18 - Birth Defects Flashcards
What are three terms used interchangeably to refer to abnormal embryonic development?
Birth defects, congenital malformations, congenital anomalies.
A birth defect is any defect present at ______ whether ______ at that time or not.
Birth, detected.
When are birth defects detected? When do they develop?
Some can be detected before or at birth, some develop a few days-years after birth, some don’t appear until adulthood.
What is the range of birth defects that can occur?
Structural, functional, behavioral, metabolic
How prevalent are birth defects?
Account for 20% of all infant deaths.
Most frequent cause of mortality during the 1st year of life and account for 30% of NICU admits.
What is the incidence (detection) of abnormal development at birth? In early childhood? What isn’t included in this?
2-3% at birth.
4-6% in early childhood.
Incidence of spontaneous abortion is usually not considered in these stats because they aren’t born and therefore can’t be detected at birth.
What are major defects? What are they usually caused by?
More common in early embryos. Most abort spontaneously.
50-60% have chrom anomalies with clinical and social consequences.
What are . minor defects? What are these a sign of?
Occur in 15% of newborns and serve as a cue to look for major defects.
The more minor defects present the higher chance of a major defect also being present.
What are five factors that are associated with increased incidence of birth defects?
- Parental age
- Season of the year (conception)
- County of residence (parents)
- Race
- Familial tendencies
What is the difference between an “anomaly” and a “morphological variation”?
Anomaly - structural deformity of any kind
Morphological variation - predictable variation of the average morphological pattern. Usually not clinically significant.
What are the major categories into which we can place structural disorders of development?
Four D’s:
Defects
Disruptions
Deformations
Dysplasia
Describe the characteristics of a developmental defect?
Morphological abnormality resulting from abnormal developmental mechanisms/processes.
Intrinsic or inherent to the process (blueprint problem)
Can be inherited.
Describe developmental disruption?
Morphological abnormality resulting from breakdown or interference with an originally normal developmental process.
Extrinsic, not inherent to the program.
NOT inherited.
What is developmental deformation?
An abnormal form, shape, or position of a normally formed body part.
Result from non-disruptive mechanical forces that mold part of the fetus over a prolonged period of time.
Sometimes reversible.
What is developmental dysplasia?
Abnormal organization of cells in tissues.
Occurs at the microscopic level.
What is a polytropic field defect? What is an example?
Pattern of anomalies derived from a disturbance of a single embryonic/developmental field.
Midlife defects: heart, anus, spine, genitals, face, and tongue.
What are characteristics of a syndrome anomaly? What are two examples?
Pattern of multiple primary anomalies which are seen together and are causally related.
Fetal alcohol syndrome, CHARGE syndrome.
What are characteristics of a sequence anomaly? What is an example?
A pattern of anomalies which result form a single cause (primary anomaly or single initiating factor).
Potter’s sequence, due to insufficient amniotic fluid.
What are association anomalies? What is an example?
Non-random occurence of two or more anomalies that occur more frequently together than expected by chance alone. (no known cause)
VACTERL - vertebral, anal, cardiac, tracheo-esophageal, renal, and limb anomalies.
What is one cause of birth defects? What percent does this make up? Give examples.
10-15% are caused by genetic factors:
Abnormal chromosome numbers, abnormal chromosome structure, gene mutations.
Other than genetic factors, what is a second cause of birth defects? What percentage does this make up?
Environmental agents: teratogens.
7-10% of birth defects.
What is a teratogen? What is required for something to be called a teratogen?
Any agent that can produce a congenital anomaly or raise the incidence of an anomaly.
Most product morphological anomalies, me extrinsic to the embryo (disrupt an ok plan), and influence development between fertilization and birth.
What are some environmental factors that affect development?
- infectious agents - can cross the placenta
- Ionizing radiation and other physical agents- detrimental to cell division
- Drugs and chemicals
- Heavy metals
- Imbalance of essential metabolites and hormones
- Maternal factors, paternal factors
- Hypoxia
What is the predictable result when a teratogenic agent is applied during development?
Week 1-3: spontaneous abortion or regulation
Week 3-8: major structural problems (MAX sensitivity during this period)
Week 9-39: primarily functional or growth related problem
What is the critical period of organ development?
Weeks 3-8.
What can effect the severity of a teratogenic agent?
Genomic imprinting, can cause the baby to be more or less sensitive to an agent.
What is another factor (besides genomic imprinting) that can effect the degree of severity of malformation from teratogen exposure?
Dose and duration of exposure. - i.e. how much actually gets to the embryo
What are the four consequences for development when an embryo is exposed to a teratogen?
- death
- malformation
- growth restriction
- functional disorders
Describe multifactorial causes of birth defects? What percentage of birth defects do they account for?
Genetics + environment
20-25%
Predisposing genetic factors combined with a particular environmental insult - gets above threshold and embryo is affected.
For 60% of birth defects, the cause is ______.
Unknown.
Known causes are genetics, environmental factors, or a combination of the two.
