Vol. 12: Fall, 1995
Teratogen Update
Facts About Neural Tube Defects and Folic Acid
Congenital malformations occur in 4 of every 100 live births (Nelson and Holmes, 1989). Etiology is unknown for 69% of infants born with congenital malformations. Currently, environmental agents or maternal states are causally attributed to approximately 3% of congenital malformations (Nelson and Holmes, 1989). Chromosomal or genetic abnormalities explain the remaining 28% for which a cause is identified (Nelson and Holmes, 1989).
A small percentage of birth defects can be prevented. Neural tube defects, one of the most common types of birth defects, can sometimes be prevented. The risk for spina bifida can be reduced by approximately 50% if folic acid is consumed prior to conception.
Neural tube defects (NTDs) encompass a spectrum of malformations of the cranium, spine and nervous system that includes anencephaly, spina bifida and encephalocele. Spina bifida occurs in approximately 60%, anencephaly 35% and encephalocele 5% of babies affected with a defect in the closure of the neural tube. These defects represent a significant class of medically serious anomalies that impact the mortality and morbidity of the affected individuals as well as their families. Today, more than 90% of all children born with spina bifida live a normal life span.
Conventionally, NTDs are felt to result from an alteration in closure of the embryonic neural tube, but precise etiology and pathogenesis are not yet understood. Neurulation is a process involving the formation of the neural plate, the neural folds and their closure to form the neural tube (Moore, 1988). An interruption of this process may produce a vast array of neural tube defects. Consequently, any causative insult must occur within the four week period following conception or have its influence prior to conception and perhaps continue throughout the first 30 days.
Thus, intervention strategies must target women in the childbearing years prior to conception. The birth prevalence of NTDs in Utah is estimated to be about 1 per 1000 total births (Jorde et al, 1984). NTDs may occur as isolated defects, multiple or part of a syndrome. Isolated NTDs appear to be etiologically distinct from syndromic patterns of malformations that include an NTD as part of their disorder (Jorde et al, 1984). These congenital malformations are heterogeneous in etiology (Khoury et al, 1982; Martin et al, 1983; Yen et al, 1992). Environmental risk factors for NTDs include insulin-dependent diabetes mellitus, valproic acid, carbamazepine, folic acid antagonists and maternal hyperthermia (Van Allen et al, 1993). There are also genetic or chromosomal abnormalities that produce a neural tube defect.
Several studies (Werler et al, 1993; Czeizel and Dudas, 1992; MRC, 1991; Mulinare et al, 1988) have consistently demonstrated a 50% to 70% reduction of spina bifida for occurrent and recurrent risk, respectively, if women consume folic acid prior to conception. How folic acid, a B vitamin, works to prevent neural tube defects is not yet understood. Despite lack of knowledge for the preventive mechanism we are obligated to educate consumers and the medical community about the potential benefit of consuming folic acid prior to conception.
Approximately 50% of pregnancies in the United States are inadvertent. The U.S. Public Health Service is asking all women of childbearing age to consume multi-vitamins or folic acid supplements that contain 400 micrograms per day in order to reduce their risk for spina bifida. This amount can be found in most over-the-counter multi-vitamins. For women who have had a previous pregnancy in which the baby had a NTD, and are planning another pregnancy, the U.S. Public Health Service recommends 4.0 mgs of folic acid at least one month prior to conception. NOTE: A woman taking diphenylhydantoin, phenobarbital or carbamezapine must consult with her physician prior to taking a folic acid supplementation.
Folic acid is a B vitamin found in certain foods. However, to obtain the recommended 400 micrograms of folic acid from food an individual must consume about 800 micrograms of food folates. Therefore, taking multivitamin supplements with folic acid is the most effective way to get adequate amounts of folate to prevent NTDs.
The Division of Community and Family Health Services at the Utah Department of Health is conducting a Folic Acid Educational Campaign to increase the awareness of women in their childbearing years about the benefits of folic acid consumption. This campaign will include the distribution of posters, pamphlets, bookmarks, televised public service announcements and in-services for local clinics and other agencies that will target women of childbearing age. We are soliciting the help of Utah physicians to distribute this information. As a result of this educational campaign we hope that women will add folic acid supplements to their daily regimen and that some NTDs will be prevented.
References are available on request joyce.hooker@state.co.us
The Genetic Drift Newsletter is not copyrighted. Readers are free to duplicate all or parts of its contents. The Genetic Drift Newsletter is published semiannually by the Mountain States Genetics Network for associates & those interested in Human Genetics. In accordance with accepted publication standards, we request acknowledgement in print of any article reproduced in another publication. The views expressed in the newsletter do not necessarily reflect local, state, or federal policy. For additional information, contact Carol Clericuzio, M.D., Editor, Department of Pediatrics, The University of New Mexico, Albuquerque, NM, 87131
Teratogen Update Table Of Contents:
Introduction
Medications
Substances of Abuse
Maternal Infections
Maternal Disorders
Mutagens
Etiology of Congenital Malformations in Humans: (Table 1)
Known Human Teratogens: (Table 2)
References
Facts About Neural Tube Defects and Folic Acid
|
