A case of deletion 14(q22.1-->q22.3) associated with anophthalmia and pituitary abnormalities

14q22.3 duplication including OTX2 in a girl with medulloblastoma: A case report with literature review

Orthodenticle homeobox 2 (OTX2) is a known oncogenic driver of medulloblastoma. Germline duplication of 14q22.3 including OTX2 is a rare condition reported in patients with combined pituitary hormone deficiency, oculo-auriculo-vertebral spectrum, and hemifacial microsomia. There has been one previously published case of a patient carrying a 14q22.3 duplication that included OTX2 with hemifacial microsomia who also developed medulloblastoma. Here, we present a case of a 6-year-old girl with a history of delayed development who was diagnosed with medulloblastoma. Genetic evaluations revealed that she inherited a germline duplication of 14q22.3, which included OTX2. This genetic alteration was passed down from her mother, who also had a history of delayed development. Results from other genetic testing, including exome sequencing, fragile X syndrome, and mtDNA testing, were negative/normal. This is the second report of a 14q22.3 duplication that included OTX2 in a patient with medulloblastoma. Further studies are necessary to establish a clear association.

Lack of association between SIX1/SIX6 locus polymorphisms and pseudoexfoliation syndrome in a population from the Republic of Korea

Previous studies have reported the association of the SIX1/SIX6 locus with open-angle glaucoma in various ethnic populations. However, the relevance of the SIX1/SIX6 locus to pseudoexfoliation syndrome (XFS) appears uncertain at present. Thus, we investigated the relationship between polymorphisms in the SIX1/SIX6 locus and XFS in a Korean XFS cohort. A total of 246 participants comprising 167 unrelated Korean patients with XFS and 79 ethnically matched control subjects were recruited. Four polymorphisms of the SIX1/SIX6 locus (rs33912345, rs12436579, rs2179970, and rs10483727) were genotyped using a TaqMan® allelic discrimination assay. Genotypic and allelic associations were analyzed using logistic regression. The minor allele frequency (MAF) of rs33912345 was found to be 0.287 and 0.247 in the XFS cases and controls, respectively, and the MAF of rs12436579 was found to be 0.383 and 0.361 in the XFS cases and control subjects, respectively. The MAF of rs2179970 was found to be 0.090 and 0.095 in the XFS cases and control subjects, respectively, and the MAF of rs10483727 was found to be 0.293 and 0.253 in the XFS cases and control subjects, respectively. Genetic association analysis of 4 SIX1/SIX6 locus single nucleotide polymorphisms (SNPs) revealed no significant difference in genotype distribution between the XFS cases and control subjects in the allelic, dominant, or recessive models (all, P > .05). The current study suggested that SIX1/SIX6 locus polymorphisms (rs33912345, rs12436579, rs2179970, and rs10483727) may not be associated with a genetic susceptibility to XFS in a Korean cohort.

Novel SIX6 mutations cause recessively inherited congenital cataract, microcornea, and corneal opacification with or without coloboma and microphthalmia

Purpose

To investigate the molecular basis of recessively inherited congenital cataract, microcornea, and corneal opacification with or without coloboma and microphthalmia in two consanguineous families.

Methods

Conventional autozygosity mapping was performed using single nucleotide polymorphism (SNP) microarrays. Whole-exome sequencing was completed on genomic DNA from one affected member of each family. Exome sequence data were also used for homozygosity mapping and copy number variation analysis. PCR and Sanger sequencing were used to confirm the identification of mutations and to screen further patients. Evolutionary conservation of protein sequences was assessed using CLUSTALW, and protein structures were modeled using PyMol.

Results

In family MEP68, a novel homozygous nucleotide substitution in SIX6 was found, c.547G>C, that converts the evolutionarily conserved aspartic acid residue at the 183^rd amino acid in the protein to a histidine, p.(Asp183His). This residue mapped to the third helix of the DNA-binding homeobox domain in SIX6, which interacts with the major groove of double-stranded DNA. This interaction is likely to be disrupted by the mutation. In family F1332, a novel homozygous 1034 bp deletion that encompasses the first exon of SIX6 was identified, chr14:g.60975890_60976923del. Both mutations segregated with the disease phenotype as expected for a recessive condition and were absent from publicly available variant databases.

Conclusions

Our findings expand the mutation spectrum in this form of inherited eye disease and confirm that homozygous human SIX6 mutations cause a developmental spectrum of ocular phenotypes that includes not only the previously described features of microphthalmia, coloboma, and congenital cataract but also corneal abnormalities.

Region Specific Brain Organoids to Study Neurodevelopmental Disorders

Region specific brain organoids are brain organoids derived by patterning protocols using extrinsic signals as opposed to cerebral organoids obtained by self-patterning. The main focus of this review is to discuss various region-specific brain organoids developed so far and their application in modeling neurodevelopmental disease. We first discuss the principles of neural axis formation by series of growth factors, such as SHH, WNT, BMP signalings, that are critical to generate various region-specific brain organoids. Then we discuss various neurodevelopmental disorders modeled so far with these region-specific brain organoids, and findings made on mechanism and treatment options for neurodevelopmental disorders (NDD).

Induction of Functional Hypothalamus and Pituitary Tissues From Pluripotent Stem Cells for Regenerative Medicine

The hypothalamus and pituitary have been identified to play essential roles in maintaining homeostasis. Various diseases can disrupt the functions of these systems, which can often result in serious lifelong symptoms. The current treatment for hypopituitarism involves hormone replacement therapy. However, exogenous drug administration cannot mimic the physiological changes that are a result of hormone requirements. Therefore, patients are at a high risk of severe hormone deficiency, including adrenal crisis.

Pluripotent stem cells (PSCs) self-proliferate and differentiate into all types of cells. The generation of endocrine tissues from PSCs has been considered as another new treatment for hypopituitarism. Our colleagues established a 3-dimensional (3D) culture method for embryonic stem cells (ESCs). In this culture, the ESC-derived aggregates exhibit self-organization and spontaneous formation of highly ordered patterning. Recent results have shown that strict removal of exogenous patterning factors during early differentiation efficiently induces rostral hypothalamic progenitors from mouse ESCs. These hypothalamic progenitors generate vasopressinergic neurons, which release neuropeptides upon exogenous stimulation.

Subsequently, we reported adenohypophysis tissue self-formation in 3D cultures of mouse ESCs. The ESCs were found to differentiate into both nonneural oral ectoderm and hypothalamic neuroectoderm in adjacent layers. Interactions between the 2 tissues appear to be critically important for in vitro induction of a Rathke’s pouch-like developing embryo. Various endocrine cells were differentiated from nonneural ectoderm. The induced corticotrophs efficiently secreted adrenocorticotropic hormone when engrafted in vivo, which rescued hypopituitary hosts.

