In this condition there is an extra chromosome 13, so that there are three number 13 chromosomes
instead of two.
The frequency is estimated to be 1 in every 5,000 births.
This syndrome ends in death - 86% die in the uterus or in the first year of life, and only a few
survive to the age of 5 years.
In most cases, midline structures are affected, and the usual manifestations are cleft lip and palate,
polydactyly (extra fingers and toes), holoprosencephaly or cyclopia,
a small head circumference, abnormalities in
the cranial skin, defects of the heart and kidneys, etc.
A small percentage of cases occur when the trisomy is present in only some of the cells, while
others cells are normal - this condition is known as mosaicism.
The risk of having a child with this syndrome increases with maternal age.
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