Trisomy 13 is caused by an extra chromosome 13.
Infants are typically small and often have major brain, eye, face, and heart defects.
Tests can be done before or after birth to confirm the diagnosis.
There is no treatment available for trisomy 13.
(See also Overview of Chromosomal Disorders Overview of Chromosome and Gene Disorders Chromosomes are structures within cells that contain a person's genes. A gene is a segment of deoxyribonucleic acid (DNA) and contains the code for a specific protein that functions in one or... read more .)
Chromosomes Chromosomes Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are structures within cells... read more are structures within cells that contain DNA DNA Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are structures within cells... read more 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 Genes and Chromosomes Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are structures within cells... read more for a discussion about genetics). Genes contain instructions that determine how the body is supposed to function.
An extra chromosome, making three of the same chromosome (instead of the normal two), 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 of Trisomy 13
In the womb, affected fetuses are typically not very active. The amount of amniotic fluid may be too much or too little.
At birth, newborns tend to be small Small-for-Gestational-Age (SGA) Newborn A newborn who weighs less than 90% of newborns of the same gestational age at birth (below the 10th percentile) is considered small for gestational age. Newborns may be small because their parents... read more . The brain typically does not develop properly, and these children have many facial abnormalities such as cleft lip and cleft palate Cleft Lip and Cleft Palate The most common birth defects of the skull and face are cleft lip and cleft palate, affecting about 2 of every 1,000 babies. Cleft lip is a separation of the upper lip, usually just below the... read more , 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 (polydactyly Finger and Toe Defects The fingers and toes may be abnormally formed, incompletely formed, or missing at birth. Birth defects of the fingers and toes can occur while a baby is developing in the womb. For example,... read more ), and poorly developed fingernails.
Cleft Lip and Cleft Palate: Defects of the Face
About 80% of newborns have severe heart defects. A defect called ventricular septal defect Atrial and Ventricular Septal Defects Atrial and ventricular septal defects are holes in the walls (septa) that separate the heart into the left and right sides. Holes can be present in the walls of the heart between the upper heart... read more , in which there is an abnormal opening between the right and left ventricles, is common. Undescended testes Undescended testes Undescended testes (cryptorchidism) are testes that remain in the abdomen or the groin instead of descending into the scrotum. Retractile testes (hypermobile testes) have descended into the... read more and an abnormal scrotum occur in boys. An abnormally formed uterus occurs in girls. Newborns frequently have prolonged periods of no breathing (apnea). Hearing loss is common and is often suspected but can be difficult to confirm because these children are severely intellectually disabled Intellectual Disability Intellectual disability is significantly below average intellectual functioning present from birth or early infancy, causing limitations in the ability to conduct normal activities of daily... read more .
Diagnosis of Trisomy 13
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 also can do a test to find deoxyribonucleic acid (DNA) from the fetus in the mother's blood and use this DNA to determine an increased risk of trisomy 13. This test is called noninvasive prenatal screening (NIPS) or cell-free fetal DNA testing. If doctors suspect trisomy 13 based on these tests, they often confirm the diagnosis using chorionic villus sampling Chorionic Villus Sampling Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic... read more , amniocentesis Amniocentesis Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic... read more , 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 of Trisomy 13
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.