UNDERSTANDING GENETIC DISEASES

Impact of Genetic Diseases

Here, you’ll learn about different types of genetic diseases that impact people around the world, and some treatments available today. Research in gene therapy aims to add potential new treatment options.

How common are genetic diseases?
There are an estimated 10,000 different types of single-gene diseases (also called monogenic diseases), which are diseases caused by mutations in a single gene. The World Health Organization estimates that 10 people out of every 1000 are affected.1 This means that between 70 million and 80 million people in the world are living with one of these diseases.

There are an estimated 10,000 different types of Single-gene diseasesalso called monogenic diseases, in which a change occurs in one gene only

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(also called monogenic diseases), which are diseases caused by mutations in a single gene. The World Health Organization estimates that 10 people out of every 1000 are affected.1 This means that between 70 million and 80 million people in the world are living with one of these diseases.1,2

For as many people that are affected, individual single-gene diseases are considered rare. Below are examples of single-gene diseases and their rates of occurrence.
EXAMPLES OF SINGLE-GENE DISEASES AND RATES OF OCCURRENCE
Single-gene diseases Rate of occurrence
Achondroplasia is a bone growth disorder that causes short-limbed dwarfism in which there is a problem converting cartilage into bone3
1 in 15,000 to 40,000 births
Beta-thalassemia is a blood disorder that reduces production of hemoglobin and causes anemia, bone, and organ damage4
Most prevalent in people from, or with ancestors from, Mediterranean countries, North Africa, Middle East, India, Central Asia, and Southeast Asia
Cystic fibrosis is an inherited disease characterized by a buildup of thick, sticky mucus that causes respiratory and digestive problems5
1 in 2500 to 3500 White Americans
1 in 17,000 African Americans 
1 in 31,000 Asian Americans
Fragile X syndrome is a condition that causes a range of developmental problems including cognitive impairment and learning disabilities6
1 in 4000 males
1 in 8000 females
Huntington’s disease is a progressive brain disorder that causes uncontrolled movements, emotional problems, and loss of cognitive ability7
3 to 7 per 100,000 people of European descent

Less common in people of Japanese, Chinese, and African descent
Sickle cell disease (SCD) is a progressive genetic disease caused by abnormal sickle hemoglobin characterized by anemia, blood vessel disease, and blocked blood vessels that lead to acute symptoms and chronic damage8
Affects over 100,000 people in the US
  • 1 in 500 African Americans
  • 1 in 1000 to 1400 Hispanic Americans
Most common in people with ancestors from Africa, Mediterranean countries, Saudi Arabia, India, and Spanish-speaking regions of South America and the Caribbean

Treatment options for genetic diseases

Maintenance Therapy

hemophilia
Relieving symptoms is one of the ways that treating a genetic disease can potentially improve patient outcomes.12 For example, people with Hemophiliaan inherited disease where blood does not clot properly

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 may need a treatment that replaces the clotting factor that their bodies fail to produce.13

Solid organ transplant

For genetic diseases that only affect one organ in the body, solid organ transplantation may be an option. Removing a diseased organ and replacing it with a donor organ can prevent disease complication and improve life expectancy. Solid organ transplant, as a potential curative option, can occur in the following diseases:

  • Metabolic liver disease
  • Polycystic kidney disease
  • Congenital heart disease
When considering treatment options like solid organ transplantation, people should discuss their specific situation and the risks and benefits with their doctor.14,15

Bone marrow transplant (BMT) stem cell transplant hematopoietic stem cell transplant (HSCT) Allogeneic BMT Autologous BMT

About 50 years ago, another approach for treating certain genetic diseases became available: the Bone marrow transplant (BMT)the process of infusing blood stem cells from another person (a donor) in a person who has a genetic disease or whose bone marrow or immune system is compromised to help correct or restore normal cell function

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, also called stem cell transplant or hematopoietic stem cell transplant (HSCT).16

