Optic Nerve Hypoplasia Plus: A New Way of Looking at Septo-Optic Dysplasia

Transcription

1 Optic Nerve Hypoplasia Plus: A New Way of Looking at Septo-Optic Dysplasia Item Type text; Electronic Thesis Authors Mohan, Prithvi Mrinalini Publisher The University of Arizona. Rights Copyright is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 24/07/ :04:27 Link to Item

2 OPTIC NERVE HYPOPLASIA PLUS: A NEW WAY OF LOOKING AT SEPTO-OPTIC DYSPLASIA By PRITHVI MRINALINI MOHAN A Thesis Submitted to The Honors College In Partial Fulfillment of the Bachelors degree With Honors in Physiology THE UNIVERSITY OF ARIZONA M A Y Approved by: Dr. Vinodh Narayanan Center for Rare Childhood Disorders

3 Abstract Septo-optic dysplasia (SOD) is a rare congenital disorder that affects 1/10,000 live births. At its core, SOD is a disorder resulting from improper embryological development of mid-line brain structures. To date, there is no comprehensive understanding of the etiology of SOD. Currently, SOD is diagnosed based on the presence of at least two of the following three factors: (i) optic nerve hypoplasia (ii) improper pituitary gland development and endocrine dysfunction and (iii) mid-line brain defects, including agenesis of the septum pellucidum and/or corpus callosum. A literature review of existing research on the disorder was conducted. The medical history and genetic data of 6 patients diagnosed with SOD were reviewed to find damaging variants. Novel mutations were found in the sequencing data in 3 of the 6 patients. I also realized that the diagnostic criteria for SOD tend to be inconsistent and I have recommended a reorganization to focus on the optic nerve hypoplasia as the central factor of the disorder. I will be writing up my findings to submit for review and potential publication in the journal Pediatric Neurology. The clinic will be pursuing further molecular studies to understand if these mutations are causes of the disorder.

4 I. Introduction and History Septo-optic dysplasia (SOD), or de Morsier syndrome, is a rare congenital disorder that is seen in about 1 in 10,000 live births 1. Currently, SOD is diagnosed based on the presence of two out of three anomalies optic nerve hypoplasia, midline brain defects, and pituitary abnormalities with associated endocrine deficits. ONH occurs in 75-80% of cases, hypopituitarism in 62%, and 60% of cases lack a septum pellucidum. Other associated features include developmental delay, epilepsy, hemiparesis, schizencephaly, grey matter heterotopia, and mental retardation 2. At its core, SOD is a disorder resulting from improper embryological development of midline brain structures. It was first discussed in 1941 by Reeves, who presented a case study of a young girl with absent septum pellucidum and bilateral optic nerve hypoplasia 3. Reeves also documented forty five cases involving an absent septum pellucidum. He concluded that multiple nervous system developmental anomalies coexisted in these cases, and that an absent septum pellucidum was not indicative of a definite clinical picture or symptom. However, the clinical diagnosis of septo-optic dysplasia was introduced in 1956 by De Morsier. He presented the case of an 84-year-old woman with absent septum pellucidum and optic chiasm malformation. After finding another eight cases with septum pellucidum agenesis and optic nerve abnormalities, he coined the term septo-optic dysplasia 4. In 1970, Hoyt et al. published a short paper in The Lancet describing the association of pituitary dwarfism with septo-optic dysplasia. They presented nine patients with maldevelopment of optic structures and retarded growth, four of whom had absent septum pellucidum. They concluded that septo-optic dysplasia was a common cerebral malformation associated with congenital pituitary dwarfism 5. Thus, the triad of anomalies considered for a diagnosis of septo-optic dysplasia was established.

