18 - Birth Defects Flashcards Preview

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Flashcards in 18 - Birth Defects Deck (30)
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1
Q

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

A

Birth defects, congenital malformations, congenital anomalies.

2
Q

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

A

Birth, detected.

3
Q

When are birth defects detected? When do they develop?

A

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

4
Q

What is the range of birth defects that can occur?

A

Structural, functional, behavioral, metabolic

5
Q

How prevalent are birth defects?

A

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.

6
Q

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

A

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.

7
Q

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

A

More common in early embryos. Most abort spontaneously.

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

8
Q

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

A

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.

9
Q

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

A
  1. Parental age
  2. Season of the year (conception)
  3. County of residence (parents)
  4. Race
  5. Familial tendencies
10
Q

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

A

Anomaly - structural deformity of any kind

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

11
Q

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

A

Four D’s:

Defects
Disruptions
Deformations
Dysplasia

12
Q

Describe the characteristics of a developmental defect?

A

Morphological abnormality resulting from abnormal developmental mechanisms/processes.

Intrinsic or inherent to the process (blueprint problem)

Can be inherited.

13
Q

Describe developmental disruption?

A

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

Extrinsic, not inherent to the program.

NOT inherited.

14
Q

What is developmental deformation?

A

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.

15
Q

What is developmental dysplasia?

A

Abnormal organization of cells in tissues.

Occurs at the microscopic level.

16
Q

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

A

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

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

17
Q

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

A

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

Fetal alcohol syndrome, CHARGE syndrome.

18
Q

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

A

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

Potter’s sequence, due to insufficient amniotic fluid.

19
Q

What are association anomalies? What is an example?

A

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.

20
Q

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

A

10-15% are caused by genetic factors:

Abnormal chromosome numbers, abnormal chromosome structure, gene mutations.

21
Q

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

A

Environmental agents: teratogens.

7-10% of birth defects.

22
Q

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

A

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.

23
Q

What are some environmental factors that affect development?

A
  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
24
Q

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

A

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

25
Q

What is the critical period of organ development?

A

Weeks 3-8.

26
Q

What can effect the severity of a teratogenic agent?

A

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

27
Q

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

A

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

28
Q

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

A
  1. death
  2. malformation
  3. growth restriction
  4. functional disorders
29
Q

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

A

Genetics + environment

20-25%

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

30
Q

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

A

Unknown.

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