What Are Neurodevelopmental Disorders?

  • Nathan Davies Bachelor of Science - BS, Pharmacology, Swansea University

The term ‘neurodevelopment disorder’ is commonly used, and there usually isn’t much context given about what a neurodevelopmental disorder is. This article hopes to give you a better understanding of the condition by giving you understandable and sensitive information gathered from trusted scientific sources.

A neurodevelopmental disorder is when a person’s brain development is atypical, affecting how the brain works.1 This change in brain development can cause difficulties with acquiring and understanding information and negatively impact communication, motor skills, and behaviour.2 Common neurodevelopmental disorders include autism spectrum disorder (ASD) and attention deficit and hyperactivity disorder (ADHD).3

This article will help give you an understanding of what typical neurodevelopment looks like, what factors affect neurodevelopment, various neurodevelopmental disorders, and some of the areas of a person’s life that can be affected by atypical brain development. 

Looking after somebody can be difficult, we acknowledge that. There is so much to look out for, making it understandable that this article, on top of all the other information that you are taking in, can seem daunting and maybe even overwhelming. However, it must be mentioned that despite any neurodevelopmental difficulties a person may face, creating and maintaining a home environment that is safe, supportive, and stimulating, along with parental responsiveness (being accepting, nurturing, supportive, sensitive, and warm), have been seen as very influential over a person’s development in life.

Typical neurodevelopment

As you have probably heard hundreds of times before, the human brain is incredibly complex. It develops from the tip of a 3-millimetre structure known as the neural tube (which the foetus develops in weeks 3-4 of pregnancy). Later, with the neural tube, the spinal cord will develop into a structure with over 100 billion neurons (brain cells).4,5

Brain development can be broken up into 5 steps, beginning roughly 5 weeks after a foetus is conceived, with more than one of these steps potentially happening at the same time.

Step 1: A lot of brain cells are produced

In the beginning, many brain cells are produced, but these cells are not yet adapted to the environment of the brain, making them all very similar at this stage. The cells reproduce in a set area of the brain known as the ventricular zone. Here, cells divide in two, with this division happening in cycles – each division cycle doubling the cells in the brain. 

A small change in the timing, duration, or number of cycles can have a major impact on the brain, possibly causing a certain layer of the brain to become underdeveloped.4 

Step 2: The brain cells (neurons) migrate to where they need to be

The brain develops from the inside outwards, with the cells able to travel as far as the outer layer of the brain (known as the cerebral cortex) from their start point – the ventricular zone. Each brain cell has a set path and destination, with different cells involved in these pathways to guide the neurons to their destination. 

Since the brain develops from the inner to the outer layers, neuron cells must move past other neurons that have already found their place in the brain. It is thought that the stationary neurons share information with the moving neurons to help with the next development stage of the brain. Issues in this process can lead to brain cells arriving at the wrong destination.4

Step 3: Forming regions in the brain

After a cell has migrated, it tends to group up with other similar cells in an organised way. Cells of the same type recognise each other and clump together to form an area of the brain, sometimes even arranging themselves to face the same direction. This grouping of cells into particular areas of the brain decides how each part of the brain forms and the function of that area. 

As more cells add themselves to an already crowded area of the brain (increasing its surface area), the outer layer of the brain will begin to scrunch up into folds and creases to accommodate a larger number of cells. While there, the cells also finish adapting themselves to their new role in that specific area of the brain.4

Step 4: Cells in the brain forming connections with each other

While the regions of the brain are developing, cells in these regions are forming connections to each other (called synapses) that allow them to send signals and information.6 

Synapses can form between any of the following parts of the neuron: 

  • Axons – which act as wires, allowing to send signals over large distances
  • Dendrites – acting as input ports in a device, receiving information sent by other brain cells 
  • Soma (cell body) – the core of the cell, receiving and sending the signals and integrating the information to control the neuron’s functions. 

Signals in these connections between the brain cells are sent through neurotransmitters – chemical signals, for example, dopamine, which allow the brain to communicate (or, instead, electrical signals in the case of connections between cell bodies). 

Many different signalling molecules are used to direct this growth of connections between the neurons. It’s done by cells by giving directions to other cells on where to form connections or by giving nutrients to another cell. It is because of the way these connections “connect everything with everything” that the brain is so effective at integrating information.

