An epidemiologic study of neural tube defects in Los Angeles County II. Etiologic factors in an area with low prevalence at birth
Article first published online: 31 MAY 2005
Copyright © 1982 Wiley-Liss, Inc., A Wiley Company
Volume 25, Issue 3, pages 323–334, June 1982
How to Cite
Sever, L. E. (1982), An epidemiologic study of neural tube defects in Los Angeles County II. Etiologic factors in an area with low prevalence at birth. Teratology, 25: 323–334. doi: 10.1002/tera.1420250309
- Issue published online: 31 MAY 2005
- Article first published online: 31 MAY 2005
- Manuscript Accepted: 10 NOV 1981
- Manuscript Received: 6 APR 1981
- University of California Academic Senate
- United States Department of Energy. Grant Number: DE-AC06-76RLO 1830
- NIH. Grant Numbers: FR-3, RR-3
Epidemiologic characteristics of neural tube defect (NTD) births occurring in Los Angeles County, California, residents during the period 1966–1972 are presented. The prevalence at birth was 0.52/1000 births for anencephalus, 0.51/1000 for spina bifida, and 0.08/1000 for encephalocele, rates considered to be low for a predominantly white population.
We hypothesized that environmental (nongenetic) factors are of less etiologic importance in a low-prevalence population than in areas or time periods with high prevalence. We tested that hypothesis by examining epidemiologic characteristics of NTDs in Los Angeles County and comparing them with high-prevalence populations. The data did not support a major etiologic role for environmental factors: (1) no significant differences between rates by month of birth or conception; (2) no significant association with maternal age or parity for anencephalus; for spina bifida a significant maternal age effect (P < 0.01) and for encephalocele a parity effect (P < 0.02); and (3) no significant relationship with father's occupational class for either anencephalus or encephalocele but a marginally significant (P < 0.05) inverse association for spina bifida when a statistic based on ordinal relationships was used.
Findings supporting the importance of genetic factors in etiology included: (1) a high percentage of males; (2) a higher twin concordance rate than in high-prevalence populations; and (3) an anencephalus rate among blacks comparable with rates for blacks in other United States populations. Our findings in conjunction with those from other areas and times of low prevalence suggest environmental factors play a relatively insignificant role in the etiology of NTDs in such populations.