For future regenerative medicine, generation of hypothalamic and pituitary tissues from human PSCs is necessary. We and other groups succeeded in establishing a differentiation method with the use of human PSCs. Researchers could use these methods for models of human diseases to elucidate disease pathology or screen potential therapeutics.

Congenital pituitary hypoplasia model demonstrates hypothalamic OTX2 regulation of pituitary progenitor cells

Pituitary develops from oral ectoderm in contact with adjacent ventral hypothalamus. Impairment in this process results in congenital pituitary hypoplasia (CPH); however, there have been no human disease models for CPH thus far, prohibiting the elucidation of the underlying mechanisms. In this study, we established a disease model of CPH using patient-derived induced pluripotent stem cells (iPSCs) and 3D organoid technique, in which oral ectoderm and hypothalamus develop simultaneously. Interestingly, patient iPSCs with a heterozygous mutation in the orthodenticle homeobox 2 (OTX2) gene showed increased apoptosis in the pituitary progenitor cells, and the differentiation into pituitary hormone-producing cells was severely impaired. As an underlying mechanism, OTX2 in hypothalamus, not in oral ectoderm, was essential for progenitor cell maintenance by regulating LHX3 expression in oral ectoderm via FGF10 expression in the hypothalamus. Convincingly, the phenotype was reversed by the correction of the mutation, and the haploinsufficiency of OTX2 in control iPSCs revealed a similar phenotype, demonstrating that this mutation was responsible. Thus, we established an iPSC-based congenital pituitary disease model, which recapitulated interaction between hypothalamus and oral ectoderm and demonstrated the essential role of hypothalamic OTX2.

Genetics of anophthalmia and microphthalmia. Part 1: Non-syndromic anophthalmia/microphthalmia

Eye formation is the result of coordinated induction and differentiation processes during embryogenesis. Disruption of any one of these events has the potential to cause ocular growth and structural defects, such as anophthalmia and microphthalmia (A/M). A/M can be isolated or occur with systemic anomalies, when they may form part of a recognizable syndrome. Their etiology includes genetic and environmental factors; several hundred genes involved in ocular development have been identified in humans or animal models. In humans, around 30 genes have been repeatedly implicated in A/M families, although many other genes have been described in single cases or families, and some genetic syndromes include eye anomalies occasionally as part of a wider phenotype. As a result of this broad genetic heterogeneity, with one or two notable exceptions, each gene explains only a small percentage of cases. Given the overlapping phenotypes, these genes can be most efficiently tested on panels or by whole exome/genome sequencing for the purposes of molecular diagnosis. However, despite whole exome/genome testing more than half of patients currently remain without a molecular diagnosis. The proportion of undiagnosed cases is even higher in those individuals with unilateral or milder phenotypes. Furthermore, even when a strong gene candidate is available for a patient, issues of incomplete penetrance and germinal mosaicism make diagnosis and genetic counseling challenging. In this review, we present the main genes implicated in non-syndromic human A/M phenotypes and, for practical purposes, classify them according to the most frequent or predominant phenotype each is associated with. Our intention is that this will allow clinicians to rank and prioritize their molecular analyses and interpretations according to the phenotypes of their patients.

Haploinsufficiency of BMP4 and OTX2 in the Foetus with an abnormal facial profile detected in the first trimester of pregnancy

Background

Interstitial microdeletion 14q22q23 is a rare chromosomal syndrome associated with variable defects: microphthalmia/anophthalmia, pituitary anomalies, polydactyly/syndactyly of hands and feet, micrognathia/retrognathia. The reports of the microdeletion 14q22q23 detected in the prenatal stages are limited and the range of clinical features reveals a quite high variability.

Case presentation

We report a detection of the microdeletion 14q22.1q23.1 spanning 7,7 Mb and involving the genes BMP4 and OTX2 in the foetus by multiplex ligation-dependent probe amplification (MLPA) and verified by microarray subsequently. The pregnancy was referred to the genetic counselling for abnormal facial profile observed in the first trimester ultrasound scan and micrognathia (suspicion of Pierre Robin sequence), hypoplasia nasal bone and polydactyly in the second trimester ultrasound scan. The pregnancy was terminated on request of the parents.

Conclusion

An abnormal facial profile detected on prenatal scan can provide a clue to the presence of rare chromosomal abnormalities in the first trimester of pregnancy despite the normal result of the first trimester screening test. The patients should be provided with genetic counselling. Usage of quick and sensitive methods (MLPA, microarray) is preferable for discovering a causal aberration because some of the CNVs cannot be detected with conventional karyotyping in these cases. To the best of our knowledge, this is the earliest detection of this microdeletion (occurred de novo), the first case detected by MLPA and confirmed by microarray. Literature review of the genotype-phenotype correlation in similar reports leads us to the conclusion that dosage imbalance of the chromosomal segment 14q22q23 (especially haploinsuffiency of the genes BMP4 and OTX2) contributes significantly to orofacial abnormalities. Association of the region with the Pierre Robin sequence appears to be plausible.

Distinct cis-acting regions control six6 expression during eye field and optic cup stages of eye formation

The eye field transcription factor, Six6, is essential for both the early (specification and proliferative growth) phase of eye formation, as well as for normal retinal progenitor cell differentiation. While genomic regions driving six6 optic cup expression have been described, the sequences controlling eye field and optic vesicle expression are unknown. Two evolutionary conserved regions 5' and a third 3' to the six6 coding region were identified, and together they faithfully replicate the endogenous X. laevis six6 expression pattern. Transgenic lines were generated and used to determine the onset and expression patterns controlled by the regulatory regions. The conserved 3' region was necessary and sufficient for eye field and optic vesicle expression. In contrast, the two conserved enhancer regions located 5' of the coding sequence were required together for normal optic cup and mature retinal expression. Gain-of-function experiments indicate endogenous six6 and GFP expression in F1 transgenic embryos are similarly regulated in response to candidate trans-acting factors. Importantly, CRISPR/CAS9-mediated deletion of the 3' eye field/optic vesicle enhancer in X. laevis, resulted in a reduction in optic vesicle size. These results identify the cis-acting regions, demonstrate the modular nature of the elements controlling early versus late retinal expression, and identify potential regulators of six6 expression during the early stages of eye formation.

Mandibular dysostosis without microphthalmia caused by OTX2 deletion

Mutations in OTX2 are mostly identified in patients with anophthalmia/microphthalmia with variable severity. The OTX2 homeobox gene plays a crucial role in craniofacial morphogenesis during early embryo development. We report for the first time a patient with a mandibular dysostosis caused by a 120 kb deletion including the entire coding sequence of OTX2, identified by array CGH. No ocular malformations were identified after extended ophthalmologic examination. Our data refine the clinical spectrum associated with OTX2 mutations and suggests that OTX2 haploinsufficiency should be considered as a possible cause for isolated mandibular dysostosis. © 2016 Wiley Periodicals, Inc.