5 Optic nerve hypoplasia (ONH) is also a congenital disorder of unknown cause involving malformations of one or both optic nerves and various degrees of visual impairment. Associated signs include brain malformations, hypothalamic and pituitary dysfunction, and neurocognitive disabilities. It is the second leading cause of congenital visual impairment and the leading cause of permanent legal blindness in children in the Western world. While it has been grouped with the absence of a septum pellucidum for a long time, many studies have shown that ONH is an independent risk factor for pituitary dysfunction. In fact, ONH might even be a better indicator to diagnose children with midline brain defects. A comprehensive look at the clinical presentations of SOD patients with ONH supports this conclusion as well. Genetic testing of these patients also provides insight into the elusive etiologies of SOD and ONH. II. Brain Development The forebrain structures arise from the prosencephalon during embryonic development. This occurs from the 4 th week of gestation, during which ventral induction occurs leading to prosencephalon development via formation, cleavage, and midline development 6. The peak period of development for the prosencephalon is the second an third months, through inductive interactions with the prechordal mesoderm. Since these inductive interactions influence the facial structures as well, prosencephalic anomalies often result in corresponding facial anomalies. After the formation stage, the prosencephalon cleaves in three ways horizontally, transversely, and sagittally. The first forms the structures including the optic vesicles and olfactory bulbs and tracts, the second separates the telencephalon and diencephalon, and the third forms the two cerebral hemispheres along with the lateral ventricles and basal ganglia. Afterwards, during midline development, the corpus callosum, septum pellucidum, optic nerve chiasm, and hypothalamic structures form 7.

6 Image 1: Divisions of the neural tube Image 2: Sagittal view of the brain with the corpus callosum, septum pellucidum, optic nerve+chiasm, pituitary gland, fornix, and mammillary body all labeled

7 A. Lamina Terminalis, Septum Pellucidum, and Corpus Callosum The septum pellucidum and corpus callosum both develop from the primitive lamina terminalis, also known as the commissural plate. The lamina terminalis forms from the closure of the anterior neuropore and the fusion of the lateral plates. It resides in the rostral wall of the prosencephalon. This structure, which routes fibers from one cerebral hemisphere to another, also forms the anterior wall of the telencephalic cavity. The corpus callosum grows first from the commissural plate arching dorsocaudally, and it is stretched ventrally between the lateral ventricles to the fornix, forming the septum pellucidum. Septum Pellucidum The septum pellucidum is an important relay station within the limbic system. It is a thin, translucent structure made up of two laminae extending from the anterior section of the corpus callosum to the superior surface of the fornix 8. It separates the anterior horns of the left and right lateral ventricles. It also has important fiber connections to the hypothalamus and hippocampus. The cavum septi pellucidi (CSP) is a cerebral spinal fluid space between the leaflets of the septum pellucidum during development. Usually, the cavum closes early on in childhood, though it persists in about 15% of the adult population 9. The CSP is a structure that can be identified early on in the fetus. During routine obstetric sonography, it should be identifiable at 18 to 20 weeks. Lack of CSP visualization is an early sign of SOD 10. Beyond its anatomical placement, the functional significance of the septum pellucidum is unknown. Thus, the full implications of an absent septum pellucidum are unclear. Williams et al. concluded that absence of the septum pellucidum alone does not result in significant neurological, behavioral, or intellectual dysfunction 11. However, several studies say that the septum pellucidum relays visceral information from the hypothalamic autonomic system to the hippocampus, amygdala, and other

8 brain structures, implicating it for sleep functions, consciousness, and memory formation, to name a few things 12. Image 3: MRIs demonstrating normal septum pellucidum and vergae. Red arrows are pointing to the septum pellucidum. Corpus Callosum The corpus callosum is the largest white matter tract in the brain that connects the two cerebral hemispheres. During development, adult morphology is reached by around week 20. After birth, the size decreases as large amounts of callosal axons are eliminated to limit contact between the cerebral hemispheres to specific cortical areas. While the fetal corpus callosum is an indicator for normal brain development, the adult corpus callosum reflects differences in hemispheric representation in cognitive abilities 13. Due to its importance for abstract reasoning, language, and the complex integration of sensory information, any insult to the development of the corpus callosum can result in a wide range of neurological and behavioral deficits 14.

