Hlt7090 Biological Basis Of Diseases: Assessment Answers

Answer:

Introduction

Also known as Trisomy 21, Down syndrome is a genetic disorder that results when there is an additional copy of chromosome 21 (Patterson, 2009). Chromosome 21 makes up the smallest of the 23 chromosomes in the human body. While people generally have two copies of chromosome 21, individuals with three copies have Down syndrome.It is named after a British doctor John Langdon Down who first adequately described the syndrome. The disorder is typically associated with a distinct facial feature, minor to moderate intellectual disability and delays in physical growth (Weijerman and De Winter, 2010). The middling Intelligence Quotient (IQ) of a young adult with this disorder is 50 which is equivalent to the mental capacity of a 9 or an 8 year old child. This can, however, fluctuate widely. The parents of individuals with this disorder typically have normal genetic makeup but the probability of the offsprings being born with Down syndrome increases with increase in the mother’s age. The extra chromosome occurs by chance with no known environmental or behavioural causative agents.

Types of Down syndrome

There are three types of Down syndrome caused by diverse types of abnormal cell division:

Trisomy 21: this is the most common form of Down syndrome. It is whereby an extra chromosome 21instigates in the developmentof either the egg or the sperm. When they unite, therefore, three chromosomes are formed in the fertilized egg rather than two. During the development and division of the cells, the added chromosome is reiterated in every cell (Theisen and Shaffer, 2010).

Mosaic: this form of Down syndrome is similar to Trisomy 21 but it is rarer. It is differentiated from trisomy 21 in that the extra chromosome is repeated in some and not all the cells. Mosaic Down syndrome is caused by abnormal cell division after fertilization. Individuals with this particular type of Down syndrome tend to have lesser symptoms than those with trisomy 21 (Gardiner et al., 2010).

Translocation: in this case, a portion of chromosome 21 is translocated and attached to another chromosome before or at conception. Thus the genetic material of the extra chromosome 21 will be located in another chromosome. The individual has the proper amount of genetic material therefore will not display any symptoms of Down syndrome (Lewis, 2009).

Prevalence of Down syndrome

The projected incidence of Down syndrome is 1 in 1000 live births worldwide (Weijerman and De Winter, 2010). In England and Wales the estimated number of adults with Down syndrome is 0.66 per 1000 persons (Wu and Morris, 2013).Before the 1960s the disorder was mainly determined by clinical features since there was no karyotype confirmation of Down syndrome. Therefore babies with no phenotypic features of Down syndrome who seemed healthier may not have been diagnosed. This bring s about a gap in the information available on the prevalence of Down syndrome in the United Kingdom over the years. Majority of Down syndrome cases are ascertained within the first few days after birth. This has greatly increased the survival rate of children born with the disorder in England and Wales(Wu and Morris, 2013). 

Symptoms

Babies with Down syndrome exhibit certain distinguishing signs at birth which include distinct physical features, variability in cognitive abilities and specified health issues.

Physical features

• Protruding tongue
• Eyes with an upward slant, white spots on the iris, folds of skin on the inner corner as well as oblique fissures
• Small ears that are atypically shaped
• Small head and short neck
• Big space between the second toe and the large toe
• Low muscle tone
• Flat nasal bridge
• Deep crease across the center of the palm
• Characteristic facial attributes

Developmental delays

Infants with Down syndrome can be born with average size but their development will be slower than healthy kids. These children have cognitive development delays which indicate mild to moderate intellectual disability. There may be a delay in speech acquisition and motor skills development. Children with Down syndrome with often require the help of speech therapy to be able to express themselves. In addition, there may be challenges in making judgments, paying attention and the children may also demonstrate impulsive behaviour and slow learning aptitudes. However, intellectual ability and cognitive development are greatly variable (Asim et al., 2015).

Health issues

People with Down syndrome characteristically have poor immune functions. They have an increased risk of health problems such as hearing difficulties, poor vision,respiratory problems,childhood leukemia, thyroid conditions, epilepsy, hip problems (such as dislocations), congenital heart defect and Alzheimer’s disease. Other medical complications include sleep apnea (interrupted breathing while sleeping), dementia, late tooth growth for children, obesity, chronic constipation and cataracts.

The risk of non-blood cancers such as cervix, breast cancer, lung cancer are low in people with Down syndrome (Malt et al., 2013). This is linked to an escalation in the expression of the antioncogene (tumor suppressor gene) extant in chromosome 21. The risk of diabetic retinopathy (damages of the retina due to the complications of diabetes mellitus) and hardening of the arteries is also low in people with Down syndrome. Conversely, the risk of blood cancers and testicular cancer in these individuals is high.

Risk Factors: Maternal age

As a woman’s eggs age, there is an increased risk of incorrect chromosome division which enhances the probability of Down syndrome.

