18 - Birth Defects

Question 1

What are three terms used interchangeably to refer to abnormal embryonic development?

Answer 1

Birth defects, congenital malformations, congenital anomalies.

Question 2

A birth defect is any defect present at ______ whether ______ at that time or not.

Answer 2

Birth, detected.

Question 3

When are birth defects detected? When do they develop?

Answer 3

Some can be detected before or at birth, some develop a few days-years after birth, some don’t appear until adulthood.

Question 4

What is the range of birth defects that can occur?

Answer 4

Structural, functional, behavioral, metabolic

Question 5

How prevalent are birth defects?

Answer 5

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.

Question 6

What is the incidence (detection) of abnormal development at birth? In early childhood? What isn’t included in this?

Answer 6

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.

Question 7

What are major defects? What are they usually caused by?

Answer 7

More common in early embryos. Most abort spontaneously.

50-60% have chrom anomalies with clinical and social consequences.

Question 8

What are . minor defects? What are these a sign of?

Answer 8

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.

Question 9

What are five factors that are associated with increased incidence of birth defects?

Answer 9

1. Parental age
2. Season of the year (conception)
3. County of residence (parents)
4. Race
5. Familial tendencies

Question 10

What is the difference between an “anomaly” and a “morphological variation”?

Answer 10

Anomaly - structural deformity of any kind

Morphological variation - predictable variation of the average morphological pattern. Usually not clinically significant.

Question 11

What are the major categories into which we can place structural disorders of development?

Answer 11

Four D’s:

Defects
Disruptions
Deformations
Dysplasia

Question 12

Describe the characteristics of a developmental defect?

Answer 12

Morphological abnormality resulting from abnormal developmental mechanisms/processes.

Intrinsic or inherent to the process (blueprint problem)

Can be inherited.

Question 13

Describe developmental disruption?

Answer 13

Morphological abnormality resulting from breakdown or interference with an originally normal developmental process.

Extrinsic, not inherent to the program.

NOT inherited.

Question 14

What is developmental deformation?

Answer 14

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.

Question 15

What is developmental dysplasia?

Answer 15

Abnormal organization of cells in tissues.

Occurs at the microscopic level.

Question 16

What is a polytropic field defect? What is an example?

Answer 16

Pattern of anomalies derived from a disturbance of a single embryonic/developmental field.

Midlife defects: heart, anus, spine, genitals, face, and tongue.

Question 17

What are characteristics of a syndrome anomaly? What are two examples?

Answer 17

Pattern of multiple primary anomalies which are seen together and are causally related.

Fetal alcohol syndrome, CHARGE syndrome.

Question 18

What are characteristics of a sequence anomaly? What is an example?

Answer 18

A pattern of anomalies which result form a single cause (primary anomaly or single initiating factor).

Potter’s sequence, due to insufficient amniotic fluid.

Question 19

What are association anomalies? What is an example?

Answer 19

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.

Question 20

What is one cause of birth defects? What percent does this make up? Give examples.

Answer 20

10-15% are caused by genetic factors:

Abnormal chromosome numbers, abnormal chromosome structure, gene mutations.

Question 21

Other than genetic factors, what is a second cause of birth defects? What percentage does this make up?

Answer 21

Environmental agents: teratogens.

7-10% of birth defects.

Question 22

What is a teratogen? What is required for something to be called a teratogen?

Answer 22

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.

Question 23

What are some environmental factors that affect development?

Answer 23

1. infectious agents - can cross the placenta
2. Ionizing radiation and other physical agents- detrimental to cell division
3. Drugs and chemicals
4. Heavy metals
5. Imbalance of essential metabolites and hormones
6. Maternal factors, paternal factors
7. Hypoxia

Question 24

What is the predictable result when a teratogenic agent is applied during development?

Answer 24

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

Question 25

What is the critical period of organ development?

Answer 25

Weeks 3-8.

Question 26

What can effect the severity of a teratogenic agent?

Answer 26

Genomic imprinting, can cause the baby to be more or less sensitive to an agent.

Question 27

What is another factor (besides genomic imprinting) that can effect the degree of severity of malformation from teratogen exposure?

Answer 27

Dose and duration of exposure. - i.e. how much actually gets to the embryo

Question 28

What are the four consequences for development when an embryo is exposed to a teratogen?

Answer 28

1. death
2. malformation
3. growth restriction
4. functional disorders

Question 29

Describe multifactorial causes of birth defects? What percentage of birth defects do they account for?

Answer 29

Genetics + environment

20-25%

Predisposing genetic factors combined with a particular environmental insult - gets above threshold and embryo is affected.

Question 30

For 60% of birth defects, the cause is ______.

Answer 30

Unknown.

Known causes are genetics, environmental factors, or a combination of the two.