C18 Conditions
Learn about C18 abnormalities
Genetic Basis
Chromosome 18 conditions are caused by a change in a person’s genetic makeup.
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18p-
18p- happens when part of the short arm of one of the two copies of chromosome 18 is missing. This means there is one copy instead of two for each of the genes in the deleted region of the chromosome.
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18q-
18q- occurs when there’s a deletion of any size, and from any region, on the long arm of chromosome 18, also called the q arm.
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Tetrasomy p18
Tetrasomy 18p occurs when there is an extra chromosome that is made up of two copies of the short arm of chromosome 18 (the p arm). Instead of having two copies of the p arm of chromosome 18, people with Tetrasomy 18p have four copies.
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Trisomy 18
Trisomy 18 is sometimes called “Edwards syndrome”. Trisomy 18 occurs when there are three copies of chromosome 18 in every cell of the body.
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Ring 18
Ring 18 happens when one of the two copies of chromosome 18 forms a ring instead of the rod shape. When a ring forms, the tips of the chromosome are usually deleted.
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Pitt-Hopkins syndrome
PTHS is caused by a mutation within or a complete deletion of the TCF4 gene.
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