DNA, Inheritance And Continuity Of Life

Rationale

Regarding the claim made that ‘Sex linked genetic diseases affect more males than females’, many queries and investigations were raised. These then led to questions such as ‘What is a sex-linked genetic disease?’ and ‘What are inheritance patterns?’. The claim did not specify what kind of diseases were studied and what quantitative number of males were affected and that meant reviewing it would be very difficult. Subsequently a detailed research question was proposed:

RQ

“Does Duchenne Muscular Dystrophy (DMD) affect more than 14000% more of males than females due to the X-linked inheritance pattern, in the world.”

Background

A genetic disease can be defined as the result of changes or mutations in an individual’s DNA (Genetic Alliance, 2019). These mutations can be due to an error in DNA replication or due to environmental factors, such as cigarette smoke and exposure to radiation, which cause changes in the DNA sequence (Your Genome, 2019).

All humans have two copies of one gene, inherited from each parent. Genes are small sections of DNA that code for proteins (Your Genome, 2019). A gene mutation is a permanent alteration in the DNA sequence that makes up a gene, such that the sequence differs from what is found in most people and they range a lot in sizes (Genetics Home Reference, 2019).

DMD is a fatal progressive neuromuscular disorder caused by a recessive mutation on the X-Chromosome. It occurs from problems with a gene called the Dystrophin gene. This disease primarily affects boys, but in some rare cases, girls can be affected. This is because boys have one X and Y sex chromosome, unlike girls who have two X chromosomes, and this means that boys do not have another copy of the X chromosome to compensate for the genetic defect in their only X chromosome (Shown on Figure 1). As females have the second X chromosome, both need to be affected in order for them to have the disease. In the usual case where the girl receives one affected and one unaffected X chromosome, they would not have the signs and symptoms of the disorder and would therefore be a DMD carrier (Muscluar Dystrophy Association, 2019).

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The symptoms of DMD can begin as early as 3 years old, who is experiencing muscle weakness. As Figure 3 shows weakness first starts affecting muscles of the hips, pelvic area, thighs and shoulders.

Evidence

From the many sources studied, all of them state that there is a much higher chance of males inheriting DMD than females. This is as explained above, the Dystrophin gene being on the X chromosome. Males have only one copy of the dystrophin gene and those who inherit the mutation get the disease because they have no second dystrophin gene to produce the protein, However, females have two copies of this gene and when they inherit a faulty dystrophin gene, usually her second gene is healthy and therefore that normally gives her enough protein to protect her form the gene (Duchenne UK, 2019). Only in extreme rare cases, such as the second x chromosome being lacking, or serious damage sustained on the second X chromosome will females develop DMD (as shown in Figure 2).

According to Duchenne UK, DMD affects approximately 1 in every 3500 boys that are born, but around only 1 in 50 million girls. This implies that males are roughly 14 286% more likely to get affected by this disease than females are. This percentage suggests how rare females are to inherit this disease. Although primarily an X-linked condition affecting males, some female carriers are symptomatic for the disorder but usually exhibit a milder phenotype (Ryder, Leadley, Armstrong, Westwood, & de Kock, 2017).

Evaluation

In order to call a fair conclusion, sources of evidence of claims need to be reliable and credible. Certain limitation factors have effects on data which can somewhat affect the answer to the research question. It is clear that males get more affected due to the lack of the second backup X chromosome, but to find an accurate percentage of how many more are affected, the source of evidence for the statistics has to be trustworthy. One limitation for the data provided in the evidence section is that the research was conducted in the UK, and this therefore means that the evidence is not an accurate representation of the whole world. To improve this problem, it is recommended to find more statistics of people affected form other parts of the world and average out the results. This will help to get a more precise understanding of the number of people affected around the world. Another limitation is that the sourcing methods included things such self- determined surveys. If dishonest people completed this survey, this would mean that the data readings are incorrect as they may or may not have that disease. To reduce the impact of this problem, all data should be obtained in a way that honesty does not affect, such as blood tests etc. and this would hence mean that the data obtained has the least amount of biased information. Another one of the limitations in this data set is that the technology method of clarifying that a person had DMD may not be very accurate. This is because that machine/device may be outdated and therefore cannot give the most accurate readings. Again, tying to use the latest technology or keep all technology devices updated would mean that the reading would be more accurate and reduce the limitations in the data obtained. The source that the data was acquired from was a fairly credible website as it runs clinical trials and it is a website dedicated to the Duchenne muscular dystrophy. The Genetics Home Reference website had information updated recently and as well as that, the information can be corroborated with the Muscular Dystrophy Association. They both provide similar information and findings about the mutation and disease. If all the addresses limitations are reduced, the investigation can be conducted more thoroughly, and more accurate inferences can be made from the evidence provided.

Conclusion

Based on the evidence provided in the investigation, it is seen that males are definitely more affected than females from Duchenne Muscular Dystrophy from the X-linked inheritance patterns due to females essentially having a ‘backup’ X chromosome. This means that they can produce the Dystrophin gene from the other chromosome and produce the protein to protect herself from the mutation. Males, on the other hand, do not have a second X chromosome and therefore if they have inherited an affected chromosome, they will have the disease. This supports the research question as males do get more affected by the X linked inheritance patterns than females do. An accurate percentage cannot be included with this judgement as there were many limitations with the data provided. A more thorough research could be done to find more data conducted to have a more precise investigation.