Neural System - Abnormalities

From Embryology

Introduction

Australian abnormalities (1981-92)
Neural groove closing to neural tube, early week 4
(Stage 10)

There are many different congenital and environmentally derived abnormalities associated with the nervous system. There are potentially 1000's of neurological abnormalities that could be listed on this page, therefore this current page is only a very brief introduction to some of these neural abnormalities. As the nervous system continues to develop postnatally, environmental issues such a nutrition (folate, iodine) and sensory abnormalities (hearing) can also impact on developmental milestones.


Neural Links: ectoderm | neural | neural crest | ventricular | sensory | Stage 22 | gliogenesis | neural fetal | Medicine Lecture - Neural | Lecture - Ectoderm | Lecture - Neural Crest | Lab - Early Neural | neural abnormalities | folic acid | iodine deficiency | Fetal Alcohol Syndrome | neural postnatal | neural examination | Histology | Historic Neural | Category:Neural

| Low Folic Acid and NTDs | International Classification of Diseases - Neural

Some Recent Findings

  • Mutations in genes encoding the glycine cleavage system predispose to neural tube defects in mice and humans[1] "Function of folate one-carbon metabolism (FOCM) has been implicated as a key determinant of susceptibility to NTDs. The glycine cleavage system (GCS) is a multi-enzyme component of mitochondrial folate metabolism, and GCS-encoding genes therefore represent candidates for involvement in NTDs. To investigate this possibility, we sequenced the coding regions of the GCS genes: AMT, GCSH and GLDC in NTD patients and controls. ... Overall, our findings suggest that loss-of-function mutations in GCS genes predispose to NTDs in mice and humans. These data highlight the importance of adequate function of mitochondrial folate metabolism in neural tube closure."
  • A randomized trial of prenatal versus postnatal repair of myelomeningoce[2] "Prenatal repair of myelomeningocele, the most common form of spina bifida, may result in better neurologic function than repair deferred until after delivery. We compared outcomes of in utero repair with standard postnatal repair. ....Prenatal surgery for myelomeningocele reduced the need for shunting and improved motor outcomes at 30 months but was associated with maternal and fetal risks. (Funded by the National Institutes of Health; ClinicalTrials.gov number, NCT00060606.)." (see also paper comments)
  • Australia 1998–2005[3] "944 births over this period affected by NTD. Of these births, 523 were live births and 421 were fetal deaths (still births and terminations after 20 weeks gestation). This equates to a prevalence of neural tube defects (NTD) among births of 4.6 per 10,000."

Neural Tube Closure

Mouse mutant showing neural tube closure defect

Dysraphism is the term often used to describe the defective fusion of the neural folds. The position and degree of failure of fusion will result in either embryonic death or a range of different neural defects. The way (mode) in which the human neural tube fuses has been a source of contention. In humans, fusion appears to initiate at multiple sites along the neural groove [4][5], this mode of closure may differ from that found in many animal species used in developmental studies.

Human Embryonic Death:

  • 5 weeks with total failure of fusion.
  • 6.5 weeks with opening over the rhombencephalon.
  • survive beyond 7 weeks with a defect at the frontal and parietal regions.


Links: Folic Acid and Neural Tube Defects

Spina Bifida (Meningomyelocele)

Neural tube defect meningomyelocele.jpg Spina Bifida Rates (USA Data)
Meningomyelocele Spina Bifida Rates (USA Data)

There are potentially many different causes of spina bifida and neural tube defects. The basis of the abnormality is a failure of the neural tube to close caudally. At least one known cause is a low maternal diet of folic acid (folate) containing foods. (see Neural Tube Defects and Low Folic Acid or Folic Acid below)

Neural tube defects from failure to close can be screened by amniocentesis or ultrasound.

Alpha-fetoproetin normally present in the CSF, leaks and can be detected in amniotic fluid.

Cephalic Disorders

Cephalic (Greek, kephale = head) are a large group of abnormalities that relate to both skeletal (skull) and neural (brain) associated defects including: anencephaly, hydrocephalus, encephalocele, colpocephaly (occipital horn enlargement), lissencephaly (smooth brain), porencephaly (cyst or cavity in cerebral hemisphere), acephaly (absence of head), exencephaly (brain outside skull), macrocephaly (large head), micrencephaly (small brain), otocephaly (absence of lower jaw), brachycephaly (premature fusion of coronal suture), oxycephaly (premature fusion of coronal suture + other), plagiocephaly (premature unilateral fusion of coronal or lambdoid sutures), scaphocephaly (premature fusion of sagittal suture), trigonocephaly.

Anencephaly

Anencephaly Rates (USA Data)[6]

This is a neural tube defect, the basis of the abnormality is a failure of the neural tube to close cranially. Also called exencephaly or craniorachischisis.