BMTs for genetic diseases treat the disease at the gene level. In some cases, the goal of BMT is to treat genetic diseases or cancer. Healthy Blood (or hematopoietic) stem cellscells found in the bone marrow and circulating blood that can help develop different types of blood cells, such as red blood cells, white blood cells, and platelets

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, which have a functional gene, are introduced, or transplanted, into a person with a genetic disorder. This is intended to allow the missing, defective, or overproduced protein to be made, or made in amounts that have a therapeutic effect on the person.17-19

Stem cells are transplanted into a patient because they have the ability to form many other types of cells in the body.19,20 Blood stem cells are found in the bone marrow and circulating blood. As they grow (mature), they can eventually become many blood cells, including21:

Example of bone marrow transplant for genetic diseases

There are two types of BMT:

  • Allogenic hematopoietic stem cell transplant (allogenic HSCT or allo HSCT)a transplant in which the person receives blood stem cells or bone marrow cells from another person (a donor)

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    for genetic diseases uses cells from another person, or a Donorin a hematopoietic stem cell transplant, the person who donates their blood stem cells

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    , who does not have the disease. The donor’s healthy cells have a functional gene that is transplanted into the person’s body.17 In allogeneic BMTs, the donor and patient cells should be as close to a match as possible. If they aren’t, there is a chance that the person’s immune system will recognize the donor cells as foreign and reject them, causing Graft rejectionwhen donated bone marrow is infused and then rejected by the person receiving the donation

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    . The opposite can also happen, in which the donor cells attack the host; this is called Graft-versus-host diseasean adverse reaction to a bone marrow transplant in which the body attacks its own cells

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    (GVHD). Donor stem cells that most closely resemble the person being treated may be found among siblings. However, matches may also be found among the general population.17,22,23 Allogeneic BMT may have limited feasibility as a treatment due to a person’s age, overall health, and donor match availability.24,25

  • Autologous hematopoietic stem cell transplant (autologous HSCT or auto HSCT)a transplant in which the patient receives their own blood stem cells or bone marrow that was previously collected

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    is a similar treatment to allogeneic BMT but uses a person’s own cells for the transplant, so no donor is required. Because the stem cells come from the person, there is a lesser chance that their own immune system will reject them (or vice versa).17,18

While BMTs have the potential to treat disease at the genetic level, they also come with serious risks. These include stem cell (graft) failure or complications, organ damage, infection, cataracts, infertility, cancers, and death.26

When considering treatment options like BMT, people should discuss their specific situation and the risks and benefits with their doctor.

Gene therapy

Another potential treatment option, thanks to continuous technological refinements and advancements over the past 30 years, is gene therapy—which is what genehome is all about.25 Gene therapy is an investigational therapeutic approach that shows potential for many genetic diseases. As you explore, you will have the opportunity to learn much more about the many aspects of gene therapy throughout genehome.

