Trisomy 10 is an extremely rare and severe genetic condition caused by the presence of an extra copy of chromosome 10 in some or all of the body’s cells. Normal human cells contain 46 chromosomes (23 pairs), including two copies of chromosome 10. In a trisomy, there are three copies of a specific chromosome instead of two. Because chromosome 10 contains a large amount of genetic information, the third copy significantly disrupts normal development. The condition is associated with a poor prognosis, and many affected pregnancies end in miscarriage.
Understanding the Genetic Mechanism
The underlying cause of Trisomy 10 is a cellular error known as non-disjunction, meaning “failure to separate.” This error occurs during meiosis, the specialized cell division that creates egg and sperm cells, or during mitosis, the cell division that happens after conception. Normally, chromosome pairs separate during meiosis so that each resulting gamete receives only one copy of each chromosome.
Non-disjunction results in a gamete containing two copies of chromosome 10. When this gamete fuses with a normal gamete, the resulting embryo has three copies. This mistake often happens spontaneously and randomly, meaning it is not inherited. While errors can occur in either parent’s gametes, advanced maternal age is associated with an increased risk for non-disjunction.
In some partial trisomy cases, the extra segment of chromosome 10 can be passed down from a parent who carries a balanced translocation. A balanced translocation means the parent has the correct amount of genetic material, just rearranged, which usually does not cause health problems. However, when the parent produces gametes, the rearranged chromosome can lead to an unbalanced amount of genetic material, resulting in the trisomy.
Full, Mosaic, and Partial Forms
The severity and outcome of Trisomy 10 depend on the specific form of the chromosomal abnormality. The condition is categorized into three types based on the cellular distribution of the extra chromosome. The most severe form is Full Trisomy 10, where every cell in the body contains the extra copy of chromosome 10.
Full Trisomy 10 is considered a lethal condition, frequently detected in spontaneous miscarriages, and rarely results in a live birth. This widespread genetic imbalance prevents fetal development from completing successfully. The other two forms, Mosaic and Partial Trisomy 10, are most often associated with live births.
Mosaic Trisomy 10 involves two different cell lines: some cells have the extra chromosome 10, while others have the normal two copies. The clinical presentation is highly variable, depending on the percentage of affected cells and which tissues or organs contain the trisomic cells.
Partial Trisomy 10 occurs when only a specific segment of chromosome 10 is duplicated, rather than the entire chromosome. This duplication can occur on the short arm (10p) or the long arm (10q). The outcome is directly related to the size and location of the duplicated segment, as this determines which genes are present in triple dose.
Health Impacts and Clinical Features
The presence of extra genetic material from chromosome 10 leads to a wide spectrum of congenital malformations and health challenges. For individuals with Mosaic or Partial Trisomy 10 who survive past infancy, severe developmental delay and intellectual disability are commonly observed.
Growth restriction is a frequent finding, often beginning prenatally and continuing postnatally. Many affected individuals exhibit specific craniofacial anomalies, which may include a prominent forehead, low-set and malformed ears, a high arched palate, and a small lower jaw (retrognathia).
Organ malformations are a serious aspect of the condition, particularly defects of the heart and kidneys. Congenital heart defects are commonly reported, as are kidney abnormalities such as renal cystic dysplasia. Skeletal and limb abnormalities are prevalent, including clubfoot, joint hyperlaxity, and malformed hands and feet.
Other reported features include central nervous system anomalies, muscular hypotonia (low muscle tone), and feeding difficulties leading to a failure to thrive. The variability in clinical presentation is due to the different forms of the trisomy and the specific genes that are overexpressed.
Detection and Supportive Care
Diagnosis of Trisomy 10 often begins during pregnancy through prenatal screening methods. Non-invasive prenatal testing (NIPT) may suggest the presence of an extra chromosome 10, but this must be confirmed by a diagnostic test. Confirmatory procedures typically involve chorionic villus sampling (CVS) or amniocentesis, which analyze fetal cells for the chromosomal structure.
Following birth, a diagnosis can be established through a postnatal karyotype or chromosomal microarray analysis, which maps the entire set of chromosomes to identify the extra copy. For mosaic cases, it is important to test cells from multiple tissues to accurately determine the level of mosaicism.
Since there is no cure for Trisomy 10, care focuses on a multidisciplinary, supportive approach to manage the various health issues. Management involves specialists from cardiology, nephrology, neurology, and orthopedics to address specific organ system defects. Early intervention services are a major component of care, including physical, occupational, and speech therapies to maximize developmental potential.