Carrier parent

Parents who are carriers of a translocated chromosome 21 have a higher risk of having a child with Down syndrome depending on the kind of translocation. Men with Down syndrome however do not have to ability to reproduce.

Previous Child with Down syndrome

In general, there is a slightly increased risk of couples who have a child with Down syndrome having another one with this condition.

Diagnosis

Screening for down syndrome during Pregnancy

The obstetrician can suspect whether the fetus has Down syndrome from the ultrasound examination or based on maternal blood tests. Screening tests portray the likelihood that a mother is carrying a child with Down syndrome without determining this for sure (Kariminejad and Kariminejad, 2009). The screening tests carried out include:

Blood test: this test measures the levels of human chorionic gonadotropin (HCG) and pregnancy-associates plasma protein-A (PAPP-A), whose abnormal levels can depict a problem with the fetus.

Nuchal translucency test: it is an ultrasound test where the definite area on the back of the baby’s neck is measured. On this neck tissue, more fluids than usual collect in cases of abnormalities.

Diagnostic tests

Chorionic villus sampling (CVS): this is test that can be carried out to identify Down syndrome. It is habitually performed during the first trimester of pregnancy and involves taking the cells from the placenta and analyzing the chromosomes of the fetus.

Amniocentesis is another test typically performed in the second trimester. A needle is used to extract a sample of the amniotic fluid which is then used to analyze the chromosomes of the fetus.

After birth, the obstetrician can perform chromosomal karyotype using the baby’s blood. This test is used to ascertain the diagnosis since even children without Down syndrome can exhibit features of the condition. Thus physical aspects of the baby are not enough to establish the sickness (Veerabhadrappa et al., 2016).

Aetiology

A random error in cell division is what causes Dawn syndrome. This nondisjunction error in cell division is believed to give rise to an extra copy of chromosomes 21. In a normal cell division, each of the two chromosomes from one pair goes to a different cell.  However in a non disjunction division, both chromosomes from a single pair find their way into one cell instead of going to different cells. In most cases however, this error in cell division takes place during the formation of a sperm or an egg. No scholarly research has linked Dawn syndrome to any environmental factors or behavioral activities of parents. Most of these cases have been found to come from the mother’s egg with a few cases coming from the father. Nondisjunction can also occur after fertilization has taken place (Kazemi, Salehi and Kheirollahi, 2016).

Research has shown that three types of chromosomal changes can be the cause of Dawn syndrome. These chromosomal changes are Translocation trisomy 21, Mosaic trisomy 21 and complete trisomy 21..

Treatment

There is no precise treatment for Down syndrome (Kazemi,Salehi and Kheirollahi, 2016). People with the condition should be treated for medical problems just like others do but ensure additional screening. Early intervention can assist the individual in maximizing his or her potential and participate in the community (Carfì et al., 2014).

Early intervention for infants with Down syndrome can help them to improve the quality of their lives. Treatment for these children is best carried out by a team of specialists. Their parents should therefore as much help as possible to enable their child to develop the required skills as fully as conceivable(Huiracocha et al., 2017). The needs of each particular child are unique and so should the treatment sought. Depending on the explicit child requirements, the team of specialists may comprise of audiologist, pediatric cardiologist, developmental pediatrician, occupational therapist, speech therapist, pediatric neurologist and physical therapist, just to mention a few. The parent should seek out therapists, educators and health care providers that he or she can trust to deliver the best care for the child (Hickey, Hickey and Summar, 2012).

Although there is no cure for Down syndrome, these interventions are essential as they will help improve the quality of the child’s life by enhancing his or her social skills, self-help skills, motor skills, cognitive and language abilities as well as sensory skills.The parent should encourage the child to be as independent as possible and to participate in societal tasks and leisure activities. In order to better cope with his or her child’s condition, the parent can join support groups for parents and families who are dealing with the same situation (Huiracocha et al., 2017).

Prognosis

The prognosis (expected outcome) of children with Down syndrome depends on the severity of the condition and the complications brought about by this medical condition. However, the general quality of life for people with Down syndrome has improved recently due to medical technology therapy and early intervention. Children are able to participate in education whether in special schooling or otherwise and also in co-curricular activities such as music programs, art and sports. Adults with Down syndrome can live and work in offices and other stations of employment and participate in various communal undertakings as they are able to take care of their needs. Unlike years back, many adults with this medical condition are healthier and live longer. They can also marry and raise families, although pregnant women with Down syndrome are at risk of miscarriage.

Emerging Perspectives of Down syndrome

Assessing genotype-phenotype relationship

Many features of Down syndrome vary. Comprehension of this variability between individuals with this condition can help inform the development of therapies to identify specific features of the syndrome. These differences include the diversity in the degree of learning difficulties experienced and the severity of illnesses among dissimilar individuals.Use of mouse models has been crucial in trying to understand this relationship (Xing et al., 2016).