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References

1. World Health Organization. Genes and human diseases. Accessed March 4, 2020. https://www.who.int/genomics/public/geneticdiseases/en/index2.html. 2. Worldometer. Current world population. Accessed March 4, 2020. https://www.worldometers.info/world-population/ 3. National Institutes of Health. Genetics Home Reference. Achondroplasia. Accessed March 4, 2020. https://ghr.nlm.nih.gov/condition/achondroplasia#statistics 4. National Institutes of Health. Genetics Home Reference. Beta thalassemia. Accessed 5. National Institutes of Health. Genetics Home Reference. Cystic fibrosis. Accessed March 4, 2020. https://ghr.nlm.nih.gov/condition/cystic-fibrosis#statistics 6. National Institutes of Health. Genetics Home Reference. Fragile-x-syndrome. Accessed March 4, 2020. https://ghr.nlm.nih.gov/condition/fragile-x-syndrome#statistics 7. National Institutes of Health. Genetics Home Reference. Huntington disease. Accessed March 4, 2020. https://ghr.nlm.nih.gov/condition/huntington-disease#statistics 8. National Institutes of Health. Genetics Home Reference. Sickle cell disease.  Accessed March 4, 2020. https://ghr.nlm.nih.gov/condition/sickle-cell-disease#statistics 9. National Institutes of Health. Genetics Home Reference. Down syndrome. Accessed March 4, 2020. https://ghr.nlm.nih.gov/condition/down-syndrome#statistics 10. National Institutes of Health. Genetics Home Reference. Turner syndrome. Accessed March 4, 2020. https://ghr.nlm.nih.gov/condition/turner-syndrome#statistics 11. Wray NR, Maier R. Genetic basis of complex genetic disease: the contribution of disease heterogeneity to missing heritability. Curr Epidemiol Rep. 2014;1:220–227. 12. National Institutes of Health. Genetics Home Reference. Help me understand genetics. Accessed March 4, 2020. https://ghr.nlm.nih.gov/primer 13. Centers for Disease Control and Prevention. What is hemophilia? Accessed March 16,2020.  https://www.cdc.gov/ncbddd/hemophilia/facts.html 14. Kim JS, Kim KM, Oh SH, et al. Liver transplantation for metabolic liver disease: experience at a living donor dominant liver transplantation center. Pediatr Gastroenterol Hepatol Nutr. 2015;18(1):48-54. 15. Moscalu R, Smith AM, Sharma HL. Diseases that can be cured only by organ donations. Arch Clin Cases. 2015 2(4):182-197. 16. Moore T. Medscape. Bone marrow transplantation. Accessed March 4, 2020. https://emedicine.medscape.com/article/1014514-overview 17. Johns Hopkins Medicine. Bone marrow transplantation. Accessed March 4, 2020. https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/bone-marrow-transplantation 18. Aiuti A, Scala S, Chabannon C. Biological properties of HSC: scientific basis for HSCT. In: Carreras E, Dufour C, Mohty M, Kroger N, eds. The EBMT Handbook: Hematopoietic Stem Cell Transplantation and Cellular Therapies [Internet]. 7th edition. Cham (CH): Springer; 2019. Accessed March 4, 2020. https://www.ncbi.nlm.nih.gov/books/NBK553952/ 19. Naldini L. Genetic engineering of hematopoiesis: current stage of clinical translation and future perspectives. EMBO Mol Med. 2019;11(3):e9958. 20. Morgan RA, Gray D, Lomova A, Kohn D. Hematopoietic stem cell gene therapy: progress and lessons learned. Cell Stem Cell. 2017;21(5):574-590. 21. National Institutes of Health. National Cancer Institute. Blood-forming stem cell transplants. Accessed March 4, 2020. https://www.cancer.gov/about-cancer/treatment/types/stem-cell-transplant/stem-cell-fact-sheet#what-are-bone-marrow-and-hematopoietic-stem-cells 22. Mattsson J, Ringdén O, Storb R. Graft failure after hematopoietic cell transplantation. Biol Blood Marrow Transplant. 2008;14(suppl 1):165-170. 23. American Cancer Society. Types of stem cell transplants for cancer treatment. Accessed March 16, 2020. https://www.cancer.org/treatment/treatments-and-side-effects/treatment-types/stem-cell-transplant/types-of-transplants.html 24. Be the Match. Donating bone marrow donation frequently asked questions. Accessed March 16, 2020. https://bethematch.org/support-the-cause/donate-bone-marrow/donation-faqs/ 25. Be the Match. Bone marrow donation medical guidelines. Accessed March 16, 2020. https://bethematch.org/support-the-cause/donate-bone-marrow/possible-match/medical-guidelines-when-you-match-a-patient/ 26. Mayo Clinic. Bone marrow transplant. Accessed March 4, 2020. https://www.mayoclinic.org/tests-procedures/bone-marrow-transplant/about/pac-20384854

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