CHROMOSOMAL DISEASES

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Author: Amina Haider

Date added: 26th August 2018

UNIT: Reproduction

STATEMENT OF INQUIRY: "Systems of reproduction in the natural world have a variety of different forms but provide the same function"

KEY CONCEPT: Systems

RELATED CONCEPTS: Form and Function

GLOBAL CONTEXT: Personal and cultural Expression - "social constructions of reality; philosophies and ways of life; belief systems; ritual and play"

According to Encyclopedia Britannica in 2017,’chromosomal disorder, are any syndrome characterized by malformations or malfunctions in any of the body’s systems, and caused by abnormal chromosome number or constitution’. Normally, humans have 23 pairs of chromosomes; of which 22 are autosomes, and 1 pair is sex chromosomes, giving humans 46 chromosomes in total.

Every chromosome contains hundreds of thousands of strands of genes[1], and chromosomal genetic disorders occur when chromosomes are partially or completely missing, altered or duplicated. An example is Down syndrome, which occurs when and extra, third copy of chromosome 21 is present in a person. This extra chromosome results in extra protein production, and upsets the body’s balanced systems (ShareCare, Inc., 2010).

Figure 1 (CK-12 Foundation, 2018)

If a person has an unusual chromosome rearrangement, there are several possibilities if they will or will not pass these characteristics down to their children. These are:

The child may inherit an entirely normal chromosome arrangement
The child may inherit the same chromosome rearrangement as the parent
The child may be born with a learning disability, developmental delay, and/or health problems
The pregnancy may end in a miscarriage. Studies show that 60% or more of first trimester miscarriages happen due to abnormalities in chromosomes.

It is usually possible for a person who carries chromosomal rearrangements to carry healthy children, and many do. But each rearrangement is unique, and children can be born with a rearrangement even though both parents’ chromosomes are normal. This is called de novo, or new rearrangement (Genetic Alliance UK , 2016).

Chromosome abnormalities usually happen as a result or errors in one, or more of the following: meiosis, mitosis, maternal age, or environment. In meiosis chromosome abnormalities happen as a result or error in cell division. If meiosis does not take place properly, it could result in sperm or egg having too many or not enough chromosomes. When fertilization happens, the baby could then either receive extra chromosomes, or have a missing one. The same can happen during mitosis of a fetus’s cells during pregnancy, and errors in mitosis are responsible for some cases of mosaicism (Standford Children's Health, 2018).

When a mother is 35 or older at the age of delivery, there is a higher risk for her children to be born with chromosome disorders. This is because, over time, there are fewer and fewer eggs in the ovaries, which also age with the woman. Scientists believe that as the eggs are aging with the woman, eggs in older women may have the incorrect number of chromosomes at the time of fertilization. Recent studies show that men over the age of 45 also have an increased risk for new autosomal dominant conditions in their children (Standford Children's Health, 2018).

During pregnancy, chromosomal abnormalities can cause the death of an embryo or fetus; they can also cause mental retardation or other developmental problems. Older pregnant women have a higher risk of passing down genetic chromosomal disorders, compared to younger pregnant women (ShareCare, Inc., 2010).

Variations of chromosomes include:

Trisomy – A chromosome is duplicated in its pair
Monosomy – A chromosome is absent from its pair
Triploidy – When fetuses are born with an extra set of chromosomes in their cells (69 in total)
Polyploidy – Containing three or more times the haploid[2] chromosome number
Deletion – One arm, or part of one arm of a single chromosome may be missing
Translocation – Part of one chromosome is transferred to another

Changes in chromosome number usually occur during sperm or egg formation, or in the early development of an embryo. When this happens in the early development of an embryo, it is usually due to a mixture of cells, some normal (euploid), and some containing abnormal chromosome complements, may occur, through a condition called mosaicism. In both cases, abnormalities of development occur due to unusual genetic signals transmitted by chromosomes (Encyclopaedia Britannica, 2017).

The most common symptoms of this syndrome are intellectual disability, heart defects, and unusual facial features (small upturned nose, wide mouth, full lips, small chin, widely spaced teeth). Low birth weight, problems in gaining weight appropriately, kidney abnormalities, and low muscle tone are other symptoms. Characteristic behaviors include hypersensitivity to loud noises, and an outgoing personality (Genetic Science Learning Center, 2018).

This symptom is diagnosed through its distinctive physical characteristics, but can also be confirmed using FISH (fluorescent in situ hybridization). Though there is no cure for Williams’s syndrome, its treatment involves easing the symptoms connected to the syndrome. Narrowed blood vessels can be treated, and physical and speech therapy are also beneficial. Regular checkups and monitoring of the person is necessary to look at the cardiovascular system and track any possible problems (Jaime Herndon, 2017).

Medical conditions can affect the lifespan of those with Williams’s syndrome. Calcium deposits can cause kidney problems, and narrowed blood vessels can lead to heart failure. Some people with Williams’s syndrome will require a caregiver, or live in a supervised home (Jaime Herndon, 2017).

The society can help those with rare chromosomal disorders by not only helping raise awareness about such disorders and why they occur, offering support groups for such people, proper medical expertise in the areas and treatments, physical and mental therapy, and generally love and support towards these people. Those with intellectual disabilities should be helped by the community with in different subjects in school life, and should be included in different sports and aspects of teen life. Support and warmth from the society is the biggest help towards those with these disorders.

