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Developmental Diseases of the Nervous System
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
James H. Tonsgard, Nikolas Mata-Machado
The causes of schizencephaly are heterogeneous. Both genetic and nongenetic causes are postulated. There are some cases associated with chromosomal aneuploidy, single gene defects, and distinct syndromes, so it is likely that there is more than one genetic cause. The EMX2 gene was initially implicated, but more recent studies do not support that. Currently, another gene, LHX2, a gene expressed in the forebrain, has been suggested, as well as the genes HESX1 and SOX2. Pathology shows a deep cleft, either unilateral or bilateral, extending the full thickness of the brain. The walls of the cleft are usually widely separated, and the clefts are commonly in the perisylvian area. The cortex lining the clefts is polymicrogyric.
Distribution and Characteristics of Brain Dopamine
Published in Nira Ben-Jonathan, Dopamine, 2020
The human pituitary gland is a size of a pea and weighs ~500 mg, while the rat pituitary gland weighs 12–15 mg. The pituitary consists of two lobes, anterior and posterior that arise from distinct parts of embryonic tissue. The posterior pituitary (PP) or neural lobe (NL) has its embryological origin in nervous tissue, given that it develops from a down-growth of the diencephalon that forms the floor of the third ventricle. On the other hand, the anterior lobe (AL), also called the pars distalis or anterior pituitary (AP), is derived from an up-growth of the oral ectoderm within the primitive oral cavity, called the Rathke’s pouch (Figure 3.10). The pituitary organogenesis is a highly complex and tightly regulated process that depends on several transcription factors such as PROP1, PIT1 (POU1F1), HESX1, LHX3, and LHX4 [39]. Mutations in these genes can result in different combinations of hypopituitarism that can be associated with structural alterations of the CNS, causing the congenital form of panhypopituitarism. Detailed information of the cellular composition and hormone synthesis and regulation by the pituitary gland is presented in Chapter 5.
Primary Pituitary Disease
Published in John C Watkinson, Raymond W Clarke, Louise Jayne Clark, Adam J Donne, R James A England, Hisham M Mehanna, Gerald William McGarry, Sean Carrie, Basic Sciences Endocrine Surgery Rhinology, 2018
Christopher M. Jones, John Ayuk
Combined pituitary hormone deficiency may also arise as part of a syndrome, as is the case in septo-optic dysplasia, Rieger’s syndrome and holoprosencephaly.6 Septo-optic dysplasia carries an incidence of approximately 1:10 000 and both sporadic and familial cases have been described with HESX1, SOX2 and SOX3 implicated in the pathogenesis of this disorder.7 Hypoplasia of both the pituitary and optic nerve is seen as a consequence, in addition to defects of the midline forebrain. This commonly results in neurological defects. Visual impairment and variable endocrine deficiencies – the most common of which are isolated GH deficiency and combined TSH and ACTH deficiency – are also seen.
Septo-optic dysplasia presenting with nystagmus, pseudo-disc edema, and fovea hypoplasia
Published in Ophthalmic Genetics, 2022
Richard Sather ΙΙΙ, Dorothy Thompson, Jacqueline Ihinger, Sandra R. Montezuma
The incidence of SOD is 1 in 10,000 live births, with boys and girls affected equally (3). The etiology is unclear, though SOD has been associated with a younger maternal age and environmental factors may play a role (4). Some of these environmental risk factors that may contribute to malformations typical of SOD include drug consumption, viral infections, and maternal diabetes (4). The underlying genetic mechanisms are still being worked out, and common genetic abnormalities include common pathogenic gene variants in two genes: HESX1 and SOX2 (5). The HESX1 homeobox gene functions as a transcriptional repressor and is responsible for pituitary organogenesis (6). The SOX2 gene has been linked as a critical component in the proper development of the pituitary gland, forebrain, and eye during human embryogenesis (7). Other genes including SOX3 and OTX2 have also been identified in some cases of SOD (8).
Selected Ophthalmological Features in Children with Septo-Optic Dysplasia and Optic Nerve Hypoplasia
Published in Neuro-Ophthalmology, 2022
Michael S. Salman, Shakhawat Hossain, Elizabeth Carson, Chelsea A. Ruth, Ian H. Clark
The aetiology remains mostly undetermined with a genetic aetiology being implicated in a minority of cases, usually mutations in the HESX1 homeodomain.3,4 An acquired pathological process in-utero has been implicated in some case reports.5 Primagravida and young maternal age at delivery are recognised risk factors in large observational studies.6–10 Developmental delay, intellectual disability, and hypopituitarism occur commonly in SOD/ONH (50–80% of cases). In addition, seizures, behavioural difficulties, and autism spectrum disorder may occur in up to 30% of patients.2,11–13
FEVR phenotype associated with septo-optic dysplasia
Published in Ophthalmic Genetics, 2019
David L. Zhang, Michael P. Blair, Janice L. Zeid, Syeda S.T. Basith, Michael J. Shapiro
Genetic studies indicate that mutations in HESX1 have been associated with both homozygous and heterozygous mutations in SOD, and its homologue Hesx1 is an early marker of pituitary development in mice (10,12). The homozygous (autosomal recessive) mutations are fully penetrant, while the heterozygous (autosomal dominant) mutations are variably penetrant. In addition, mutations in SOX2 occasionally result in anterior pituitary hypoplasia and corpus callosum defects (13). Despite these findings, genetic mutations are found in less than one percent of patients with SOD, with the remaining cases having an unclear etiology (1,14).