Spondylo-epiphyseal dysplasia (SED)
disorder of the development of the vertebrae and the heads of the long bones
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Types
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There are many types, described below, of spondylo-epiphyseal dysplasia.
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Clinical signs
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This is a heterogeneous group of diseases, all of which are characterized by flattened
vertebrae with or without irregular borders and/or defects and a delay/disorder
of the development of the heads of the long bones (epiphyses). There are different
types and degrees of severity.
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precise diagnosis is important, and a diagnosis made in the past may not always
have been made according to today-s standards and methods and is not always accurate
by today-s standards.
Because of this, the diagnosis must always be confirmed in a genetic institute by
examining the patient, or at least by looking at the clinical picture, photographs,
X-rays and other data.
Even though we know a lot about the inheritance patterns, the risk of recurrence,
the mechanism of the manifestations of the disease, etc., most of these diseases
have exceptions, and each case/family must be examined individually in a genetic
institute.
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Inheritance pattern
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These conditions can be transmitted by both autosomal dominant and autosomal recessive inheritance.
Usually, but not always, the milder types that have a later age of onset are transmitted
by autosomal dominant inheritance while the more severe cases are generally transmitted
by autosomal recessive inheritance. The inheritance pattern is determined in each
family within genetic counseling
by the type and distribution of cases.
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Penetrance
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Usually full.
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Associated features that can be demonstrated in tests performed during pregnancy
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These depend on the severity. In the severe cases, there may be signs of a reduction
in the growth of the long bones. The condition may sometimes not be detectable by
ultrasound examination
in pregnancy, especially if the shortening of the long bones only appears after
birth or even after the age of two years.
In all these cases it is important to refer the couple for genetic counseling, to
which they should bring all data, including the results of other tests performed
during the pregnancy such as alpha-fetoprotein, nuchal translucency, etc.
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What is the risk of recurrence in a subsequent pregnancy?
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This depends on the inheritance pattern and the degree of relationship to the affected
individual, according to the laws of inheritance. This must be established at a
genetic institute.
The risk for more distant relatives depends on the number of affected individuals
in the family, the degree of relationship between the relatives and the affected
individuals, consanguinity
between the parents, if present, etc. This risk is established within genetic counseling.
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Molecular genetic information
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The gene for the disease
Usually the genes for the proteins comprise a molecule of collagen 2.
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Genetic testing
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Diagnostic testing
In spondylo-epiphyseal dysplasia, the test is complex and requires the testing of
a number of genes. Collagen 2 can be examined in skin cells, or chorionic villus or amniotic fluid cells, directly
using biochemical methods. This test is performed in a laboratory abroad. See: Indirect
testing for genetic markers in a family with a number of patients in the family
- when there are a number of different genes that can each cause the disease - all
of the genes having been located / identified / mapped - autosomal dominant disease.
See also: Screening
test for identifying defects (mutations) using various methods such as SSCP - autosomal
dominant diseases.
Carrier testing
In families in whom the mutation in the gene responsible for the disease has been
found, other relatives may be tested both for signs of the disease itself and for
carrier status. There are no carrier tests for the healthy population.
Fetal testing
As for diagnostic testing.
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