Fetal Alcohol Spectrum Disorder (FASD)

Fetal alcohol spectrum disorder is the umbrella term for the range of neurodevelopmental and structural abnormalities caused by prenatal alcohol exposure. Alcohol is the single most common preventable cause of intellectual disability in developed countries: clinically central because it has no threshold, no safe trimester, and a recognizable craniofacial signature. Severity ranges from full fetal alcohol syndrome (FAS), with the classic facial triad and growth restriction, to alcohol-related neurodevelopmental disorder (ARND), where neurobehavioral effects exist without overt facial features.

Alcohol exerts teratogenic effects through multiple converging mechanisms:

• Direct neurotoxicity: acetaldehyde and reactive oxygen species damage migrating neurons; widespread apoptosis in the developing CNS.
• NMDA-receptor antagonism + GABA-A potentiation: disrupts neural-circuit refinement during the synaptogenic window of the third trimester.
• Methylation interference: alcohol depletes one-carbon donors and disrupts DNA methylation, with downstream epigenetic effects on gene expression.
• Disrupted neural-crest cell migration: contributes to the craniofacial phenotype (midline defects, mandibular and maxillary hypoplasia).
• Vascular disruption: secondary contributor to growth restriction and structural defects.

No threshold has been established. Even low-dose chronic exposure has been associated with subtle neurodevelopmental effects in epidemiologic studies. Genetic susceptibility (alcohol dehydrogenase variants such as ADH1B, ADH1C) modulates risk but doesn't eliminate it.

• First trimester (organogenesis): alcohol exposure produces the classic facial dysmorphism (philtrum and upper-lip features form between days 19–21 post-conception) and structural malformations.
• Second and third trimesters: predominantly affect brain growth, neuronal migration, and synaptic refinement → microcephaly, IQ reduction, executive dysfunction.

This is why "she stopped drinking when she found out she was pregnant" is not fully reassuring: facial features are determined within ~3 weeks post-conception, often before pregnancy is recognized.

1. Characteristic facial features (all three must be present):
   • Short palpebral fissures
   • Smooth philtrum (loss of the vertical ridges between nose and lip)
   • Thin vermilion border (thin upper lip)
2. Growth restriction (height and/or weight ≤10th percentile, prenatal or postnatal).
3. CNS involvement: structural (microcephaly, corpus callosum abnormalities), neurologic (seizures, motor impairment), or functional (IQ <70, executive dysfunction, attention deficits, behavioral disturbance).

A fourth criterion, confirmed maternal alcohol exposure, is usually required, though some diagnostic schemes allow FAS diagnosis based on the first three when exposure history is unknown.

The 2016 Hoyme criteria provide standardized diagnostic categories.

• Cardiac: ventricular septal defects, atrial septal defects, conotruncal anomalies (~30–40% of FAS).
• Skeletal: radioulnar synostosis, scoliosis, joint contractures, hand crease abnormalities.
• Renal: horseshoe kidney, hydronephrosis, hypoplasia.
• Ophthalmologic: optic nerve hypoplasia, strabismus, refractive errors.
• Auditory: conductive and sensorineural hearing loss.
• Behavioral: ADHD-like symptoms (often refractory), executive dysfunction, social-judgment problems persisting into adulthood.

The behavioral phenotype is often more disabling than the structural one:

• Executive function deficits: planning, working memory, cognitive flexibility.
• Adaptive function deficits: disproportionate to IQ; affected individuals often function below their measured IQ would suggest.
• Attention and impulse control problems (many meet ADHD criteria).
• Social judgment and consequences: characteristic difficulty learning from experience.
• Comorbid mental health conditions: depression, anxiety, substance use in adulthood.

• Detailed maternal exposure history: timing, frequency, quantity. Quantify in standard drinks.
• Dysmorphology evaluation: measure palpebral fissure length against age-specific norms.
• Growth parameters: prenatal and postnatal.
• Neurodevelopmental assessment: formal cognitive, executive, adaptive function testing.
• Imaging: brain MRI may show corpus callosum thinning, cerebellar hypoplasia, ventriculomegaly.
• Cardiac evaluation: echocardiogram if examination or history suggests CHD.

The chasm between diagnosis and recognition is wide; most affected individuals are never formally diagnosed because exposure history is unavailable, facial features are subtle, or the neurobehavioral profile is mistaken for primary ADHD.

• No safe amount, no safe trimester. This is the public-health recommendation. Even periconceptional exposure can affect facial features (formed days 19–21) before pregnancy is recognized.
• Risk reduction: even cutting back during pregnancy reduces risk relative to continued heavy use. The harm-reduction frame matters clinically even if the absolute message is "none."
• Once a child has been diagnosed, family planning counseling for future pregnancies is critical. Recurrence depends entirely on continued exposure pattern.
• Resources: NIAAA, CDC FASD Practitioner toolkit, FASD United for family support.