Step 5: Removing extra cells and connections plus fixing errors

Far too many synapses and a few too many neurons are formed during early brain development. The brain removes many of these connections and a few neurons to work at its best. The connections in each person’s brain are unique and affected by many experiences and exposures. It is theorised a person may have too many synapses and neurons at birth so that the body can choose which are most useful to keep.

Neurons and synapses must compete for nutrients. The following are thought to help decide if a connection or neuron stays: 

  • A cell targeted by the connection gives nourishment 
  • The targeted cell’s outer surface has enough space to maintain a connection
  • An active brain cell communicates back to its cell body to increase its growth.

The process of modifying connections also removes cells that were misplaced in the brain due to misreading directions given during the migration process. If these misplaced cells are not removed, they can contribute to certain developmental disorders of the brain.4 

What happens next?

After 18 months, no new neurons are added, and the cells have roughly finished grouping together in specific regions. The removal of excess connections in the brain is a process that happens for years after the first 5 weeks of gestation (pregnancy).4 The brain continues to develop until a person is in their late 20s.

Factors affecting neurodevelopment

The widespread changes in the brain’s structure that lead to neurodevelopmental disorders are caused by the brain’s development process being interrupted by factors affecting the foetus in the womb or an individual in early life. There are usually multiple causes of a neurodevelopmental disorder rather than one specific reason.8,9 These factors include:

  • Genetics – certain genes have been associated with some neurodevelopmental disorders. However, genetic factors alone do not explain a direct cause of ‘most’ neurodevelopmental disorders.9
  • Toxicities – many toxins, including toxins in the environment such as lead, methylmercury, and PCBs (polychlorinated biphenyls) can contribute to the risk of neurodevelopmental disorders arising. Foetuses are particularly vulnerable due to a lack of protection from the blood-brain barrier (a barrier that stops harmful substances from getting into the blood that reaches the brain). Children are also more sensitive than adults due to children having worse detoxifying mechanisms and worse immune systems. Substances such as illicit drugs and alcohol can also negatively impact brain development.9-12
  • Environmental – for a foetus, the mother can be considered as their external ‘environment’, so alcohol, tobacco and illicit drug use during pregnancy are risks for neurodevelopmental disorders. There are also certain contaminants in the environment (like those mentioned under toxicities) that impact neurodevelopment.9
  • Social – Maternal stress, the composition of the family (whether there are two parents and if those parents are living together or separated), and even the child’s order of birth compared to their siblings.13,14
  • Psychological – maternal psychological well-being during pregnancy has been shown to impact the neurodevelopment of the child. Additionally, socioeconomic status and early life stress experienced by the child were considered factors affecting the brain’s development.9,14-15
  • Educational – the brain is both physically and chemically changed during learning, allowing for new connections to form. For this reason, making a good school environment, having quality early childhood education, and increasing parental involvement is beneficial for neurodevelopment.16
  • If the baby was born preterm or with a low birthweight.9
  • Sometimes, some connections even form accidentally.4

There are also factors related to the foetus itself which affect its brain development (through synaptic formation), such as;

  • The foetus moving (kicking, turning, and thumb sucking)
  • The foetus’ senses picking up on its’ environment including; temperature, pressure, and what the foetus hears (although the foetus’ brain isn’t able to associate the sound with anything yet).4

Types of neurodevelopmental disorders

Often, a person will suffer from multiple neurodevelopmental disorders at once.17 Some of the examples include:

Areas of life typically impacted by neurodevelopmental disorders 

The symptoms and behaviours caused by neurodevelopmental disorders and the impact that a condition has on an individual are dependent on its severity. The condition is likely to alter as a child grows - however, some disabilities are permanent.

Areas that can be affected in an individual’s life include

  • Language and speech
  • Motor skills and function
  • Behaviour
  • Memory
  • Learning
  • Mental health
    It is not known for certain whether having neurodevelopmental disorders makes a person more prone to poor mental health. 20 However, additional mental health problems are much more common in people with certain neurodevelopmental conditions. For example, high levels of anxiety arise from difficulties with communication or being overwhelmed.

