Abnormal Development - Teratogens

Introduction

Human critical periods of development

How and why do things go wrong in development? Embryological development is a robust biological system able to cope with many stresses without long-term consequences. When development does go wrong there are generally 3 major types groups: Genetic (inherited), Environmental (maternal) derived and Unknown (not determined or known) abnormalities. Also often not considered, is that pregnancy itself can also expose abnormalities in the mother (congenital heart disease, diabetes, reproductive disorders) that until the pregnancy had gone undetected.

• Infections, collectively grouped under the acronym TORCH for Toxoplasmosis, Other organisms (parvovirus, HIV, Epstein-Barr, herpes 6 and 8, varicella, syphilis, enterovirus) , Rubella, Cytomegalovirus and Hepatitis. See also the related topics on maternal hyperthermia and bacterial infections.

• Maternal diet the best characterised is the role of low folic acid and Neural Tube Defects (NTDs) see also abnormal neural development and Neural Tube Defects (NTDs). More recently the focus has been on dietary iodine levels and the role they also play on neural development.

• Maternal drugs effects either prescription drugs (therapeutic chemicals/agents, thalidomide limb development), non-prescription drugs (smoking), and illegal drugs (Cannabis/Marijuana, Methamphetamine/Amphetamine, Cocaine, Heroin, Lysergic Acid Diethylamide)

• Environment (smoking, chemicals, heavy metals, radiation) and maternal endocrine function (maternal diabetes, thyroid development) and maternal stress.

• Teratogen synergism, different environmental effects can act individually or in combination on the same developing system. For example, neural development can be impacted upon by alcohol (fetal alcohol syndrome), viral infection (rubella) and/or inadequate dietry folate intake (neural tube defects). These effects may also not be seen as a direct effect on a system or systems but result in a reduced birth weight and the potential postnatal developmental effects. Consider also this in relation to the increasing support to the fetal origins hypothesis.

Use the page links below to explore specific teratogens.

Some Recent Findings

Teratogen Screening Using Transcriptome Profiling of Differentiating Human Embryonic Stem Cells "Teratogens are substances that may cause defects in normal embryonic development while not necessarily being toxic in adults. Identification of possible teratogenic compounds has been historically beset by the species-specific nature of the teratogen response. To examine teratogenic effects on early human development we performed non-biased expression profiling of differentiating human embryonic and induced-pluripotent stem cells treated with several drugs; ethanol, lithium, retinoic acid, caffeine and thalidomide, which is known to be highly species specific. Our results point to the potency of specific teratogens and their affected tissues and pathways. Specifically, we could show that ethanol caused dramatic increase in endodermal differentiation, retinoic acid caused misregulation of neural development, and thalidomide affected both these processes. We thus propose this method as a valuable addition to currently available animal screening approaches."

Birth Defects Res B Dev Reprod Toxicol. 2011 Feb;92(1):69-76. doi: 10.1002/bdrb.20283. Epub 2011 Jan 19.

• Maternal exposure to multi-wall carbon nanotubes does not induce embryo-fetal developmental toxicity in rats. "The results show that repeated oral doses of multi-wall CNTs (MWCNTs) during pregnancy induces minimal maternal toxicity and no embryo-fetal toxicity at 1,000 mg/kg/day in rats. The no-observed-adverse-effect level of MWCNTs is considered to be 200 mg/kg/day for dams and 1,000 mg/kg/day for embryo-fetal development. In this study, the dosing formulation was not analyzed to determine the degree of reaggregation (or not), nor were blood levels of CNT's measured in the dosed animals to verify or characterize absorption."

Critical Periods of Development

When studying this topic remember the concept of "critical periods of development" that will affect the overall impact of the above listed factors, as outlined in the table below. This can be extended to the potential differences between prenatal and postnatal effects, for example with infections and outcomes.

Dark Orange = major abnormality | Light Orange = minor abnormality

Conceptus		Embryonic development (weeks)													Fetal period (weeks)
1	2	3		4			5	6		7		8			9		16	20-36	38
		Neural
			Heart
				Upper limbs
					Lower limbs
					Ear
						Eye
									Palate
									Teeth
											External genitalia
Loss		Major abnormalities										Functional and Minor abnormalities

'

Dark Orange = major abnormality | Light Orange = minor abnormality

References

Journals

• Birth Defects Research Part A: Clinical and Molecular Teratology
• Birth Defects Research Part B: Developmental and Reproductive Toxicology
• Part C: Embryo Today: Reviews

Search Pubmed

Search Pubmed: teratogen | teratogenesis

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

---

Cite this page: Hill, M.A. (2024, April 18) Embryology Abnormal Development - Teratogens. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Abnormal_Development_-_Teratogens

What Links Here?

© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G