9 Image 4: Sagittal MRI of the brain with red arrows pointing at the corpus callosum or a normal individual. B. Optic Nerve The optic nerve develops from the diencephalon. An optic evagination grows out from each side to later develop into parts of the eyeball and optic nerve. It is important to note that the eyeball is also derived mesodermal (sclera, choroid, extraocular muscles, etc.) and ectodermal (retina, ciliary body, iris, lens) tissues. The optic nerve develops from the inner layer of the optic cup, specifically the posterior portion known as the pars optica retinae. This layer undergoes histological changes, transitioning from a single layer of columnar neural epithelium to ependymal, mantle, and marginal layers. The inner layer (the optic layer) of the mantle zone contains axons, which extend into the marginal zone and continue to grow towards the optic stalk attachment. The region of growth into the marginal zone of the stalk eventually turns into a brain tract, also known as the optic nerve 15. The optic nerve chiasm forms from the chiasmatic plate of tissue.

10 Image 5: MRI demonstrating normal optic nerves and chiasm C. Hypothalamus and Pituitary The hypothalamus and the pituitary gland are both the centers of endocrine function in the brain. The hypothalamus controls the pituitary, and the tissues that form Rathke s pouch (the anterior pituitary precursor) and the hypothalamus are adjacent. Rathke s pouch is derived from the roof of the oropharynx, anterior to the buccopharyngeal membrane. The hypothalamus, along with the posterior lobe, intermediate lobe, and the pituitary stalk, forms from anterior neuroepithelium of the diencephalon and Rathke s pouch forms from ectodermal cell layers. The hypothalamus induces the development of Rathke s pouch. At the midline of the rostral ectoderm, the tissue thickens to form the hypophyseal placode. The hypophyseal placode is pulled upward and forms Rathke s pouch, eventually separating from the underlying ectoderm. This structure eventually matures into the anterior pituitary lobe. Meanwhile, the hypothalamus and remaining pituitary structures form from the diencephalon 16.

11 Image 6: Sagittal MRI of the brain with the red arrow pointing at a normal pituitary gland. Other important structures that derive from prosencephalon midline formation include the fornix and mammillary bodies. The fornix is a major white matter tract that connects efferently and afferently to the hippocampus. The mammillary bodies have input connections from the hippocampus and major output connections to the anterior thalamic nuclei 17. As such, both structures have significant roles in mnemonic and spatial memory and are associated with each other structurally 18. D. Disorders of Prosencephalic Development The disorders associated with prosencephalic development range from mild to extremely severe. These disorders can also be grouped by the stage of development that they affect formation, cleavage, or midline development. The disorders of greatest severity occur during prosencephalic formation. These are aprosencephaly (failure of prosencephalon to form) and atelencephaly (failure of telencephalon to form). Disorders of prosencephalic cleavage fall within the spectrum of holoprosencephaly. The mildest disorder in this spectrum is Solitary Median

12 Maxillary Central Incisor, which can occur alone or with other symptoms associated with midline brain defects 19. The most severe phenotype of holoprosencephaly presents with cyclopia. Other symptoms in less severe cases include close-set eyes (hypotelorism), pituitary dysfunction, and intellectual disabilities 20. Midline developmental disorders include corpus callosum agenesis, septum pellucidum agenesis, and the range of symptoms involved with septo-optic dysplasia. III. Current Knowledge on Etiology A. Genetics While the actual etiology of SOD is unknown, a few genes (Sox2, Sox3, and HESX1) have been implicated in its pathology. However, mutations in these genes have only been identified as disease causing in very rare cases. Other genes implicated in SOD and ONH are NTN1 (axon development), PROP1 (pituitary development), PITX2 (pituitary development). However, mutations in these genes do not account for optic and pituitary dysfunction. HESX1 HESX1 is a homeobox gene that encodes the transcriptional repressor HESX1. HESX1 is important in early brain development and formation, specifically the pituitary, forebrain structures, and optic nerves. It is initially expressed during the gastrulation stage in the future forebrain region. Early on, its expression is restricted to the ventral diencephalon and the portion of ectoderm that gives rise to Rathke s pouch. As such, it is very important for the development of the anterior pituitary. HESX1 null mice presented with a phenotype very similar to SOD, albeit variable. Features include reduced forebrain tissue, hypothalamic abnormalities, optic vesicle developmental problems, and other developmental issues of the midline. Studies have shown that mutations in HESX1 primarily affects pituitary development, along with some ONH and agenesis of the corpus