Association of common SIX6 polymorphisms with peripapillary retinal nerve fiber layer thickness: the Singapore Chinese Eye Study

PURPOSE

Recently the common SIX6 missense variant rs33912345 was found to be highly associated with glaucoma. The aim of this study was to investigate the association between this SIX6 variant and peripapillary retinal nerve fiber layer (RNFL) thickness measured by spectral-domain optical coherence tomography (SD-OCT) in a population setting.

METHODS

Study subjects were enrolled from the Singapore Chinese Eye Study (SCES), a population-based survey of Singaporean Chinese aged 40 years or older. Subjects underwent a comprehensive ocular examination. Spectral-domain OCT was used to measure RNFL thicknesses. Genotyping of SIX6 rs33912345 (Asn141His) was performed using HumanExome BeadChip.

RESULTS

A total of 2129 eyes from 1243 SCES subjects (mean age: 55.0 ± 7.4 years) with rs33912345 genotype data and SD-OCT images were included for the analysis. Of these, 26 eyes of 21 subjects had glaucoma. The frequency of rs33912345 risk variant C (His141) was 80% in the study subjects. Each rs33912345 C allele was associated with a decrease of 1.44 μm in RNFL thickness after adjusting for age, sex, genetic principal components, and axial length (P = 0.001). These associations remained similar in 2096 nonglaucoma eyes in which each C allele was associated with a decrease of 1.39 μm in RNFL thickness (P = 0.001). The strongest association was observed in the superior RNFL sector (a decrease of 2.83 μm per risk allele, P < 0.001) followed by the inferior RNFL sector (a decrease of 2.24 μm per risk allele, P = 0.003), while the association did not reach significance in the nasal and temporal sectors.

CONCLUSIONS

Nonglaucomatous individuals with the SIX6 missense variant have reduced RNFL thickness in regions known to be particularly affected in those with glaucoma. This may be the primary mechanism for increased risk of POAG in individuals who carry the SIX6 His141 risk variant.

DNA copy number variants of known glaucoma genes in relation to primary open-angle glaucoma

PURPOSE

We examined the role of DNA copy number variants (CNVs) of known glaucoma genes in relation to primary open angle glaucoma (POAG).

METHODS

Our study included DNA samples from two studies (NEIGHBOR and GLAUGEN). All the samples were genotyped with the Illumina Human660W_Quad_v1 BeadChip. After removing non-blood-derived and amplified DNA samples, we applied quality control steps based on the mean Log R Ratio and the mean B allele frequency. Subsequently, data from 3057 DNA samples (1599 cases and 1458 controls) were analyzed with PennCNV software. We defined CNVs as those ≥5 kilobases (kb) in size and interrogated by ≥5 consecutive probes. We further limited our investigation to CNVs in known POAG-related genes, including CDKN2B-AS1, TMCO1, SIX1/SIX6, CAV1/CAV2, the LRP12-ZFPM2 region, GAS7, ATOH7, FNDC3B, CYP1B1, MYOC, OPTN, WDR36, SRBD1, TBK1, and GALC.

RESULTS

Genomic duplications of CDKN2B-AS1 and TMCO1 were each found in a single case. Two cases carried duplications in the GAS7 region. Genomic deletions of SIX6 and ATOH7 were each identified in one case. One case carried a TBK1 deletion and another case carried a TBK1 duplication. No controls had duplications or deletions in these six genes. A single control had a duplication in the MYOC region. Deletions of GALC were observed in five cases and two controls.

CONCLUSIONS

The CNV analysis of a large set of cases and controls revealed the presence of rare CNVs in known POAG susceptibility genes. Our data suggest that these rare CNVs may contribute to POAG pathogenesis and merit functional evaluation.

Midbrain-hindbrain involvement in septo-optic dysplasia

BACKGROUND AND PURPOSE

Midbrain-hindbrain involvement in septo-optic dysplasia has not been well described, despite reported mutations of genes regulating brain stem patterning. We aimed to describe midbrain-hindbrain involvement in patients with septo-optic dysplasia and to identify possible clinical-neuroimaging correlations.

MATERIALS AND METHODS

Using MR imaging, we categorized 38 patients (21 males) based on the presence (group A, 21 patients) or absence (group B, 17 patients) of visible brain stem anomalies. We measured height and anteroposterior diameter of midbrain, pons, and medulla, anteroposterior midbrain/pons diameter (M/P ratio), vermian height, and tegmento-vermian angle, and compared the results with 114 healthy age-matched controls. Furthermore, patients were subdivided based on the type of midline anomalies. The associations between clinical and neuroradiological features were investigated. Post hoc tests were corrected according to Bonferroni adjustment (pB).

RESULTS

Patients with brain stem abnormalities had smaller anteroposterior pons diameter than controls (pB < .0001) and group B (pB = .012), higher M/P ratio than controls (pB < .0001) and group B (pB < .0001), and smaller anteroposterior medulla diameter (pB = .001), pontine height (pB = .00072), and vermian height (pB = .0009) than controls. Six of 21 patients in group A had thickened quadrigeminal plate, aqueductal stenosis, and hydrocephalus; 3 also had agenesis of the epithalamus. One patient had a short midbrain with long pons and large superior vermis. There was a statistically significant association between brain stem abnormalities and callosal dysgenesis (P = .011) and developmental delay (P = .035), respectively.

CONCLUSION

Midbrain-hindbrain abnormalities are a significant, albeit underrecognized, component of the septo-optic dysplasia spectrum, and are significantly associated with developmental delay in affected patients.

Gene dosage of Otx2 is important for fertility in male mice

Together, the hypothalamus, pituitary and gonads direct the development and regulation of reproductive function in mammals. Gonadotropin-releasing hormone (GnRH) expression is limited to ∼800 neurons that originate in the olfactory placode then migrate to the hypothalamus. Coordination of the hypothalamic-pituitary-gonadal (HPG) axis is dependent upon correct neuronal migration of GnRH neurons into the hypothalamus followed by proper synthesis and pulsatile secretion of GnRH. Defects in any one of these processes causes infertility. Otx2, the vertebrate homologue of Drosophila orthodenticle, is a transcription factor that has been shown to be critical for normal brain and eye development and is expressed in both the developing GnRH neurons and the pituitary, suggesting that this gene may play a critical role in development of the HPG axis. As Otx2-null mice are embryonic lethal, we have analyzed the reproductive capacity of heterozygous Otx2 mice to determine the contribution of Otx2 gene dosage to normal HPG axis function. Our data reveal that correct dosage of Otx2 is critical for normal fertility as loss of one allele of Otx2 leads to a discernible reproductive phenotype in male mice due to disruption of the migration of GnRH neurons during development.