New technologies offer the opportunity to broaden animal models to include primates and rats. A joint multidisciplinary research as well as a global initiative is required to better understand the complex nature of Down syndrome. Representations developed in other species, for example rats, are expected to validate the relationship between phenotype and genotype and thus advance the outcome of preclinical treatments such as therapies (Herault et al., 2017).

Conclusion

In summary, this paper discusses the causes and symptoms of Down syndrome a non-communicable disease which has no specified cure. The condition is as a result of an extra chromosome 21 within an individual’s genetic makeup. It is responsible for symptoms such as protruding tongue, white spots in the iris, small head and neck. People with Down syndrome are at a higher risk of suffering from various diseases such as blood cancer, example leukemia, respiratory and digestive problems as well as congenital heart defect. However, their risk of non-blood cancers is low. Children with this condition have developmental delays such as cognitive and language disabilities. Down syndrome can be diagnosed both during pregnancy and after birth. The treatment of this condition entails therapies and regular medical checkups to improve the quality of the patient’s lives but there is no definite cure. Technology in medicine has greatly helped people with this condition as they live healthier, longer and are able to participate in the community as opposed to years ago. Continued research in a multidisciplinary perspective is required to thoroughly understand the genotype-phenotype relationship and thus further improve the outcomes of treatments and patients’ quality of life.

References

Patterson, D., 2009. Molecular genetic analysis of Down syndrome. Human genetics, 126(1), pp.195-214.

Weijerman, M.E. and De Winter, J.P., 2010. Clinical practice. European journal of pediatrics, 169(12), pp.1445-1452.

Wu, J. and Morris, J.K., 2013. The population prevalence of Down’s syndrome in England and Wales in 2011. European Journal of Human Genetics, 21(9), p.1016.

Herault, Y., Delabar, J.M., Fisher, E.M., Tybulewicz, V.L., Yu, E. and Brault, V., 2017. Rodent models in Down syndrome research: impact and future opportunities. Disease models & mechanisms, 10(10), pp.1165-1186.

Xing, Z., Li, Y., Pao, A., Bennett, A.S., Tycko, B., Mobley, W.C. and Yu, Y.E., 2016. Mouse-based genetic modeling and analysis of Down syndrome. British medical bulletin, 120(1), p.111.

Asim, A., Kumar, A., Muthuswamy, S., Jain, S. and Agarwal, S., 2015. Down syndrome: an insight of the disease. Journal of biomedical science, 22(1), p.41.

Kariminejad, M.H. and Kariminejad, A., 2009. A review on prenatal screening and diagnosis. Genetics in the 3rd Millennium, 7(1), pp.1558-1566.

Kazemi, M., Salehi, M. and Kheirollahi, M., 2016. Down syndrome: Current status, challenges and future perspectives. International journal of molecular and cellular medicine, 5(3), p.125.

Gardiner, K., Herault, Y., Lott, I.T., Antonarakis, S.E., Reeves, R.H. and Dierssen, M., 2010. Down syndrome: from understanding the neurobiology to therapy. Journal of Neuroscience, 30(45), pp.14943-14945.

Carfì, A., Antocicco, M., Brandi, V., Cipriani, C., Fiore, F., Mascia, D., Settanni, S., Vetrano, D.L., Bernabei, R. and Onder, G., 2014. Characteristics of adults with Down syndrome: prevalence of age-related conditions. Frontiers in medicine, 1, p.51.

Malt, E.A., Dahl, R.C., Haugsand, T.M., Ulvestad, I.H., Emilsen, N.M., Hansen, B., Cardenas, Y.E., Skøld, R.O., Thorsen, A.T. and Davidsen, E.M., 2013. Health and disease in adults with Down syndrome. Journal of Norwegian Medical Association, 133(3), pp.290-294.

Hickey, F., Hickey, E. and Summar, K.L., 2012. Medical update for children with Down syndrome for the pediatrician and family practitioner. Advances in pediatrics, 59(1), p.137.

Lewis, R., 2009. Human genetics. McGraw-Hill Higher Education.

Theisen, A. and Shaffer, L.G., 2010. Disorders caused by chromosome abnormalities. The application of clinical genetics, 3, p.159.

Veerabhadrappa, S.K., Chandrappa, P.R., Roodmal, S.Y., Shetty, S.J., Shankari, G.S.M. and Kumar, K.P.M., 2016. Karyotyping: Current perspectives in diagnosis of chromosomal disorders. Sifa Medical Journal, 3(2), p.35.

Huiracocha, L., Almeida, C., Huiracocha, K., Arteaga, J., Arteaga, A. and Blume, S., 2017. Parenting children with Down syndrome: Societal influences. Journal of Child Health Care, 21(4), pp.488-497.