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Who
is most commonly affected by alopecia areata?
Research into the demographics of AA suggest
that 0.05%-0.1% of the population will be affected with AA at
any one time (Rook
1991, Gollinck 1990, Safavi 1992). On this basis, it can be
estimated there are between 30 and 60 thousand sufferers in
the UK, between
112 and 224 thousand in the USA and worldwide - between 2.25
and 4.5 million! Of course, these figures are only estimates
based
on regional studies, and cover all forms of AA from small patches
of hair loss through to alopecia universalis. The actual expression
of AA in a population probably varies from region to region.
Information
on how AA affects different groups of people is lacking but,
as an example, it is believed that AA is slightly more common
in
Japanese people - particularly people of Japanese decent living
in Hawaii (Arnold 1952). A recent study has put the average
lifetime
risk of experiencing AA at 1.7%, considerably higher than most
previous estimates at around 1% (Safavi 1995).
There are two schools of thought as to what extent AA affects
males and females. Either AA affects males and females in equal
numbers or it affects a greater number of women. There have been
claims that the female to male ratio is between 1:1 (Muller 1963,
Safavi 1995) and 2:1 (Friedman 1985). In most other autoimmune
diseases, a greater number of women are affected with ratios of
up to 10:1 for Systemic Lupus Erythematosus (SLE) (Ollier 1989).
This is believed to be due in part to differences in hormone levels
between the two sexes.
The first expression of AA is most likely to occur in people
in their teenage years or early twenties (Gollinck 1990), but
individual cases have been reported in children younger than two
years of age or older than 70 years (Muller 1963). Between approximately
10% and 25% of patients show a family history of AA. With 10%
quoted by Muller (1963), 11% by De Weert (1984), 18% by De Waard-van
der Spek (1989) and 24% by Friedman (1981) - among others.
The vast majority of patients with AA are in excellent health
and have no associated clinical conditions but a number of diseases
have been reported showing increased prevalence in conjunction
with AA for a minority of people. These include Down's syndrome
(Du Vivier 1975), Addison's disease (Kern 1974, Zauli 1975), thyroid
disorders (Muller 1963, Cunliffe 1969) and vitiligo (Muller 1963,
Cunliffe 1969, Main 1975) among other conditions.
Why
is the first episode of alopecia areata most likely to occur in
late teens to early twenties - particularly for women?
The female humoral and cell mediated immune system response is
on average more active than males and in theory may account for
the increased longevity of women (Grossman 1989). In general, women
are far better than men in fighting off bacterial and viral infection
(Janeway 1993), but a more sensitive immune system will be more
likely to develop autoimmune activity. Typically, autoimmune disease
is far more common in females than males (Ollier 1992). Hormones
including gonadal steroids, adrenal glucocorticoids, thymic hormones
and prolactin are known to influence lymphocyte activity - but the
most potent hormone affecting the immune system directly and indirectly
is estrogen (Grossman 1989, Schuurs 1990).
Allergies are classed as hypersensitivity reactions - an inappropriate
over-reaction to foreign antigens whereas autoimmune diseases are
an inappropriate over-reaction to self antigens. Extensive studies
into allergy susceptibility show that for women the first symptoms
most often occur between the ages of 10 and 29 (Wormald 1977) and
laboratory/in vitro studies have shown that estrogen can directly
stimulate lymphocytes and cytokine chemical signal production (Stimson
1988, Schuurs 1990, Fox 1991). Consequently, the hormonal changes
at and after puberty are believed to increase an individual's immune
system sensitivity and lead to increased potential for autoimmune
disease development (Grossman 1989, Schuurs 1990). It is possible
similar mechanisms are at work in AA.
Women with AA can sometimes go into spontaneous, temporary remission
when pregnant (Sulen 1956 in Rook 1991, Muller 1963). Equally, women
have reported the first onset of AA during pregnancy (Muller 1963).
Presumably induction or remission is due to the associated fluctuations
in hormone levels.
I
have alopecia areata. What are the chances it will pass to my child?
This question is very difficult to answer. Statistical research
shows that on average 20% of people with alopecia areata report
having at least one other blood relative with the condition (Muller
1963, De Weert 1984, Friedman 1981, Shellow 1992). Although this
family history of alopecia areata suggests a genetic component for
at least 20% of cases, we cannot say just how likely it will pass
from generation to generation. Close analysis of family trees shows
that very often alopecia areata expressed in one generation does
not always reappear in the next. It can be several generations down
the line before alopecia areata develops in another individual.
It would seem that even the transfer of susceptibility genes for
alopecia areata to offspring does not automatically mean they will
have alopecia areata. Perhaps there needs to be an environmental
influence, or trigger, that may also activate certain genes. Because
there are several genes involved in alopecia areata, not all of
the genes may be passed from adult to child. Maybe a few genes are
passed on but not enough to allow alopecia areata to develop and
so this branch of the family loses the trait entirely. Equally,
if parents who are carriers for a few of the alopecia areata susceptibility
genes have offspring, the child with both sets of genes may be more
likely to develop hair loss.
I should also say here that the statistical data covers all types
of blood relations, not just parent to child. In light of this,
and the apparent need for environmental influence, the risk of children
of an alopecia areata-affected parent developing the condition is
much less than 20% - let's say 4% (a guess/best estimate on my part).
This risk is so small that some dermatologists just don't rate it
as significant. Other dermatologists would argue that there are
no reliable statistics on family inheritance anyway. One or two
reports suggest there is NO significant family history of
alopecia areata and this all adds to the confusion (Saenz 1963,
Olivetti 1965, Lutz 1988).
Finally, don't forget that every person is carrying potentially
destructive genes for some form of disease. In theory we are each
carriers for at least two lethal genes. There are many more serious
conditions possible and so when placed in context, transmission
of alopecia areata to children should not be seen as a dominant
factor. Be aware that there may actually be advantages in having
alopecia areata. A recent report suggests people with alopecia areata
have a reduced risk of developing type I diabetes compared to the
general population (Wang 1994). |
