Question # 44 FONT>
Are you aware of any known correlation
between in utero mercury exposure and NLD?
Answer (courtesy of Dr.
Roberta F. White):
The evidence on mercury is mostly based on methylmercury.
If mercury exposure is from thimerosol, which is used in
injections, then we are talking about ethylmercury, which
is less neurotoxic. The research to date on ethylmercury
does not provide much support for cognitive deficits associated
with early developmental exposures at levels experienced
in the US (or the Faroe Islands).
If exposure was to methylmercury from seafood consumption,
there is much more evidence. The epidemiologic data suggests
that prenatal MeHg exposure is most associated with deficits
in language and attention at ages 7 and 14. There is other
evidence suggesting a decrement in IQ. I know of no information
on relationships to diagnostic syndromes such as ADHD or NLD.
There is some evidence from the Faroes (and South America)
that prenatal exposure affects visual memory (Bender recall,
S-B Copying Test) but the children in the Faroes did very well
on tests like Block Design. I have some very pilot level
imaging data that suggest brain reorganization of function
may occur with prenatal MeHg exposure, but I do not at all
see a consistent “right hemisphere” pattern.
In general, exposures to metals like lead early in development
can be related to a number of syndromes, and my clinical
impression is that the consequences of such exposures are
often related to inherited vulnerabilities (e.g., verbal
learning disabilities or language disorders in children
whose parents are relatively weak in verbal abilities).