Trisomy 13

Diagnosis and Testing

Is there newborn testing for Trisomy 13?

As of January 2016, trisomy 13 is not on the Recommended Uniform Screen Panel (RUSP). The RUSP is created by the Health Resources and Services Administration. Individual States refer to this list to guide what conditions are included on their newborn screening panels. Generally, newborn testing tries to identify babies who have rare conditions and outcomes are improved with prompt diagnosis and therapy. Because babies with trisomy 13 typically have structural birth defects, identification after birth is not improved with broad-based testing.

References
  • http://www.hrsa.gov/advisorycommittees/mchbadvisory/heritabledisorders/recommendedpanel/
  • Semin Perinatol. 2015 Apr;39(3):171-87. doi: 10.1053/j.semperi.2015.03.002.Current status of newborn screening worldwide: 2015.Therrell BL1, Padilla CD2, Loeber JG3, Kneisser I4, Saadallah A5, Borrajo GJ6, Adams J7.
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Is there more than one type of test for Trisomy 13?

How do babies get tested for Trisomy 13?

What are the common findings on ultrasound for Trisomy 13?

Is there more than one type of test for Trisomy 13?

There are a few types of genetic tests that can diagnose Trisomy 13. Trisomy 13 can be diagnosed through fluorescence in situ hybridization (FISH) testing, karyotype, or chromosomal microarray. The basic test is called a karyotype, where the chromosomes are counted and examined in a laboratory called a cytogenetic lab. This test takes about 7-10 days for a result. A rapid, preliminary test for trisomy 13 is called fluorescence in situ hybridization or FISH. This test uses a brightly colored probe to quickly count the number of copies of a given chromosome and can provide an early result in 2-3 days. A newer way to examine genetic material is called a chromosome microarray, which looks for extra or missing pieces of genetic material. This test can also be used to diagnose trisomy 13. Your healthcare provider may order one type of test or another based on turnaround time, the capability of their genetics laboratory and how strong his/her suspicion is for trisomy 13.

References
  • http://rarediseases.org/rare-diseases/trisomy-13-syndrome/
  • Curr Probl Pediatr Adolesc Health Care. 2012 Mar;42(3):47-73. doi: 10.1016/j.cppeds.2011.10.004.Advances in whole-genome genetic testing: from chromosomes to microarrays.Crotwell PL1, Hoyme HE.
How do babies get tested for Trisomy 13?

There are a few types of genetic tests that can diagnose trisomy 13. After birth, trisomy 13 can be diagnosed by examining the cells from a blood sample. The basic test is called a karyotype, where the chromosomes are counted and examined in a laboratory called a cytogenetic lab. This test takes about 7-10 days for a result. A rapid, preliminary test for trisomy 13 is called fluorescence in situ hybridization or FISH. This test uses a brightly colored probe to quickly count the number of copies of a given chromosome and can provide an early result in 2-3 days. A newer way to examine genetic material is called a chromosome microarray, which looks for extra or missing pieces of genetic material. This test can also be used to diagnose trisomy 13.

Before the baby is born, these same tests can be completed on a sample of amniotic fluid, which contains skin cells from the baby. A physician would use a procedure called an amniocentesis to withdraw a small amount of fluid from around the baby for genetic testing. Another way to use these tests during pregnancy is chorionic villus sampling (CVS). In this procedure, a physician obtains a small sample of the placental tissue. The placenta and the baby come from the same fertilized egg, so performing genetic testing on the placental cells should give the same results as testing the baby.

References
  • http://rarediseases.org/rare-diseases/trisomy-13-syndrome/
  • Curr Probl Pediatr Adolesc Health Care. 2012 Mar;42(3):47-73. doi: 10.1016/j.cppeds.2011.10.004.Advances in whole-genome genetic testing: from chromosomes to microarrays.Crotwell PL1, Hoyme HE.
What are the common findings on ultrasound for Trisomy 13?

It is not uncommon for babies with trisomy 13 to have abnormal ultrasound findings. The discovery could vary from inadequate growth (intrauterine growth restriction) to a heart defect. Other findings could be hydrocephalus (build up of fluid in the brain) or oligohydramnios (too little amniotic fluid surrounding the baby). Some babies with trisomy 13 have an abdominal defect which leads to some of the baby's intestines being outside of the body. This is called an omphalocele, and is easily seen on a prenatal ultrasound.

References
  • Baty, B.J., Blackburn, B.L., and Carey, J.C. Natural History of Trisomy 18 and Trisomy 13: I. Growth, Physical Assessment, Medical Histories, Survival, and Recurrence Risk. American Journal of Medical Genetics. 1994; 49: 175-188
  • Radiol Clin North Am. 2014 Nov;52(6):1191-9. doi: 10.1016/j.rcl.2014.07.004. Epub 2014 Aug 24.Ultrasound evaluation of the first trimester.Doubilet PM1.
  • Clin Obstet Gynecol. 2012 Mar;55(1):226-48. doi: 10.1097/GRF.0b013e3182446c11.The Sherlock Holmes approach to diagnosing fetal syndromes by ultrasound.Benacerraf BB1

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