The aetiology of congenital defects.
1. Big picture
Congenital defects are abnormalities present at birth, caused by disturbances in genetic programming, embryonic development, fetal growth, or intrauterine environment.
For the exam, classify causes into:
Genetic causes
+ Chromosomal causes
+ Multifactorial inheritance
+ Teratogens
+ Maternal disease
+ Infections
+ Mechanical/uterine factors
+ Unknown causes
Most congenital defects are multifactorial or unknown, not purely single-gene.
2. Definition
A congenital defect is a structural, functional, metabolic, or genetic abnormality present at birth, even if detected later.
Examples:
- Structural: cleft lip, congenital heart disease, neural tube defect
- Functional: congenital hypothyroidism, hearing loss
- Metabolic: phenylketonuria
- Chromosomal: Down syndrome
3. Classification of congenital defects
| Type | Meaning | Example |
|---|---|---|
| Malformation | Intrinsic abnormal development | Spina bifida, cleft palate |
| Deformation | Abnormal shape from mechanical force | Clubfoot from oligohydramnios |
| Disruption | Destruction of previously normal tissue | Amniotic band limb defect |
| Dysplasia | Abnormal tissue organization | Skeletal dysplasia |
Mnemonic: M-D-D-D Malformation = made wrong Deformation = molded wrong Disruption = destroyed Dysplasia = tissue built wrong
4. Main etiologic groups
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