Human Abnormal Development
How and why do things go wrong in development?
These notes cover abnormalities that can occur during development often described as congenital defects or birth defects. There are many different ways that developmental abnormalities can occur the 3 major types are Genetic (inherited), Environmental (maternal) and Unknown (not determined) derived abnormalities.
While genetic abnormalites will have well-defined impacts upon development, environmentally derived effects can be harder to define and often variable depending on many different factors (timing, exposure level, and the combination effects with other factors). This combination effect can also be seen between genetic and environmental interacting to give an even broader spectrum of both major and minor abnormalities.
It is the group now classified as "unknown causes" that require further research to place them in one of the two other real categories.
Prenatal diagnosis are the clinical tools used to determine both normal and abnormal development. There are a growing number of new diagnostic techniques that are being applied to human embryonic development.
Often not considered, is that pregnancy itself can also expose abnormalities in the mother (congenital heart disease, diabetes, reproductive disorders) that until then had gone undetected. This section of notes also includes links to prenatal diagnosis techniques, twinning and statistical information relating to abnormalities at birth from several different countries.
Statistics - Top Ten
The ten most frequently reported birth defects in Victoria between 2003-2004 (More? Australian Statistics - Victoria)
- Obstructive Defects of the Renal Pelvis
- Ventricular Septal Defect
- Congenital Dislocated Hip
- Trisomy 21 or Down syndrome
- Cleft Palate
- Trisomy 18 or Edward Syndrome - multiple abnormalities of the heart, diaphragm, lungs, kidneys, ureters and palate 86% discontinued.
- Renal Agenesis/Dysgenesis - reduction in neonatal death and stillbirth since 1993 may be due to the more severe cases being identified in utero and being represented amongst the increased proportion of terminations (approximately 31%).
- Cleft Lip and Palate - occur with another defect in 33.7% of cases.
Neural Tube Defects
Neural tube defects that were just outside the top ten most common birth defects but are widely known.
Spina Bifida - (73%) of parents choose to discontinue a pregnancy affected by spina bifida.
Anencephaly - (94%) of parents choose to discontinue a pregnancy affected by anencephaly.
(Data from the Victorian Perinatal Data Collectionn Unit)
Australian Birth Anomalies System
- "The national collation and reporting of birth anomalies data has been suspended in recent years due to concerns about data quality and comparability."
- Variability among states and territories in scope of birth anomalies data collections
- sources of birth anomalies notifications
- definitions and classifications used
- method of data collection
- available resources
- Variability among the states and territories in the timing and method of the provision of birth anomalies data to the AIHW National Perinatal Statistics Unit (NPSU) for national collation and reporting.
- New Australian Birth Anomalies System should be data for birth anomalies detected up to 1 year of age
- including data on terminations of pregnancies with birth anomalies
- regardless of gestational age (i.e. including less than 20 weeks gestation)
- System will initially be based on data from the states able to detect birth anomalies at least up to 1 year of age
- NSW, VIC, WA and SA
- further extending the period of detection in the future
(Reference: modified from Australian Institute of Health and Welfare (AIHW))
Now consider how different environmental effects during pregnancy may influence developmental outcomes. The terms listed below are often used to describe these environmental effects
- Teratogen (Greek, teraton = monster) any agent that causes a structural abnormality (congenital abnormalities) following fetal exposure during pregnancy. The overall effect depends on dosage and time of exposure. (More? Critical Periods of Development)
- Absolute risk the rate of occurrence of an abnormal phenotype among individuals exposed to the agent. (e.g. fetal alcohol syndrome)
- Relative risk the ratio of the rate of the condition among the exposed and the nonexposed. (e.g. smokers risk of having a low birth weight baby compared to non-smokers) A high relative risk may indicate a low absolute risk if the condition is rare.
- Mutagen a chemical or agent that can cause permanent damage to the deoxyribonucleic acid (DNA) in a cell. DNA damage in the human egg or sperm may lead to reduced fertility, spontaneous abortion (miscarriage), birth defects and heritable diseases.
- Fetotoxicant is a chemical that adversely affects the developing fetus, resulting in low birth weight, symptoms of poisoning at birth or stillbirth (fetus dies before it is born).
- Synergism when the combined effect of exposure to more than one chemical at one time, or to a chemical in combination with other hazards (heat, radiation, infection) results in effects of such exposure to be greater than the sum of the individual effects of each hazard by itself.
- Toxicogenomics the interaction between the genome, chemicals in the environment, and disease. Cells exposed to a stress, drug or toxicant respond by altering the pattern of expression of genes within their chromosomes. Based on new genetic and microarray technologies.
UNSW Embryology Links
- Abnormal Development
- Abnormal Development- Australian Statistics | Abnormalities by Systems
- Prenatal Diagnosis
- Genetic Abnormalities | Down Syndrome | Edwards Syndrome | Fragile X | Lesch-Nyhan Syndrome
- Maternal Factors | Maternal Diabetes | Maternal Hyperthermia | Neural Tube Defects | Fetal Alcohol Syndrome | Smoking | Chemical | Drugs | Illegal Drugs | Radiation | Heavy Metal | Iodine Deficiency | Viral Infection | Rubella | Polio | Parvovirus | Varicella | Bacterial Infection | Malaria | Toxoplasmosis | Autism
- Fetal Origins Hypothesis
- Intrauterine Growth Retardation
- 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. (2020, May 27) Embryology Human Abnormal Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Human_Abnormal_Development
- © Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G