13 callosum. Overall, while HESX1 mutations may be implicated in rare familial forms of SOD, it is not a mutated gene found in the majority of patients 21. SOX3 (X chromosome) SOX3 is a member of the SOX family of transcription factors, specifically the SOXB1 subfamily, which is the most similar to SRY (mammalian sex determining gene). SOXB1 also includes SOX1 and SOX2. The entire SOXB1 group plays a role in neuronal determination of the central nervous system. SOX3 plays a role in neurogenesis, and it is expressed both in the brain and the spinal cord. It has been noted particularly in the diencephalon, specifically the hypothalamus and infundibulum. SOX3 disrupted mice display symptoms including midline CNS defects, craniofacial abnormalities, variable endocrine deficit, and reduced size and fertility. In humans, SOX3 mutations have been tied to mental retardation, hypopituitarism, affected males and females differently due to the gene s X- linked mode of inheritance 21. SOX2 (X chromosome) SOX2 is also a member of the SOX family and the SOX1B subfamily, as described previously. SOX2 is expressed in the CNS, brachial arches, gut endoderm, esophagus, and trachea. SOX2 heterozygous mice show reduction in size and male fertility, while homozygous loss of SOX2 is lethal. It is suspected to have a role in hypopituitarism. De novo mutations in SOX2 in human patients has been associated with microphthalmia with several additional abnormalities. SOX2 is thought to be critical for gonadotrophin production and eye development 21.

14 B. Environmental Factors From an epidemiology standpoint, SOD has an incidence of 1/10,000 live births. A study by Patel et al. (2006) in Northwest England showed that SOD and ONH were more common in areas with higher unemployment and teenage pregnancy rates 22. It was originally thought that this condition had associations to low maternal age, but this point is disputed. There is also thought to be association between primigravida mothers and SOD 21. Borchert suggested that numerous perinatal and prenatal factors were implicated in ONH: preterm birth, low birth weight, young maternal age, primiparity, smoking, alcohol, recreational drugs, a variety of prescription medications, gestational diabetes, maternal anemia, and viral infections. However, most of these reports are retrospective and anecdotal. For both SOD and ONH, young maternal age and primiparity persist as risk factors 23. IV. Methods The method for this project was a two- part approach a literature review and the clinical aspect. The literature review aspect involved studying the existing literature on septo- optic dysplasia, along with the relevant embryology and genetics. The clinical aspect involved analyzing the medical and genetic information of a cohort of six patients diagnosed with SOD, at the Center for Rare Childhood Disorders (C4RCD). Patient Enrollment The children recruited for the study were already patients at C4RCD. They were selected based on prior diagnoses of septo- optic dysplasia. All the patients and their parents provided with written consent to join Genetic Studies of Patients and their Families with Diseases of Unknown Etiology, sponsored by the Translational Genomics Institute

15 (TGen). Blood samples were collected from the patients and their parents and sent to TGen for exome sequencing. Two patients (F354- P001 and F420- P001) already had sequencing done through a commercial laboratory (GeneDx, Gaithersberg, MD). Exome Sequencing Genomic DNA from the family was extracted from peripheral blood and processed in a CLIA lab using the DNeasy extraction kit (Qiagen, Hilden, Germany). Genomic libraries were prepared for sequencing with the Kapa Biosystems Hyper DNA Prep Kit for Illumina Platforms (Woburn, MA, USA). Exome capture was performed with the Aligent SureSelectXT Target Enrichment Platform using Clinical Research Exome baits (Santa Clara, CA, USA). Sequencing was performed by 100bp paired- end sequencing on a HiSeq2000 instrument (Illumina Inc, San Diego, USA). Mean target exome coverage was X. Genetic Data Analysis Filtered reads were aligned to the Human genome (Hg19/GRC37) using the Burrows- Wheeler transform (BWA v ). Reads were sorted and PCR duplicates were removed using Picard v1.79. Base quality recalibration and indel realignment were performed using the Genome Analysis Toolkit (GATK v3.1-1). Data was filtered against dbsnp137, 1000 Genomes, an in- house exome database of over 2,600 exomes, and then annotated with SnpEff 3.0a against Ensembl GRCh37.66 to identify novel damaging mutations. Variants were jointly called with HaplotypeCaller, annotated with SnpEff and selected (SnpSift) for protein- coding events. Prediction scores were loaded from dbnsfp (Database for Nonsynonymous SNP s Functional Predictions) and used for filtering (Supplimental Table). Relatedness and gender for the nuclear family was checked using Plink v1.07. The genetic analysis was completed using the final exome sequencing data. The

