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Genetic diseases

Harmful mutations: genetic diseases

Sickle cell anemia

What is a “sickle”? A hand-held agricultural tool with a curved blade used for harvesting grain crop.

The hammer and sickle (☭) is a communist symbol that was conceived during the Russian Revolution. The hammer stood for industrial labourers; the sickle for the peasantry.

{ http://kidshealth.org/parent/medical/heart/sickle_cell_anemia.html }

Sickle cell disease is an inherited disorder in which red blood cells (RBCs) are abnormally shaped. This abnormality can result in painful episodes, serious infections, chronic anemia, and damage to body organs.

These complications can, however, vary from person to person depending on the type of sickle cell disease each has. Some people are relatively healthy and others are hospitalized frequently.

But thanks to advancements in early diagnosis and treatment, most kids born with this disorder grow up to live relatively healthy and productive lives.

sickle cell

{ http://www.nhlbi.nih.gov/health/health-topics/topics/sca }

Sickle cell blood flow

Why do some genetic diseases persist?

The heterozygote advantage

A. Sickle-cell anemia is only caused by the presence of two recessive alleles.

1. Someone with only one SCA allele has a mixed” phenotype, will not be sick. Only some of their red blood cells are misshapen.

2. People with only one SCA allele are carriers.

3. In areas with persistent malaria outbreaks, individuals with the heterozygous
state have an advantage – they are resistant to malarial infection.


Cystic fibrosis (CF)

{ http://learn.genetics.utah.edu/content/disorders/singlegene/cf/ }

Cystic fibrosis is a genetic disorder that affects the respiratory and digestive systems.

People with cystic fibrosis inherit a defective gene… The protein produced by this gene normally helps salt (sodium chloride) move in and out of cells.

If the protein doesn’t work correctly, that movement is blocked.

Then an abnormally thick sticky mucus is produced on the outside of the cell.

Cells most seriously affected by this are the lung cells. This mucus clogs the airways in the lungs, and increases the risk of infection by bacteria.

Cystic fibrosis is a recessive disorder: If a child inherits only one copy of the faulty gene, he or she will be a carrier. Carriers don’t actually have the disease, but they can pass it on to their children.

What are the symptoms of cystic fibrosis?

Coughing or wheezing, respiratory illnesses (such as pneumonia or bronchitis), low weight, salty-tasting skin, and greasy stools.

Because the lungs are clogged and repeatedly infected, lung cells don’t last as long as they should. Therefore, cystic fibrosis patients who don’t receive treatment have shortened lifespans.
Cystic fibrosis cf-channel

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{ http://www.drugdevelopment-technology.com/projects/ivacaftor—treatment-for-cystic-fibrosis/ }
1 in 4 chance of genetic disease

B2. Why does CF persist? Perhaps this is an example of the heterozygote advantage

A single CF allele may influence survivorship of people affected by diseases involving water loss, e.g. diarrhea, especially cholera. However, note that this hypothesis has been called into question in recent years.

Another hypothesis for the prevalence of the CF mutation is that it provides resistance to tuberculosis. Tuberculosis was responsible for 20% of all European deaths between 1600 and 1900, so even partial protection against the disease could account for the current gene frequency.

C1. Huntington’s disease

{ http://education-portal.com/academy/lesson/what-is-huntingtons-disease-symptoms-genetic-cause-treatment.html }

Huntington’s disease is an autosomal dominant degenerative neurological disease. Usually, people who have Huntington’s disease don’t start showing any symptoms until they are in their 30s or 40s.

Mood changes, depression, irritability, or paranoia are often the first signs of the disease and are followed by a decline in coordination and an unsteady gait.

Movements will become increasingly uncoordinated and jerky in nature as the disease progresses, and the mental capabilities of the person will continue to slowly decline.

Eventually, the person may not remember who they are or recognize close family members. This progressive loss of cognitive capabilities is called dementia. Huntington’s disease progresses slowly but steadily, and patients generally live for about 20 years after the first symptoms appear.



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