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Neural Tube Defect (NDT) cluster in Washington State

Neural tube defects (NTDs) are serious birth defects of the brain (anencephaly and encephalocele) or spinal cord (spina bifida). They are important birth defects to monitor because they can be severely debilitating and even fatal, and yet in many cases are preventable through supplementation with folic acid before and during pregnancy.1

The Centers for Disease Control and Prevention (CDC) recently reported2 an abnormally large cluster of babies in Washington State born with neural tube defects, or NTDs. Among the cluster were 27 pregnancies over the three-year period from January 2010 to January 2013. Of these, 23 pregnancies were affected by anencephaly, 3 were affected by spina bifida (SB), and 1 with encephalocele. The anencephaly rate in this period in the three counties affected in Washington was four times as high as the national rate (8.4 per 10,000 live births vs. 2.1 per 10,000 live births), but the rate of spina bifida was only about 40% of the national rate (1.3 per 10,000 live births vs. 3.5 per 10,000 live births), suggesting that the more severe anencephaly may have displaced some SB births.

A follow-up case-control study by the CDC compared pregnancies affected by NDTs with those unaffected by the birth defects with respect to factors including age, race or ethnicity, height and weight, smoking, underlying health problems, prenatal vitamin and folic acid use, and private well water use. The study failed to find any significant differences between the NTD births and the normal controls, and no causal link to the defects has been determined. As a precaution, the CDC is continuing surveillance in the area through the end of 2013.2

Anencephaly is a condition in which portions of the brain, skull, and scalp fail to form during pregnancy.3 The condition has major neurological and physiological consequences, and for those born alive, life expectancy is measured in hours rather than days or years. One study reported that 50% of newborns with anencephaly die within 24 hours, and only 5% survive longer than 7 days.4 Another reported a median neonatal survival time of 55 min with a range of 10 minutes to 8 days.5

Spina bifida is a general term for NTDs in which the spinal canal, vertebrae, and/or skin fails to close over the spinal cord.6 Those with SB are usually at least partially paralyzed due to a spinal cord lesion, with the level of the lesion determining the extent to which sensory and motor function is disrupted, much like in spinal cord injuries. A recent study of the mortality of children with SB in California and the United Kingdom (UK) found that survival is related to mobility; those with greater levels of independent mobility having significantly lower mortality rates.7 Overall mortality in the UK cohort was especially high in the first few years of life, and prior to age 3 years or so comparison with the California cohort was not possible. Beyond age three, survival probabilities between the two cohorts were similar, with 25-year survival (to age 28) being approximately 70%.7 Under some basic assumptions regarding mortality rates of the cohorts beyond the period covered in the study, this would correspond to a life expectancy of about 40 remaining years for a 3-year-old with spina bifida. This does not account for level of mobility however, which was, again, found to be strongly associated with survival. An ambulatory 3-year-old with spina bifida would have a life expectancy greater than 40 remaining years, while a child with severe limitations in purposeful mobility would have a much shorter life expectancy.

Encephalocele is a rare NTD in which the spinal canal fails to close at the back of the head, resulting in a sac-like protrusion of the brain and its membranes. (8) Children born with this condition often have symptoms common among children with severe cerebral palsy or other encephalopathies, including: loss of muscle tone; spasticity; mental retardation; and hydrocephalus. (8) A 20-year study of survival in 83 consecutive live births with encephalocele revealed that early mortality is high: 30% die within the first year of life. (9) However, two-thirds of such children survive to age 20. (9)

NTDs are tragic, and the survival prospects of infants with such conditions can be grim. This is undoubtedly one of the reasons the CDC monitors these birth defects and continues to make efforts to determine their causes. Through continued primary prevention and scientific diligence in researching possible causes of NTDs, their incidences may continue to fall.

References

  1. Centers for Disease Control and Prevention (CDC). Preventing Neural Tube Defects: A Prevention Model and Resource Guide.
  2. Notes from the Field: Investigation of a Cluster of Neural Tube Defects — Central Washington, 2010–2013. Morbidity and Mortality Weekly Report (MMWR) 2013:62(35);728-728.
  3. Division of Birth Defects and Developmental Disabilities, NCBDDD, Centers for Disease Control and Prevention. Anencephaly.
  4. Baird PA, Sadovnick AD. Survival in infants with anencephaly. Clin Pediatr (Phila). 1984;23(5):268-71.
  5. Obeidi N, Russell N, Higgins JR, O'Donoghue K. The natural history of anencephaly. Prenat Diagn. 2010 Apr;30(4):357-60.
  6. National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention. Spina Bifida.
  7. Oakeshott P, Hunt GM, Kerry S, Strauss DJ, Shavelle RM, Reynolds RJ. Survival and mobility in open spina bifida: Comparison of results from the United States and the United Kingdom. International Journal on Disability and Human Development 2008; 7:101-106.
  8. Division of Birth Defects and Developmental Disabilities, NCBDDD, Centers for Disease Control and Prevention. Encephalocele.
  9. Siffel C, Wong LY, Olney RS, Correa A. Survival of infants diagnosed with encephalocele in Atlanta, 1979-98. Paediatr Perinat Epidemiol. 2003 Jan;17(1):40-8.
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