar malformation characterized by consistent absence of the caudal portions of the cerebellar vermis and, to a lesser degree, the caudal portions of the cerebellar hemispheres in association with large retrocerebellar fluid accumulations was recognized in 14 closely related Eurasier dogs. Hydrocephalus was an additional feature in some dogs. All dogs displayed non-progressive ataxia, which had already been noted when the dogs were 5 – 6 weeks old. The severity of the ataxia varied between dogs, from mild truncal sway, subtle dysmetric gait, dysequilibrium and pelvic limb ataxia to severe cerebellar ataxia in puppies and episodic falling or rolling. Follow-up examinations in adult dogs showed improvement of the cerebellar ataxia and a still absent menace response. Epileptic seizures occurred in some dogs. The association of partial vermis agenesis with an enlarged fourth ventricle and an enlarged caudal (posterior) fossa resembled a Dandy-Walker-like malformation in some dogs. Pedigree analyses were consistent with autosomal recessive inheritance.

Moebius syndrome with Dandy-Walker variant and agenesis of corpus callosum

Moebius syndrome is a rare congenital neurological disorder. The most frequent mode of presentation is facial diplegia with bilateral lateral rectus palsy, but there are variations. Here, we report a rare case of Moebius syndrome in a 15-month-old child with unilateral facial palsy, bilateral abducens nerve palsy with Dandy Walker variant, and complete agenesis of corpus callosum.