Irish Families with Neural Tube Defects

The purpose of this project was to use epidemiologic tools to identify factors in families that might be related to neural tube defects (NTDs). The epidemiologic tools were the presence of adverse pregnancy outcomes, including miscarriage, preterm birth and stillbirth, and the presence of birth defects. All of these outcomes were either self-reported, or reported by proxy by near relatives (siblings or parents).

PHASE I. Nuclear Families
The nuclear families each had at least one child born with a neural tube defect, or a pregnancy affected with a neural tube defect. Between 1995 and 2003, 79 such families [28kb Word doc] were identified and interviewed from the East Coast of the Island of Ireland, including Northern Ireland. Families were eligible if the affected individual (the "proband") had any one of four types of NTD—anencephaly, spina bifida, spina bifida occulta or encephalocele.

Results: As expected, siblings had higher rates of birth defects, including neural tube defects, than the general population. These results are being prepared for publication.

PHASE II. Uncles & Aunts
As part of the initial interview with the nuclear families, each uncle and aunt of the proband was identified, including pregnancies that did not end in a live birth. Since the person being interviewed was most usually a parent, they were telling us about the pregnancy histories of their parents, and the birth defect status of their brothers and sisters (the uncles and aunts). To interview the uncles and aunts, we went back to the nuclear families and asked them for the contact information for the uncles and aunts. Interviews were conducted with 378 uncles and aunts between 2000 and 2003 in-person or on the telephone.

Results: Two reports were planned from this study. The first concerns adverse pregnancy outcomes to the aunts and (spouses of) the uncles and was published in 2006 in the American Journal of Medical Genetics.

Pubmed abstract
Published article (1200Kb PDF)

This report describes an increased risk for adverse pregnancy outcomes to spouses of uncles and to aunts, especially those related to a person with spina bifida occulta. The risk was greater among maternal relatives than among paternal relatives.

The second report concerns birth defects reported by and about the uncles and aunts themselves, and was published in the US Journal Birth Defects Research Part A in 2008

Pubmed abstract
Published article (133Kb PDF)

PHASE III. First Cousins
Following the interviews with the uncles and aunts, we obtained the contact information from them for their children, the first cousins of the proband. Between 2002 and 2004, we interviewed 431 first cousins by telephone. They told us about their own birth defects and the outcomes of their own pregnancies, as well as the occurrence of birth defects in their children, the first cousins once removed of the proband.

Results: We wrote three reports from these interviews.

The first report concerned the rate of birth defects among the first cousins themselves. We found that maternal relatives had more birth defects overall, and more neural tube defects than paternal relatives, the same pattern that occurred among uncles and aunts.

The graph below shows the numbers of birth defects according to type of birth defect among maternal first cousins compared to paternal first cousins. Maternal first cousins had more defects of the cranio-facial type, of the heart, vertebrae, limbs, eyes and neural tube defects. Paternal first cousins had more defects of the genito-urinary system.

graph of results from first report

PubMed abstract
Published article (188Kb PDF)

The second report described the birth defects among first cousins once removed, the children of the first cousins. This report showed the same pattern of excess birth defects among maternal relatives compared to paternal birth defects. In other words, three generations of the same group of families show this unusual pattern of inheritance. No neural tube defects occurred among the first cousins once removed. It would be prudent to add the excess risk of birth defects among maternal relatives to the information provided at pre-pregnancy counselling sessions. Maternal relatives in NTD families really should be taking folic acid. Among the first cousins once removed no pregnancy was affected by a neural tube defect, probably because of better nutrition and because many mothers took folic acid.

The graph below shows the numbers of different types of birth defects present in maternal vs paternal first cousins once removed. There were more endocrine, limb, vertebral, cranio-facial and heart anomalies among maternal first cousins once removed, compared to more genitor-urinary anomalies among paternal first cousins once removed.

graph of results from second report

PubMed abstract
Published article (233Kb PDF)

The third report took advantage of the fact that the first cousins once removed were born more recently, within the era when folic acid recommendations were being promoted. We evaluated the risk of miscarriage in relation to folic acid supplementation. We found that the risk of miscarriage was reduced when mothers took folic acid as recommended. This association has been reported in some earlier studies, but some other studies did not find this effect. However, there is enough evidence in sum to add miscarriage prevention to the list of benefits of periconceptional folic acid.

