Background
Dandy-Walker malformation (DWM, MIM%220200) represents one of the commonest (1:30,000 live births) congenital defects of cerebellar development, and a frequent cause of termination of fetuses diagnosed prenatally [
1]. The key anatomical elements include hypoplasia and upward rotation of the cerebellar vermis associated to cystic dilatation of the fourth ventricle. This usually communicates with a retrocerebellar cyst, causing enlargement of the posterior fossa (PF) and elevation of the tentorium [
2]. The severity of this malformation is highly variable, and conditions characterized by less hypoplasia, mild or absent vermis rotation, and mild cystic dilatation of the PF are part of the DWM spectrum. Hydrocephalus is found in 70-90% of patients, and in several cases DWM is part of a syndromic condition variably associated with heart, face and ocular abnormalities. Clinical presentation includes apnea episodes, hypotonia, seizures, cerebellar signs such as ataxia and nystagmus, spasticity, as well as macrocephaly and other features suggestive of hydrocephalus. Moderate to severe intellectual disability is common, although rare cases have been reported with normal intelligence, who were incidentally diagnosed in adult age [
3,
4].
DWM is usually a sporadic disorder and its genetic background remains poorly understood. Several cytogenetic abnormalities have been detected in syndromic cases, with involvement of large genomic regions that justify the multiorgan involvement [
5]. In 2004, overlapping deletions including 3q24q25.1 chromosome region were reported in eight DWM patients displaying marked clinical and neuroradiological variability. Haploinsufficiency of
ZIC1 and
ZIC4 genes, mapping within the deleted region, has been implicated as causative of DWM, based on mouse models. Seven patients shared a 7 Mb critical region including both genes. In another patient, in which the deletion did not contain
ZIC1 and
ZIC4, the expression level of both genes was found to be halved, suggesting a position effect [
6]. Following this report, at least six additional cases with features of the DWM spectrum have been published, who carried a 3q chromosomal deletion encompassing the
ZIC1 and
ZIC4 genes [
7‐
12].
Here we report on three novel patients with an interstitial deletion of 3q including both ZIC1 and ZIC4, only two of which presented with DWM.
Discussion
The genetic basis of DWM is complex and the involved genes are still largely unknown. The identification of seven DWM patients with overlapping deletions at 3q first implicated the
ZIC1 and
ZIC4 genes as causative of the malformation [
6]. These genes encode for zinc finger transcription factors homologs of Drosophila melanogaster odd-paired genes, and are widely expressed in the dorsal central nervous system, including the developing cerebellum and spinal cord. Doubled
Zic1+/− Zic4+/− heterozygous mice display a mild to severe cerebellar phenotype, with foliar defects and disproportionate hypoplasia of the vermis compared to the hemispheres, mimicking the cerebellar morphology of human DWM [
6]. A recent study demonstrated that
Zic1 and
Zic4 have both a Shh-dependent and independent function, promoting proliferation of granule cell progenitors and regulating expression of genes involved in cerebellar anlage patterning and vermis foliation [
15].
Here we report two novel patients (CCM067 and CCM095) with a severe DWM phenotype and large deletions encompassing both
ZIC1 and
ZIC4 genes. Furthermore, six additional DWM patients with 3q deletions have been published since the original report [
7‐
12], defining a critical region clearly implicated in DWM pathogenesis (DWM-CR in Figure
3). In a patient (LR01-325) [
6], whose deletion did not encompass
ZIC1-ZIC4, their expression levels were significantly reduced compared to controls, implying a position effect, possibly exerted by distally located regulatory elements.
On the other hand, some evidence suggests that
ZIC1 and
ZIC4 haploinsufficiency is neither necessary nor sufficient
per se to cause DWM. In fact, we failed to identify deletions of these genes in 11 patients with a diagnosis of isolated or syndromic DWM. Furthermore, we report here on a patient (CCM001), heterozygous for a small 3q24 deletion encompassing both
ZIC1-
ZIC4 genes, who did not display any of the neuroradiological features defining the DWM spectrum. By reviewing the clinical data of well characterized individuals with deletions encompassing the
ZIC1 and
ZIC4 genes, we found three additional patients lacking any cerebellar or posterior fossa anomalies at ultrasound or CT scan [
16‐
18]. Noticeably, the telomeric boundaries of 3q deletions map well beyond the DWM-CR in several DWM patients, suggesting that another locus, distal to
ZIC1 and
ZIC4, could contribute with a possible additive effect to DWM pathogenesis.
Patient CCM001 also showed a
de novo deletion at 11p11.2 of about 3 Mb. The deletion partially overlaps to the critical region of PSS, characterized by developmental delay and intellectual disability, hypotonia, craniofacial and ophthalmologic anomalies, multiple exostoses and parietal foramina [
19]. In our patient, the lack of exostoses and parietal foramina is in agreement with the presence of two copies of the causative genes
EXT2 and
ALX4. Conversely, the deletion includes the
PHF21A gene, which has been recently implicated as contributing to the intellectual disability and craniofacial anomalies typical of PSS, such as brachycephaly, midfacial and mandibular hypoplasia [
20].
