Trisomy 13, also known as Patau syndrome, occurs at the moment of conception when a gene mutation occurs in either the egg or the sperm. An egg and a sperm each carry 23 chromosomes that unite to create a child with 46 chromosomes. When the 13th chromosome of either has an extra chromosome, this faulty DNA occurs in the cells of the child; it may appear in all the cells or only part of the child's cells. The locations of the faulty cells determine the type and severity of the child's birth defects. When the extra chromosome is present in only some cells the condition is called mosaicism. When only part of an extra chromosome appears it is called a partial trisomy. Trisomy 13 is not a hereditary disease; it occurs as the result of an isolated gene mutation and is seen in around one out of every 10,000 births.
Eighty percent of the children born with trisomy 13 have heart defects. Most will have severe mental retardation, cleft lip and cleft palate, small eyes, extra fingers and toes, close-set eyes, and low set ears. Internal organ abnormalities include malformed kidneys, malformed reproductive organs, high blood pressure, and incomplete brain formation. Skeletal characteristics involve spine curvatures, spina bifida, small skulls and malformed feet.
Trisomy 13 is easily diagnosed with a visual examination but the doctor will likely perform tests to determine the child's particular issues since the syndrome presents such varied abnormalities. Ultrasounds and X-rays often show that the child's internal organs are rotated inside the abdomen. Brain scans reveal that both sides of the child's brain have fused together. More than 80% of the children born with trisomy 13 die in their first month, most of them from congenital heart defects.
Those who have a child with trisomy 13 have a one percent chance of having another child with the disorder.