A child with deletion (14)(q24.3q32.13) and auditory neuropathy

Chromosome 14 deletions, rings, and epilepsy genes: A riddle wrapped in a mystery inside an enigma

The ring 14 syndrome is a rare condition caused by the rearrangement of one chromosome 14 into a ring-like structure. The formation of the ring requires two breakpoints and loss of material from the short and long arms of the chromosome. Like many other chromosome syndromes, it is characterized by multiple congenital anomalies and developmental delays. Typical of the condition are retinal anomalies and drug-resistant epilepsy. These latter manifestations are not found in individuals who are carriers of comparable 14q deletions without formation of a ring (linear deletions). To find an explanation for this apparent discrepancy and gain insight into the mechanisms leading to seizures, we reviewed and compared literature cases of both ring and linear deletion syndrome with respect to both their clinical manifestations and the role and function of potentially epileptogenic genes. Knowledge of the epilepsy-related genes in chromosome 14 is an important premise for the search of new and effective drugs to combat seizures. Current clinical and molecular evidence is not sufficient to explain the known discrepancies between ring and linear deletions.

A rare exonic NRXN3 deletion segregating with neurodevelopmental and neuropsychiatric conditions in a three-generation Chinese family

Members of the neurexin gene family, neurexin 1 (NRXN1), neurexin 2 (NRXN2), and neurexin 3 (NRXN3) encode important components of synaptic function implicated in autism and other neurodevelopmental/neuropsychiatric disorders. Loss of function variants have been reported predominantly in NRXN1, with fewer such variants detected in NRXN2 and NRXN3. Evidence for segregating NRNX3 variants has particularly been lacking. Here, we report identification by chromosomal microarray analysis of a rare exonic deletion affecting the NRXN3 alpha isoform in a three-generation Chinese family. The proband, a 7-year-old boy, presented with motor and language delay and met the clinical diagnostic criteria for autism. He also presented with moderate intellectual disability, attention-deficit hyperactivity disorder and facial dysmorphic features. The mother and maternal grandfather, both deletion carriers, presented with variable degrees of language and communication difficulties, as well as neuropsychiatric problems such as schizophrenia and temper tantrums. A compilation of sporadic cases with deletions involving part or all of NRXN3 revealed that 9 of 23 individuals (39%) displayed features of autism. The evidence for cosegregation in our family further supports a role for NRXN3 in autism and neurodevelopmental/neuropsychiatric disorders but demonstrates intrafamily variable expressivity due to this NRXN3 deletion, with schizophrenia and facial dysmorphism being potential novel features of NRXN3 haploinsufficiency.

"Minimal" holoprosencephaly in a 14q deletion syndrome patient

We report on a patient with terminal deletion of the long arm of chromosome 14 displaying brain interhemispheric fusion limited to the midline anterior frontal cortex associated with hypoplastic corpus callosum and incomplete rotation of the left hippocampus in a clinical setting of motor and intellectual disability with poor language, and social behavior abnormalities with aggressiveness. Some possible correlations between clinical signs and symptoms and various aspects of the complex brain malformation are briefly discussed and compared with other known abnormalities of chromosome 14. The different neuropathology of the most common forms and the new forms of holoprosencephaly recently described is also discussed and leads us to suggest classifying the interhemispheric fusion of this case as a "minimal" form of holoprosencephaly. This appears to be the first description in a 14q deletion patient.

Spemann organizer gene Goosecoid promotes delamination of neuroblasts from the otic vesicle

Neurons of the Statoacoustic Ganglion (SAG), which innervate the inner ear, originate as neuroblasts in the floor of the otic vesicle and subsequently delaminate and migrate toward the hindbrain before completing differentiation. In all vertebrates, locally expressed Fgf initiates SAG development by inducing expression of Neurogenin1 (Ngn1) in the floor of the otic vesicle. However, not all Ngn1-positive cells undergo delamination, nor has the mechanism controlling SAG delamination been elucidated. Here we report that Goosecoid (Gsc), best known for regulating cellular dynamics in the Spemann organizer, regulates delamination of neuroblasts in the otic vesicle. In zebrafish, Fgf coregulates expression of Gsc and Ngn1 in partially overlapping domains, with delamination occurring primarily in the zone of overlap. Loss of Gsc severely inhibits delamination, whereas overexpression of Gsc greatly increases delamination. Comisexpression of Ngn1 and Gsc induces ectopic delamination of some cells from the medial wall of the otic vesicle but with a low incidence, suggesting the action of a local inhibitor. The medial marker Pax2a is required to restrict the domain of gsc expression, and misexpression of Pax2a is sufficient to block delamination and fully suppress the effects of Gsc The opposing activities of Gsc and Pax2a correlate with repression or up-regulation, respectively, of E-cadherin (cdh1). These data resolve a genetic mechanism controlling delamination of otic neuroblasts. The data also elucidate a developmental role for Gsc consistent with a general function in promoting epithelial-to-mesenchymal transition (EMT).

Neurological features of 14q24-q32 interstitial deletion: report of a new case

Background

Interstitial deletions of the long arm of chromosome 14 involving the 14q24-q32 region have been reported in less than 20 patients. Previous studies mainly attempted to delineate recognizable facial dysmorphisms; conversely, descriptions on neurological features are limited to the presence of cognitive and motor delay, but no better characterization exists.

