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Trisomy 13 -ˈthər(t)-ˈtēn

(Patau Syndrome; Trisomy D)

By Nina N. Powell-Hamilton, MD, Clinical Assistant Professor of Pediatrics ;Medical Geneticist , Sidney Kimmel Medical College at Thomas Jefferson University;Nemours/Alfred I. duPont Hospital for Children

Trisomy 13 is a chromosomal disorder caused by an extra chromosome 13 that results in severe intellectual disability and physical abnormalities.

  • Trisomy 13 caused by an extra copy of chromosome 13.

  • Infants are small and have severe brain, eye, facial, and heart defects.

  • Several tests can be done before or after birth to confirm the diagnosis.

  • There is no treatment available for trisomy 13.

Chromosomes are structures within cells that contain DNA and many genes. A gene is a segment of deoxyribonucleic acid (DNA) and contains the code for a specific protein that functions in one or more types of cells in the body (see Genes and Chromosomes for a discussion about genetics). Genes contain instructions that determine how the body is supposed to function.

An extra chromosome, making three of a kind, is called trisomy. Children who have trisomy 13 have a third chromosome 13. Trisomy 13 occurs in about 1 out of 10,000 live births. The extra chromosome usually comes from the mother. Mothers who are over age 35 are at increased risk of having a child with trisomy 13.

Symptoms

In the womb, affected fetuses are typically not very active. The amount of amniotic fluid may be too much or too little.

Physical abnormalities

At birth, newborns tend to be small. The brain typically does not develop properly, and these children have many facial abnormalities such as cleft lip and cleft palate, small eyes, defects of the iris (the colored area of the eye), and underdeveloped retinas (the clear, light-sensitive structures at the back of the eyes). The ears are abnormally shaped and usually low-set. Defects in the scalp and openings in the skin are common. Loose folds of skin often are present over the back of the neck. Newborns commonly have a single crease in the palm, extra fingers and toes, and poorly developed fingernails.

Cleft Lip and Cleft Palate: Defects of the Face

Other abnormalities

About 80% of newborns have severe heart defects. A defect called ventricular septal defect, in which there is an abnormal opening between the right and left ventricles, is common. Undescended testes and an abnormal scrotum occur in boys. An abnormally formed uterus occurs in girls. Newborns frequently have prolonged periods of no breathing (apnea). Deafness is often suspected but can be difficult to confirm because these children are severely intellectually disabled.

Diagnosis

  • Before birth, ultrasonography of the fetus or blood tests of the mother

  • Chorionic villus sampling, amniocentesis, or both

  • After birth, the appearance of the infant and blood tests of the infant

Before birth, trisomy 13 may be suspected based on findings detected during an ultrasound of the fetus. Doctors can sometimes find deoxyribonucleic acid (DNA) from the fetus in the mother's blood and use this DNA to determine an increased risk of trisomy 13. If doctors suspect trisomy 13 based on these tests, they often confirm the diagnosis using chorionic villus sampling, amniocentesis, or both.

After birth, the infant's physical appearance may suggest the diagnosis of trisomy 13. To confirm the diagnosis, the infant's chromosomes are analyzed using a blood test.

Prognosis and Treatment

  • Support for the family

There is no specific treatment available for trisomy 13. Most children (80%) are so severely affected that they die before 1 month of age, and less than 10% survive longer than 1 year. Family members should seek support.

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