Molecular and Clinical Findings in Patients with LHX4 and OTX2 Mutations

The pituitary gland produces hormones that play important roles in both the development and homeostasis of the body. Ontogeny of the anterior and posterior pituitary is orchestrated by inputs from neighboring tissues, cellular signaling molecules and transcription factors. Disruption of expression or function of these factors has been implicated in the etiology of combined pituitary hormone deficiency (CPHD). These include the transcription factors HESX1, PROP1, POU1F1, LHX3, LHX4, OTX2, SOX2, SOX3 and GLI2. This review focuses on summarizing most recent mutations in LHX4 and OTX2 responsible for pituitary hormone deficiency. In both genetic defects of LHX4 and OTX2, there is high variability in clinical manifestations even in the same family. In addition, there is no clear phenotype-genotype correlation. These findings indicate that the other genetic and/or environmental factors influence the phenotype. In addition, the variability might reflect a plasticity during pituitary development and maintenance. Over the past two decades, a genetic basis for pituitary hormone deficiency and the mechanism of pituitary development have been clarified. It should be kept in mind that this review is not comprehensive, and defects of other transcriptional factors have been described in patients with CPHD. Furthermore, the causes in many patients with CPHD have not yet been determined. Therefore, continuing efforts for the clarification of the etiology are necessary.

Molecular and Clinical Findings in Patients with LHX4 and OTX2 Mutations

The pituitary gland produces hormones that play important roles in both the development and homeostasis of the body. Ontogeny of the anterior and posterior pituitary is orchestrated by inputs from neighboring tissues, cellular signaling molecules and transcription factors. Disruption of expression or function of these factors has been implicated in the etiology of combined pituitary hormone deficiency (CPHD). These include the transcription factors HESX1, PROP1, POU1F1, LHX3, LHX4, OTX2, SOX2, SOX3 and GLI2. This review focuses on summarizing most recent mutations in LHX4 and OTX2 responsible for pituitary hormone deficiency. In both genetic defects of LHX4 and OTX2, there is high variability in clinical manifestations even in the same family. In addition, there is no clear phenotype-genotype correlation. These findings indicate that the other genetic and/or environmental factors influence the phenotype. In addition, the variability might reflect a plasticity during pituitary development and maintenance. Over the past two decades, a genetic basis for pituitary hormone deficiency and the mechanism of pituitary development have been clarified. It should be kept in mind that this review is not comprehensive, and defects of other transcriptional factors have been described in patients with CPHD. Furthermore, the causes in many patients with CPHD have not yet been determined. Therefore, continuing efforts for the clarification of the etiology are necessary.

A novel OTX2 mutation in a patient with combined pituitary hormone deficiency, pituitary malformation, and an underdeveloped left optic nerve

Orthodenticle homolog 2 (OTX2) is a homeobox family transcription factor required for brain and eye formation. Various genetic alterations in OTX2 have been described, mostly in patients with severe ocular malformations. In order to expand the knowledge of the spectrum of OTX2 mutation, we performed OTX2 mutation screening in 92 patients with combined pituitary hormone deficiency (CPHD). We directly sequenced the coding regions and exon-intron boundaries of OTX2 in 92 CPHD patients from the Dutch HYPOPIT study in whom mutations in the classical CPHD genes PROP1, POU1F1, HESX1, LHX3, and LHX4 had been ruled out. Among 92 CPHD patients, we identified a novel heterozygous missense mutation c.401C>G (p.Pro134Arg) in a patient with CPHD, pituitary malformation, and an underdeveloped left optic nerve. Binding of both the wild-type and mutant OTX2 proteins to bicoid binding sites was equivalent; however, the mutant OTX2 exhibited decreased transactivation. We describe a novel missense heterozygous OTX2 mutation that acts as a dominant negative inhibitor of target gene expression in a patient with CPHD, pituitary malformation, and optic nerve hypoplasia. We provide an overview of all OTX2 mutations described till date, which show that OTX2 is a promising candidate gene for genetic screening of patients with CPHD or isolated GH deficiency (IGHD). As the majority of the OTX2 mutations found in patients with CPHD, IGHD, or short stature have been found in exon 5, we recommend starting mutational screening in those patients in exon 5 of the gene.

The role of homeodomain transcription factors in heritable pituitary disease

The anterior pituitary gland secretes hormones that regulate developmental and physiological processes, including growth, the stress response, metabolic status, reproduction and lactation. During embryogenesis, cellular determination and differentiation events establish specialized hormone-secreting cell types within the anterior pituitary gland. These developmental decisions are mediated in part by the actions of a cascade of transcription factors, many of which belong to the homeodomain class of DNA-binding proteins. The discovery of some of these regulatory proteins has facilitated genetic analyses of patients with hormone deficiencies. The findings of these studies reveal that congenital defects-ranging from isolated hormone deficiencies to combined pituitary hormone deficiency syndromes-are sometimes associated with mutations in the genes encoding pituitary-acting developmental transcription factors. The phenotypes of affected individuals and animal models have together provided useful insights into the biology of these transcription factors and have suggested new hypotheses for testing in the basic science laboratory. Here, we summarize the gene regulatory pathways that control anterior pituitary development, with emphasis on the role of the homeodomain transcription factors in normal pituitary organogenesis and heritable pituitary disease.

Heterozygous orthodenticle homeobox 2 mutations are associated with variable pituitary phenotype

CONTEXT

Although recent studies have suggested a positive role of OTX2 in pituitary as well as ocular development and function, detailed pituitary phenotypes in OTX2 mutations and OTX2 target genes for pituitary function other than HESX1 and POU1F1 remain to be determined.

OBJECTIVE

We aimed to examine such unresolved issues.

SUBJECTS

We studied 94 Japanese patients with various ocular or pituitary abnormalities.

RESULTS

We identified heterozygous p.K74fsX103 in case 1, p.A72fsX86 in case 2, p.G188X in two unrelated cases (3 and 4), and a 2,860,561-bp microdeletion involving OTX2 in case 5. Clinical studies revealed isolated GH deficiency in cases 1 and 5; combined pituitary hormone deficiency in case 3; abnormal pituitary structures in cases 1, 3, and 5; and apparently normal pituitary function in cases 2 and 4, together with ocular anomalies in cases 1-5. The wild-type Orthodenticle homeobox 2 (OTX2) protein transactivated the GNRH1 promoter as well as the HESX1, POU1F1, and IRBP (interstitial retinoid-binding protein) promoters, whereas the p.K74fsX103-OTX2 and p.A72fsX86-OTX2 proteins had no transactivation functions and the p.G188X-OTX2 protein had reduced ( approximately 50%) transactivation functions for the four promoters, with no dominant-negative effect. cDNA screening identified positive OTX2 expression in the hypothalamus.

