Central nervous system embryogenesis and its failures

Subarachnoid cerebrospinal fluid is essential for normal development of the cerebral cortex

The central nervous system develops around a fluid filled space which persists in the adult within the ventricles, spinal canal and around the outside of the brain and spinal cord. Ventricular fluid is known to act as a growth medium and stimulator of proliferation and differentiation to neural stem cells but the role of CSF in the subarachnoid space has not been fully investigated except for its role in the recently described "glymphatic" system. Fundamental changes occur in the control and coordination of CNS development upon completion of brain stem and spinal cord development and initiation of cortical development. These include changes in gene expression, changes in fluid and fluid source from neural tube fluid to cerebrospinal fluid (CSF), changes in fluid volume, composition and fluid flow pathway, with exit of high volume CSF into the subarachnoid space and the critical need for fluid drainage. We used a number of experimental approaches to test a predicted critical role for CSF in development of the cerebral cortex in rodents and humans. Data from fetuses affected by spina bifida and/or hydrocephalus are correlated with experimental evidence on proliferation and migration of cortical cells from the germinal epithelium in rodent neural tube defects, as well as embryonic brain slice experiments demonstrating a requirement for CSF to contact both ventricular and pial surfaces of the developing cortex for normal proliferation and migration. We discuss the possibility that complications with the fluid system are likely to underlie developmental disorders affecting the cerebral cortex as well as function and integrity of the cortex throughout life.

Holoprosencephaly with Clefts: Data of 85 Patients, Treatment and Outcome: Part 1: History, Subdivisions, and Data on 85 Holoprosencephalic Cleft Patients

CONTEXT

Cleft patients with Holoprosencephaly (HPE) constitute a controversy due to a variable facial appearance. HPE appearance varies from only a columella to a prolabium-premaxilla complex agenesis up to a common unilateral or bilateral cleft lip and palate with a single central incisor, various brain deformities, and/or even normal brain development. It is challenging to designate such various appearances, to understand their etiopathogenesis, and to choose the most appropriate management. Literature was reviewed for diagnostic criteria, pregnancy history, clinical findings, brain development, survival rate, initial perioperative management, and postsurgical midfacial growth in cleft patients with HPE. The findings were compared with a clinical database of 85 cleft patients with HPE at the Department of Maxillofacial and Oral Surgery, University of Pretoria.

AIMS OF PART 1

The aim of the study is to overcome disparities widely existing among clinicians regarding definitive diagnostic criteria, especially in cases with a common appearance of a uni- or bilateral cleft lip alveolus or cleft lip, alveolus and palate deformity, and cases presenting facial structural agenesis.

MATERIALS AND METHODS

A literature search related to diagnostic criteria was compared to results of a cleft HPE database from a single tertiary institution.

RESULTS

HPE cleft cases can be allocated to one of the following subdivisions: (1) columella complex agenesis (Ag-Colum), (2) prolabium-premaxilla-columella complex agenesis in cleft lip-alveolus deformities (Ag-CLA), (3) prolabium-premaxilla-columella agenesis in cases with complete cleft lip alveolus palate (Ag-CLAP), and (4) standard type (holoprosencephaly in patients with a standard cleft) with uni- or bilateral CLA or CLAP, hard and soft palate cleft (hPsP), and atrophic premaxillae, with or without single central incisor. Further, incidence, variation in brain development, and appearances in HPE cleft patients of different races and gender, epilepsy, and early death are discussed. Conclusion: This paper adds new data and facts to the existing literature related to cleft lip and palate patients suffering from HPE.

Toxoplasma gondii: the effects of infection at different stages of pregnancy on the offspring of mice

Congenital toxoplasmosis can cause fetal damage in humans and domestic animals. This study was focused on the effects of Toxoplasma gondii (Prugniaud strain) infection at different stages of pregnancy on the offspring of mice. Results showed that newborn mice from all infected groups were significantly lower in weight than those from the control group but significant difference was not found among these groups at day 60 after birth. The survival rate of the offspring from the group of mice infected at the earlier stage of pregnancy was significantly lower than those of infected and control groups. The positive offspring (with cysts found in their brain tissues) born from the mice infected at the earlier and intermediate stages of pregnancy showed a shorter latency and greater number of errors in the step-through passive avoidance test than those born from the mice infected at the late stage of pregnancy, the control group and the negative offspring from the infected groups. The number of cysts in the brain tissue was significantly higher in the offspring born from the groups of mice infected at the earlier and intermediate stages of pregnancy than those from the group of mice infected at the late stage of pregnancy. In addition, our results indicated that a high congenital transmission rate (90%) occurred in this NIH mouse model. In conclusion, the earlier and intermediate maternal infection of T. gondii can result in severe congenital toxoplasmosis, exhibiting conditions such as stillbirth or non-viability, and learning or memory capability damage in this mouse model. These results not only provide useful data for better understanding the effects of T. gondii infection on the offspring of mice infected at different stages of pregnancy but also for better consideration of the effect of this infection on other mammalian hosts including humans.