Summary 

Neurodevelopmental disorders are conditions forming as a result of atypical brain development, resulting in problems with cognition, communication, motor skills and behaviours of an affected individual. Typical neurodevelopment takes place from early pregnancy and early childhood and continues till the early 20s. During that time, the brain develops in five key stages: production of cells, their migration, formation of brain regions, making connections and refining them. 

Multiple factors can alter the brain’s development, including genetics, environment, social, psychological and educational aspects of life. Atypical neurodevelopment may lead to widely known ADHD and autism spectrum disorder, as well as learning difficulties, impairment of sensory systems, schizophrenia and bipolar disorder. Each of those conditions comes with particular difficulties of different severity that can negatively affect an individual’s well-being. It’s important to note that as the presentation of the disease may change over time, some of the disabilities may be permanent. 

References

  1. Parenti I, Rabaneda LG, Schoen H, Novarino G. Neurodevelopmental disorders: from genetics to functional pathways. Trends in Neurosciences [Internet]. 2020 Aug [cited 2024 Jan 24];43(8):608–21. Available from: https://linkinghub.elsevier.com/retrieve/pii/S0166223620301223
  2. Mullin AP, Gokhale A, Moreno-De-Luca A, Sanyal S, Waddington JL, Faundez V. Neurodevelopmental disorders: mechanisms and boundary definitions from genomes, interactomes and proteomes. Transl Psychiatry [Internet]. 2013 Dec 3 [cited 2024 Jan 24];3(12):e329–e329. Available from: https://www.nature.com/articles/tp2013108
  3. Scandurra V, Emberti Gialloreti L, Barbanera F, Scordo MR, Pierini A, Canitano R. Neurodevelopmental disorders and adaptive functions: a study of children with autism spectrum disorders (Asd) and/or attention deficit and hyperactivity disorder(Adhd). Front Psychiatry [Internet]. 2019 Sep 4 [cited 2024 Jan 24];10:673. Available from: https://www.frontiersin.org/article/10.3389/fpsyt.2019.00673/full
  4. Ackerman S. Discovering the brain. [Internet]. Washington: National Academies Press; 194 p. Available from: https://www.ncbi.nlm.nih.gov/books/NBK234146/#:~:text=According%20to%20this%20scheme%2C%20the
  5. Singh R, Munakomi S. Embryology, neural tube. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 [cited 2024 Jan 24]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK542285/
  6. Caire MJ, Reddy V, Varacallo M. Physiology, synapse. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 [cited 2024 Jan 24]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK526047/
  7. Sheffler ZM, Reddy V, Pillarisetty LS. Physiology, neurotransmitters. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 [cited 2024 Jan 24]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK539894/
  8. Hadders-Algra M. Early diagnostics and early intervention in neurodevelopmental disorders—age-dependent challenges and opportunities. JCM [Internet]. 2021 Feb 19 [cited 2024 Jan 24];10(4):861. Available from: https://www.mdpi.com/2077-0383/10/4/861
  9. Neurodevelopmental Disorders [Internet]. Washington, D.C.: U.S. Environmental Protection Agency; 2013. (America’s Children and the Environment). Report No.: Third Edition. Available from: https://www.epa.gov/sites/default/files/2015-10/documents/ace3_neurodevelopmental.pdf
  10. Daneman R, Prat A. The blood–brain barrier. Cold Spring Harb Perspect Biol [Internet]. 2015 Jan [cited 2024 Jan 24];7(1):a020412. Available from: http://cshperspectives.cshlp.org/lookup/doi/10.1101/cshperspect.a020412
  11. Gorini F, Muratori F, Morales MA. The role of heavy metal pollution in neurobehavioral disorders: a focus on autism. Rev J Autism Dev Disord [Internet]. 2014 Dec [cited 2024 Jan 24];1(4):354–72. Available from: http://link.springer.com/10.1007/s40489-014-0028-3
  12. Squeglia LM, Gray KM. Alcohol and drug use and the developing brain. Curr Psychiatry Rep [Internet]. 2016 May [cited 2024 Jan 24];18(5):46. Available from: http://link.springer.com/10.1007/s11920-016-0689-y
  13. Kundakovic M, Jaric I. The epigenetic link between prenatal adverse environments and neurodevelopmental disorders. Genes [Internet]. 2017 Mar 18 [cited 2024 Jan 24];8(3):104. Available from: http://www.mdpi.com/2073-4425/8/3/104
