A low estriol level in the mother's blood biochemical screening: Ichthyosis and
A very low level of estriol in the mother's blood is associated with a number of
medical conditions for which testing is available. The most common is a skin disease
known as ichthyosis. The main manifestation of this disease is scaly skin, particularly
over the front of the lower legs, but possibly in other areas as well. The skin
is very dry, and the condition is subject to seasonal exacerbation and resolution.
In a milder form of the disease, which has a different origin, the skin symptoms
can be alleviated by rubbing oily creams into the skin. When the level of estriol
in the mother's blood, detected in the second trimester blood biochemical screening
blood test, is low, this indicates that the fetus has a very specific form of ichthyosis
arising from a deficiency of the enzyme steroid sulfatase. This disease is expressed
only in males, although girls can carry the defective gene without suffering from
the disease (sex-linked inheritance).
When there are already cases of this
condition in the family: Often, taking detailed information about the
family reveals that there are other family members on the mother's side who suffer
from ichthyosis, but who did not know that they had this condition and/or this enzyme
The enzyme deficiency can be demonstrated in the fetus's cells in the amniotic fluid in order to establish the diagnosis.
In cases where there are other family members on the mother's side who have the
same symptoms, provided that they do not have any other problems as well, it can
be assumed that they also suffer from the same condition.
When there are family members on the
mother's side who are known to suffer from this condition, demonstration
of a deficiency of the enzyme steroid sulfatase in the amniotic fluid is not sufficient
because a small percentage of these "new" cases are a result of a chromosomal deletion
involving not only the steroid sulfatase gene, but also adjacent genes, one of which
is known to be associated with mental retardation. In even rarer cases, additional
genes next to the steroid sulfatase gene can be missing. These genes can cause congenital
bone disease (identifiable by ultrasound) etc. Therefore when a case appears for
the first time in a family, in order to be completely certain about the correct
diagnosis, despite a risk of less than 5%, the area around the steroid sulfatase
gene should be examined for deletions. If the defect is limited to the deletion
of this gene alone, the skin disease will be the only manifestation.
The mother can be tested for carrier status - in a third of the cases, the mother
is not a carrier, and the mutation (the defect in the steroid sulfatase gene) occurred
for the first time in the ovum or sperm cell from which the embryo was created (fresh
mutation). The carrier test can indicate whether there is a risk of recurrence in
each pregnancy and whether other women on the mother's side might be carriers. The
carrier test can be performed using a quantitative enzymatic test or FISH. However,
if the disease is limited to only a skin condition, and the couple will not be terminating
the pregnancy for any other reason, the carrier test may be omitted. However, if
the mother's blood estriol level is also low in the next pregnancy, it will be obvious
that this is a recurrence of the same disease.
Other problems involving steroid sulfatase deficiency:
Some women do not experience labor, requiring artificial induction of labor in weeks
41 - 42. As mentioned above, some of these patients may have other problems arising
from extensive damage (deletion) around the steroid sulfatase gene.
Smith Lemli Opitz syndrome
This syndrome, which affects both males and females, is characterized by a large
number of defects including mental retardation, changes in the external genitalia,
slightly reduced head circumference and body dimensions, etc. It is also associated
with a low estriol level in the mother's blood. It is transmitted by autosomal recessive
inheritance, meaning that a couple who have a child with this disease have a 25%
risk in each pregnancy of having another affected child. The presence of this disease
can be confirmed or ruled out by testing for cholesterol metabolites in the amniotic
fluid - this is not performed as part of the regular test, but is added in cases
where the disease is suspected.
Hormonal disorders as a result of diseases of the suprarenal (adrenal) gland
These disorders are also associated with a low level of estriol in the mother's
blood. Compared to the other causes they are relatively rare. They can be identified
by sending the amniotic fluid for testing for the metabolites of the hormones secreted
by this gland.
Other diseases associated with low estriol levels in the mother's blood
Chromosome disorders such as trisomy 18.
Low estriol levels are also present in cases of threatened miscarriage where there
is concern for the fetus's life. In these cases, alpha-fetoprotein and hCG levels may be high.