The epidemiology of anencephaly and spina bifida in Izmir, Turkey, in the light of recent aetiological theories

Etiology of chronic renal failure in Turkish children

The etiology of chronic renal failure (CRF) was studied in 459 Turkish children (205 girls, 254 boys) for the period January 1979-December 1993. Their mean age at onset of CRF was 9.5 +/- 4.2 years (range 1-16 years); CRF was defined as a glomerular filtration rate (GFR) below 50 ml/min per 1.73 m2 for at least 6 months. When a GFR determination was not available, the serum creatinine concentration was used: greater than 1 mg/dl for children aged 1-3 years, greater than 1.5 mg/dl for those 3-10 years and greater than 2 mg/dl for those 10-16 years. Primary renal disorders were as follows: reflux nephropathy 32.4% glomerular diseases 22.2%, hereditary renal disorders 11.4%, amyloidosis 10.6%, urinary stones 8% and other renal disorders 15.4%. Twenty-three cases of reflux nephropathy (15.4%) were associated with neural tube defects (NTD) and 20 (13.4%) were caused by infravesical obstruction. CRF caused vesicoureteral reflux associated with NTD and amyloidosis are more frequent in our series compared with west European and Nordic countries.

The Chernobyl accident, congenital anomalies and other reproductive outcomes

Studies of the association between the Chernobyl accident in April 1986 and reproductive outcome, with particular reference to congenital anomalies, are reviewed. All of the studies so far have been based on the detection of a change in frequency over time. An increased frequency of trisomy 21 in the former West Berlin in January 1987, and increases in the frequency of neural tube defects in several small hospital-based series in Turkey, are not confirmed in larger and more representative series in Europe. No clear changes in the prevalence at birth of anomalies which might be associated with the accident are apparent in Byelorussia or the Ukraine, the republics with the highest exposure to fallout. However, these data are difficult to interpret as the methods of acquisition have not been described and they have not yet been reported in full. Thus, there is no consistent evidence of a detrimental physical effect of the Chernobyl accident on congenital anomalies. This is also the case for other measured outcomes of pregnancy. There is evidence of indirect effects--an increase in induced abortions substantial enough to show as a reduction in total births, due to anxieties created. Data are not available on the reproductive outcomes of women pregnant at the time of the accident who were evacuated from the 30 km zone of immediate contamination, of workers in the plant at the time of the accident or of decontamination workers. Moreover, no data are available from several of the other countries closest to the Chernobyl area.

Changing trend of neural tube defects in eastern Turkey

STUDY OBJECTIVE

The aim was to study the relationship between birth prevalence of neural tube defect (including anencephaly) in Eastern Turkey before and after the Chernobyl disaster.

DESIGN

This was a prospective study of time trends in live births and stillbirths over the years 1985-1990. Medical and sociodemographic data were recorded for the mothers.

SETTING

Elazig, Eastern Turkey.

SUBJECTS

There were 5240 live births and stillbirths during the study period, 24 of whom had neural tube defect and of these 20 had anencephaly.

MAIN RESULTS

Of the 5240 newborns, 24 had a neural tube defect, giving a birth prevalence of 4.5 per 1000 total births. Of these, 20 were anencephalic (3.8 per 1000). In all, of the 2355 conceptions estimated to have occurred prior to the Chernobyl disaster in May 1986, the birth prevalences of total neural tube defect and anencephaly were the same (1.7 per 1000). This contrasts with the years following after Chernobyl, when the birth prevalence of total neural tube defect was 6.9 per 1000 (5.5 per 1000 for anencephaly). The differences were statistically significant (p < 0.001). These two increased rates reached a peak of 12.4 (for total neural tube defects) and 8.9 (for anencephaly) in 1988. In 1989 the rate of total neural tube defects decreased to 10.0 and that of anencephaly to 8.6 per 1000. In 1990 the rate of total neural tube defects fell to 5.6 and that of anencephaly fell to 4.2.

CONCLUSIONS

The changes in birth prevalence of neural tube defects might be due to the Chernobyl disaster. However, the increases observed occurred mainly in infants conceived well over a year after the Chernobyl disaster, suggesting that other factors may be responsible.

Changing incidence of anencephaly in the eastern Black Sea region of Turkey and Chernobyl

The incidence of neural tube defects (NTD) was 2.12 per 1000 births and that of anencephaly was 1.29 per 1000 births when we reviewed the 40,997 consecutive births between 1981 and 1986 in the major maternity hospital in the eastern Black Sea region of Turkey. There was a significant increase in the incidences of NTD and anencephaly after 1986 to 4.39 and 2.46 per 1000 births respectively (P less than 0.0001; P less than 0.005). Although this might be a coincidence, it may be due to the nuclear contamination of the region following the Chernobyl accident.

Incidence of anencephaly in Jamaica

Information was collected on 2,197 stillbirths and neonatal deaths on the island of Jamaica during the 12 month period September 1986 to August 1987 as part of the population based nationwide Jamaican Perinatal Morbidity and Mortality Survey. There were 14 cases of anencephalus giving an incidence of 0.26 per 1,000 total births. One of these cases was associated with the amniotic band syndrome; excluding this, the incidence would be even lower (0.24 per 1,000). There was no apparent association with social class, maternal age, or parity. The rate found in Jamaica is considerably lower than found in any other national population study.

