Inheritance and allergy

I want to find out exactly what is causing my son’s
eczema. How can I get him tested?
You have asked one of the most difficult questions to answer
because we do not have a complete understanding of the cause or
causes of the various types of eczema. Your son is likely to have
atopic eczema as this is the most common childhood form, so it is
unlikely to be due to a single allergy, for which avoidance of the
‘allergen’ (the cause or trigger of the allergy) would result in a cure.
This approach might apply in contact allergic eczema, which is
much more common in adult life, but even then there is usually
more than one trigger.
We do know that there is a strong inherited or genetic component
to atopic eczema. If you son has inherited a certain gene, or
combination of genes, this predisposes him to being ‘atopic’, buthe would still need some other trigger to cause him to have eczema.
To date, several genes have been identified that show a link with
atopic disease, but it seems likely that there are other, as yet
unidentified, genes that are important, and we hope that these will
be discovered over the next few years. We still do not understand
the function of these genes as we do not know whether they can
all lead to asthma, eczema or hay fever – the three atopic diseases
– or whether individual genes are linked to just one of the diseases.
It is more likely that various different gene combinations can lead
to atopic eczema as this would help to explain why different triggers
are important in different patients and why eczema has more that
one ‘cause’.
In other words, if your son has a susceptibility to developing
eczema by having a particular group of genes, the eczema may be
triggered by several different factors. Despite much research, the
evidence for any one trigger is very limited, and trials excluding or
limiting exposure to different environmental factors (e.g. pets,
woollen clothing, dust, car pollution) have been very disappointing
in terms of improving eczema. There is therefore no simple way
to get your son tested, and it is more likely that simple detective
work, looking at when it gets worse, may give you more of a clue.
(For more about testing, though, see the section ‘Are there any
tests?’ later in this chapter.)