Trisomy 13, also known as Patau syndrome, is a severe genetic condition caused by an extra copy of chromosome 13. This additional genetic material disrupts normal development, leading to a wide array of severe physical and intellectual challenges. It is considered rare, affecting approximately 1 in 10,000 to 20,000 newborns.
Genetic Basis
Normally, human cells contain 23 pairs of chromosomes, with one copy inherited from each parent. In trisomy, an individual has three copies of a specific chromosome instead of two. For Trisomy 13, this means three copies of chromosome 13, which interferes with normal development.
The most common form is full Trisomy 13, where every cell has an extra chromosome 13. This typically arises from random errors during egg or sperm formation (nondisjunction) and is generally not inherited.
A less common form is mosaic Trisomy 13, where only some cells contain the extra chromosome 13. The severity of symptoms in mosaic cases can vary significantly, depending on the proportion of cells with the extra chromosome. Partial Trisomy 13 can occur when only a segment of chromosome 13 is duplicated and attached to another chromosome, which can sometimes be inherited.
Physical and Developmental Characteristics
Trisomy 13 is associated with a wide range of severe physical and intellectual abnormalities. Infants with this condition are often born small for their gestational age. They typically exhibit severe intellectual disability and developmental delays, impacting their ability to reach milestones like walking or talking.
Central nervous system abnormalities are common, including holoprosencephaly, where the forebrain fails to divide properly. This can lead to craniofacial features such as a cleft lip or palate, closely set or very small eyes (microphthalmia), and a small head (microcephaly). Other facial characteristics include low-set or abnormally shaped ears and scalp defects where skin is missing.
Heart defects are present in about 80% of infants, often involving openings between the heart’s chambers, such as ventricular or atrial septal defects. Limb abnormalities, such as polydactyly (extra fingers or toes), are frequently observed. Other physical challenges include abdominal wall defects like omphalocele, kidney malformations, and low muscle tone. Feeding difficulties, breathing problems, and seizures are also common concerns.
Diagnosis and Identification
Trisomy 13 can be identified both before and after birth. During pregnancy, non-invasive prenatal screening (NIPS) assesses the risk of chromosomal abnormalities by analyzing cell-free fetal DNA in the mother’s blood. While NIPS indicates a potential risk, it is not a definitive diagnosis.
Ultrasound examinations during pregnancy often reveal structural abnormalities that may suggest Trisomy 13, such as heart defects, brain anomalies, or limb malformations. If screening tests or ultrasounds indicate a higher risk, definitive prenatal diagnostic tests are offered. These include chorionic villus sampling (CVS), which involves taking a placental tissue sample between 10 and 13 weeks, or amniocentesis, which analyzes amniotic fluid and is performed after 15 weeks. These tests provide a chromosomal analysis to confirm the presence of an extra chromosome 13.
Following birth, Trisomy 13 is often suspected based on the infant’s characteristic physical features. Confirmation relies on chromosomal analysis, such as karyotyping, performed on a blood sample. This laboratory test allows for a detailed examination of the chromosomes to identify the extra copy of chromosome 13.
Prognosis and Support
The prognosis for infants with Trisomy 13 is generally poor due to the severity of associated medical complications. Many infants do not survive beyond their first days or weeks of life, often succumbing to life-threatening issues such as severe heart defects or respiratory problems. For babies born with full Trisomy 13, median survival is between 7 and 10 days, with 86% to 91% not surviving past their first year.
Survival rates can vary, with some infants, particularly those with mosaic Trisomy 13, living longer. Around 5% to 10% of babies with Trisomy 13 survive beyond their first year. For those who survive longer, ongoing medical care and support are necessary to manage their complex health needs, which may include frequent hospitalizations and surgeries.
Support for families of children with Trisomy 13 often involves a multidisciplinary team, including genetic counselors, social workers, and medical specialists. Care often focuses on palliative care, which aims to provide comfort and manage symptoms, rather than curative interventions. Perinatal palliative care supports expectant parents who choose to continue their pregnancy after receiving a life-limiting diagnosis for their baby. Organizations like the Support Organization for Trisomy 18, 13, and Related Disorders (SOFT) offer networks for families to share information and receive emotional support. These resources help families navigate complex decisions regarding their child’s care and overall well-being.