Lis Rodriguez
Lab 1
ASA College
Abstract
Patau’s syndrome is a rare genetic disorder that involves trisomy 13. The condition is characterised by either an extra copy of the autosomal chromosome number 13 or a translocation to chromosome 13 from another chromosome. There are severe symptoms observed in the unborn and newborn children having this defect. Polydactyly, cleft lips, physical retardation, mental retardation, heart defects are few of the many symptoms. The disease can be diagnosed during gestation via screening methods followed by several analytical procedures like FISH, karyotyping and microarray on samples of blood and serum from the pregnant mother. There are no treatments available till date but early diagnosis gives an opportunity to the parents for deciding the rightful depending on the situation. Many counselling and support forums are available for the survivors.
Keywords: Patau, symptoms, defects, trisomy 13, counselling
Genetic defects exist in the population affecting infants to adults. They can result from several reasons at molecular level but the basis of all lies in the genetic makeup of an individual. Genes constitute the genetic makeup of an individual being in the DNA that forms a person’s genome. Genes store the information for constructing proteins that performs all the functional and building roles in the body. Mutations, chromosomal aberrations, irradiations, etc are few of the many causes for arousal of genetic disorders by deforming the proteins expressed by the gene that becomes modified. These genetic defects are not always harmful and may remain silent in the genome without being noticed as they do not impose any role in disturbing the overall body metabolism. But, there are many genetic defects that do express their phenotype in a way that disturbs the metabolism and normal functioning of the individual leading the condition to be deleterious. Down’s syndrome, sickle-cell anaemia, Marfan syndrome, cystic fibrosis, albinism, thalassemia, and many more are examples of genetic defects that either involves a gene or more than one gene to cause the defective phenotype. Amongst such defects, Patau’s syndrome is a genetic defect resulting from chromosomal abnormality.
What is Patau’s Syndrome?
Patau syndrome is said to occur when the autosomal chromosome number 13 triplicates its number instead of being present in normal two copies. It is popularly known as trisomy 13. Normally, there are 23 pairs of chromosomes in an individual where 22 are autosomes and one is the sex chromosome. In cases of trisomy, an extra chromosome adds to the total number making it 47 instead of 46 (Summar and Lee, 2011). It may not be the case in every cell of the body but happens in some cells (mosaic trisomy) while others having the normal constitution of chromosomes. Patau’s syndrome is considered as the third most common trisomy of autosomal chromosomes after Down syndrome (trisomy 21) and Edward syndrome (trisomy 18). The names are given after their discoverers. These are congenital defects and new born infants are born with these genetic defects. The main identified cause has been the increased maternal age that leads to all the trisomy genetic defects. The prevalence of trisomy 13 is seen to be one in around 25000 births (Polli et al, 2013). The babies born with the trisomy 13 either aborts during pregnancy or only survives for first few weeks of life due to cardiopulmonary issues (Hossain, Nanjiani and Mahgoub, 2007).
Symptoms associated with Patau Syndrome
Being a congenital disease, it is prevalent in infants with the most common symptom being reduced physical and mental growth. Congenital heart defects (like ventricular septal defect) are very common in such situation with abnormal brain and spinal cord functioning and a small skull (GARD, 2016). The muscles are found weak with absence of a cleft palate between the cleft lips. Microphthalmia (poorly developed tiny eyes), abnormal formations of sex organs and appearance of an extra finger or a toe (polydactyly) are also seen in Patau syndrome cases.
Inheritance of Patau Syndrome
Many genetic defects are inherited but others occur randomly. Patau syndrome cases are mostly not inherited from either of the parents in the child but happen randomly during formation of sex cells (eggs and sperms). The separation of chromosomes does not take place during cell division appropriately that leads to nondisjunction of sister chromatids in reproductive cells. It results in appearance of an entirely extra copy of chromosome 13 in the resulting cells (Summar and Lee, 2011). Such cases do not usually show reoccurrence of the trisomy 13 in the pregnancy again. In other cases, there is translocation of a part of a part of a chromosome to chromosome 13 that leads to Patau syndrome. In such cases, the disease might be inherited from parent to the offspring and recurring pregnancies may have the trisomy 13 condition again.
Diagnosis of Patau Syndrome
Patau syndrome can be identified during pregnancy by observation of several signs and symptoms like polyhydramnios i.e. baby being surrounded by more than usual amniotic fluid, reduced activity of the baby, small placenta than normal and most of the defects described above are detected during ultrasounds. The earliest diagnosis for the first time was done through antenatal screening in the 19th gestational week in a 42 year old pregnant woman (Butler et al, 1973). Due to the age factor, the woman was diagnosed for genetic defects like Down’s syndrome during 17th week of pregnancy via screening for banding patterns and trisomy 13 was observed. The fetus was taken out carefully for analysis and several of the described symptoms in the previous section were observed like cleft lips, extra digits with a cardiovascular defect.
