MUTATION ANALYSIS

Factor II Prothrombin Mutation

Prothrombin is a protein that is required for the blood to clot. It is also called ‘factor II’. Blood clots are composed of a combination of blood platelets and a meshwork of the blood clotting protein fibrin. Prothrombin is a blood clotting protein that is needed to form fibrin. Mutation in the gene prothrombin G20210A, or a factor II, would lead to overproduction of prothrombin protein. Testing for the factor II prothrombin mutation is indicated for those with the family history of deep vein thrombosis (DVT), pulmonary embolism, mesenteric or cerebral sinus vein, myocardial infarction or stroke at a young age or history of recurrent pregnancy loss or stillbirth.

There are certain implications of the prothrombin mutation that are specifically relevant for women. For instance, it is well known that using oestrogen-containing oral contraceptives and hormones increases the risk of blood clots. It has been shown that women who have the prothrombin mutation increase the risk of developing a DVT by about 16 times, using oestrogen-containing oral contraceptives. The risk of developing a blood clot in the brain (cerebral thrombosis, sinus vein thrombosis) is also significantly increased. The first 6 to 12 months of oral contraceptive therapy seem to be the most common time in which clots occur. However, clots can also occur after having taken birth control pills for several years. Although progestin-only contraceptives (tablet, Depo Provera injection, or a slow-release intrauterine device) do not appear to increase the risk for venous blood clots in the majority of women, it is not known whether they are absolutely safe in women with a preexisting clotting disorder, such as the prothrombin mutation. Hormone replacement therapy increases the risk of DVT by 2 to 4 times in those with the prothrombin 20210 mutation. Therefore, women with the prothrombin mutation should discuss the risks and benefits of hormone use with their physician.

There are also implications of the prothrombin mutation for pregnancy. For years, it has been recognised that blood has an increased tendency to clot during pregnancy and in the 6 weeks after delivery. Pregnancy in any woman is thought to increase the risk of a blood clot by approximately 5 times compared with the risk of non-pregnant women; however, in women with a prothrombin mutation, the risk is further magnified.

Recently, there has been the suggestion that the prothrombin mutation occurs more commonly among women with certain pregnancy complications. These complications may include stillbirth (pregnancy loss after week 20), second trimester pregnancy loss, placental abruption (where the placenta detaches from the uterus), and preeclampsia (elevated blood pressure that can lead to dangerous consequences). Some studies have also shown a relationship between a mother having the prothrombin mutation and delivering a baby of small size. At this time, it does seem that having the prothrombin mutation may increase the risk of these situations, but it is unclear how strong the association may be. Testing for the prothrombin mutation may be performed in combination with tests for other hereditary risk factors (factor V Leiden, protein C, S, and antithrombin deficiencies), acquired risk factors (antiphospholipid antibodies), or risk factors about which it is not known whether they are inherited or acquired (elevated homocysteine, clotting factors VIII, IX, XI, or fibrinogen).

In Al-Jawhara Centre Molecular Diagnostic Unit, the diagnosis of a prothrombin mutation is proposed using real time-polymerase chain reaction RT-PCR technique.

 

Factor V Leiden Mutation

Factor V Leiden thrombophilia is an inherited disorder of blood clotting. Factor V Leiden is the name of a specific gene mutation that results in thrombophilia, which is an increased tendency to form abnormal blood clots that can block blood vessels. A particular mutation in the F5 gene causes factor V Leiden thrombophilia.

People with factor V Leiden thrombophilia have a higher than average risk of developing deep venous thrombosis (DVT). Factor V Leiden thrombophilia also increases the risk of pulmonary embolism. In addition, factor V Leiden mutation is associated with a slightly increased risk of pregnancy loss (miscarriage). Women with this mutation are 2 to 3 times more likely to have multiple (recurrent) miscarriages or a pregnancy loss during the second or third trimester. Some research suggests that the factor V Leiden mutation may also increase the risk of other complications during pregnancy, including pregnancy-induced high blood pressure (preeclampsia), slow fetal growth, and early separation of the placenta from the uterine wall (placental abruption).

Other factors also increase the risk of developing blood clots in people with factor V Leiden thrombophilia. These factors include increasing age, obesity, injury, surgery, smoking, pregnancy, and the use of oral contraceptives (birth control pills) or hormone replacement therapy. The risk of abnormal clots is also much higher in people who have a combination of the factor V Leiden mutation and another mutation in the F5 gene. Additionally, the risk is increased in people who have the factor V Leiden mutation together with a mutation in another gene involved in the coagulation system.

In Al-Jawhara Centre Molecular Diagnostic Unit, the diagnosis of a factor V Leiden mutation is proposed using real time-polymerase chain reaction RT-PCR technique.