Williams Syndrome

Williams’s syndrome is a rare genetic disorder that affects a child’s growth, physical appearance, and cognitive development. It is caused due to missing genetic material from chromosome 7, including the gene elastin. This gene’s protein products give blood vessels the elasticity and strength required to withstand lifetime usage. As people who have Williams’s syndrome lack this gene, they have disorders of the circulatory system and heart (Genetic Science Learning Center, 2018).

As most people who have this syndrome rarely have children, it is unlikely that children inherit this broken chromosome from a parent who has this syndrome.

Figure 3 (Genetic Science Learning Center, 2018)

Figure 2 (Genetic Science Learning Center, 2018)

Klinefelter Syndrome (XXY)

The sex chromosomes in the human body determine whether you’re a male or female. If a human is female, they have (XX) chromosomes, and if it’s a male, they have (XY) chromosomes. In rare cases, males are born with an extra X chromosome, making their sex chromosomes (XXY). This is called Klinefelter’s Syndrome. Many men usually do not even realize they have Klinefelter’s Syndrome until they have trouble conceiving a child and consult specialists. Though there is no cure for this syndrome, it can be treated, and with right care, most men with Klinefelter Syndrome can lead normal, healthy lives (WebMD LLC., 2018).

The extra X chromosome these men have happens by chance. Either the egg or sperm that came together had an extra X chromosome. Older pregnant women have a slightly increased chance of having children with this syndrome. A person may have one of the following (WebMD LLC., 2018):

An extra X chromosome in every cell, most common
An extra X chromosome in some cells, called mosaic Klinefelter, not as many symptoms present
More than one extra X chromosome, extremely rare and more severe

Symptoms of this syndrome vary with age, and not everyone gets all of them. Some males show symptoms early on, but others don’t realize they have Klinefelter’s Syndrome until they reach puberty or adulthood. Many men do not even realize they have this disease (WebMD LLC., 2018).

Symptoms in babies:

Hernias
Testicles that haven’t dropped into the scrotum
More quiet than usual
Slower to learn to sit up, crawl and talk
Weaker muscles

Symptoms in children:

Boys have low energy levels
A hard time making friends, talking about feelings
Problems learning to read, write, and do math
Shyness and low confidence

Symptoms in teenagers:

Puberty may come late, not finish, or not happen at all
Larger breasts than normal
Less facial and body hair (comes in later)
Less muscle tone, muscles grow slower than usual
Longer arms and legs, wider hips, and a shorter torso than other boys
Small penis, and small, firm testicles
Taller than usual (for the family)

Symptoms in adults:

Infertility
Low sex drive
Low testosterone levels
Problems getting/keeping an erection

Many problems caused by Klinefelter are due to lower testosterone levels. Having this condition could lead to having a higher chance of having autoimmune problems[3], breast cancers and blood, bone and lymph cancers, conditions affecting hormone glands (e.g. diabetes), heart disease and blood vessel problems, lung disease, mental health problems (anxiety and depression), and osteoporosis (WebMD LLC., 2018).

Starting with a physical exam, there are two tests that a doctor might run to detect this syndrome. The first is a chromosome analysis, also called a karyotype analysis, and the second is a hormone test.

The most common treatment for this syndrome is testosterone replacement therapy, which can help spur typical body changes that happen at puberty, and can help with penis size, stronger muscles and bones. This won’t affect testicle size or fertility though. Other treatments for this syndrome include (WebMD LLC., 2018):

[1] Provide instructions for building proteins that help bodies grow and function properly.

[2] In humans, gametes are haploid cells that contain 23 chromosomes, each of which are one of a chromosome pair that exists in diploid cells (Nature Education, 2014).

[3] Like lupus and rheumatoid arthritis, where your immune system attacks healthy parts of the body

References

CK-12 Foundation. (2018). Human Chromosomes and Genes. Retrieved January 21, 2018, from ck-12:

https://www.ck12.org/biology/chromosome/lesson/Human-Chromosomes-and-Genes-BIO/

Encyclopaedia Britannica. (2017, May 2). Chromosomal disorder. Retrieved January 21, 2018, from

Encyclopaedia Britannica: https://www.britannica.com/science/chromosomal-disorder

Genetic Alliance UK . (2016, May 10). CHROMOSOMAL DISORDERS. Retrieved January 21, 2017, from

Genetic Alliance UK: http://www.geneticalliance.org.uk/information/learn-about-genetics/chromosomal-disorders/

Genetic Science Learning Center. (2018). Chromosomal Abnormalities. Retrieved January 22, 2018, from

Learn. Genetics: http://learn.genetics.utah.edu/content/disorders/chromosomal/

Jaime Herndon. (2017, March 29). Williams Syndrome. Retrieved January 22, 2018, from healthline: https://www.healthline.com/health/williams-syndrome

Nature Education. (2014). haploid. Retrieved January 21, 2018, from Scitable:

https://www.nature.com/scitable/definition/haploid-309

ShareCare, Inc. (2010). Chromosomal Disorders. Retrieved January 21, 2018, from Sharecare:

https://www.sharecare.com/health/chromosomal-disorders/chromosomal-disorders-affect-life

Standford Children's Health. (2018). How Chromosome Abnormalities Happen: Meiosis, Mitosis, Maternal Age, Environment. Retrieved

January 21, 2018, from Stanford Children's Health:

http://www.stanfordchildrens.org/en/topic/default?id=how-chromosome-abnormalities-happen-meiosis-mitosis-maternal-age-environment-90-P02126

WebMD LLC. (2018). What is Klinefelter Syndrome? Retrieved January 22, 2018, from WebMD:

https://www.webmd.com/a-to-z-guides/klinefelter-syndrome#1