Since the old times, the diagnostic techniques have been advanced and there are many options available now to know the genetic and physiological conditions of the unborn fetus. Screening is the primary and the most important measure to detect the possibility of any genetic defect in the fetus. It is performed during 10 to 14 weeks of gestational period by performing a blood test like alphafetoprotein test and a sonography (combined test). Once any indication is seen, the further analysis is done to be sure of the condition based on the results being high-risk or low-risk. Both the situations do not rule out the chances of the baby being disease free. Hence, parents have the discretion to go for the further diagnostic tests. These include amniocentesis i.e. the examining of the amniotic fluid taken from the mother during 15th week of pregnancy, chorionic villi sampling (CVS) i.e. the tissue sample extracted from chorion during 11 – 14 weeks of pregnancy that forms the placental cells is examined and serum screening whereby a blood test is conducted on maternal serum sample (NHS, 2015). Another latest test includes non- invasive prenatal testing (NIPT) that screens the blood sample from the expecting mother that also contains fetal DNA sample.
The methods used to perform the genetic diagnosis for the tests mentioned above include karyotyping, microarray analysis or florescence in situ hybridization (ACOG, 2016). Karyotyping involves the imaging of the chromosomal set of an individual so as to identify the abnormality in arrangement, sizes and numbers of chromosomes. It is the most conventional testing methodology and takes a little longer to diagnose. Florescence in situ hybridization is advancement over karyotying and detects chromosomal abnormalities swiftly. Microarray provides a further detailed analysis of the chromosomes with plenty of information to ponder.
Treatments
Patau Syndrome cannot be prevented as it is a genetic disease that has no role howsoever of the lifestyles, environment, etc that can be managed and taken care of. It does not have any definitive treatment or cure. Rather, it can be diagnosed at the right time to allow the concerned individuals to take decisions regarding their unborn child. The symptoms of the disease are many but not necessarily all are seen in every child that survives term. There are measures to manage such symptoms like surgeries to correct cosmetic defects of eyes, lips, etc, visual aids, and hearing aids (Shoummojit, 2013). Therapies for speech, physical and mental abilities to reach the potential are quite helpful for children that are able to survive.
The exact causes for the syndrome are not clear but an increased age of mother has been considered one of the major factors contributing to the development of the disease in the newborn. But, not always this is the case as a report published by Saikia, Das and Sarma in 2014 details about a 34 weeks new born diagnosed with Patau syndrome. It was a male child born to a mother aged 29 years only who already had a normal surviving healthy five years old baby. The family and maternal history was devoid of any earlier evidences of genetic disorders. The pregnancy was free of complications and any unwanted drugs. FISH revealed the occurrence of trisomy 13 in the child. The child showed many symptoms like cleft lips, slanted eyes, heart defects, polydactyly and low set ears (Saikia, Das and Sarma, 2014). The baby survived for only 19 days after developing hypoglycaemia, haemorrhages and being unresponsive towards mechanical ventilation.
Another interesting case was of a 51 year old lady who was diagnosed with Patau syndrome (Hossain, Nanjiani and Mahgoub, 2007). It was thought that majority of cases do not survive beyond one year of age to the maximum as 45% is estimated to die within a month of birth and rest till one year of age. The woman with Patau syndrome did not have a complete extra copy of chromosome 13 but was a case of translocation of a part of chromosome 14 to 13. Many of her close cousins were seen to be sufferers and some died in their initial months. Although she had several symptoms at the time of birth like cleft lips, small eyes and head, polydactyly and low set ears with some mental retardation, still she pursued education. But, psychosis was the most significant effect observed in adolescence stage. She was reported to have hallucinations and being delusional.
References
American Congress of Obstetricians and Gynecologists (ACOG). (2016). Diagnostic Tests for Birth Defects. Women’s Health Care Physicians. Accessed at http://www.acog.org/Patients/FAQs/Diagnostic-Tests-for-Birth-Defects on 4 April 2016.
Butler, J, L., Reiss, E, H., France, E, N., et al. (1973). Antenatal Diagnosis of Patau’s Syndrome (Trisomy 13) including a Detailed Pathological Study of the Fetus. Journal of Medical Genetics. 10:367-370.
Genetic and Rare Diseases Information Centre (GARD). (2016). Trisomy 13. National Centre for Advancing Translational Sciences. Accessed at https://rarediseases.info.nih.gov/gard/7341/trisomy-13/resources/1 on 4 April 2016.
Hossain, A., Nanjiani, A, and Mahgoub, N. (2007). Patau Syndrome. The Journal of Neuropsychiatry and Clinical Neurosciences. 19(2):201-202.
NHS. (2015). Screening for Down’s, Edward’s and Patau’s Syndromes. Accessed at http://www.nhs.uk/conditions/pregnancy-and-baby/pages/screening-amniocentesis-downs-syndrome.aspx on 3 April 2016.
Polli, J, B., Groff, Dd, P., Petry, P., et al. (2013). Trisomy 13 (Patau Syndrome) and Congenital Heart Defects. American Journal of Medical Genetics. Part A(164A); 272-275.
Saikia, B., Das, K, B., and Sarma, A. (2014). Patau Syndrome – A Case Report. National Journal of Clinical Anatomy. 3(2):87-89.
Shoummojit. (2013). Patau Syndrome. Genetics and Birth Defects, Prime Health Channel. Accessed at http://www.primehealthchannel.com/patau-syndrome.html on 3 April 2016.
Summar, K., and Lee, B. (2011). Cytogenetics. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, PA: Saunders Elsevier; Chap 76.