PubMed abstract
Published article (176Kb PDF)

PHASE IV. Siblings
From April to September 2006, we completed interviews with 150 siblings. They told us about their own birth defects and their own pregnancies. The analysis of the data will include descriptions of the birth defects to the children of the siblings—the niece and nephews of the proband.

PHASE V. Probands
In 2006/7 29 probands, that is, the affected individual in each family, were interviewed. We plan a report on the nuclear families as a whole—probands and their offspring, siblings and their offspring.

Summary: These studies of self-reported and proxy reported birth defects in a large group of relatives in Irish families with neural tube defects is unique in seeking information directly from each individual concerned where possible, and not relying on proxy reporting by other relatives. The results show higher than expected rates of birth defects and adverse pregnancy outcomes. Further analyses will clarify these trends within families. The promise is that these studies will uncover new factors that underlie the occurrence of these potentially lethal birth defects and lead directly to new clinical trials aimed at prevention.

Fortification Study
In 2006 the Irish Government announced plans to fortify flour with folic acid. Folic acid, a B vitamin, prevents many cases of neural tube defects. As a result governments everywhere recommend that every woman who is capable of becoming pregnant should take a 400 µg tablet of folic acid every day. Studies by the Boyne Research Institute and others show that most women do not follow the recommendations. Therefore, countries like the US and Canada, among others, have started fortification programmes (that is, adding folic acid to flour) to ensure that the population is getting enough folic acid.

In 2007 the Boyne Research Institute started a project called the Fortification Study. The objective was to see if relatives in NTD families benefitted from the Irish government's planned fortification programme. Benefit was to be measured as a change in levels of blood folate from the baseline level before fortification, to the level achieved after fortification. Since the government's fortification programme was called off, we presented results only of the baseline study.

Results: We found that maternal uncles/aunts were slightly more likely to have low folate compared to all other relatives (34.1% vs 22.5%, odds ratio=1.68, 95% confidence interval (CI) 0.83, 3.45, p=0.15). We looked at factors that were associated with higher folate levels. These included intake of enriched/fortified foods (p=0.001) and supplemental folic acid (p<0.0001). Naturally-occurring food folate was weakly associated with serum folate (p=0.14). Increasing amounts of dietary folate were directly associated with levels of serum folate in this cohort of relatives in Irish NTD families.

Conclusions: The weak association of low levels of serum folate with maternal line probably did not explain the excess risk for birth defects seen among maternal relatives in this cohort.

For more details, read a report of the study [647Kb PDF].

Currently our work into Neural Tube Defects focuses on molecular markers obtained from the blood samples donated in 2007. The Boyne Research Institute is a member of a new international consortium, established by scientists from Trinity College Dublin and the USA, which should enable a better understanding of the origins of these complex conditions.

Folate-related Gene Variants
Irish Families with Neural Tube Defects: a long-term investigation into the epidemiological and molecular factors that are linked to the occurrence of neural tube defects.

With our colleagues from CDC Atlanta, USA, we examined 5 gene variants involved with the metabolism of folic acid in 322 members of Irish families. We obtained blood samples from all categories of relatives, including individuals with NTDs (n=13), offspring (N=2), fathers (N=29), mothers (N=37), siblings (N=59), nieces and nephews (N=2), uncles and aunts (N=66), first cousins (N=105), and grandparents (N=2) from 47 families. Paternal relatives (N=65) and maternal relatives (N=115) comprised uncles and aunts, first cousins, first cousins once removed, and grandparents, who were related to the affected individual through the father and mother, respectively. The average age of the study participants was 41 years.

In line with our earlier results we found that, compared to paternal relatives, maternal relatives had a higher number of gene variants linked to lower folate metabolism. This suggests an epigenetic mode of inheritance for NTDs.

For more details, read a report of the study.[346Kb PDF]

Follow-Up Study
From 2008/9 the Boyne Research Institute carried out a study intended to follow-up on relatives in NTD families. The objective was to determine their health and pregnancy history and the health of offspring. Relatives in their reproductive years were interviewed by telephone no matter where in the world they lived. Data from this study will be incorporated into existing data for analysis.