Hydrocephalus

Hydrocephalus (historic image from Hess, 1922)

This is a defect of cerebrospinal fliud (CSF) flow, excess fluid production or impaired fluid absorption and can be congenital or acquired. Estimated incidence of 1 in 1000 live births the condition leads to enlarged ventricles and head, separated skull cranial sutures and fontanelles. Obstruction of CSF flow can occur at any time (prenatally or postnatally) and leads to accumulation of within the ventricles. The time of onset will have different effects and should be compared to the equilivant neurological events that are occuring.

Ventricular obstruction usually occurs at the level of the cerebral aqueduct (narrowest site), but can occur elsewhere, and can be caused by viral infection or zoonotic disease.

Encephalocele

This defect is generally mesodermal in origin, leading to protrusion of brain and meninges outside the crainal cavity. The severity of the disorder can vary dependent upon the degree of mesodermal abnormality.

Encephalitis

Normally a postnatal clinical syndrome of the central nervous system resulting in inflammation of the brain parenchyma and caused by a range of pathogens (viral, bacterial and protozoal infections). This infectious disease is due mainly to viral pathogens: Herpes simplex encephalitis 10%–20% of cases, Murray Valley encephalitis virus, Japanese encephalitis virus, Australian bat lyssavirus, West Nile virus, Hendra virus and Nipah virus. The pathogen is generally included in the specific encephalitis naming; Varicella encephalitis and Toxoplasma meningoencephalitis.

Links: Neural System - Abnormalities | TORCH Infections | PMC2700670)

Fragile X Syndrome

Fragile X Syndrome (FXS) is the most common form of inherited mental retardation and autism. The condition is caused by a loss of the functional fragile X mental retardation protein (FMRP) an RNA-binding protein that can regulate the translation of specific mRNAs. There are several suggested additional roles for this protein including synaptic development and function[7] and in adult neurogenesis.[8]


Links: Fragile X Association of Australia |

Autism

Autism (autism spectrum disorder, ASD) is a behaviourally defined brain disorder in children. Features include: impoverished verbal and non-verbal communication skills, reduced social interactions (bias their attention towards objects rather than the surrounding social situation), behavioural impairments in attention engagement/disengagement, poor emotional discrimination and facial recognition, and fail to response to their own names. There exist many different and unproven claims as to the origins of autism.

Developmentally associated with neural maturation changes in cortical thickness and organization, and particularly affecting pyramidal neurons. A rat model shows structural and behavioural features of autism as a result of altering the trajectory of early postnatal cortical development.[9]

Newborn Neural Exam

Newborn Abnormal Links: behaviour | cranial nerves | Newborn Tone - resting posture | upper extremity‎ | arm traction | arm recoil | scarf sign | hand position | lower extremity | leg traction‎ | leg recoil‎‎ | popliteal angle‎ | heel to ear | neck tone | head lag‎ | head control | Newborn Positions - prone | ventral suspension | vertical suspension | Newborn Reflexes - deep tendon reflexes | plantar reflex‎ | suck, root | Moro | Galant | stepping‎ | grasp | Newborn Head - head shape and sutures‎ | head circumference‎


Links: Neural Exam Movies -Newborn Abnormal

International Classification of Diseases

The International Classification of Diseases (ICD) World Health Organization's classification used worldwide as the standard diagnostic tool for epidemiology, health management and clinical purposes. This includes the analysis of the general health situation of population groups. It is used to monitor the incidence and prevalence of diseases and other health problems. Within this classification "congenital malformations, deformations and chromosomal abnormalities" are (Q00-Q99) but excludes "inborn errors of metabolism" (E70-E90).

Congenital malformations of the nervous system (Q00-Q07)

Links: Neural System - Abnormalities | Neural Crest Abnormalities | WHO Links

Q00 Anencephaly and similar malformations

  • Q00.0 Anencephaly, Acephaly, Acrania, Amyelencephaly, Hemianencephaly, Hemicephaly
  • Q00.1 Craniorachischisis
  • Q00.2 Iniencephaly

Q01 Encephalocele

Incl.: encephalomyelocele, hydroencephalocele, hydromeningocele, cranial meningocele, cerebral meningoencephalocele

Excl.: Meckel-Gruber syndrome (Q61.9)

  • Q01.0 Frontal encephalocele
  • Q01.1 Nasofrontal encephalocele
  • Q01.2 Occipital encephalocele
  • Q01.8 Encephalocele of other sites
  • Q01.9 Encephalocele, unspecified

Q02 Microcephaly

Incl.: Hydromicrocephaly Micrencephalon Excl.: Meckel-Gruber syndrome (Q61.9)

Q03 Congenital hydrocephalus

Incl.: hydrocephalus in newborn Excl.: Arnold-Chiari syndrome (Q07.0) hydrocephalus: acquired (G91.-) due to congenital toxoplasmosis (P37.1) with spina bifida (Q05.0-Q05.4)