Facial dysmorphisms in our patient CCM067 are characteristic of BPES, consistent with her 3q deletion encompassing
FOXL2, the BPES causative gene [
21]. However, this patient also had additional distinctive features, including upslanting palpebral fissures, high arched bushy eyebrows, coarse facies, prominent nose, large mouth, full lower lip, and a peculiar short IV metatarsus. Intriguingly, patient CCM095 also had a similar phenotype. Taken together, these features were highly reminiscent of Wisconsin syndrome (WS), a condition first described in 2000 by Cohen based on a patient seen in 1976 by Opitz [
22], and then confirmed in another patient carrying a 3q deletion [
23].
Three subjects with 3q deletions and the WS phenotype, including the patient described by Ko et al. [
23], have been recently re-evaluated by microarray analysis, mapping the critical region to chromosome 3q24q25 [
24]. Indeed, our patients CCM067 and CCM095 corroborated a relationship between WS and interstitial 3q deletions, prompting us to perform a detailed assessment of the available photographs and clinical features of published cases with deletions encompassing 3q24 and/or 3q25 (Additional file
1: Table S1). Based on this analysis, we propose the diagnosis of WS to be made based on the occurrence of at least four out of five core gestaltic features (coarse facies; prominent or wide triangular shaped nasal tip; high arched or upsweeping eyebrows; full/everted lower lip; bushy eyebrows often with synophrys). Accordingly, we diagnosed 12 patients with WS [
6,
9,
22,
23,
25‐
29] and compared them with 15 patients who did not match the proposed criteria [
7,
8,
12,
16‐
18,
30‐
37] (Table
1 and Additional file
1: Table S1). Among this second group, the occurrence of each gestaltic feature was much rarer than in the WS group. Moreover, we identified additional features frequently observed in WS patients. Some of these, such as intellectual disability, smooth philtrum and ear anomalies, were found at similar frequencies also in non-WS patients, while others appeared to be more specific of the WS phenotype. In particular, digital anomalies were described in ten out of 12 WS patients, of whom four presented a peculiar brachydactyly of the 4th toe (see Figure
1). Conversely, some features reported in the original WS patients, such as craniosynostosis [
22] or hypogonadism [
23,
24], do not appear to be common features in WS.
Table 1
Comparison of selected clinical features in WS vs non-WS patients with 3q deletions
Core gestaltic features
|
Coarse facies | 12 (100%) | 0 |
Prominent or wide triangular shaped nasal tip | 12 (100%) | 3 (20%) |
High arched or upsweeping eyebrows | 11 (92%) | 0 |
Full/everted lower lip | 11 (92%) | 5 (33%) |
Bushy eyebrows | 10 (83%) | 3 (20%) |
Other recurrent clinical features
|
Developmental delay/intellectual disability | 12 (100%) | 15 (100%) |
Digital anomalies: | 10 (83%) | 6 (40%) |
-of which short IV metatarsus | 4 (33%) | 0 |
Ear anomalies | 9 (75%) | 13 (87%) |
Macrostomia | 8 (67%) | 1 (7%) |
Smooth/simplified philtrum | 7 (58%) | 7 (47%) |
A molecular characterization of the deletions’ breakpoints was available for eight of the 12 WS patients [
6,
9,
24,
25], allowing to define a critical region of 7 Mb in 3q25 (WS-CR, Figure
3). This region contains 43 RefSeq genes, none of which appears as a strong candidate for WS.
Acknowledgements
This work was supported by grants from the Italian Ministry of Health (Ricerca Corrente 2013), the European Research Council (ERC Starting Grant 260888), the Pierfranco and Luisa Mariani Foundation. We thank Dr Andrea Rossi (G. Gaslini Hospital, Genoa) and Dr Lorenzo Pinelli (Spitali Riuniti, Brescia), for their valuable help in assessing patients’ neuroimaging, and Drs. Lekovska Olivera, Natalija Angelkova and Tatjana Zorcec (St Cirilus and Methodius University, Skopje) for their collaboration in recruiting patients. We are also very grateful to Dr. Iosif Lurie for help with literature review of 3q deleted patients.
Other members of the CBCD Study Group are: F. Arrigoni, R. Borgatti, R. Romaniello (Bosisio Parini); P. Accorsi, E. Fazzi, L. Giordano, L. Pinelli (Brescia); R. Biancheri, M. Mirabelli, A. Rossi (Genoa); M. Briguglio, G. Tortorella (Messina); L. Chiapparini, S. D’Arrigo, I. Moroni, C. Pantaleoni, L. Spaccini, G. Uziel (Milan); A. D’Amico, E. Del Giudice (Napoli); A. Pichiecchio, S. Signorini (Pavia); R. Battini, M. Casarani (Pisa); S. Colafati, M.C. Digilio, V. Leuzzi, A. Micalizzi, M. Romani, A. Spalice, L. Travaglini, G. Vitiello (Rome); M. Silengo (Turin); A. Simonati (Verona).
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
Patients’ recruitment and analysis of clinical and imaging data: AF, LB, FM, EMV; SNP-array studies: LB, SL, VP, AC, AN, SB; patients referral and clinical data collection: VS-A, GZ, ES-A, ST, LT, FD, EM, LT, EB, BD; literature review and dysmorphological evaluation: AF, BD; study conception and design, manuscript drafting: AF, LB, EMV. All authors read and approved the final manuscript.