Congenital anomalies in twins in Northern Ireland. II: Neural tube defects, 1974-1979

In a large population-based study in Northern Ireland during the period 1974-1979, the rate of anencephalus in twins (9.1/10,000) was found to be less than that in singletons (24.3/10,000). This finding is in contrast with most other studies and the possibility of underascertainment of twin cases is considered, but it is concluded that chance is the likeliest explanation. The rate of spina bifida in twins (36.4/10,000) was similar to that in singletons (31.9/10,000). All of the twins with anencephalus were female and from pairs of like sex. Rates of spina bifida in twins from pairs of the two sex types were similar but, unusually, there was a male preponderance. As in previous studies, the great majority of twins with NTDs had unaffected cotwins.

Changing incidence of neural tube defects in Aegean Turkey

The incidence of neural tube defects was monitored among all live- and still-births delivered between June 1986 and July 1988. In all there were 19,115 total births. The incidence of neural tube defects (NTD) was 1.9 per 1000 among those whose conception time was prior to May 1986. However, in conceptions occurring in May, June and July 1986, the NTD rate increased to a level of 8.9 per 1000, subsequently gradually declining to previous levels within 9 months. This dramatic change in incidence, which parallels a previous finding from Turkey, suggests that this finding may be associated with the Chernobyl disaster of May 1986.

Incidence of anencephalus and spina bifida in Greece

A cross-sectional national survey of 11,048 births in the whole of Greece in April 1984 identified 7 cases of anencephalus and 9 of spina bifida. There was thus an incidence of 1.45 neural tube defects per 1,000 total births. This is the first geographically defined population study from southern Europe. In comparison with hospital-based data from the 2 countries on its borders, the Greek rates are rather similar to those of Yugoslavia but much lower than reports from Turkey.

High incidence of neural tube defects in Bursa, Turkey

A radiological survey of 1204 members of the population of Bursa revealed a high prevalence of spina bifida occulta (16.3%). Hospital deliveries in the area also showed a high incidence of anencephalus and spina bifida aperta (5.8 per 1000 total births) in the years 1983 to 1986. In the first 6 months of 1987, however, there was an increase in incidence to 20 per 1000 births (P less than 0.01). The possibility is raised that the Chernobyl disaster of May 1986 might have resulted in the elevation of the rate in an already susceptible population.

Neural tube defects among twin births

To obtain accurate, unbiased rates of neural tube defects (NTDs) in twins, we conducted a population-based study that included live births and fetal deaths in Los Angeles County, California, ascertaining cases by multiple methods. Twenty-eight twin cases yielded a prevalence-at-birth of 1.6/1,000 twin births, which is significantly higher than the singleton prevalence of 1.1/1,000 births. In twins compared with singletons, the prevalences of both encephalocele and anencephaly are increased, whereas spina bifida is decreased. The twin case male/female sex ratio (.55) is lower than the singleton case sex ratio (.77). Concordance is relatively low at 3.7%, but appears to be higher than recently reported recurrence risks in other low prevalence areas. Stillbirths were most common among female cases and like-sex twins. Our study tends to support proposed etiologic theories associating NTDs with females or monozygotic twins, or both. There is increasing evidence that the etiology of NTDs may differ in high and low prevalence areas. We suggest also that twins and singletons may differ in their response to etiologic factors. The variations among anencephaly, spina bifida, and encephalocele in their association with twinning suggest that there may be different factors that influence the development of each specific NTD. The noted differences among the malformations also indicate that some of the variation among results of other studies of NTDs and twinning may be due to case ascertainment. Including spina bifida cases would decrease the proportion of twins in a study population, while including anencephalics would increase the proportion. Importantly, ascertaining fetal deaths would increase the proportion of anencephalics and case females, so studies of NTDs that do not include fetal deaths will show fewer twins than expected. On the basis of our findings and those of Layde et al., excluding encephaloceles will also decrease the number of twins among NTD cases. When investigating etiologic hypotheses for NTDs, these potential biases must be recognized.

The association of twinning and neural tube defects: studies in Los Angeles, California, and Norway

Accurate, unbiased malformation rates in twins must be obtained unselectively from population-based studies that include livebirths and stillbirths after a thorough ascertainment of cases. This type of study was conducted in Los Angeles County, California, where 28 twins with a neural tube defect (NTD) were identified. The prevalence in twins (1.6/1,000) was significantly higher than in singletons (1.1/1,000). The study then was expanded to include population-based data from the Medical Birth Registry of Norway which has a comparable overall NTD prevalence (1.0/1,000) and twinning rate (2%). The combined material shows a higher prevalence of anencephaly and encephalocele but not of spina bifida in twins compared to singletons. The male/female ratios in total twin and singleton cases were comparable (0.8), but varied by specific defect. Like-sex twin females appeared at highest risk for NTD as well as for fetal death. This study supports theories which associate NTDs with monozygotic twins, either through developmental disruptions that cause susceptibility to environmental agents or through a common etiology. Furthermore, it suggests that twins and singletons differ in their response to etiologic factors for the development of NTDs and that the development of each type of NTD may be related to different factors.