CONCLUSIONS

The results imply that OTX2 mutations are associated with variable pituitary phenotype, with no genotype-phenotype correlations, and that OTX2 can transactivate GNRH1 as well as HESX1 and POU1F1.

A rare de novo nonsense mutation in OTX2 causes early onset retinal dystrophy and pituitary dysfunction

PURPOSE

To describe the clinical findings of a patient with an early onset retinal dystrophy and a novel mutation in OTX2, and to compare these findings with previously reported cases.

METHODS

Using direct sequencing, we screened 142 patients, who had either Leber congenital amaurosis (LCA) or early onset retinal dystrophy (EORD), for mutations in OTX2. All patients received a detailed ophthalmic examination including electroretinography and retinal imaging.

RESULTS

Only one mutation in OTX2 was identified. A novel heterozygous p.S138X stop mutation was identified in a seven-year-old male who had an infantile onset retinal dystrophy. The mutation was not present in either parent or in 181 blood donor samples. There was a history of failure to thrive in infancy, poor feeding, and growth hormone deficiency. Poor vision and nyctalopia was present from the first year. Funduscopy revealed a hyperpigmented peripapillary ring with a fine granular pigmentation of the RPE throughout the fundus. The scotopic bright flash ERG a-wave was subnormal and the waveform electronegative, in keeping with dysfunction both at the level of the photoreceptor and post-phototransduction. Visual function has been stable to date.

CONCLUSIONS

Mutations in OTX2 have been reported in association with major developmental malformations of the eye, with retinal dystrophies such as LCA, and with pituitary dysfunction and seizure activity in some cases. This case adds further support for a role of OTX2 both in retinal development and pituitary function, and highlights a novel retinal dystrophy phenotype seen in association with mutations in OTX2.

Anterior segment anomalies of the eye, growth retardation associated with hypoplastic pituitary gland and endocrine abnormalities: Jung syndrome or a new syndrome?

We report on two children from an inbred Arab family with anterior segment anomalies of the eyes, growth retardation, associated with small pituitary gland, and endocrine abnormalities. The features in the sibs in this report are similar to those described in Peters-plus syndrome. However, small pituitary gland associated with growth hormone deficiency has not been reported in Peters-plus syndrome. In addition, sequencing of the B3GALTL gene, the gene implicated in Peters-plus syndrome did not reveal any mutation in the sibs reported here. The association of anterior segment anomalies of the eye, growth retardation, and endocrine problems has previously been described by Jung et al. in 1995. We suggest that the features in the children in this report could represent variable manifestation of this syndrome or previously not described syndrome.

Chromosomal rearrangements and novel genes in disorders of eye development, cataract and glaucoma

Disorders of eye development such as microphthalmia and anophthalmia (small and absent eyes respectively), anterior segment dysgenesis where there may be pupillary and iris anomalies, and associated cataract and glaucoma, often lead to visual impairment or blindness. Currently treatment options are limited, as much is unknown about the molecular pathways that control normal eye development and induce the aberrant processes that lead to ocular defects. Mutation detection rates in most of the known genes are generally low, emphasizing the genetic heterogeneity of developmental ocular defects. Identification of the disease genes in these conditions improves the clinical information available for affected individuals and families, and provides new insights into the underlying biological processes for facilitation of better treatment options. Investigation of chromosomal rearrangements associated with an ocular phenotype has been especially powerful for disease gene identification. Molecular characterization of such rearrangements, which pinpoints the region by physically disrupting the causative gene or its regulatory sequences, allows for rapid elucidation of underlying genetic factors that contribute to the phenotype. Genes including PAX6, PITX2, FOXC1, MAF, TMEM114, SOX2, OTX2 and BMP4 have been identified in this way to be associated with developmental eye disorders. More recently, new methods in chromosomal analysis such as comparative genomic hybridization (CGH) microarray, have also enhanced our ability in disease gene identification.

OTX2 loss of function mutation causes anophthalmia and combined pituitary hormone deficiency with a small anterior and ectopic posterior pituitary

CONTEXT

Orthodenticle homeobox 2 (OTX2) is a transcription factor necessary for ocular and forebrain development. In humans, heterozygous mutations of OTX2 cause severe ocular malformations. However, whether mutations of OTX2 cause pituitary structural abnormalities or combined pituitary hormone deficiency (CPHD) has not been clarified.

OBJECTIVES

We surveyed the functional consequences of a novel OTX2 mutation that was detected in a patient with anophthalmia and CPHD.

PATIENT

We examined a Japanese patient with growth disturbance, anophthalamia, and severe developmental delay. He showed deficiencies in GH, TSH, LH, FSH, and ACTH. Brain magnetic resonance imaging revealed a small anterior pituitary gland, invisible stalk, ectopic posterior lobe, and Chiari malformation.

RESULTS

Sequence analysis of OTX2 demonstrated a heterozygous two bases insertion [S136fsX178 (c.576-577insCT)] in exon 3. The mutant Otx2 protein localized to the nucleus, but did not activate the promoter of the HESX1 and POU1F1 gene, indicating a loss of function mutation. No dominant negative effect in the presence of wild-type Otx2 was observed.

CONCLUSION

This case indicates that the OTX2 mutation is a cause of CPHD. Further study of more patients with OTX2 defects is necessary to clarify the clinical phenotypes and endocrine defects caused by OTX2 mutations.

Heterozygous deletion at 14q22.1-q22.3 including the BMP4 gene in a patient with psychomotor retardation, congenital corneal opacity and feet polysyndactyly

Here we report on a 1-year-old Japanese girl with psychomotor retardation, bilateral congenital corneal opacity and bilateral postaxial polysyndactyly of the feet. Although she had a normal female karyotype, our in-house bacterial artificial chromosome (BAC)-based array-CGH analysis successfully detected at least a 2.7-Mb heterozygous deletion at 14q22.1-q22.3 harboring 18 protein-coding genes. Among the genes, BMP4 was a candidate for the gene causing the abnormalities of both the eye and digits. It was previously reported that the BMP family was correlated with the morphogenesis of digits and ocular development, and Bmp4 heterozygous null mice revealed skeletal abnormalities including polydactyly and ocular anterior segment abnormalities. Patients with a deletion including BMP4 also hadabnormalities of the eye and digits. These previous reports support that a haplo-insufficiency of the BMP4 gene likely caused the congenital ocular and digit abnormalities. Moreover, among the other genes contained in the deletion, GMFB is a candidate for the gene responsible for the psychomotor retardation.

