Source: National Human Genome Research Institute / Mayo Clinic Foundation
Huntington's disease (HD) is an inherited neurological illness causing involuntary movements, severe emotional disturbance and cognitive decline.
In the United States alone, about 30,000 people have HD. In addition, 35,000 people exhibit some symptoms and 75,000 people carry the abnormal gene that will cause them to develop the disease. There is no cure for this fatal disease.
A single abnormal gene produces the HD gene on chromosome 4. The gene codes for production of a protein called "huntingtin," whose function is still unknown. But the defective version of the gene has excessive repeats of a three-base sequence, "CAG." In the normal huntingtin gene, this sequence is repeated between 11 and 29 times. In the mutant gene, the repeat occurs over and over again, from 40 times to more than 80. This defect causes the resulting huntingtin protein to be malformed, prone to clumping in the brain and causing the death of nearby nerve cells. Cells of the basal ganglia, a brain area responsible for coordinating movement, and of the cortex, which controls thought, perception and memory, are most often affected. Since the gene that causes HD is dominant, each child of an HD parent has a 50-50 chance of inheriting the HD gene. The child needs only one copy of the gene from either parent to develop the disease. A person who inherits the HD gene, and survives long enough, will sooner or later develop the disease. If the child does not inherit the defective gene, the child will not get the disease nor pass the gene on to subsequent generations. Symptoms of HD generally appear in mid-life.
People with a known family history of Huntington's disease are understandably concerned about whether they may pass the Huntington gene on to their children. These people may consider genetic testing and family planning options. If an at-risk parent is considering genetic testing, it can be helpful to meet with a genetic counselor. A genetic counselor will discuss the potential risks of a positive test result, which would indicate the parent will develop the disease. Also, couples will need to make additional choices about whether to have children or to consider alternatives, such as prenatal testing for the gene or in vitro fertilization with donor sperm or eggs. Another option for couples is in vitro fertilization and preimplantation genetic diagnosis. In this process, eggs are removed from the ovaries and fertilized with the father's sperm in a laboratory. The embryos are tested for presence of the Huntington gene, and only those testing negative for the Huntington gene are implanted in the mother's uterus.Read More: https://www.mayoclinic.org/diseases-conditions/huntingtons-disease/symptoms-causes/syc-20356117
Source: National Human Genome Research Institute
Sickle cell disease is caused by a mutation in the hemoglobin-Beta gene found on chromosome 11. Hemoglobin transports oxygen from the lungs to other parts of the body. Red blood cells with normal hemoglobin (hemoglobin-A) are smooth and round and glide through blood vessels. In people with sickle cell disease, abnormal hemoglobin molecules - hemoglobin S - stick to one another and form long, rod-like structures. These structures cause red blood cells to become stiff, assuming a sickle shape. Their shape causes these red blood cells to pile up, causing blockages and damaging vital organs and tissue. Sickle cells are destroyed rapidly in the bodies of people with the disease, causing anemia. This anemia is what gives the disease its commonly known name - sickle cell anemia. The sickle cells also block the flow of blood through vessels, resulting in lung tissue damage that causes acute chest syndrome, pain episodes, stroke and priapism (painful, prolonged erection). It also causes damage to the spleen, kidneys and liver. The damage to the spleen makes patients - especially young children - easily overwhelmed by bacterial infections. A baby born with sickle cell disease inherits a gene for the disorder from both parents. When both parents have the genetic defect, there's a 25 percent chance that each child will be born with sickle cell disease. If a child inherits only one copy of the defective gene (from either parent), there is a 50 percent chance that the child will carry the sickle cell trait. People who only carry the sickle cell trait typically don't get the disease, but can pass the defective gene on to their children.
Sickle cell disease is the most common inherited blood disorder in the United States. Approximately 100,000 Americans have the disease.In the United States, sickle cell disease is most prevalent among African Americans. About one in 12 African Americans and about one in 100 Hispanic Americans carry the sickle cell trait, which means they are carriers of the disease.