Case presentation

In this paper we report on a patient with a de novo interstitial deletion of 5.5 Mb at 14q24.3-q31.1. The deletion encompasses 84 genes, including fourteen Mendelian genes. He presented with dysmorphic face, developmental delay, paroxysmal non-epileptic events and, subsequently, epilepsy.

Conclusions

The clinical and molecular evaluation of this patient and the review of the literature expand the phenotype of 14q23-q32 deletion syndrome to include paroxysmal non-epileptic events and infantile-onset focal seizures.

Interstitial 14q24.3 to q31.3 deletion in a 6-year-old boy with a non-specific dysmorphic phenotype

BACKGROUND

Few patients with interstitial deletions in the distal long arm of chromosome 14 have been reported, and these patients showed rather indistinct features, including growth and mental retardation and phenotypic alterations.

RESULTS

We describe a de novo 14q interstitial deletion in a 6-year-old boy with dysmorphic facial traits such as hypertelorism, short and narrow palpebral fissures, broad nose with anteverted nostrils, long philtrum, thin upper lip with cupid's bow, prominent and everted lower lip, mildly low-set ears, as well as moderate developmental delay and mild mental retardation. Array-CGH mapped the deletion to the region 14q24.3 to 14q31.3, including 13.11 Mb, proximal to the imprinted genomic region of 14q32.

CONCLUSION

This mild phenotypic presentation suggests that the deleted segment does not contain essential genes for early organ development. Twenty-two genes with known functions, including Neurexin III (NRXN3, OMIM 600567), map to the region deleted in the propositus.

Cranial muscles in amphibians: development, novelties and the role of cranial neural crest cells

Our research on the evolution of the vertebrate head focuses on understanding the developmental origins of morphological novelties. Using a broad comparative approach in amphibians, and comparisons with the well-studied quail-chicken system, we investigate how evolutionarily conserved or variable different aspects of head development are. Here we review research on the often overlooked development of cranial muscles, and on its dependence on cranial cartilage development. In general, cranial muscle cell migration and the spatiotemporal pattern of cranial muscle formation appears to be very conserved among the few species of vertebrates that have been studied. However, fate-mapping of somites in the Mexican axolotl revealed differences in the specific formation of hypobranchial muscles (tongue muscles) in comparison to the chicken. The proper development of cranial muscles has been shown to be strongly dependent on the mostly neural crest-derived cartilage elements in the larval head of amphibians. For example, a morpholino-based knock-down of the transcription factor FoxN3 in Xenopus laevis has drastic indirect effects on cranial muscle patterning, although the direct function of the gene is mostly connected to neural crest development. Furthermore, extirpation of single migratory streams of cranial neural crest cells in combination with fate-mapping in a frog shows that individual cranial muscles and their neural crest-derived connective tissue attachments originate from the same visceral arch, even when the muscles attach to skeletal components that are derived from a different arch. The same pattern has also been found in the chicken embryo, the only other species that has been thoroughly investigated, and thus might be a conserved pattern in vertebrates that reflects the fundamental nature of a mechanism that keeps the segmental order of the head in place despite drastic changes in adult anatomy. There is a need for detailed comparative fate-mapping of pre-otic paraxial mesoderm in amphibians, to determine developmental causes underlying the complicated changes in cranial muscle development and architecture within amphibians, and in particular how the novel mouth apparatus in frog tadpoles evolved. This will also form a foundation for further research into the molecular mechanisms that regulate rostral head morphogenesis. Our empirical studies are discussed within a theoretical framework concerned with the evolutionary origin and developmental basis of novel anatomical structures in general. We argue that a common developmental origin is not a fool-proof guide to homology, and that a view that sees only structures without homologs as novel is too restricted, because novelties must be produced by changes in the same framework of developmental processes. At the level of developmental processes and mechanisms, novel structures are therefore likely to have homologs, and we need to develop a hierarchical concept of novelty that takes this into account.

Interstitial deletion of 14q24.3-q32.2 in a male patient with plagiocephaly, BPES features, developmental delay, and congenital heart defects

Distal interstitial deletions of chromosome 14 involving the 14q24-q23.2 region are rare, and only been reported so far in 20 patients. Ten of these patients were analyzed both clinically and genetically. Here we present a de novo interstitial deletion of chromosome 14q24.3-q32.2 in a male patient with developmental delay, language impairment, plagiocephaly, BPES features (blepharophimosis, ptosis, epicanthus), and congenital heart defect. The deletion breakpoints were fine mapped using fluorescence in situ hybridization (FISH) and the size of the deletion is estimated to be approximately 23 Mb. Based on genotype-phenotype comparisons of the 10 previously published patients and the present case, we suggest that the shortest regions for deletion overlap may include candidate genes for speech impairment, mental retardation, and hypotonia.

A 24-Mb deletion in 14q in a girl with corpus callosum hypoplasia

Interstitial deletions of 14q including band 14q31 are uncommon. We report on a 3 year-old Tunisian girl who had a de novo interstitial deletion of the long arm of chromosome 14. The molecular cytogenetic study has identified the deletion as a del(14)(q24.3q32.2) covering nearly 24Mb. This abnormality was associated to phenotypic manifestations, mainly peculiar face, developmental delay and hypoplastic corpus callosum.