Trisomy 2 mosaicism

The long-term outlook (prognosis) associated with trisomy 2 mosaicism is difficult to predict and depends on many factors. These factors may include the level of mosaicism (proportion of cells affected); the location and type of the cells affected (which cannot be predicted); the nature of abnormal ultrasound findings (if detected); and potential pregnancy-related or health-related complications that may arise before or after birth. A range of outcomes have been reported, including miscarriage, stillbirth, pregnancy termination after abnormal ultrasound findings or prenatal diagnosis, favorable pregnancy outcome, apparently healthy newborn, and any of many mild to severe birth defects.^[1][2] Few cases of trisomy 2 mosaicism have been reported in livebirths.^[3]

When trisomy 2 mosaicism is diagnosed (in a fetus or child), it can be difficult to estimate the true level of mosaicism because levels can differ depending on the nature of the sample tested. Different levels of mosaicism may be found in the same pregnancy using various lab techniques in samples obtained by chorionic villus sampling, amniocentesis (both uncultured and cultured cells), and cord blood sampling.^[2] Likewise, different levels of mosaicism may be found in a liveborn when samples are obtained for urinary analysis, blood analysis, or tissue analysis. For example, a blood test can only determine the level of mosaicism in the blood cells.

During pregnancy, because it is not possible to predict the outcome for all fetuses diagnosed with trisomy 2 mosaicism, health care professionals may recommend a variety of additional tests to obtain as much information as possible about how a fetus is developing. Tests that may be recommended may include analysis of other types of prenatal samples, more detailed ultrasound exams, fetal echocardiography to evaluate the fetal heart, and/or fetal MRI. Prognosis information in each individual case may be based on results of these tests and the outlook associated with specific findings.

The severity and specific symptoms associated with trisomy 2 mosaicism can vary considerably and generally depend on the level of mosaicism (proportion of affected cells) and the location and type of cells affected. Children with no significant medical problems have been reported, as well as children with major birth defects and serious health issues.^[4]

During pregnancy (prenatally), trisomy 2 mosaicism may be associated with various findings, such as:

• elevated maternal serum alpha-fetoprotein (MSAFP)
• abnormal results of other maternal serum screening tests
• ultrasound findings such as intrauterine growth restriction; low amniotic fluid level (oligohydramnios); congenital heart defects; enlargement of fluid-filled structures in the brain (ventriculomegaly); spina bifida; and swelling of the kidneys (hydronephrosis)^[1]

Signs and symptoms that have been reported in livebirths with trisomy 2 mosaicism include:

• distinctive head and facial features such as a flattened appearance of the middle part of the face (midface hypoplasia), absence of one or both eyes (anophthalmia) or abnormally small eyes (microphthalmia), cleft lip and palate, wide-set eyes (hypertelorism), and small head size (microcephaly)
• growth and motor delay
• intellectual disability
• congenital heart defects
• neural tube defects
• diaphragmatic hernia
• inguinal hernia
• radioulnar hypoplasia
• rocker-bottom feet (feet with a rounded bottom, resembling the bottom of a rocking chair)
• abnormal development of the lower end of the spine (caudal dysgenesis)
• portal fibrosis
• intestinal malrotation (twisting of the intestines)
• Hirschsprung disease
• hypomelanosis of Ito
• polydactyly
• deafness
• undescended testes
• face and body asymmetry
• clubfoot
• lack of sacrum^[1][3]

Because few cases have been reported in the literature and the level of mosaicism differs among affected fetuses and individuals, it is not possible to predict how a pregnancy or person may be affected by trisomy 2 mosaicism.

We recommend that you contact Unique, which collects and provides information about rare chromosome disorders, and links families whose children have similar chromosome disorders. Unique does have several registered genotypes for trisomy 2 mosaicism, which can be viewed here. You can request a description of the symptoms associated with these results by contacting Unique.

Additionally, you can find relevant articles on trisomy 2 mosaicism through PubMed, a searchable database of biomedical journal articles. Although not all of the articles are available for free online, most articles listed in PubMed have a summary available. To obtain the full article, contact a medical/university library or your local library for interlibrary loan. You can also order articles online through the publisher’s Web site. Using "trisomy 2 mosaicism" or "mosaic trisomy 2" as your search term should help you locate articles. View our sample PubMed search for this condition here.

The National Library of Medicine (NLM) Web site has a page for locating libraries in your area that can provide direct access to these journals (print or online). The Web page also describes how you can get these articles through interlibrary loan and Loansome Doc (an NLM document-ordering service). You can access this page at the following link: http://nnlm.gov/members/. You can also contact the NLM toll-free at 888-346-3656 to locate libraries in your area.