Hypothyroidism
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This is a condition in which there is decreased or no secretion of thyroid hormone.
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Types and clinical signs
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There are many causes of hypothyroidism, some of which are environmental and some
genetic. Cases discovered in newborn babies immediately after birth are mostly genetic.
There are many hereditary types - in each there is a deficiency of a different enzyme
in the thyroid gland. This is an endocrine gland that produces the hormone thyroxin.
It is important to diagnose this condition early and treat it immediately in order
to prevent developmental damage. The treatment is to administer the missing thyroid
hormone. When the disease starts at an older age, it is usually secondary to inflammation
of the thyroid gland or to another environmental cause.
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Inheritance pattern
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Usually autosomal
recessive.
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Penetrance
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In the hereditary types the penetrance is almost always complete.
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Associated features that can be demonstrated in tests performed during pregnancy
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There are usually no defects. If the hormonal deficiency is part of a syndrome,
there may be additional findings.
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What is the risk of recurrence in a subsequent pregnancy?
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The risk that the parents of a child with congenital hypothyroidism will have another
affected child depends on the cause and the exact type of the disease. The risk
of recurrence is determined within
genetic counseling after reviewing all the data. It is usually approximately
25%.
The risk for more distant relatives is not known. This can also be determined within
genetic counseling based on the pedigree and which enzyme is deficient.
In the adult-onset types, the risk of recurrence also depends on the cause. Usually
relatives are at risk of developing this type of hypothyroidism, which is non-congenital,
but not to the extent seen in the congenital form.
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Molecular genetic information
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The gene for the disease
If the exact enzyme deficiency causing the hypothyroidism is identified, then the
gene can also be identified.
Location
Depends on the gene if the cause is genetic.
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Genetic testing
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Diagnostic testing
The disease is diagnosed by a blood test to measure the level of the thyroid hormone
and the levels of the hormones that regulate its activity: TSH and TRH. Additional
tests can also be performed, such as mapping of the thyroid gland, etc.
Carrier testing
This depends on the type and whether the basic enzyme deficiency has already been
identified.
Fetal testing
The condition can be diagnosed in pregnancy by an enzyme test performed on the fetal blood (see fetal blood) and a comparison with norms. Such
norms are only available in certain centers, and the test can be arranged through
genetic institutes. These tests are carried out in women who have already had children
with hypothyroidism. It is possible and desirable to commence thyroxin therapy during
pregnancy if it is found that the fetus is affected. A genetic test can be performed
in pregnancy only if the basic defect has already been identified - this occurs
in a very small number of cases.
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Treating Hypothyroidism Naturally
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