16 final sequencing data was consolidated in an annotated variant file containing the variants of the proband, mother, and father. These were analyzed based on mode of inheritance de novo, homozygous, phase- compound heterozygote, or X- linked. The variants were predicted to be damaging using the CADD score (Combined Annotation Dependent Depletion), with a score higher than 10 considered damaging. Variants were also cross- referenced with the Exome Aggregation Consortium (ExAc) and Genome Aggregation Database (gnomad) to check their frequencies within the sequenced populations. Higher frequency variants were not considered damaging. Clinical Data Analysis The patients medical histories were summarized and analyzed using the existing literature data to see how their conditions compared to various accounts of septo- optic dysplasia. This information was also used in conjunction with the sequencing data to ascertain any damaging mutations. The clinical data was also analyzed to evaluate the efficacy of the diagnostic criteria for septo- optic dysplasia. V. Clinical Summaries A cohort of six patients previously diagnosed with SOD was used for this study. The patients were all deidentified and issued numbers to protect their identities. The available medical files for all the patients were reviewed and the major symptoms were summarized. Patient F354-P001 Patient is a 22- month- old female diagnosed with SOD, right hemisphere closed lip schizencephaly, right microphthalmia, and bilateral congenital cataracts. She has left hemiparesis. Her eyes presented with right microphthalmia and poor tracking. The right retina has a congenital abnormality and blindness. There is possible optic nerve hypoplasia

17 and legal blindness of the left eye. She is almost walking independently (uses a walker) and is more verbal. Midline Brain Defects: NO ONH: Yes, left eye possibly Pituitary Abnormalities: NO Image 7: MRI of the brain of patient F354 showing right sided closed lip schizencephaly (top three), optic nerve hypoplasia (bottom left), and agenesis of the septum pellucidum (bottom right)

18 Patient F420-P001 Patient is a 16 month old female with various issues including septo optic dysplasia. An MRI demonstrated multiple CNS malformations, including cortical dysplasia with an absent septum pellucidum, ectopic posterior- located pituitary, optic nerves and chiasm hypoplasia, and gray matter heterotopia. She also has deformity and hypoplasia of the corpus callosum. While she has visual impairment and nystagmus, she has responsive pupils and fair visual acuity. She has panhypopituitarism for which she takes supplemental medicines. She has heightened sensitivity in her right ear. Her whole genome chromosome SNP microarray was normal. Midline Brain Defects: Yes ONH: Yes Pituitary Abnormalities: Yes Patient F488-P001 Patient is a 6- month- old male diagnosed with Septo- optic Dysplasia (SOD) within 24 hours of birth after hypothermia and seizure episodes. Imaging studies showed an absent septum pellucidum, hypoplasia of optic nerves, and ectopic posterior pituitary bright spot. The patient has strabismus (esotropia) for which he is supposed to receive surgery on 9/13/2016. He has adreno- cortical deficiency and hypothyroidism. Midline Brain Defects: Yes ONH: Yes Pituitary Abnormalities: Yes

19 Image 8: MRI of Patient F488 showing agenesis of the septum pellucidum, optic nerve hypoplasia, and ectopic posterior pituitary Patient F498-P001 Patient is a 12 year old male diagnosed with SOD and polymicrogyria, with cerebral dysgenesis, left hemiparesis, and intractable epilepsy. The brain imaging showed polymicrogyria, hypoplasia of the corpus callosum, cerebral asymmetry, and absent septum pellucidum. His left hemisphere is larger than his right. He is essentially blind due to optic nerve hypoplasia with minimal light perception. He is developmentally delayed. He has no evidence of endocrinopathy. He is wheelchair bound. He has a history of hypotonia, weight loss, and constipation. He is on medication for his seizures.

