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Etiology of the disease
etiology,
aetiology
1.
the branch of medical
science that studies the
causes of diseases and the
factors underlying their
spread.
2. the accumulated
knowledge of disease causes.
— etiologist, n.
— etiologic,
etiological, adj.
Ichthyosis
is caused by
reduced cell desquamation
(the process by which cells
are shed from the skin), or
increased production of
cells in the outer layer of
the epidermis, the stratum corneum, making it thicker
and impairing its normal
function. The stratum
corneum consists of various
structural proteins,
moisture-binding substances,
and fats that combine to
make the skin a barrier
between the body and the
environment.
The
aetiology of the disorder
has been determined for some
forms of lamellar ichthyosis
and ichthyosiform
erythroderma, all forms of
bullous ichthyosis, Sjögren-Larsson
syndrome, and for Netherton
syndrome.
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In approximately a third of all
cases of lamellar ichthyosis
(ichthyosiform erythroderma)
the skin is deficient in an
enzyme called
transglutaminase 1. This
enzyme is essential for the
development of the cornified
cell envelope in the horny
layer of the skin. The
result of reduced or absent
enzyme production is
disturbed keratinisation and
accumulation of defective
horn cells on the skin
surface. Lamellar ichthyosis
can also be caused by lack
of ichthyin, a protein which
binds fat, or by mutations
of certain ALOX genes
which encode the production
of enzymes that participate
in the formation of
specialized lipids important
for the skin barrier.
Mutations of three other
genes have recently been
found to cause the disorder,
among them the ABCA12
gene that encodes a protein
needed for transportation of
lipids in the skin. A
mutation causing total lack
of this protein results in
an extremely severe form of
the disease called harlequin
ichthyosis. More research is
needed, however, to gain a
full understanding of the
genetic background of the
congenital forms of
ichthyosis.
In
bullous ichthyosis, the
defect is located in one of
the keratins (proteins) that
form the cellular skeleton
of epidermal cells. The
anomalous keratin molecules
are erroneously built into
the cellular skeleton, which
becomes fragile, resulting
in cellular break-up.
Moreover, excessive keratin
accumulates in the remaining
horny cells, thickening the
stratum corneum.
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