Bone Marrow Transplantation: The Only Cure:
Currently the only cure for sickle cell disease is bone marrow transplantation. In this procedure a sick
patient is transplanted with bone marrow from healthy, genetically compatible sibling donors. However only
about 18 percent of children with sickle cell disease have a healthy, matched sibling donor. Bone marrow
transplantation is a risky procedure with many complications.
Gene Therapy Offers Promise of a Cure: Researchers are experimenting with attempts to cure sickle cell disease by correcting the defective gene and inserting it into the bone marrow of those with sickle cell to stimulate production of normal hemoglobin. Recent experiments show promise.
Researchers used bioengineering to create mice with a human gene that produces the defective hemoglobin causing sickle cell disease. Bone marrow containing the defective hemoglobin gene was removed from the mice and genetically "corrected" by the addition of the anti-sickling human beta-hemoglobin gene. The corrected marrow was then transplanted into other mice with sickle cell disease. The genetically corrected mice began producing high levels of normal red blood cells and showed a dramatic reduction in sickled cells. Scientists are hopeful that the techniques can be applied to human gene transplantation using autologous transplantation, in which some of the patient's own bone marrow cells would be removed and genetically corrected.
Source: National Human Genome Research Institute
Thalassemia is actually a group of inherited diseases of the blood that affect a person's ability to produce hemoglobin, resulting in anemia. Hemoglobin is a protein in red blood cells that carries oxygen and nutrients to cells in the body. About 100,000 babies worldwide are born with severe forms of thalassemia each year. Thalassemia occurs most frequently in people of Italian, Greek, Middle Eastern, Southern Asian and African Ancestry. The two main types of thalassemia are called "alpha" and "beta," depending on which part of an oxygen-carrying protein in the red blood cells is lacking. Both types of thalassemia are inherited in the same manner. The disease is passed to children by parents who carry the mutated thalassemia gene. A child who inherits one mutated gene is a carrier, which is sometimes called "thalassemia trait." Most carriers lead completely normal, healthy lives. A child who inherits two thalassemia trait genes - one from each parent - will have the disease. A child of two carriers has a 25 percent chance of receiving two trait genes and developing the disease, and a 50 percent chance of being a thalassemia trait carrier. Most individuals with alpha thalassemia have milder forms of the disease, with varying degrees of anemia. The most severe form of alpha thalassemia, which affects mainly individuals of Southeast Asian, Chinese and Filipino ancestry, results in fetal or newborn death. A child who inherits two copies of the mutated gene for beta thalassemia will have beta thalassemia disease. The child can have a mild form of the disease, known as thalassemia intermedia, which causes milder anemia that rarely requires transfusions.
Gene Therapy Offers Hope for a Cure Scientists are working to develop a gene therapy that may offer a cure for thalassemia. Such a treatment might involve inserting a normal beta globin gene (the gene that is abnormal in this disease) into the patient's stem cells, the immature bone marrow cells that are the precursors of all other cells in the blood. Another form of gene therapy could involve using drugs or other methods to reactivate the patient's genes that produce fetal hemoglobin - the form of hemoglobin found in fetuses and newborns. Scientists hope that spurring production of fetal hemoglobin will compensate for the patient's deficiency of adult hemoglobin.Read More: https://www.genome.gov/10001221/
Source: National Cancer Institute
Summary: BRCA1 and BRCA2 Cancers
BRCA1 and BRCA2 are human genes that produce tumor suppressor proteins. These proteins help repair damaged DNA and, therefore, play a role in ensuring the stability of each cell’s genetic material. When either of these genes is mutated, or altered, such that its protein product is not made or does not function correctly, DNA damage may not be repaired properly. As a result, cells are more likely to develop additional genetic alterations that can lead to cancer. Specific inherited mutations in BRCA1 and BRCA2 most notably increase the risk of female breast and ovarian cancers, but they have also been associated with increased risks of several additional types of cancer. People who have inherited mutations in BRCA1 and BRCA2 tend to develop breast and ovarian cancers at younger ages than people who do not have these mutations. A harmful BRCA1 or BRCA2 mutation can be inherited from a person’s mother or father. Each child of a parent who carries a mutation in one of these genes has a 50% chance (or 1 chance in 2) of inheriting the mutation. The effects of mutations in BRCA1 and BRCA2 are seen even when a person’s second copy of the gene is normal.
