What is a Hereditary Disease?

Disorders caused by mutations (changes) in specific genes or chromosomes that are passed down from parent to child are called hereditary disorders.

 In other words, hereditary disorders occur when one or more genes are altered. 

 If this genetic change is passed on to offspring,  it is a hereditary disease. 

 Therefore, it is necessary to clarify that not all hereditary diseases are hereditary, as they are often not inherited by children. 

 For a hereditary disease to be inherited, the altered gene must be found in the germ cells of the affected individual. In other words, within an egg or sperm cell. Therefore, the genetic combination of biological parents is influential when it comes to communicating the disease to children.


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Hereditary disease In Human Beings


Examples and symptoms of some hereditary disorders 

 Achondroplasia;

 The first example of hereditary disease is achondroplasia. In this condition, the cartilage does not develop normally, so the patient has short limbs, macrocephaly, and short stature, usually reaching 130 cm for men and 124 cm for women. It is a hereditary congenital disorder whose symptoms have been present since birth. 

 Disability does not impair intellectual development at all, but motor skills can develop more slowly. The prognosis for this disease is good, and life expectancy for people with achondroplasia is normal, but for cardiovascular disease, it is slightly shorter. 

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Achondroplasia In Human Beings



 Genes and Inheritance Related to  97% of cases of achondroplasia is associated with mutations in the FGFR3 gene that are involved in the regulation of the linear growth of long bones. The mode of inheritance  is autosomal dominant, ie: 

 • If only one parent has the disease, there is a 50% chance that the disease will be transmitted to the baby each time she becomes pregnant. 

 • If both parents suffer from achondroplasia, the consequences can be very severe if their offspring inherit two modified copies of the gene. When they do, they develop a very serious form of disability that can be fatal to the baby before or after birth. 

 Achondroplasia is hereditary and can be passed on to children if the parent has it, but in 80%  it is caused by a "denovo mutation". H. It is a naturally occurring mutation during embryogenesis and is therefore not inherited from the parent.

Marfan syndrome;

 It is another hereditary disease that affects connective tissue, primarily blood vessels, heart, eyes, and skeleton. 

 Connective tissue supports protects and supports the formation of various tissues and organs, including blood vessels, organs, muscles, and even skin. It also contributes to the development of the body before and after childbirth and also serves as a cushion for joints. Symptoms of 

-Marfan syndrome varies from person to person, even among members of the same family, and ranges from mild to very severe.


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Marfan Syndrome In Human Beings

 The most dangerous complications are those that affect blood vessels and the heart. This defect in connective tissue affects the aorta, the artery that carries oxygen from the heart to other organs, and can lead to aneurysms and even dissections. One of the most serious cardiac complications that can occur is valvular heart disease. In addition, pregnant women should be especially careful because of the potential for bone and eye complications and the increased risk of aortic rupture and fatal dissection.

Symptoms ;

The most common symptoms of Marfan syndrome are: 

 • Tall, thin, disproportionately long limbs and toes.  • Curved spine.  • A sunken sternum or a protruding sternum instead. • Arched palate and crowding of teeth. 

 • Flat feet. There is no definitive treatment for Marfan syndrome, but there are treatments based on regular monitoring and pharmacological treatment that can prevent complications such as the aorta. The life expectancy of patients has been extended from 45 to 72 years thanks to early diagnosis and current treatment. 

 Genes involved and mode of inheritance  

 The gene associated with this disease is FBN1 and produces proteins that are structural constituents of microfibrils. Microfibrils are part of connective tissue and, among other things, control the release of growth factors. When this gene is modified, microfibrils do not function properly and cause the above symptoms. 

 The mode of inheritance of Marfan syndrome is autosomal dominant. H. If the parent has it, there is a 50% chance that it will be passed on to the child. As seen in achondroplasia, de novo mutations can also occur, accounting for 25% of cases of this disease.

Sickle cell anemia; 

 Sickle cell disease affects the shape of red blood cells and their ability to carry oxygen. 

 Red blood cells are usually round, but in people with this hereditary disease, the appearance is crescent-shaped, which can cause red blood cells to stick together and clog small blood vessels. This can cause pain and injured areas that blood cannot reach.



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Sickle Cells In Human Body Blood


Symptoms;

  Some of the symptoms that patients have with this illness are: 

 • Anemia: These red blood cells have a shorter half-life than unaffected red blood cells. 

 • Pain episodes that last for hours or days. 

 • Damage to the spleen, heart, brain, etc. 

 • Swelling of the limbs. Only bone marrow transplants can cure the disease, but due to the associated complications, it is only an option in some cases. 

Treatment;

 Common treatments focus on helping people lead a near-normal life, including penicillin vaccines to prevent infections, folic acid supplements to help synthesize new red blood cells, and painkillers. .. 

