Trisomy 13
Introduction to Trisomy 13
Trisomy 13, also known as Patau syndrome, is a chromosomal disorder characterized by the presence of an extra copy of chromosome 13. It is the third most common autosomal trisomy among live births, occurring in approximately 1 in 8,000 to 12,000 live births.
Key points:
- First described by Klaus Patau in 1960
- Associated with severe intellectual disability and multiple congenital anomalies
- Most affected individuals do not survive beyond infancy
- Slightly more common in female infants
- Risk increases with maternal age
Genetics of Trisomy 13
Trisomy 13 is caused by the presence of an extra copy of chromosome 13. There are three types of Trisomy 13:
- Full Trisomy 13: Accounts for about 95% of cases. All cells have three copies of chromosome 13.
- Mosaic Trisomy 13: Accounts for about 5% of cases. Only some cells have the extra chromosome 13.
- Partial Trisomy 13: Rare. Only a portion of the extra chromosome 13 is present.
Risk factors for Trisomy 13 include:
- Advanced maternal age (risk increases after age 35)
- Previous pregnancy with a chromosomal abnormality
- Parental balanced translocation involving chromosome 13
Clinical Features of Trisomy 13
Trisomy 13 is characterized by a wide range of severe congenital anomalies affecting multiple organ systems. Common features include:
Physical Characteristics:
- Microcephaly
- Holoprosencephaly (failure of forebrain to divide properly)
- Severe scalp defects
- Microphthalmia or anophthalmia
- Cleft lip and/or palate
- Low-set ears
- Polydactyly (extra fingers or toes)
- Rocker-bottom feet
- Omphalocele or umbilical hernia
- Single palmar crease
Developmental Characteristics:
- Profound intellectual disability
- Severe developmental delays
- Seizures
- Feeding difficulties
- Limited responsiveness to environment
Diagnosis of Trisomy 13
Trisomy 13 can be diagnosed prenatally or after birth. Diagnostic methods include:
Prenatal Screening and Diagnosis:
- Non-invasive prenatal testing (NIPT): Cell-free fetal DNA analysis
- First-trimester combined test: Nuchal translucency ultrasound and maternal blood tests
- Quad screen: Second-trimester maternal blood test
- Ultrasound findings: May show characteristic abnormalities
- Diagnostic tests:
- Chorionic villus sampling (CVS): 10-13 weeks gestation
- Amniocentesis: After 15 weeks gestation
Postnatal Diagnosis:
- Physical examination: Characteristic features may be apparent at birth
- Chromosomal karyotype: Confirms diagnosis and determines type of Trisomy 13
Associated Conditions in Trisomy 13
Individuals with Trisomy 13 often have multiple congenital anomalies affecting various organ systems:
- Central Nervous System:
- Holoprosencephaly
- Neural tube defects
- Cerebellar anomalies
- Cardiovascular defects (80% of cases):
- Ventricular septal defect
- Atrial septal defect
- Patent ductus arteriosus
- Dextrocardia
- Ocular abnormalities:
- Microphthalmia or anophthalmia
- Coloboma
- Retinal dysplasia
- Genitourinary abnormalities:
- Polycystic kidneys
- Hydronephrosis
- Cryptorchidism in males
- Bicornuate uterus in females
- Gastrointestinal issues:
- Omphalocele
- Malrotation of intestines
- Pancreatic abnormalities
- Respiratory problems:
- Pulmonary hypoplasia
- Congenital diaphragmatic hernia
Management of Trisomy 13
Management of Trisomy 13 is primarily supportive and palliative, focusing on the individual's quality of life. The approach includes:
Medical Management:
- Neonatal intensive care for severe cases
- Management of respiratory difficulties
- Feeding support (nasogastric tube or gastrostomy)
- Seizure control
- Treatment of infections
- Pain management
Surgical Interventions:
- Decisions regarding surgery are complex and individualized
- May include repair of life-threatening defects in selected cases
- Ethical considerations play a significant role in decision-making
Supportive Care:
- Physical therapy
- Occupational therapy
- Nutritional support
Family Support:
- Genetic counseling
- Psychological support
- Palliative care consultation
- Support groups and resources
Prognosis in Trisomy 13
The prognosis for individuals with Trisomy 13 is generally poor:
- Approximately 50% of infants with Trisomy 13 survive beyond the first week of life
- About 5-10% of infants survive beyond the first year
- Median survival for live births is 7-10 days
- Survival rates are slightly higher for females compared to males
- Individuals with mosaic Trisomy 13 may have a better prognosis
Factors affecting prognosis include:
- Severity of congenital anomalies, particularly brain and heart defects
- Presence of holoprosencephaly
- Degree of medical intervention provided
- Type of Trisomy 13 (full, mosaic, or partial)
Long-term survivors face significant medical challenges and developmental delays. However, some individuals with Trisomy 13, particularly those with mosaic forms, have survived into adulthood with appropriate medical care and support.
