1342 COMBINED RATE OF NEURAL-TUBE DEFECTS IN NEW SOUTH WALES AND PREVIOUS YEAR USAGE OF
2, 4, 5-T IN AUSTRALIA
5-T in the U.S. where an emergency suspension is in force pending further actions by the Environmental Protection
Agency. We thank Prof. M. S. T. Hobbs for
helpful criticism.
Department of Preventive and Social Medicine, School of Public Health and
Tropical Medicine, University of Sydney, Sydney, New South Wales 2006, Australia
BARBARA FIELD CHARLES KERR
HLA HOMOZYGOSITY AND NEURAL-TUBE DEFECTS
S:R,—The provocative article by Dr Schacter and colleagues (April 14, p. 796) demonstrates that increased homozygosity for HLA-A,B alleles is accompanied by fetal wastage
New South Wales combined birth-rate of anencephaly and meningomyelocele (table and figure). There is significant seasonal variation in birth-rates of babies with neural-tube defects in New South Wales.2 Highest rates are for conceptions during the summer months of December, January, and February. By contrast, northern hemisphere rates peak for spring conceptions.4 A survey by questionnaire of local-government authorities in New South Wales (the main users of 2, 4, 5-T to control woody plants) revealed maximum spraying during the summer months. Total usage was dependent on climatic conditions. We favour the view that neural-tube defects originate from the interaction of a "predisposed" embryonic genotype with environmental factors. Seasonal variation of incidence in New South Wales suggests that a seasonal factor or factors may influence summer conceptions. Our data and the record-linkage nature of analysis cannot be taken as direct evidence of any causal association involving 2, 4, 5-T. Moreover, the figure suggests that linear correlation disappeared in 1975 and 1976. During these two years, monitoring of 2, 4, 5-T herbicide was established in Australia to ensure that its concentration of T.C.D.D., regarded as the most significant potential teratogen, remained below 0.1parts per million.5Nevertheless we believe that further retrospective analyses undertaken in other countries may throw some light on the significance of seasonal events in the origin or neural-tube defects, as such studies did with the disproving of Renwick’s potato-blight hypothesis. More informative would be careful evaluation of prospective avoidance trials such as currently pertains two the use of 2, 4, M. S. T., Carney, A., Field, B., Simpson, D., Kerr, C. Br. J. prev. med. 1974, 28, 66. 5. Report of the Consultative Council on Congenital Abnormalities in the Yarram District Government of Victoria, Melbourne, 1978.
4.
Hobbs, soc.
2,
2, 4, 5-T IN AUSTRALIA
5-T in the U.S. where an emergency suspension is in force pending further actions by the Environmental Protection
Agency. We thank Prof. M. S. T. Hobbs for
helpful criticism.
Department of Preventive and Social Medicine, School of Public Health and
Tropical Medicine, University of Sydney, Sydney, New South Wales 2006, Australia
BARBARA FIELD CHARLES KERR
HLA HOMOZYGOSITY AND NEURAL-TUBE DEFECTS
S:R,—The provocative article by Dr Schacter and colleagues (April 14, p. 796) demonstrates that increased homozygosity for HLA-A,B alleles is accompanied by fetal wastage
New South Wales combined birth-rate of anencephaly and meningomyelocele (table and figure). There is significant seasonal variation in birth-rates of babies with neural-tube defects in New South Wales.2 Highest rates are for conceptions during the summer months of December, January, and February. By contrast, northern hemisphere rates peak for spring conceptions.4 A survey by questionnaire of local-government authorities in New South Wales (the main users of 2, 4, 5-T to control woody plants) revealed maximum spraying during the summer months. Total usage was dependent on climatic conditions. We favour the view that neural-tube defects originate from the interaction of a "predisposed" embryonic genotype with environmental factors. Seasonal variation of incidence in New South Wales suggests that a seasonal factor or factors may influence summer conceptions. Our data and the record-linkage nature of analysis cannot be taken as direct evidence of any causal association involving 2, 4, 5-T. Moreover, the figure suggests that linear correlation disappeared in 1975 and 1976. During these two years, monitoring of 2, 4, 5-T herbicide was established in Australia to ensure that its concentration of T.C.D.D., regarded as the most significant potential teratogen, remained below 0.1parts per million.5Nevertheless we believe that further retrospective analyses undertaken in other countries may throw some light on the significance of seasonal events in the origin or neural-tube defects, as such studies did with the disproving of Renwick’s potato-blight hypothesis. More informative would be careful evaluation of prospective avoidance trials such as currently pertains two the use of 2, 4, M. S. T., Carney, A., Field, B., Simpson, D., Kerr, C. Br. J. prev. med. 1974, 28, 66. 5. Report of the Consultative Council on Congenital Abnormalities in the Yarram District Government of Victoria, Melbourne, 1978.
4.
Hobbs, soc.
2,