A novel dominant negative mutation of OTX2 associated with combined pituitary hormone deficiency

CONTEXT

Combined pituitary hormone deficiency (CPHD) is characterized by deficiencies in more than one anterior pituitary hormone. Mutations in developmental factors responsible for pituitary cell specification and gene expression have been found in CPHD patients. OTX2, a bicoid class homeodomain protein, is necessary for both forebrain development and transactivation of the HESX1 promoter, but as of yet, has not been associated with CPHD.

OBJECTIVE

The goal of this study was to identify and characterize novel mutations in pituitary specific transcription factors from CPHD patients.

DESIGN

Genomic DNA was isolated from patients with hypopituitarism to amplify and sequence eight pituitary specific transcription factors (HESX1, LHX3, LHX4, OTX2, PITX2, POU1F1, PROP1, and SIX6). Characterization of novel mutations is based on structural and functional studies.

RESULTS

We describe two unrelated children with CPHD who presented with neonatal hypoglycemia, and deficiencies of GH, TSH, LH, FSH, and ACTH. Magnetic resonance imaging revealed anterior pituitary hypoplasia with an ectopic posterior pituitary. A novel heterozygous OTX2 mutation (N233S) was identified. Wild-type and mutant OTX2 proteins bind equivalently to bicoid binding sites, whereas mutant OTX2 revealed decreased transactivation.

CONCLUSIONS

A novel mutation in OTX2 binds normally to target genes and acts as a dominant negative inhibitor of HESX1 gene expression. This suggests that the expression of HESX1, required for spaciotemporal development of anterior pituitary cell types, when disrupted, results in an absent or underdeveloped anterior pituitary with diminished hormonal expression. These results demonstrate a novel mechanism for CPHD and extend our knowledge of the spectrum of gene mutations causing CPHD.

OTX2 mutation in a patient with anophthalmia, short stature, and partial growth hormone deficiency: functional studies using the IRBP, HESX1, and POU1F1 promoters

CONTEXT

OTX2 is a transcription factor gene essential for eye development. Although recent studies suggest the involvement of OTX2 in pituitary function, there is no report demonstrating a positive role of OTX2 in the pituitary function.

OBJECTIVE

The objective of the study was to report the results of functional studies indicating the relevance of OTX2 to pituitary function.

PATIENT

A Japanese female patient with bilateral anophthalmia was found to have short stature (height, -3.3 sd) and isolated partial GH deficiency (peak serum GH 3.1 and 9.7 mug/liter after insulin and arginine stimulations, respectively; serum IGF-I 37 ng/ml) at 3 yr 9 months of age. Magnetic resonance imaging delineated apparently normal pituitary gland.

RESULTS

Mutation analysis showed a de novo heterozygous frameshift mutation (c.402insC) that is predicted to retain the homeodomain but lose the transactivation domain. Functional studies revealed that the wild-type and mutant OTX2 proteins localized to the nucleus and bound to the target sequences within the IRBP (interstitial retinoid-binding protein), HESX1 (HESX homeobox 1), and POU1F1 promoters. Furthermore, the wild-type OTX2 protein markedly transactivated the promoters of IRBP ( approximately 27-fold), HESX1 ( approximately 4.5-fold), and POU1F1 ( approximately 19-fold), whereas the mutant OTX2 protein barely retained the transactivation activities and had no dominant-negative effects.

CONCLUSIONS

The results provide direct evidence for OTX2 being involved in the pituitary function. It is likely that the heterozygous severe OTX2 loss-of-function mutation caused GH deficiency and short stature, primarily because of decreased transactivation function for HESX1 and POU1F1.

Mutations in BMP4 cause eye, brain, and digit developmental anomalies: overlap between the BMP4 and hedgehog signaling pathways

Developmental ocular malformations, including anophthalmia-microphthalmia (AM), are heterogeneous disorders with frequent sporadic or non-Mendelian inheritance. Recurrent interstitial deletions of 14q22-q23 have been associated with AM, sometimes with poly/syndactyly and hypopituitarism. We identify two further cases of AM (one with associated pituitary anomalies) with a 14q22-q23 deletion. Using a positional candidate gene approach, we analyzed the BMP4 (Bone Morphogenetic Protein-4) gene and identified a frameshift mutation (c.226del2, p.S76fs104X) that segregated with AM, retinal dystrophy, myopia, brain anomalies, and polydactyly in a family and a nonconservative missense mutation (c.278A-->G, p.E93G) in a highly conserved base in another family. MR imaging and tractography in the c.226del2 proband revealed a primary brain developmental disorder affecting thalamostriatal and callosal pathways, also present in the affected grandmother. Using in situ hybridization in human embryos, we demonstrate expression of BMP4 in optic vesicle, developing retina and lens, pituitary region, and digits strongly supporting BMP4 as a causative gene for AM, pituitary, and poly/syndactyly. Because BMP4 interacts with HH signaling genes in animals, we evaluated gene expression in human embryos and demonstrate cotemporal and cospatial expression of BMP4 and HH signaling genes. We also identified four cases, some of whom had retinal dystrophy, with "low-penetrant" mutations in both BMP4 and HH signaling genes: SHH (Sonic Hedgehog) or PTCH1 (Patched). We propose that BMP4 is a major gene for AM and/or retinal dystrophy and brain anomalies and may be a candidate gene for myopia and poly/syndactyly. Our finding of low-penetrant variants in BMP4 and HH signaling partners is suggestive of an interaction between the two pathways in humans.

Deletion at 14q22-23 indicates a contiguous gene syndrome comprising anophthalmia, pituitary hypoplasia, and ear anomalies

Anophthalmia and pituitary gland hypoplasia are both debilitating conditions where the underlying genetic defect is unknown in the majority of cases. We identified a patient with bilateral anophthalmia and absence of the optic nerves, chiasm and tracts, as well as pituitary gland hypoplasia and ear anomalies with a de novo apparently balanced chromosomal translocation, 46,XY,t(3;14)(q28;q23.2). Translocation breakpoint analysis using FISH and high-resolution microarray comparative genomic hybridization (CGH) has identified a 9.66 Mb deleted region on the long arm of chromosome 14 which includes the genes BMP4, OTX2, RTN1, SIX6, SIX1, and SIX4. Three other patients with interstitial deletions involving 14q22-23 have been described, all with bilateral anophthalmia, pituitary abnormalities, ear anomalies, and a facial phenotype similar to our patient. OTX2 is involved in ocular developmental defects, and the severity of the ocular phenotype in our patient and the other 14q22-23 deletion patients, suggests this genomic region harbors other gene/s involved in ocular development. BMP4 haploinsufficiency is predicted to contribute to the ocular phenotype on the basis of its expression pattern and observed murine mutant phenotypes. In addition, deletion of BMP4 and SIX6 is likely to contribute to the abnormal pituitary development, and SIX1 deletion may contribute to the ear and other craniofacial features. This indicates that contiguous gene deletion may contribute to the phenotypic features in the 14q22-23 deletion patients.