20 Midline Brain Defects: Yes ONH: Yes Pituitary Abnormalities: No Developmental Delay** Patient F504-P001 Patient is a 4 ½ year old male with SOD, diabetes insipidus, spastic hemiplegia, severe visual impairment, developmental delay, and behavioral problems. MRI shows cranial nerve hypoplasia of the left olfactory bulb, trigeminal, and bilateral optic nerves. There was also posterior white matter loss with ex- vacuo dilation of the lateral ventricles, and a diminutive pituitary with absence of the posterior bright spot. He presents with panhypopituitarism. The patient has nystagmus, vision loss, and photophobia, along with a tendency to poke his eyes. He has muscle weakness and difficulty chewing. He is in a special education classroom and has gross and fine motor delays and speech delays. He also has behavioral problems (scratches his eyes, pulls hair, kicks, throws himself backwards) and temper tantrums. The patient and both parents had chromosomal microarrays done. Patient showed 258kb interstitial deletion of 4q35.1q35.2. Father had the same deletion while mother was normal. Midline Brain Defects: No ONH: Yes Pituitary Abnormalities: Yes Developmental Delay** Patient F515-P001 Patient is a 10 year old female with SOD, delayed development, and a seizure disorder. Her imaging studies showed bilateral optic nerve hypoplasia. She began having seizures at 14 months of age. She has visual difficulties and wandering eye movements. She also had congenital hip dysplasia, for which she had surgery.

21 Midline Brain Defects: No ONH: Yes Pituitary Abnormalities: No Developmental Delay** Image 9: MRI of Patient F515 showing optic nerve hypoplasia (yellow arrows) Image 10: MRI of Patient F515 showing agenesis of the septum pellucidum

22 VI. Results Genetics As mentioned in the Methods section, the genetic analysis was completed using the final exome sequencing data. The final sequencing data was consolidated in an annotated variant file containing the variants of the proband, mother, and father. These were analyzed based on mode of inheritance de novo, homozygous, phase- compound heterozygote, or X- linked. The variants were predicted to be damaging using the CADD score (Combined Annotation Dependent Depletion), with a score higher than 10 considered damaging. Variants were also cross- referenced with the Exome Aggregation Consortium (ExAc) and Genome Aggregation Database (gnomad) to check their frequencies within the sequenced populations. Higher frequency variants were not considered damaging. Possible damaging variants were found for three of the patients F354, F420, and F504. Patient F498 was not sequenced, and no possible variants were found for F488 or F515. Patient De Novo Homozygous Compound X-Linked Heterozygous F354-P001 KIAA1324L No No No F420-P001 TMEM200A MUC20 ENTPD4 No F488-P001 No No No No F498-P001 Not sequenced Not sequenced Not sequenced Not sequenced F504-P001 No No No BCOR F515-P001 No No No No Table 2: A summary of the possible damaging variants found in the SOD patients. Clinical The clinical analysis of the cohort of patients showed a large degree of variability in phenotypic presentation. All six patients had some degree of optic never hypoplasia. Three

23 out of six patients had agenesis of the septum pellucidum, and two of those had deformity of the corpus callosum as well. Three out of six patients had hypopituitarism or some form of hormonal deficiency. Three patients had additional cortical malformations, and three were developmentally delayed. Patient F354- P001 F420- P001 Panhypopituitarism F488- P001 Adrenocortical deficiency, Hypothyroidism N/A F498- P001 F504- P001 Panhypopituitarism F515- P001 Midline Brain Defects ONH and Symptoms Hormone Deficiency Other symptoms N/A Present (left) N/A Bilateral congenital cataracts, Left hemiparesis, Schizencephaly Absent septum pellucidum Deformity of the corpus callosum Absent septum pellucidum Absent septum pellucidum Hypoplasia of the corpus callosum N/A N/A Present, Hypoplasia of optic chiasm, Nystagmus Present, Strabismus (esotropia) Present, Visual Impairment Present, Nystagmus Present, Visual difficulties N/A Gray matter heterotopia N/A Left hemiparesis, Intractable epilepsy, Hypotonicity, Polymicrogyria, Cerebral asymmetry Diabetes insipidus, Spastic hemiplegia Congenital hip dysplasia Developmental Delay N/A N/A N/A Present Present Present

