Learning Objectives
Master the clinical presentation and neurobiological basis of Fetal Alcohol Syndrome (FAS). Identify high-yield facial dysmorphisms and structural brain defects for the USMLE Step 1.
1. Pathogenesis and Etiology
Fetal Alcohol Syndrome is a leading preventable cause of intellectual disability in the United States, occurring secondary to maternal alcohol consumption during pregnancy.
| Mechanism | Clinical Impact |
|---|---|
| Cellular Migration | Impaired migration of neuronal and glial cells. |
| Structural Defect | Holoprosencephaly (failure of the prosencephalon to divide) may occur in severe cases. |
| Development | Leads to microcephaly and significant developmental delay. |
2. Classic Facial Dysmorphisms
The diagnosis is often clinical, based on a specific constellation of facial features that are high-yield for board exams.
| Feature | Description |
|---|---|
| Philtrum | Smooth philtrum (loss of the vertical groove between the nose and upper lip). |
| Upper Lip | Thin vermillion border (very thin upper lip). |
| Eyes | Small palpebral fissures (short horizontal eye openings). |
| Nose | Flat nasal bridge. |
3. Associated Systemic Defects
Beyond the face and brain, alcohol is a potent teratogen affecting multiple organ systems.
| System | Associated Defect |
|---|---|
| Cardiac | Heart defects (e.g., VSD, ASD, or Tetralogy of Fallot). |
| Skeletal | Limb dislocation and joint anomalies. |
| Management | Supportive care; multidisciplinary approach for developmental needs. |
Activity:
High-Yield Clinical Pearls:
- The Smooth philtrum: This is often the most specific physical clue mentioned in board vignettes.
- Holoprosencephaly: If a question mentions “failure of the brain to divide into two hemispheres,” think of alcohol or Patau syndrome (Trisomy 13).
- Intellectual Disability: Remember that alcohol is the #1 preventable cause, while Fragile X is the #1 inherited cause, and Down Syndrome is the #1 genetic/chromosomal cause.