SCIENTIFIC BACKGROUND

trisomy 13

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Scientific background

The average incidence of Patau syndrome is estimated to be 1:5,000 newborns. Free trisomy 13 is detected in 75%, mosaic trisomy in 5%, and an unbalanced translocation in 20%. The characteristic external abnormalities include a usually bilateral cleft lip and palate, various eye defects (microophthalmia, anophthalmia, coloboma), microcephaly, hexadactyly, ear dysplasia, scalp defects, and omphalocele. Organ malformations include heart defects and cystic kidneys and CNS anomalies such as arhinecephaly or holoprosencephaly. Psychomotor development is severely impaired. About 50% of the patients die within the first month of life and more than 90% within the first year of life.

 

References

Vendola et al. 2010, Am J Med Genet 152A:360 / Wyllie et al. 1994, Arch Dis Child 71:343 / Baty et al. 1994, Am J Med Genet 49:189 / Fujinaga et al. 1990, Teratology 41:233 / Hassold et al. 1987, J Med Genet 24:725

 

Trisomy 13 - March 13 is Trisomy 13 Awareness Day

 

Trisomy 13 is a genetic condition in which cells in the body have 3 copies of chromosome 13 instead of 2. The condition arises when mistakes occur during cell division and fertilization when the egg or the sperm carry an additional copy of chromosome 13 and pass it on to the embryo. The extra chromosome affects the genetic balance resulting in a variety of symptoms and health problems, ranging from miscarriages and stillbirths to short life span and compromised life quality of affected individuals [1, 2]. Additionally, one of the greater obstacles is the conflict between the medical professionals regarding treatment intervention, which undoubtedly colors the expecting parents’ decision on their options following a trisomy 13 diagnosis.

 

Initially described in 1656 as a case study by Thomas Bartholin, trisomy 13 was first reported in 1960 by Klaus Patau, his wife, Eeva Therman – also known as Mrs. X Chromosome for her extensive research into sex chromosomes – and by Smith, Inhorn, and Wagner [3]. In honor of the scientists who described it, the condition is also referred to as Bartholin-Patau, more commonly as Patau syndrome.

 

Trisomy 13 occurs in 1 in 16,000 births [1]. The risk of having a baby with trisomy 13 increases with maternal age, as mistakes in the egg happen more frequently and are not corrected. The risk of trisomy 13 recurrence is around 1% [2]. This risk is higher only in cases where one of the parents unknowingly carries a translocation, i.e. all the genetic material is present, but it is found in the wrong chromosomes. Consequently, mistakes during cell division are more frequent – but with proper genetic testing and fertility treatments, having a healthy baby for translocation carriers is possible.

 

The majority of cases with Patau’s syndromes have a full trisomy 13, where there is an extra whole chromosome. There are cases of partial trisomy 13, and of mosaic trisomy 13 — where some cells have 3 copies of chromosome 13, while other cells have 2. Because of this, the symptoms of trisomy 13 vary [1]. The individuals that survive longer are the ones with partial and mosaic trisomies, as symptoms are fewer and less severe.

 

Trisomy 13 is often characterized as ‘the most lethal chromosomal trisomy’. Indeed, the most severe trisomy 13 cases – accounting for 95% overall – die in utero during early pregnancy [2, 4]. Of the babies with trisomy 13 carried to term, some are stillborn while others die within the first days or weeks of life. Babies born with trisomy 13 may have low birth weight and fail to thrive (gain weight), and exhibit heart, kidney, vision, and hearing problems. Additionally, congenital defects like spina bifida, cleft lip and palate, exomphalos, polydactyly, and curved feet, referred to as ‘rocker's bottom’ are common. Neurological problems like seizures, microcephaly (small head), or cutis aplasia (skin missing from the scalp) may also be present [1, 2, 5]. A very small percentage (5-15%) of children with trisomy 13 survive past their first year of life [4], so parents and support groups want to stop the classification of this disorder as ‘universally lethal’ or ‘incompatible with life’.

Unfortunately, trisomy 13 cannot be prevented and there is no cure; although corrective surgeries and comfort measures have been found beneficial in some cases. As very few babies with trisomy 13 survive, there is a debate amongst healthcare professionals on how much medical intervention should be given to trisomy 13 infants. Mortality rates of trisomy 13 were calculated at a time when withholding care for trisomy 13 patients was common practice [6, 7], so it is fathomable that the survival rate of trisomy 13 would not be so low if medical care had been provided to patients. Accurate information, and awareness of the condition and the spectrum of symptoms’ severity are instrumental in clinical management so that expecting parents are well-informed in their decisions.

 

Trisomy 13 can be detected prenatally through ultrasound, serum marker screening, and non-invasive prenatal testing (NIPT). NIPT has the highest detection accuracy and can be performed from the 10th week of pregnancy. Prenatal diagnosis is integral in trisomy 13 management, as it reduces postnatal diagnostic delays, and facilitates earlier and better decision-making by parents and physicians.

 

Each patient with trisomy 13 is different, and their length of life is impossible to predict from the time of diagnosis as it depends on the level of medical care they will receive, and the severity of their symptoms. Importantly, the change in attitudes and knowledge on trisomy 13 was brought by support groups and families with affected children that spread awareness and demanded medical care. Living with and caring for trisomy 13 children can be challenging, but knowing in advance can help in preparing parents to come to terms with the diagnosis and decide on which – and how much – medical intervention they would like; a decision that only they can make.

 

VERACITY and VERAgene can detect Trisomy 13 from the 10th week of pregnancy with >99% of accuracy.

 

References

  1. Genetics Home Reference (2019) https://ghr.nlm.nih.gov/condition/trisomy-13
  2. Orphanet (2019) https://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=en&Expert=3378
  3. Patau K. et al. (1960) ‘Multiple congenital anomaly caused by an extra autosome’. Lancet. April 9;1(7128):790-3 https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(60)90676-0/fulltext
  4. Peroos S. et al. (2012). ‘Longevity and Patau syndrome: what determines survival?’ BMJ case reports; December 6, 2012: bcr0620114381. https://casereports.bmj.com/content/2012/bcr-06-2011-4381.long
  5. National Health Service (2016) https://www.nhs.uk/conditions/pataus-syndrome/
  6. International Trisomy Alliance (2014) ‘Trisomy 13 and Trisomy 18: Preparing for your baby’s arrival’. http://www.internationaltrisomyalliance.com/uploads/1/4/8/3/14838122/preparing_for_babys_arrival_9.25.pdf
  1. Morrison et al. (2010) ‘American Heart Association Guidelines for Cardiopulmonary resuscitation and emergency cardiovascular care. Part 3: Ethics’. Circulation, Volume 122, Issue 18. https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.110.970905

 

Last updated in March 2019

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