Risk of Breast and Ovarian Cancer:
A woman’s lifetime risk of developing breast and/or ovarian cancer is greatly increased if she inherits a harmful mutation in BRCA1 or BRCA2. Breast cancer: About 12% of women in the general population will develop breast cancer sometime during their lives. By contrast, a recent large study estimated that about 72% of women who inherit a harmful BRCA1 mutation and about 69% of women who inherit a harmful BRCA2 mutation will develop breast cancer by the age of 80. Like women from the general population, those with harmful BRCA1 or BRCA2 mutations also have a high risk of developing a new primary cancer in the opposite (contralateral) breast in the years following a breast cancer diagnosis. It has been estimated that, by 20 years after a first breast cancer diagnosis, about 40% of women who inherit a harmful BRCA1 mutation and about 26% of women who inherit a harmful BRCA2 mutation will develop cancer in their other breast. Ovarian cancer: About 1.3% of women in the general population will develop ovarian cancer sometime during their lives. By contrast, it is estimated that about 44% of women who inherit a harmful BRCA1 mutation and about 17% of women who inherit a harmful BRCA2 mutation will develop ovarian cancer by the age of 80.
Source: Mayo Clinic Foundation
Lupus is a systemic autoimmune disease that occurs when your body's immune system attacks your own tissues and organs. Inflammation caused by lupus can affect many different body systems — including your joints, skin, kidneys, blood cells, brain, heart and lungs. Lupus can be difficult to diagnose because its signs and symptoms often mimic those of other ailments. The most distinctive sign of lupus — a facial rash that resembles the wings of a butterfly unfolding across both cheeks — occurs in many but not all cases of lupus. Some people are born with a tendency toward developing lupus, which may be triggered by infections, certain drugs or even sunlight. While there's no cure for lupus, treatments can help control symptoms.
Lupus occurs when your immune system attacks healthy tissue in your body (autoimmune disease). It's likely that lupus results from a combination of your genetics and your environment.
It appears that people with an inherited predisposition for lupus may develop the disease when they come into contact with something in the environment that can trigger lupus. The cause of lupus in most cases, however, is unknown. Some potential triggers include:
Sunlight. Exposure to the sun may bring on lupus skin lesions or trigger an internal response in susceptible people.
Infections. Having an infection can initiate lupus or cause a relapse in some people.
Medications. Lupus can be triggered by certain types of blood pressure medications, anti-seizure medications and antibiotics. People who have drug-induced lupus usually get better when they stop taking the medication. Rarely, symptoms may persist even after the drug is stopped.
Factors that may increase your risk of lupus include:
Your sex. Lupus is more common in women.
Age. Although lupus affects people of all ages, it's most often diagnosed between the ages of 15 and 45.
Race. Lupus is more common in African-Americans, Hispanics and Asian-Americans.
Source: Mayo Clinic Foundation
Leukemia is a broad term for cancers of the blood cells. The type of leukemia depends on the type of blood cell that becomes cancer and whether it grows quickly or slowly. Leukemia occurs most often in adults older than 55, but it is also the most common cancer in children younger than 15. Explore the links on this page to learn more about the types of leukemia plus treatment, statistics, research, and clinical trials.
Scientists don't understand the exact causes of leukemia. It seems to develop from a combination of genetic and
How leukemia forms
In general, leukemia is thought to occur when some blood cells acquire mutations in their DNA — the instructions inside each cell that guide its action. There may be other changes in the cells that have yet to be fully understood that could contribute to leukemia.
Certain abnormalities cause the cell to grow and divide more rapidly and to continue living when normal cells would die. Over time, these abnormal cells can crowd out healthy blood cells in the bone marrow, leading to fewer healthy white blood cells, red blood cells and platelets, causing the signs and symptoms of leukemia.