24 Table 1: A breakdown of the symptoms of the cohort of patients for this study based on the presence of midline defects (excluding the optic nerve and pituitary), ONH, pituitary dysfunction, other major symptoms, and developmental delay VI. Discussion From the genetic testing and review, possible disease causing variants were found in patients F354, F420, and F504. For patient F354, KIAA1324L (chr7: :c:a) was a de novo variant that had a CADD score of This particular variant was not listed in gnomad (extremely rare). Several papers have been published describing studies of this gene, which suggest that it might be implicated in neurodevelopment. This variant requires further research and seems to be a promising avenue of exploration. For patient F420, TMEM200A (chr6: :a:g) was the patient s only filtered de novo mutation, with a CADD score of This particular variant was not listed in gnomad or OMIM. There have been no comprehensive studies on this gene. There was a homozygous mutation in MUC20, but it had a low CADD score and 6 homozygotes. There was a compound heterozygous mutation for ENTPD4 but it has no known associations for SOD- like symptoms. TMEM200A looks very promising and the lab will be pursuing further molecular and animal studies to test this variant. For patient F504, BCOR (chrx: :c:g) was an X- linked variant with a CADD score of It has been associated with microphthalmia. However, it is listed as an RNA splice variant, and thus it will be hard to associate to the patient s phenotype for sure. From the clinical review of the patients, it can clearly be seen that they are very phenotypically heterogeneous. The unifying characteristic for all of these patients is the

25 presence of some degree of ONH. Furthermore, a review of several published case studies revealed the same finding Signorini et al. performed a clinical study on 17 children diagnosed with SOD, and all the patients had either unilateral or bilateral ONH 1. An extensive literature review demonstrated that the diagnostic criteria and focus of septo- optic dysplasia tend to be ineffective and inconsistent. Using the 2/3- symptom rule, two of the patients in this study would technically not be diagnosed with SOD. Moreover, this points out that those guidelines are not universally applied by the healthcare community to diagnose patients with SOD. The term septo- optic dysplasia also places a misleading amount of emphasis on the septum pellucidum. As discussed previously, the absence of the septum pellucidum alone does not imply significant deficits. Thus, it seems prudent to restructure the diagnostics of this syndrome around the ONH, along with midline brain defects, hypopituitarism, cortical malformations, developmental delay, and other symptoms as secondary diagnostic characteristics. Instead of septo- optic dysplasia, the term Optic Nerve Hypoplasia Plus is a better categorical diagnostic name. However, it is important that each patient diagnosed with ONH+ be evaluated carefully due to the symptom variability. In the case of gene discovery through exome sequencing analysis, it is imperative to have as fine of phenotypic classification as possible, so that a cohort of patients might be defined with potential defects in a single gene. As such, it might be useful to break ONH+ down into several subgroups, for example 1. ONH with panhypopituitarism, without midline brain defects 2. ONH with midline brain defects, without pituitary dysfunction 3. ONH with both midline brain defects and pituitary dysfunction 4. ONH with cortical malformations

26 Until further etiological findings come to light about midline brain embryological malformations, the streamlining of clinical diagnosis could help with the symptom management of these patients.

