Trisomy 13

Alternate names

Patau syndrome; Chromosome 13, trisomy 13 complete; Complete trisomy 13 syndrome; D trisomy syndrome (formerly)

Definition

Trisomy 13 is a type of chromosome disorder characterized by having 3 copies of chromosome 13 in cells of the body, instead of the usual 2 copies. In some affected people, only a portion of cells contains the extra chromosome 13 (called mosaic trisomy 13), whereas other cells contain the normal chromosome pair. Trisomy 13, also called Patau syndrome, is a chromosomal condition associated with severe intellectual disability and physical abnormalities in many parts of the body.

Epidemiology

Trisomy 13 occurs in about 1 in 16,000 newborns. Although women of any age can have a child with trisomy 13, the chance of having a child with this condition increases as a woman gets older.

Cause

• Most cases of trisomy 13 result from having three copies of chromosome 13 in each cell in the body instead of the usual two copies.
• The extra genetic material disrupts the normal course of development, causing the characteristic features of trisomy 13.
• Trisomy 13 can also occur when part of chromosome 13 becomes attached (translocated) to another chromosome during the formation of reproductive cells ([[eggs] and sperm) or very early in fetal development.
• Affected people have two normal copies of chromosome 13, plus an extra copy of chromosome 13 attached to another chromosome.
• In rare cases, only part of chromosome 13 is present in three copies.
• The physical signs and symptoms in these cases may be different than those found in full trisomy 13.
• A small percentage of people with trisomy 13 have an extra copy of chromosome 13 in only some of the body's cells.
• In these people, the condition is called mosaic trisomy 13.
• The severity of mosaic trisomy 13 depends on the type and number of cells that have the extra chromosome.
• The physical features of mosaic trisomy 13 are often milder than those of full trisomy 13.

Inheritance

• Most cases of trisomy 13 are not inherited and result from random events during the formation of eggs and sperm in healthy parents.
• An error in cell division called nondisjunction results in a reproductive cell with an abnormal number of chromosomes.
• For example, an egg or sperm cell may gain an extra copy of chromosome 13.
• If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra chromosome 13 in each cell of the body.

Translocation trisomy 13 can be inherited.

• An unaffected person can carry a rearrangement of genetic material between chromosome 13 and another chromosome.
• These rearrangements are called balanced translocations because there is no extra material from chromosome 13.
• A person with a balanced translocation involving chromosome 13 has an increased chance of passing extra material from chromosome 13 to their children.

Signs and symptoms

• Trisomy 13 is associated with severe intellectual disability and physical abnormalities in many parts of the body.
• People with this condition often have congenital heart defects, brain or spinal cord abnormalities, very small or poorly developed eyes (microphthalmia), extra fingers and/or toes (polydactyly), cleft lip or palate, and decreased muscle tone (hypotonia).
• Many infants with trisomy 13 fail to grow and gain weight at the expected rate (failure to thrive); have severe feeding difficulties; and episodes in which there is temporary cessation of spontaneous breathing (apnea).

Other features or trisomy 13 may include:

• Clenched hands (with outer fingers on top of the inner fingers)
• Close-set eyes
• Hernias: umbilical hernia, inguinal hernia
• A hole, split, or cleft in the iris of the eye (coloboma)
• Low-set ears
• Scalp defects such as missing skin
• Seizures
• Single palmar crease
• Skeletal (limb) abnormalities
• Small head (microcephaly)
• Small lower jaw (micrognathia)
• Undescended testicle (cryptorchidism)

Diagnosis

• While most cases of trisomy 13 occur randomly, a few cases are due to the presence of a translocation involving chromosome 13 in a parent.
• Parents who are at risk to have a translocation due to their family history can have a blood test called a karyotype, which can determine if a translocation is present.
• Prenatal testing or screening (such as maternal blood screening, fetal ultrasound, chorionic villus sampling, or amniocentesis) is also available to determine if a current pregnancy is at risk for, or is affected by, trisomy 13 or other chromosome disorders.
• People with a family history of trisomy 13 who are interested in learning about genetic screening or testing for themselves or family members are encouraged speak with a genetic counselor or other genetics professional.

Treatment

• Treatment for trisomy 13 depends on the affected person's signs and symptoms, and is generally symptomatic and supportive.
• Surgeries are generally withheld for the first few months of life because of the high mortality rate associated with trisomy 13.
• Parents and medical personnel must carefully weigh decisions about extraordinary life-prolonging measures against the severity of the neurological and physical defects that are present and the likelihood of post-surgical recovery or prolonged survival.

Prognosis

Trisomy 13 involves multiple abnormalities, many of which are life-threatening. More than 80% of children with trisomy 13 do not survive past the first month of life. For those that do survive, complications are common and may include:

• Breathing difficulty or lack of breathing (apnea)
• Deafness
• Feeding problems
• Heart failure
• Seizures
• Vision problems
• People with trisomy 13 who survive infancy have severe intellectual disability and developmental delays, and are at increased risk for cancers.

NIH genetic and rare disease info

• NIH info on Trisomy 13

Trisomy 13 is a rare disease.

Trisomy 13 Resources
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