 

MTHFR C677T Mutation

The MTHFR gene provides instructions for production of methylenetetrahydrofolate reductase. This enzyme plays a role in processing amino acids, the building blocks of proteins. Methylenetetrahydrofolate reductase is important for a chemical reaction involving forms of the vitamin folate (also called folic acid or vitamin B9). Specifically, this enzyme converts 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate. This reaction is required for the multistep process that converts the homocysteine to methionine. Homocystinuria is caused by mutations in the MTHFR gene. At least 24 mutations in the MTHFR gene have been identified in people with homocystinuria. Most of these mutations change single amino acids in methylenetetrahydrofolate reductase. These substitutions disrupt the function of the enzyme, and may inactivate it completely. Other mutations lead to the production of an abnormally small, nonfunctional version of the enzyme. Without methylenetetrahydrofolate reductase, homocysteine cannot be converted to methionine. Variant of the MTHFR gene may increase the risk of cardiovascular disease and birth defects. This variant is relatively common in many populations worldwide. It replaces the nucleotide cytosine with the nucleotide thymine at position 677 in the MTHFR gene (C677T). This change in the MTHFR gene produces a form of methylenetetrahydrofolate reductase that has reduced activity at higher temperatures (thermolabile). People with the thermolabile form of the enzyme have increased levels of homocysteine in their blood.

The C677T variant has been associated with an increased risk of cardiovascular disease, including coronary heart disease and stroke, in adults. It may also play a role in the risk of high blood pressure in pregnancy (preeclampsia). Additionally, research suggests that the variant may be a risk factor for birth defects that occur during the development of the brain and spinal cord (neural tube defects).

In Al-Jawhara Centre Molecular Diagnostic Unit, the diagnosis of a MTHFR mutation is proposed using real time-polymerase chain reaction RT-PCR technique.

 

Human Epidermal Growth Factor Receptor 2 HER2/NUE

Human epidermal growth factor receptor is a gene that sends control signals to cells for growth, divide, and repairs. HER2 is a cell membrane surface-bound receptor tyrosine kinase which is normally involved in the signal transduction pathways leading to cell growth and differentiation. It is encoded within the genome by HER2/neu, a known proto-oncogene. Approximately 30% of breast cancers have an amplification of the HER2/neu gene or overexpression of its protein product. Overexpression of this receptor in breast cancer is associated with increased disease recurrence and worse prognosis. Because of its prognostic role as well as its ability to predict response to trastuzumab (Herceptin), breast tumors are routinely checked for overexpression of HER2/neu. Overexpression also occurs in other cancers such as ovarian cancer, stomach cancer, and biologically aggressive forms of uterine cancer, like uterine serous endometrial carcinoma.

In clinical usage, HER2/neu is important as the target of the monoclonal antibody trastuzumab (marketed as Herceptin). Trastuzumab is effective only in breast cancer where the HER2/neu receptor is overexpressed. One of the mechanisms of how trastuzumab works after it binds to HER2 is by increasing p27, a protein that halts cell proliferation.

In Al-Jawhara Centre Molecular Diagnostic Unit, the full quantitaion of HER2/nue is proposed using real time-polymerase chain reaction RT-PCR technique.


Pax 8 Gene Mutations for Congenital Hypothyroidism

The PAX8 gene belongs to a family of genes that plays a critical role in the formation of tissues and organs during embryonic development. The PAX gene family is also important for maintaining the normal function of certain cells after birth. To carry out these roles, the PAX genes provide instructions for making proteins that attach to specific areas of DNA. By attaching to critical DNA regions, these proteins help control the gene expression. On the basis of this action, PAX proteins are called ‘transcription factors’.
During embryonic development, the PAX8 protein is thought to activate genes involved in the formation of the kidney and the thyroid gland. Thyroid is has an important role in regulating growth, brain development, and the rate of metabolism. Following birth, the PAX8 protein regulates several genes involved in the production of thyroid hormones.

Congenital hypothyroidism caused by mutations in the PAX8 gene. Several PAX8 gene mutations have been identified, but the effect of these mutations on health is variable. Some mutations cause congenital hypothyroidism, while others mildly reduce thyroid hormone levels or have no detectable effect.

In some cases, identical mutations in members of the same family have varied effects. Most mutations change one of the amino acids used to make the PAX8 protein. Other mutations disrupt protein production, resulting in an abnormally small version of the PAX8 protein. Nearly all PAX8 gene mutations prevent the PAX8 protein from effectively binding to DNA. The thyroid gland is unusually small in people with PAX8 mutations. This finding suggests that PAX8 gene mutations disrupt the normal growth or survival of thyroid cells during embryonic development. As a result, the thyroid gland is reduced in size and may be unable to produce the normal amount of thyroid hormones.

The PAX8 gene is sometimes involved in the formation of abnormal growth follicular thyroid cells. Some of these growths can be follicular adenomas (benign), other tumors are follicular carcinomas (malignant).


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