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As indicated by many animal experiments, effects of chemical
exposure usually appear most conspicuously in the following
generation, as is the case of infantile nerve system
development. Consequently, studies on populations of pregnant
women and infants, particularly long-term cohort studies
addressing prenatal exposure, are desired. Japan's good maternal
and child health system, including the mother-child pocketbooks
and newborn screening, should serve as a basis for large-scale,
long-term longitudinal studies, thus helping obtain a plenty of
pioneering data. What is important is systematic research design
including accurate estimation of prenatal exposure linked with
postnatal development data, as well as ethical considerations.
Hypospadias and cryptorchidism could be covered by such cohort
studies, but the number of actual cases can be insufficient.
These disorders should consequently be addressed by case-control
studies. A model could be the Scandinavian systems in which
affected newborns are registered along with healthy babies born
around the same time as a control, with data on prenatal
exposure and other risk factors obtained by a standardized
questionnaire. Interviews with parents in later days would
complicate the problem by bias of memory.
While a group supported by Health and Labor Sciences Research
Grants (Studies on Chemical Risks) has started a prospective
cohort study involving pregnant women, a new long-term cohort
study including evaluation of exposure in the organogenetic
period and nerve development is desired.
- Epidemiologic studies on male fertility
While cases of high-level exposure on accidents in chemical
plants or other occupational situations that caused reproductive
problems have been reported, practically nothing is known about
the possible influences of chemical agents on fertility in the
ordinary environment. In particular, reliable data on the
variations in time and space of male fertility, e.g. sperm
findings, do not exist because techniques are not standardized
and large fluctuations in a single person. Accumulation of
relevant longitudinal data according to a standardized protocol
on a global scale is needed. Japan participates in the
international collaborative study program, presided by
Skakkebaek, and is now collecting comparative data on semen
concentration and sperm motility under strict precision control.
It is desirable to develop this activity into synchronic and
ecological studies to investigate relationships with chemical
exposure. Another important task is to develop a new biomarker
for fertility, because the labor-intensive semen examination is
not an ideal index.
A study group supported by Health and Labor Sciences Research
Grants (Studies on Chemical Risks) has started development of
biomarkers along with a cross-sectional study on chemical
effects on reproductive functions. This program should further
be enhanced.
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