Trisomy 13
- What is the genetic cause of Trisomy 13?
An extra copy of chromosome 13, resulting in 47 chromosomes instead of the typical 46. - What is another name for Trisomy 13?
Patau syndrome - What is the approximate incidence of Trisomy 13?
About 1 in 16,000 live births - Which age group of mothers has a higher risk of having a child with Trisomy 13?
Mothers over 35 years of age - What percentage of Trisomy 13 cases are caused by meiotic nondisjunction?
Approximately 80% of cases - What is the most common structural abnormality seen in Trisomy 13?
Holoprosencephaly (failure of the forebrain to divide properly) - Which facial feature is commonly observed in infants with Trisomy 13?
Cleft lip and/or cleft palate - What cardiac defect is frequently associated with Trisomy 13?
Atrial or ventricular septal defects - What is the typical life expectancy for infants born with Trisomy 13?
Most infants do not survive beyond the first year of life - Which diagnostic test can confirm Trisomy 13 prenatally?
Amniocentesis or chorionic villus sampling (CVS) - What is the recurrence risk for parents who have had a child with Trisomy 13?
Approximately 1% for future pregnancies - Which ocular abnormality is commonly seen in Trisomy 13?
Microphthalmia (abnormally small eyes) - What is the most common form of polydactyly observed in Trisomy 13?
Postaxial polydactyly (extra digit on the ulnar side of the hand) - Which non-invasive prenatal test can screen for Trisomy 13?
Cell-free fetal DNA testing - What percentage of Trisomy 13 cases are due to Robertsonian translocations?
About 20% of cases - Which neurological finding is often present in infants with Trisomy 13?
Microcephaly (abnormally small head) - What is the typical karyotype notation for Trisomy 13?
47,XX,+13 or 47,XY,+13 - Which renal abnormality is frequently associated with Trisomy 13?
Polycystic kidneys - What is the approximate male to female ratio in Trisomy 13?
1:1 (equal distribution between males and females) - Which skin abnormality is often observed in Trisomy 13?
Capillary hemangiomas - What percentage of fetuses with Trisomy 13 are thought to be lost before birth?
Approximately 95% of conceptuses - Which growth parameter is typically affected in infants with Trisomy 13?
Intrauterine growth restriction (IUGR) - What is the recommended management approach for infants with Trisomy 13?
Supportive care and palliative measures - Which chromosomal region is most commonly involved in Robertsonian translocations causing Trisomy 13?
The long arm of chromosome 13 and the long arm of chromosome 14 or 21 - What is the typical presentation of the ears in Trisomy 13?
Low-set and malformed ears - Which endocrine abnormality is sometimes observed in Trisomy 13?
Hypopituitarism - What is the approximate percentage of Trisomy 13 cases that are mosaic?
About 5% of cases - Which gastrointestinal malformation is often associated with Trisomy 13?
Omphalocele (abdominal wall defect) - What is the typical appearance of the nose in infants with Trisomy 13?
Flattened nasal bridge - Which molecular technique can be used to confirm Trisomy 13 in tissue samples?
Fluorescence in situ hybridization (FISH)
