Human Chromosomes and Trisomy
All of the living things have various numbers of chromosomes. Human beings typically have 22 pairs of chromosomes plus a pair of sex chromosomes. The process of the Meiosis is the cell division created by chromosomes of parents. If the Meiosis process does not occur correctly, a sperm or egg can create fewer chromosomes or more chromosomes, such as Trisomy. Trisomy is a polysomy that contains two chromosomes with an extra copy of the chromosome in the cell nuclei instead of two chromosomes. Therefore, the Trisomy causes developmental abnormalities in embryos and shortens infants' possibility to live.
Meiosis and Trisomy
Trisomy occurs during Meiosis. The non-disjunction, the reason for Trisomy, is caused during stage I and stage II of Meiosis. In normal Meiotic division, starting with 46 chromosomes from parents (Mother: 23 chromosomes + Father: 23 chromosomes), the process results in 4 daughter cells, and each daughter cell includes 23 chromosomes.
However, the nondisjunction in Meiosis generates abnormal results, although the meiotic division starts with 46 chromosomes from parents. In nondisjunction Meiotic stage I and II (Anaphase I and II), centrosomes divide 46 chromosomes in different ratios instead of 1:1. Therefore, Telophase I and II resulted in more and fewer chromosomes. Trisomy shows that a pair of chromosomes contains the three chromosomes instead of Three chromosomes.
According to the picture, the nondisjunction in Anaphase I produces 2 daughter cells with an extra copy of the chromosome and 2 daughter cells with one less chromosome. On the other hand, the nondisjunction in Anaphase II generates 2 normal daughter cells, 1 daughter cell with an extra copy of chromosome, and 1 daughter cell with one less chromosome.
Trisomy Disorders
Nondisjunction in Meiosis results in Trisomy disorders. A doctor often suspects Trisomy disorders during a pregnancy ultrasound. Typically, Down syndrome, Edward syndrome, and Patau syndrome are the most common Trisomy disorders.
Down syndrome, or Trisomy 21, is a Trisomy disorder that contains an extra copy of the number 21 chromosome. Down syndrome patients show a low range of IQ (intelligence quotient) and slow speed of speaking with some physical features (flattened face, Almond-shaped eyes, short neck, and small ears).
Edward syndrome, or Trisomy 18, has an extra copy of the number 18 chromosome. Affected individuals experience the slow development of organs and brain. Like Trisomy 21, Edward syndrome patients accompany physical abnormalities such as small jaw and mouth. 5 to 10 percent of affected individuals live their first years, and they often experience intellectual disability.
Moreover, Patau Syndrome, or Trisomy 13, is defined by having an extra copy of the number 13 chromosome. As with most trisomy disorders, Patau syndrome shows physical abnormality (cleft lip and cleft palate) and slow intellectual development. Ninety percent of affected infants usually face death during their first or second weeks. However, a doctor cannot predict how long the baby affected by Patau Syndrome will live and the severity of the infants. Also, the possibility to live into teenagers is significantly low.
Treatment for Trisomy Disorders
The treatments for Trisomy Disorders depend on the severity of the symptoms, intellectual development, and self-control ability.
As Down Syndrome has the highest possibility to survive during infants' period, the researchers have studied the treatment for Down Syndrome. The doctors recommend approximately four different methods- Early Intervention & Educational Therapy, Treatment Therapy, Drugs and Supplements, and DS-Connect. Early Intervention & Educational Therapy helps the family with Down Syndrome children to adapt to society, such as applying to public schools. Like Early Intervention & Educational Therapy, Treatment Therapy teaches the abilities to control themselves: physical therapy, speech-language therapy, occupational therapy, and emotional and behavioral therapy. If the patients do not show any improvements, a doctor may inject drugs or supplements to help develop the brain. Usually, Down Syndrome patients take Amino acid or Antioxidants, but recent research suggests that the drugs for Down Syndrome do not benefit to development and brain activities. Furthermore, the DS-Connect method connects many families with Down Syndrome children to treat and to educate them effectively.
However, there are no particular treatments or cure for Edward Syndrome and Patau Syndrome because the possibility to survive is too low. Additionally, the NHS organization emphasizes the treatment for Edward Syndrome by saying, "Treatment will focus on the symptoms of the condition, such as heart conditions, breathing difficulties and infections" instead of behavioral and physical treatments.
Causation of Increasing The Risk of Trisomy Disorder
The most common causation to increase the risk of Trisomy disorders is maternal age. The maternal age has shown a fast, remarkable incline gradually like the picture down below. Hultén MA, Öijerstedt L, Iwarsson E, and Jonasson J proved the relationship between maternal age and the risk of Trisomy Disorders. The researchers say, “It has now been over 50 years since it was discovered that Down syndrome is caused by an extra chromosome 21, i.e., trisomy 21. In the interim, it has become clear that in the majority of cases, the extra chromosome is inherited from the mother, and there is, in this respect, a strong maternal age effect” (Hultén).
Furthermore, recent research suggests that the paternal age affects the abnormal meiosis process causing Trisomy Disorders (Down syndrome, Edward syndrome, and Patau Syndrome).
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