  14. Bush NR, Wakschlag LS, LeWinn KZ, Hertz-Picciotto I, Nozadi SS, Pieper S, et al. Family environment, neurodevelopmental risk, and the environmental influences on child health outcomes (Echo) initiative: looking back and moving forward. Front Psychiatry [Internet]. 2020 Jun 19 [cited 2024 Jan 24];11:547. Available from: https://www.frontiersin.org/article/10.3389/fpsyt.2020.00547/full
  15. Smith KE, Pollak SD. Early life stress and development: potential mechanisms for adverse outcomes. J Neurodevelop Disord [Internet]. 2020 Dec [cited 2024 Jan 24];12(1):34. Available from: https://jneurodevdisorders.biomedcentral.com/articles/10.1186/s11689-020-09337-y
  16. Finocchiaro E. Neurodevelopment and early childhood education for low-income students: an analytical literature review. INT-JECSE [Internet]. 2016 Dec 30 [cited 2024 Jan 24];8(2):100–100. Available from: https://www.int-jecse.net/abstract.php?id=122
  17. Francés L, Quintero J, Fernández A, Ruiz A, Caules J, Fillon G, et al. Current state of knowledge on the prevalence of neurodevelopmental disorders in childhood according to the DSM-5: a systematic review in accordance with the PRISMA criteria. Child Adolesc Psychiatry Ment Health [Internet]. 2022 Dec [cited 2024 Jan 24];16(1):27. Available from: https://capmh.biomedcentral.com/articles/10.1186/s13034-022-00462-1
  18. Williams C, Northstone K, Borwick C, Gainsborough M, Roe J, Howard S, et al. How to help children with neurodevelopmental and visual problems: a scoping review. Br J Ophthalmol [Internet]. 2014 Jan [cited 2024 Jan 24];98(1):6–12. Available from: https://bjo.bmj.com/lookup/doi/10.1136/bjophthalmol-2013-304225
  19. Morris-Rosendahl DJ, Crocq MA. Neurodevelopmental disorders—the history and future of a diagnostic concept. Dialogues in Clinical Neuroscience [Internet]. 2020 Mar 31 [cited 2024 Jan 24];22(1):65–72. Available from: https://www.tandfonline.com/doi/full/10.31887/DCNS.2020.22.1/macrocq
  20. Gajwani R, Minnis H. Double jeopardy: implications of neurodevelopmental conditions and adverse childhood experiences for child health. Eur Child Adolesc Psychiatry [Internet]. 2023 Jan 1 [cited 2024 Feb 28];32(1):1–4. Available from: https://doi.org/10.1007/s00787-022-02081-9
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Nathan Davies

Bachelor of Science - BS, Pharmacology, Swansea University

I am currently studying for a bachelor’s degree in medical pharmacology at Swansea University in Wales (UK), Medical pharmacology involves many different skills including understanding how the body functions in health and in illness along with how different substances (like medicines) act inside the body. The study of pharmacology can be used in drug discovery and in helping us better understand the impact certain substances can have inside our bodies. There is so much that goes into the study of pharmacology, and I could talk with you for hours about what it involves and why I love it.

As an author I do try my best to include the most credible sources in the articles that I am a part of (because I don’t do all the work, in-fact far from it as I also have a dedicated team of editors to double and triple check what I write). I look for sources I can trust because I can’t stand giving people wrong information, because if you the reader are concerned or interested in a certain topic, the last thing you want is to be doing is having to figure out what parts of the article are true or false.

my.klarity.health presents all health information in line with our terms and conditions. It is essential to understand that the medical information available on our platform is not intended to substitute the relationship between a patient and their physician or doctor, as well as any medical guidance they offer. Always consult with a healthcare professional before making any decisions based on the information found on our website.
Klarity is a citizen-centric health data management platform that enables citizens to securely access, control and share their own health data. Klarity Health Library aims to provide clear and evidence-based health and wellness related informative articles. 
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