  • Q03.0 Malformations of aqueduct of Sylvius Aqueduct of Sylvius: anomaly obstruction, congenital stenosis
  • Q03.1 Atresia of foramina of Magendie and Luschka Dandy-Walker syndrome
  • Q03.8 Other congenital hydrocephalus
  • Q03.9 Congenital hydrocephalus, unspecified

Q04 Other congenital malformations of brain

Excl.: cyclopia (Q87.0) macrocephaly (Q75.3)

  • Q04.0 Congenital malformations of corpus callosum, Agenesis of corpus callosum
  • Q04.1 Arhinencephaly
  • Q04.2 Holoprosencephaly
  • Q04.3 Other reduction deformities of brain, Absence, Agenesis, Aplasia, Hypoplasia of part of brain, Agyria, Hydranencephaly, Lissencephaly, Microgyria, Pachygyria Excl.: congenital malformations of corpus callosum (Q04.0)
  • Q04.4 Septo-optic dysplasia
  • Q04.5 Megalencephaly
  • Q04.6 Congenital cerebral cysts, Porencephaly, Schizencephaly, Excl.: acquired porencephalic cyst (G93.0)
  • Q04.8 Other specified congenital malformations of brain, Macrogyria
  • Q04.9 Congenital malformation of brain, unspecified Congenital: anomaly, deformity, disease or lesion, multiple anomalies NOS of brain

Q05 Spina bifida

Incl.: hydromeningocele (spinal), meningocele (spinal), meningomyelocele, myelocele, myelomeningocele, rachischisis, spina bifida (aperta)(cystica), syringomyelocele Excl.: Arnold-Chiari syndrome (Q07.0), spina bifida occulta (Q76.0)

  • Q05.0 Cervical spina bifida with hydrocephalus
  • Q05.1 Thoracic spina bifida with hydrocephalus Spina bifida: dorsal thoracolumbar with hydrocephalus
  • Q05.2 Lumbar spina bifida with hydrocephalus, Lumbosacral spina bifida with hydrocephalus
  • Q05.3 Sacral spina bifida with hydrocephalus
  • Q05.4 Unspecified spina bifida with hydrocephalus
  • Q05.5 Cervical spina bifida without hydrocephalus
  • Q05.6 Thoracic spina bifida without hydrocephalus Spina bifida: dorsal NOS, thoracolumbar NOS
  • Q05.7 Lumbar spina bifida without hydrocephalus, Lumbosacral spina bifida NOS
  • Q05.8 Sacral spina bifida without hydrocephalus
  • Q05.9 Spina bifida, unspecified

Q06 Other congenital malformations of spinal cord

  • Q06.0 Amyelia
  • Q06.1 Hypoplasia and dysplasia of spinal cord, Atelomyelia, Myelatelia, Myelodysplasia of spinal cord
  • Q06.2 Diastematomyelia
  • Q06.3 Other congenital cauda equina malformations
  • Q06.4 Hydromyelia Hydrorachis
  • Q06.8 Other specified congenital malformations of spinal cord
  • Q06.9 Congenital malformation of spinal cord, unspecified Congenital: anomaly, deformity, disease or lesion, NOS of spinal cord or meninges

Q07 Other congenital malformations of nervous system

Excl.: familial dysautonomia [Riley-Day] (G90.1), neurofibromatosis (nonmalignant) (Q85.0)

  • Q07.0 Arnold-Chiari syndrome
  • Q07.8 Other specified congenital malformations of nervous system Agenesis of nerve, Displacement of brachial plexus, Jaw-winking syndrome, Marcus Gunn's syndrome
  • Q07.9 Congenital malformation of nervous system, unspecified Congenital: anomaly, deformity, disease or lesion, NOS of nervous system

References

  1. ↑ <pubmed>22171071</pubmed>
  2. ↑ <pubmed>21306277</pubmed>
  3. ↑ Abeywardana S & Sullivan EA 2008. Neural tube defects in Australia. An epidemiological report. Cat. no. PER 45. Sydney: AIHW National Perinatal Statistics Unit | PDF.
  4. ↑ <pubmed>8267004</pubmed>
  5. ↑ <pubmed>10909899</pubmed>
  6. ↑ Mathews TJ. Trends in spina bifida and anencephalus in the United States, 1991-2005, National Vital Statistics System.
  7. ↑ <pubmed>18957214</pubmed>
  8. ↑ <pubmed>20386739</pubmed>
  9. ↑ Chomiak T, Karnik V, Block E, Hu B. Altering the trajectory of early postnatal cortical development can lead to structural and behavioural features of autism. BMC Neurosci. 2010 Aug 19;11:102. PMID: 20723245| BMC Neurosci.


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Cite this page: Hill, M.A. (2024, April 27) Embryology Neural System - Abnormalities. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Neural_System_-_Abnormalities

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