Ocular manifestations of chromosome 14 terminal deletion

A boy with chromosome 14 terminal (14q32.3) deletion presented with typical facial dysmorphism, mental retardation, and hypotonia. Ocular examination revealed esotropia, jerk nystagmus, microcornea, and retinal-choroidal colobomas. We report the first case of microcorneas and colobomas in association with chromosome 14 terminal deletion to help further define this clinical syndrome.

Dear old dad

The origin and frequency of spontaneous mutations that occur with age in humans have been a topic of intense discussion. The mechanisms by which spontaneous mutations arise depend on the parental germ line in which a mutation occurs. In general, paternal mutations are more likely than maternal mutations to be base substitutions. This is likely due to the larger number of germ cell divisions in spermatogenesis than in oogenesis. Maternal mutations are more often chromosomal abnormalities. Advanced parental age seems to influence some mutations, although it is not a factor in the creation of others. In this review, we focus on patterns of paternal bias and age dependence of mutations in different genetic disorders, and the various mechanisms by which these mutations arise. We also discuss recent data on age and the frequency of these mutations in the human male germ line and the impact of these data on this field of research.

14q(22) deletion in a familial case of anophthalmia with polydactyly

We report a family of anophthalmia with ocular and extraocular manifestations. The proband, his three sisters, and two sons had anophthalmia and preaxial polydactyly in the right hand. Cytogenetic analysis was done for the proband and two of his sons, one of whom was affected. Another male child was affected but was not available for cytogenetic analysis. Karyotypes of both affected individuals showed deletion on long arm of 14q22q23. Literature review shows four cases of anophthalmia with extra ocular anomalies associated with 14q (q22q23) deletion. Recently it has been suggested that the human homeobox gene, SIX6, and the BMP-4 gene are responsible for eye development. Both are located in the chromosome 14q22.3-q23 region. Deletion in this region has been known to be associated with anophthalmia and pituitary anomalies. This is the first family of anophthalmia, which showed polydactyly with a chromosomal deletion in the 14q22-q23 region and its familial transmission in two generations with a total of six affected individuals.

[Treatment of congenital clinical anophthalmos with high hydrophilic hydrogel expanders]

INTRODUCTION

Children presenting with congenital anophthalmos usually develop a smaller bony orbit, a constricted mucosal socket, and a shortened eyelid fissure. This causes problems when fitting these patients with a prosthesis. Clinical evaluation of the Wiese self-inflating hydrogel expanders has demonstrated their ability to expand the socket and eyelid fissure for inserting a more realistic prosthesis in shorter periods of time.

PATIENTS AND METHOD

The study included 13 consecutive anophthalmic patients, eight unilateral and five bilateral. Each patient received a hemispherical osmotic tissue expander in the rudimentary mucosal socket and later a sphere implanted in the deeper soft orbital tissue.

RESULTS

The use of hydrogel expanders enlarged the lid and palpebral fissure in all children, with good cosmetic results. It allowed insertion of custom-made glass prostheses with good cosmetic appearance very early in life. Growth of the bony orbit may be stimulated successfully by these expanders in the soft orbital tissue.

CONCLUSIONS

The enlargement of constricted mucosal sockets and short palpebral fissures using self-inflating hydrogel expanders is a new and successful concept in treating congenital anophthalmos.

Facial dysgenesis: a novel facial syndrome with chromosome 7 deletion p15.1-21.1

We describe a female neonate with a unique constellation of features including anophthalmia and cryptophthalmos, temporal remnant "eye tags," bilateral cleft lip, unilateral cleft palate, a proboscis with absent nasal septum, choanal atresia, micrognathia, square stoma, and bilateral external auditory canal atresia. Gross brain structure, pituitary function, limbs, trunk, and genitalia were normal. Skeletal survey, echocardiogram and abdominal viscera were unremarkable except for a split central sinus of the right kidney. BAER exam indicated she could hear and temporal CT confirmed the presence of cochlea and possible ossicles. Cytogenetic evaluation revealed an interstitial deletion at chromosome 7p15.1-21.1. TWIST, a gene encoding a transcription factor involved in craniofacial development, is deleted by FISH analysis. The absence of a mutation on the non-deleted allele of TWIST as determined by sequencing virtually eliminates complete loss of the TWIST gene as the cause of this patient's severe phenotype. The HOXA gene cluster also encodes transcription factors that are crucial for directing cephalad to caudad somatic fetal development. HOXA1, the most telomeric of the 13 members of the HOXA gene cluster, is located at the centromeric boundary of the patient's chromosome 7 deletion. By FISH analysis, neither allele of HOXA1 is deleted and sequencing reveals no mutations. Haploinsufficiency or complete loss of the HOXA1 gene also does not appear to cause this patient's severe phenotype. Previous reports of chromosome 7p15-21 deletions do not have phenotypes similar to this patient.

A case of growth hormone and gonadotropin deficiency associated with unilateral anophthalmia, microphallus, cryptorchidism, and mental retardation

We report a rare case of growth hormone and gonadotropin deficiency associated with dysmorphic features. A 16-year-old boy had left anophthalmia, microphallus, bilateral cryptorchidism, and mental retardation. His chromosomal karyotype was normal, 46, XY. Endocrinological studies revealed growth hormone and gonadotropin deficiency, attributed to hypothalamic dysfunction. Magnetic resonance imaging scan of the head showed a hypoplastic pituitary gland, decreased high intensity signals in the pituitary posterior lobe, absence of the left eye, and a hypoplastic left optic nerve with no abnormality of the pituitary stalk, corpus callosum, or septum pellucidum. Although not completely consistent with the features of septo-optic dysplasia (SOD), his condition was considered within the spectrum of SOD. Despite similarities to the Hesx1 knockout mouse, a model of human SOD, mutation analyses revealed no mutations or polymorphisms in coding regions of any exons or intron-exon boundaries of the HESX1 gene. Further genetic studies of this patient may improve understanding of molecular mechanisms involved in pituitary development.

Exclusion of SIX6 hemizygosity in a child with anophthalmia, panhypopituitarism and renal failure

We report a patient who presented with anophthalmia, panhypopituitarism, early onset of end stage renal failure, and craniofacial abnormalities. MRI at age 3 revealed that the pituitary was absent and renal biopsy demonstrated nephronophthisis as the cause of the renal failure. A similar syndrome has been associated with interstitial deletions of chromosome 14q22 and in one case hemizygosity for SIX6 was demonstrated. The patient reported here had a normal karyotype and Southern blot did not reveal loss of one copy of SIX6. We discuss other possible candidate genes that could be implicated in this syndrome.