 Genes involved and mode of inheritance Changes in the HBB gene, which is essential for the formation of hemoglobin, are responsible for this disease. Because heredity is autosomal recessive,  both parents must have changes in at least one of the two copies of the gene to be a risk factor for the disease.

 If both parents are carriers, their offspring are at a 25% risk of getting sick. If one parent is ill, two copies have been modified, and the other parent is just a carrier, the risk of developing the disease for the offspring is 50%.

Color blindness; 

 This inherited condition affects the ability to distinguish between green and red, or blue and yellow. 

 Color blindness most often exists from birth and is a congenital disorder. People with color blindness lead a completely normal life, but their deficiencies vary. The most serious form is when people can only see different shades of gray. 


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Color Blindness In Human Eye


 Genes involved and mode of inheritance.

 Genes involved in this deficiency include OPN1LW, OPN1MW, and OPN1SW. 

 In the first two genes, the genetic pattern of color blindness is associated with the X chromosome, so it occurs in 8-10% of men and rarely in women. Women may be carriers, but they are usually asymptomatic. However, the third gene associated with color blindness is not located on the X chromosome and follows an autosomal dominant inheritance pattern.



Phenylketonuria; 

 A hereditary disease that interferes with the metabolism of amino acids. Amino acids are the building blocks of proteins. In this disorder, the body cannot break down the amino acid phenylalanine and accumulates it in the body. 


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phenylketonuria In Human Beings

Symptoms

 Symptoms  appear in the first few months of life, with the following symptoms: 

 • The smell of moisture in your baby's breathing, skin, or urine. 

 • Neurological problems that may include seizures 

 •eczema 

 • Microcephaly 

 • Growth retardation 

 • Hyperactivity 

 As you can see, some of the symptoms caused by this disease are serious but can be prevented if they are treated in the first few weeks of a child's life and the levels in the body do not rise too much. Treatment is primarily a diet, a lifelong low phenylalanine diet found primarily in protein-rich foods.

 If you start this diet after birth and follow it strictly throughout adulthood, you have a better prognosis and better physical and mental health than those who do not. It is important to recognize that if this diet is not followed early in life, the brain damage that occurs can lead to severe intellectual disability. Genes involved and mode of inheritance.


 This condition is caused by mutations in the PAH gene, which produces enzymes essential for degrading the amino acid phenylalanine. These mutations reduce the performance of this protein and cause abnormal levels of phenylalanine that are toxic to the body, especially the brain. 

 Because the genetic pattern of this disease is autosomal recessive, both parents have at least one copy of the modified gene for the disease to occur, as seen in the other examples in this article must be.


Genetics and environment; 

 All the examples of hereditary diseases we have seen so far are the result of genetic changes. That is, they have a genetic origin. However, many illnesses have both genetic and environmental risk factors. 

  In these cases, genetic loading plays a major role, but certain situations are also required to cause the disease. In these cases, the parent informs the child of the risk of a particular multifactorial hereditary disorder. 

 Below are some examples. 

Diabetes

 There are many different types of diabetes, including:
 
 • MODY Diabetes: In this case,  a mutation in one of the genes involved is sufficient for the onset of the disease. There are different types of MODY, each linked to a different gene. These mutations generally affect the ability of our body's pancreatic beta cells to produce insulin or interfere with the body's ability to detect elevated blood sugar levels, causing diabetes. 

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Diabetes In Human Beings


 • Type 1 diabetes: 
Due to the large number of genetic factors involved in this type of diabetes, the predisposition to the condition increases, and environmental factors cause the onset of the condition.
 In some cases, this diabetes is caused by an autoimmune reaction in which our own body attacks the beta cells of the pancreas. Type 2 diabetes is the most common form and is affected by both genetic and lifestyle factors. Genetic risk is associated with about 150 mutations in  DNA. 

 Myopia; 

 As you may know, myopia is a very common vision problem. It is a hereditary disease that affects 25% of the Spanish population. People with this problem will look blurry when looking at objects from a certain distance, but not near-transparent objects. 

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Myopia In Human Beings


 In other words, they don't look good from a distance. This is due to the focus problem caused by the shape of the eye, which causes the light to refract incorrectly in front of the retina rather than on the retina. 

Treatment

 Treatment includes gradual prescription biconcave lenses or contact lenses with patient diopter. Refraction correction corneal surgery  (LASIK) can also correct up to 6 diopters of myopia. Another surgical procedure is intraocular lens transplantation, which is primarily considered for people with very high myopia or adults over 50 years with presbyopia and/or cataracts. Genes involved and other environmental factors.
 There are about 24 genes that cause different types of myopia. Among them are 
  •  ANTXR2, KCNQ5, LAMA2 and PRSS56. 
 In addition to genetic factors, for example, reading too close, reading in the dark, or spending a lot of time in front of the screen can cause myopia.