Holoprosencephaly and holoprosencephaly-like phenotypes: Review of facial and molecular findings in patients from a craniofacial hospital in Brazil

Here we report on the clinical and genetic data for a large sample of Brazilian patients studied at the Hospital de Reabilitação de Anomalas Craniofaciais-Universidade de São Paulo (HRAC-USP) who presented with either the classic holoprosencephaly or the holoprosencephaly-like (HPE-L) phenotype. The sample included patients without detected mutations in some HPE determinant genes such as SHH, GLI2, SIX3, TGIF, and PTCH, as well as the photographic documentation of the previously reported patients in our Center. The HPE-L phenotype has been also called of HPE "minor forms" or "microforms." The variable phenotype, the challenge of genetic counseling, and the similarities to patients with isolated cleft lip/palate are discussed.

Cerebellar migration defects in aicardi syndrome: an extension of the neuropathological spectrum

The Aicardi syndrome is characterized by infantile spasms, corpus callosum agenesis, and chorioretinal lacunae and almost exclusively affects females (very rarely, 47, XXY males). The crucial genetic mishap likely occurs in the postzygotic stage, but the variable clinical phenotype among the approximately 450 known cases has not been explained. No consistent mutations or deletions exist among patients. We encountered a baby girl with early onset infantile spasms. She had left-sided cleft lip/palate, costovertebral defects, scoliosis, callosal agenesis, and microphthalmia. She expired at the age of 3 months of respiratory infection. On autopsy she had thoracic hemivertebrae with rib defects, bilateral microphthalmia, microcornea, posterior colobomata, abnormalities of the retinal pigment epithelium, absence of normal ganglion cells in the retina, gross asymmetry of the brain with cerebral polymicrogyria, total callosal agenesis, cerebral subcortical and subependymal nodular heterotopias, cerebellar nodular heterotopias, and tegmental/basal unilateral brainstem hypoplasia. Cerebellar and retinal migration defects have not been described before in Aicardi syndrome and may have had a bearing on this patient's eventual outcome.

Language skills and neuropsychological performance in patients with SHH mutations and a holoprosencephaly-like phenotype

Here, we evaluate linguistic skills and neuropsychological performance in a sample of patients with SHH mutations and a holoprosencephaly (HPE)-like phenotype, a minor form of classic HPE. Our findings suggest that patients with SHH mutations and a HPE-like phenotype have normal cognitive ratios and significant language impairment. Imaging evaluation by magnetic resonance imaging (MRI) was normal in three patients and in one there was hypoplasia of the anterior commissure and the presence of a temporal cyst, apparently not related to the clinical findings.

The interplay of genetic and environmental factors in craniofacial morphogenesis: holoprosencephaly and the role of cholesterol

Cyclopia, the paradigmatic "face [that] predicts the brain" in severe holoprosencephaly (HPE) (DeMyer et al., 1964), has been recognized since ancient times. Descriptive embryologists and pathologists have noted the continuum of defective separation of the forebrain and loss of central nervous system (CNS) midline structures for more than a century. It has been recognized more recently that inhibitors of cholesterol biosynthesis, whether consumed in native plants by range sheep, or experimentally applied to early embryos, could phenocopy the natural malformation, as could a variety of other teratogens (maternal diabetes, alcohol). Yet it has been less than a decade that the genomic knowledge base and powerful analytic methods have brought the sciences of descriptive, molecular, and genetic embryology within range of each other. In this review, we discuss the clinical presentations and pathogenesis of HPE. We will outline various genetic and teratogenic mechanisms leading to HPE. Lastly, we will attempt to examine the pivotal role of cholesterol and the Sonic Hedgehog (Shh) pathway in this disorder and in normal embryonic forebrain development.