27 References 1. SIGNORINI SG, DECIO A, FEDELI C, et al. Septo-optic dysplasia in childhood: the neurological, cognitive and neuro-ophthalmological perspective: Septo-optic dysplasia in Childhood. Developmental Medicine & Child Neurology. 2012;54: Kelberman D, Dattani MT. Septo-optic dysplasia - Novel insights into the aetiology. Hormone Research. 2008;69: John JRS, Reeves DL. Congenital absence of the septum pellucidum. A review of the literature with case report. The American Journal of Surgery. 1957;94: Borchert M, Garcia-Filion P. The syndrome of optic nerve hypoplasia. Current Neurology and Neuroscience Reports. 2008;8: Hoyt WF, Kaplan SL, Grumbach MM, Glaser JS. SEPTO-OPTIC DYSPLASIA AND PITUITARY DWARFISM. The Lancet. 1970;295: Volpe P, Campobasso G, De Robertis V, Rembouskos G. Disorders of prosencephalic development. Prenatal Diagnosis. 2009;29: Volpe JJ. Overview: Normal and abnormal human brain development. Mental Retardation and Developmental Disabilities Research Reviews. 2000;6: Sarwar M. The septum pellucidum: normal and abnormal. American Journal of Neuroradiology. 1989;10: Farruggia S, Babcock DS. The cavum septi pellucidi: its appearance and incidence with cranial ultrasonography in infancy. Radiology. 1981;139 (1): Winter TC, Kennedy AM, Byrne J, Woodward PJ. The cavum septi pellucidi: Why is it important? Journal of Ultrasound in Medicine. 2010;29: Williams J, Brodsky MC, Griebel M, Glasier CM, Caldwell D, Thomas P. Septo-optic dysplasia: the clinical insignificance of an absent septum pellucidum. Developmental medicine and child neurology. 1993;35: Zeman W, King FA. Tumors of the septum pellucidum and adjacent structures with abnormal affective behavior: an anterior midline structure syndrome. J Nerv Ment Dis 1958;127: Achiron R, Achiron A. Development of the human fetal corpus callosum: a high resolution, cross sectional sonographic study. Ultrasound in Obstetrics and Gynecology. 2001;18: Edwards T, Sherr E, Barkovich A, Richards L. Clinical, genetic and imaging findings identify new causes for corpus callosum development syndromes. BRAIN. 2014;137: Hamilton WJ, 1903, Boyd, J. D (James Dixon), Mossman, Harland W (Harland Winfield). Hamilton, Boyd and Mossman's Human Embryology: Prenatal Development of Form and Function. 4th ed. Cambridge: Heffer; Rizzoti K, Lovell-Badge R. Regenerative Medicine: Organ recital in a dish. Nature. 2011;480: Vann SD. Re-evaluating the role of the mammillary bodies in memory. Neuropsychologia. 2010;48: Vann SD, Erichsen JT, O'Mara SM, Aggleton JP. Selective disconnection of the hippocampal formation projections to the mammillary bodies produces only mild deficits on spatial memory tasks: Implications for fornix function. Hippocampus. 2011;2010;21:

28 19. Poelmans S, Kawamoto T, Christofoli F, et al. Genotypic and phenotypic variation in six patients with solitary median maxillary central incisor syndrome. American Journal of Medical Genetics Part A. 2015;167A: Holoprosencephaly. National Institutes of Health. Accessed April 20, Kelberman D, Dattani MT. Septo-optic dysplasia - Novel insights into the aetiology. Hormone Research. 2008;69: Patel L, McNally RJQ, Harrison E, Lloyd IC, Clayton PE. Geographical Distribution of Optic Nerve Hypoplasia and Septo-optic Dysplasia in Northwest England. The Journal of Pediatrics. 2006;148: Borchert M, Garcia-Filion P. The syndrome of optic nerve hypoplasia. Current Neurology and Neuroscience Reports. 2008;8: Kumar, V., Karunakaran, A. & Valakada, J. Int Ophthalmol (2017). doi: /s Jabeen M, Hairfield A, Swischuk L, Jain S. Septo-Optic Dysplasia in a Newborn Presenting with Bilateral Dilated and Fixed Pupils. AJP Rep. 2016;6:e112-e Musgrove JM, Riley C. Septo-Optic Dysplasia: A Case Study. Neonatal Network: NN. 2016;35: Maurya VK, Ravikumar R, Bhatia M, Ral R. Septo-optic dysplasia: Magnetic Resonance Imaging findings. Medical journal, Armed Forced India. 2015;71: