The World of Pregnancy

Top 10 Most Frequent Inherited Genetic Diseases

There are a lot of theories about why genetic diseases occur. We know that both environmental factors as genetics play an important role in their development, but we don`t understand exactly how.

A genetic disorder is caused by an abnormality in a person`s genetic material (DNA or genome). There are 4 different types of genetic disorders:

  • One mutated gene.
  • Several genes have mutated.
  • Chromosomal changes – whole years of the chromosome may be missing or be in another area.
  • Mitochondrion – maternal genetic material in the mitochondrion may also suffer from a mutation.

We know that some ethnic groups are more likely to have certain genetic disorders (for instance, people from the Mediterranean areas of Europe are more likely to have a genetic form of anemia which is thalassemia). Also, we know that some genetic disorders, such as sickle cell anemia (also known as ACS), represent an attempt of the body to combat environmental stress factors. In ACS, the mutation, which helps red cells to change, also help to minimize infection with the malaria parasite.

At the same time, we know that a woman is born with all the eggs in her ovaries – and the more waits to have children, the greater the risk of a genetic disorder in that child. Also, there are tests which can be performed to detect certain genetic disorders, such as cystic fibrosis, Down syndrome, Fragile X syndrome, Bloom syndrome, Canavan disease, Fanconi anemia, Gaucher`s disease, type IV Mucolipidosis, Tay-Sachs disease, neural tube defects, sickle cell anemia, thalassemia and Turner syndrome.

Cystic Fibrosis

Cystic fibrosis is one of the most common inherited diseases among Caucasians and is caused by lack of protein which controls chloride balance in the body. This leads to breathing difficulties and lung recurrent infections. Also, it involves digestive and reproductive problems. The symptoms vary from weak to severe. Both parents need to have this condition for a child to be affected – each child has a change of 25% (1 out of 4 cases) to be affected. Cystic fibrosis is more common among Caucasians, especially Ashkenazi Jews, but is found among all ethnic groups.

Down Syndrome

Down syndrome is a chromosomal abnormality caused by an additional copy of the genes found on the chromosome 21. This syndrome affects around 1 out 800 – 1.000 newborns. It can be detected by prenatal examination. There`s a pattern of characteristics, some of them being visible immediately after birth, such as facial features, low muscle tone, digestive or heart system defects and developmental delays. Children with Down syndrome are affected in a varied way, from moderate to severe. Any ethnic group can be affected and is often associated with the older age of the mother.

Fragile X Syndrome

Fragile X syndrome is associated with the most common type of developmental delays and inherited form of mental retardation. Cognitive difficulties and delays may vary from mild symptoms to severe ones, and sometimes are associated with autism. Around 1 out of 1.500 males and 1 out of 2.500 women suffer of Fragile X syndrome. Normally, males have 1 chromosome X and women have 2. Chromosome X can break when this syndrome is concerned. The area of chromosome X which causes fragility may be repeated on the same chromosome. The more areas of this type, the greater is the fragility and the serious is the syndrome.

Inherited Clotting Problems

Blood clotting is one of the most complicated biochemical pathways of the body and there`s a number of different inherited clotting problems. These problems may result in an abundant bleeding and in an abnormal clot formation in the body, most of them being common in veins. The most common abnormality is represented by Factor V Leiden and may be a problem that appears during pregnancy, leading to preeclampsia, low birth weight, stillbirth and placental problems.

There are also other inherited clotting problems, such as prothrombin (Factor II), protein S, protein C and antithrombin III deficiencies.

Haemophilia is a common blood disorder – the most common types are: haemophilia A (where there`s a factor VIII deficiency), haemophilia B (where there`s a factor IX deficiency) and Von Willebrand`s disease (where there`s factor Von Willebrand deficiency, also known as VWD).

The symptoms of these clotting disorders are:

  • Excessive external bleeding of gums and nose, and internal in the gastrointestinal system and joints.
  • Abnormal menstrual bleeding.
  • Excessive bruising.

Familial Hypercholesterolemia & Combined Hypercholesterolemia

These inherited disorders may result in an increase of blood lipids and cholesterol. They may lead to obesity, glucose intolerance and diabetes, stroke and heart diseases. The treatment includes dietary and lifestyle changes.

Huntington’s Disease (HD)

This is an inherited disease which causes as certain brand nerve cells and central nervous system to degenerate. The loss of these nerve cells cause symptoms, such as behavior changes, unusual movements which are similar to those a snake (chorea), uncontrolled movements, walking problems, loss of memory, speech problems, cognitive problems and swallowing difficulties. The treatment usually focuses on the stagnation of the disease. There`s a Huntington`s diseases with an adult onset, this being the most common form, and usually develops when a person is between 30 and 40 years old. Also, there`s also an early form that usually starts around childhood. This is an autosomal dominant disease, which means that if a parent has it, the child has a 50%-50% to inherit it – and if you inherited, the disease may be transmitted to your children as well. – More info!

Muscle Dystrophies

A lot of muscle dystrophies – characterized by a worsening of muscle weakening – are inherited disorders. The most common are:

Duchenne Muscular Dystrophy

The symptoms are apparent in this disease, usually, before the age of 6, and sometimes even earlier. These symptoms are: fatigue, possible mental retardation, muscle weakness starting with the legs and then spreading to the superior part of the body. Also, there may be associated various heart problems, breathing issues and back deformities. The muscle weaknesses can aggravate walking progressively. This weakness becomes more and more worse – until the age of 12, most children are in a wheelchair. Boys are more likely to inherit this disease.

Becker Muscular Dystrophy

For this dystrophy, the symptoms are similar to Cuchenne muscular dystrophy, but they are harder to occur and worsen. They may be: fatigue, possible mental retardation and muscle weakness starting with the legs. Muscle weakness in the superior part of the body isn`t so severe like in Duchenne muscular dystrophy. Again, boys are more likely to have this disorder, and also are limited to wheelchair until the age of 25 – 30 years.

Sickle Cell Anemia

Sickle cell anemia is an inherited disease where red blood cells, which normally have a disc shape, present a crescent or sickle shape. This reduces the ability of red blood cells to transport oxygen towards the body`s tissues – may result in a painful crisis of sickle cells and may appear of a few or many times, depending from person to person. Besides pains (abdominal, chest and bones), there are other symptoms that may appear, such as fatigue, respiratory failure, increased heart rate, developmental delays, fever and leg ulcers. Treatment includes analgesics, hydroxyurea to decrease the number of painful episodes, folic acid to support red blood cells, blood transfusions and kidney dialysis. Sickle cell anemia is more common in person of African or Mediterranean origin, but also in persons of other origins.

Thalassemias

Thalassemias (beta-thalassemia is the most common, alpha-thalassemia is less common) represents a group of inherited blood disorders, where hemoglobin, a molecule which carries oxygen, isn`t synthesized properly by red blood cells. This leads to anemia – where symptoms when they appear consist in fatigue, increase spleen, bones that break easily, bone pains and breathing insufficiency. Persons who have thalassemia may suffer from a weak appetite, dark color urine and jaundice (a yellowish decoloration of the skin and white part of the eyes) – jaundice is a signal of liver dysfunction). Infections are common in persons who suffer of thalassemia.

Mutations which Affect Biochemical Pathways

Phenylketonuria (PKU) is the result of a lack of an enzyme in the liver which transforms an amino acid, phenylalanine, in another amino acid, tyrosine. If this isn`t discovered in time, high levels of phenylalanine can cause mental retardation, brain damage and seizures. Treatments consist in a poor diet of phenylalanine and using a cofactor – tetrahydrobiopterin (BH4), to reduce the amount of phenylalanine in blood.

Deficiency of alpha 1 antitrypsin leads to a low amount of alpha-1 antitrypsin in the lungs and blood – this in turn leading to lung diseases, such as emphysema. The first symptoms are wheezing and respiratory failure. Other signs, which may appear later, may be: weight loss, frequent infections of the respiratory tract, fatigue and increased heart rate.

There are many diseases which may be transmitted genetically. There isn`t a treatment for these disorders, although therapy with genes may have potential. A lot of these disorders may be treated and those who have one of them may live a normal life.

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