Trisomy 14 is a rare genetic condition characterized by the presence of an extra copy of chromosome 14. This chromosomal abnormality can affect an individual’s development and health. This extra genetic material disrupts cellular processes, leading to physical and developmental challenges.
The Genetic Basis of Trisomy 14
Trisomy 14 arises from an error in cell division, resulting in an individual having three copies of chromosome 14 instead of the usual two. The most common form seen in live-born individuals is mosaic trisomy 14, where the extra chromosome 14 is present in only some cells.
Full trisomy 14, where every cell in the body has an extra chromosome 14, is typically lethal and usually results in spontaneous abortion. Mosaic trisomy 14 often occurs due to errors in cell division during early fetal development, known as post-zygotic mitotic nondisjunction. In some cases, it can also arise from errors during the formation of reproductive cells, followed by “trisomy rescue,” where some cells lose the extra chromosome.
Partial trisomy 14 occurs when only a segment of chromosome 14 is duplicated. This can happen due to an unbalanced translocation or the formation of a small supernumerary marker chromosome (sSMC) containing material from chromosome 14.
Recognizing the Characteristics
Individuals with trisomy 14, particularly the mosaic form, often exhibit a variety of physical and developmental characteristics. Growth delays are common, including intrauterine growth restriction before birth and failure to thrive during infancy. Developmental delays are frequently observed, impacting psychomotor skills and intellectual abilities.
Distinctive facial features are also commonly reported. These can include a prominent forehead, deeply set and widely spaced eyes, a broad nasal bridge, and low-set or unusually formed ears. Other craniofacial abnormalities may involve a small lower jaw (micrognathia), a large mouth with thick lips, or an incomplete closure or high arch of the roof of the mouth (palate).
Many affected infants also have structural malformations of the heart that are present at birth. These congenital heart defects can include holes between the heart’s chambers, such as atrial septal defects (ASDs) or ventricular septal defects (VSDs), or narrowing of blood vessels leading from the heart, like pulmonary stenosis. Additionally, kidney abnormalities such as enlarged kidneys (hydronephrosis), renal insufficiency, cysts, or even a missing kidney have been noted. Skeletal issues and abnormal skin pigmentation are other potential findings, and males may present with genital anomalies like undescended testicles.
Diagnosis and Supportive Care
The diagnosis of trisomy 14 can occur both before birth and after. Prenatal diagnostic methods include chorionic villus sampling (CVS), typically performed between 10 and 14 weeks of gestation, and amniocentesis, usually done after 15 weeks of gestation. These procedures involve collecting fetal cells for genetic analysis to identify chromosomal abnormalities. Abnormal ultrasound findings, such as congenital heart defects or intrauterine growth restriction, may prompt these prenatal investigations.
After birth, diagnosis is confirmed through genetic testing, often involving karyotyping, which examines an individual’s complete set of chromosomes. Fluorescence in situ hybridization (FISH) and microarray technology can also be used to detect the extra chromosome 14, including low levels of mosaicism that might be missed by conventional karyotyping. Identifying the specific chromosomal arrangement is important for understanding the condition’s potential impact.
There is no cure for trisomy 14; management focuses on supportive care to address symptoms and improve quality of life. This involves a multidisciplinary approach tailored to the individual’s specific needs. Therapies such as physical, occupational, and speech therapy can help with developmental delays and improve motor skills, daily functioning, and communication. Medical interventions may include cardiac surgery for heart defects or renal management for kidney issues.
Outlook and Family Resources
The outlook for individuals with trisomy 14 is highly variable, largely depending on the specific type of trisomy (full versus mosaic) and the severity of associated health issues. Those with mosaic trisomy 14 have a range of outcomes. The proportion of cells containing the extra chromosome can influence the presentation and severity of symptoms; individuals with a lower percentage of affected cells may experience fewer or less severe symptoms.
Families navigating a diagnosis of trisomy 14 can access various resources and support systems. Genetic counseling provides information about the condition, inheritance patterns, and recurrence risks for future pregnancies. Patient advocacy groups and rare disease organizations offer emotional support, connect families with similar experiences, and provide educational materials. Specialized medical teams, often found in university or research hospitals, can offer comprehensive care and coordinate various therapies and medical interventions.