Search for imprinted regions on chromosome 14: comparison of maternal and paternal UPD cases with cases of chromosome 14 deletion

Over the past few years, regions of genomic imprinting have been identified on a small number of chromosomes through a search for the etiology of various disorders. Distinct phenotypes have been associated with both maternal and paternal uniparental disomy (UPD) for chromosome 14. This observation indicates that there are imprinted genes present on chromosome 14, although none have been identified to date. In order to focus the search for imprinted genes on chromosome 14, we analyzed cases of maternal and paternal UPD 14 and compared them with cases of chromosome 14 deletions. Cases of paternal UPD were compared with maternal deletions and maternal UPD compared with paternal deletions. The paternal UPD anomalies seen in maternal deletion cases allowed us to associate the following features and chromosomal regions: Hirsute forehead: del(14)(q12q13. 3) and del(14)(q32); blepharophimosis: del(14)(q32); small thorax: del(14)(q11.2q13); and joint contractures: del(14)(q11.2q13) and del(14)(q31). Comparison of maternal UPD and paternal deletion cases revealed fleshy nasal tip to be most often associated with del(14)(q32), scoliosis with del(14) (q23q24.2), and del(14)(q32. 11qter) and small size at birth to be associated with del(14)(q11q13) and del(14)(q32). Our study, in conjunction with a prior study of UPD 14 and partial trisomy 14 cases, and what is known of imprinting in regions of mouse chromosomes homologous to human chromosome 14, leads us to conclude that 14q23-q32 is likely an area where imprinted genes may reside.

Isolated bilateral anophthalmia in a girl with an apparently balanced de novo translocation: 46,XX,t(3;11)(q27;p11.2)

Primary anophthalmos is a heterogeneous condition. In its nonsyndromal form, it is usually considered an autosomal recessive trait. However, other causes such as chromosomal abnormalities and prenatal insults need to be considered. We report on a unique reciprocal translocation 46,XX,t(3;11)(q27;p11.2) in a baby with isolated anophthalmos. Both Chitayat et al. [1996] and Alvarez Arratia et al. [1984] have reported on cases of terminal deletion of the long arm of chromosome 3. In each case the child had multiple anomalies including microphthalmia or anophthalmia. Because our patient appears to have no other anomalies, this break point may indicate that a genetic locus for eye formation exists at chromosome site 3q27. Published 1999 Wiley-Liss, Inc.

Genomic cloning and characterization of the human homeobox gene SIX6 reveals a cluster of SIX genes in chromosome 14 and associates SIX6 hemizygosity with bilateral anophthalmia and pituitary anomalies

The Drosophila gene sine oculis (so), a nuclear homeoprotein that is required for eye development, has several homologues in vertebrates (the SIX gene family). Among them, SIX3 is considered to be the functional orthologue of so because it is strongly expressed in the developing eye. However, embryonic SIX3 expression is not limited to the eye field, and SIX3 has been found to be mutated in some patients with holoprosencephaly type 2 (HPE2), suggesting that SIX3 has wide implications in head development. We report here the cloning and characterization of SIX6, a novel human SIX gene that is the homologue of the chick Six6(Optx2) gene. SIX6 is closely related to SIX3 and is expressed in the developing and adult human retina. Data from chick and mouse suggest that the human SIX6 gene is also expressed in the hypothalamic and the pituitary regions. SIX6 spans 2567 bp of genomic DNA and is split in two exons that are transcribed into a 1393-nucleotide-long mRNA. Chromosomal mapping of SIX6 revealed that it is closely linked to SIX1 and SIX4 in human chromosome 14q22.3-q23, which provides clues about the origin and evolution of the vertebrate SIX family. Recently three independent reports have associated interstitial deletions at 14q22.3-q23 with bilateral anophthalmia and pituitary anomalies. Genomic analyses of one of these cases demonstrated SIX6 hemizygosity, strongly suggesting that SIX6 haploinsufficiency is responsible for these developmental disorders.

Six6 (Optx2) is a novel murine Six3-related homeobox gene that demarcates the presumptive pituitary/hypothalamic axis and the ventral optic stalk

We report on the isolation of a murine homeobox-containing gene, Six6 (Optx2), that shows extended identity in its coding region with Six3, the only member of the mammalian Six gene family known to be expressed in the optic primordium. Phylogenetic analysis demonstrates that Six6 and Six3 belong to a separate group of homeobox-genes that are closely related to the recently identified Drosophila optix. Earliest Six6 expression was detected in the floor of the diencephalic portion of the primitive forebrain, a region predicted to give rise to the neurohypophysis and to the hypothalamus. Later on, Six6 mRNA was found in the primordial tissues giving rise to the mature pituitary: the Rathke's pouch and the infundibular recess. In the optic primordium, Six6 demarcates the presumptive ventral optic stalk and the ventral portion of the future neural retina. In the developing eye. Six6 expression was detected in the neural retina, the optic chiasma and optic stalk, but not in the lens. When compared to Six6, Six3 expression pattern was highly similar, but with a generally broader transcripts distribution in the brain and in the visual system. We finally show that Six6 does not require Pax6 for its expression in the optic primordium, suggesting that Six6 acts on a parallel and/or independent pathway with Pax6 in the genetic cascade governing early development of the eye.

The optx2 homeobox gene is expressed in early precursors of the eye and activates retina-specific genes

Vertebrate eye development begins at the gastrula stage, when a region known as the eye field acquires the capacity to generate retina and lens. Optx2, a homeobox gene of the sine oculis-Six family, is selectively expressed in this early eye field and later in the lens placode and optic vesicle. The distal and ventral portion of the optic vesicle are fated to become the retina and optic nerve, whereas the dorsal portion eventually loses its neural characteristics and activates the synthesis of melanin, forming the retinal pigment epithelium. Optx2 expression is turned off in the future pigment epithelium but remains expressed in the proliferating neuroblasts and differentiating cells of the neural retina. When an Optx2-expressing plasmid is transfected into embryonic or mature chicken pigment epithelial cells, these cells adopt a neuronal morphology and express markers characteristic of developing neural retina and photoreceptors. One explanation of these results is that Optx2 functions as a determinant of retinal precursors and that it has induced the transdifferentiation of pigment epithelium into retinal neurons and photoreceptors. We also have isolated optix, a Drosophila gene that is the closest insect homologue of Optx2 and Six3. Optix is expressed during early development of the fly head and eye primordia.

Bilateral clinical anophthalmos

We report on the risk factors, associations and outcome of 5 children with bilateral clinical anophthalmos. Our study showed no gestational, environmental or hereditary association but confirmed strong association with multiple systemic abnormalities.