Rare Diseases and African Americans
The National Institutes of Health Office of Rare Diseases defines a rare disease as one affecting less than 200,000 people in the United States.1 That may seem like a small number but consider that there are more than 7,000 known rare diseases which affect about 25-30 million people.1 That is roughly nine percent of the U.S. population.2
Some rare conditions—especially more well known ones like sickle cell anemia, sarcoidosis, and lupus, as well as lesser known diseases like thalassemia and hereditary ATTR (hATTR) amyloidosis—occur at a higher frequency in African Americans than they do in other populations.3,4,5
Why are some rare conditions more common in particular ethnic groups? Some genetic disorders, such as sickle cell anemia, thalassemia, and hATTR amyloidosis, are more likely to occur among people who trace their ancestry to a particular geographic area.3,4,5 People in an ethnic group often share certain versions of their genes, which have been passed down from common ancestors. If one of these shared genes contains a disease-causing mutation, a particular genetic disorder may be seen more frequently in the group.6
In diseases like lupus, which can occur across populations, there are significant disparities in risk of disease development, severity of symptoms, and mortality. In fact, racial and ethnic minorities are likely to face greater barriers to screening, diagnosis, and treatment of rare diseases due to a variety of cultural, socioeconomic, and environmental factors.3
Sickle cell anemia, the most common blood disorder in the U.S. among African Americans, is an inherited form of anemia—a condition in which there aren’t enough healthy red blood cells to carry adequate oxygen throughout the body.7 Normally, red blood cells are flexible and round, moving easily through blood vessels. In sickle cell anemia, red blood cells become rigid, sticky and sickle shaped. These irregularly shaped cells can get stuck in small blood vessels, which slows blood flow and oxygen to parts of the body. Symptoms of sickle cell anemia can include anemia, episodes of pain, repeated infections, swelling of hands and feet, and vision problems. Complications of the disorder include stroke, organ damage, and blindness. The sickle cell gene is passed from generation to generation in a pattern of inheritance called autosomal recessive inheritance, which means both the mother and the father must pass on the defective form of the gene for a child to be affected.7
Thalassemia is a blood disorder caused by mutations in the DNA of cells that make hemoglobin (the substance in red blood cells that carries oxygen throughout the body).5 These mutations disrupt normal production of healthy red blood cells, causing a number of symptoms including fatigue, weakness, pale or yellowish skin, and facial bone deformities. Complications of thalassemia can include iron overload, infections, and heart problems such as congestive heart failure and arrhythmias. The type of thalassemia depends on the number of gene mutations inherited from parents and which part of the hemoglobin molecule is affected by the mutations. The more number of mutated genes, the more severe the thalassemia.5
Sarcoidosis is the growth of tiny collections of inflammatory cells, called granulomas, in different parts of your body, most commonly the lungs, lymph nodes, and may also impact the eyes and skin.8 Experts don’t know exactly what causes sarcoidosis, but many believe some people have a genetic predisposition to develop the disease that is triggered by bacteria, chemicals, dust or viruses. Though anyone can be diagnosed with sarcoidosis, African Americans have a higher incidence of it than people of other races. For most people, sarcoidosis goes away on its own without causing lasting consequences. In some folks, however, it can cause long-lasting problems, including breathing difficulties, kidney failure, eye inflammation and abnormal heart rhythms. A family history of sarcoidosis increases the likelihood of developing the disease.8
Lupus is an autoimmune disease that occurs when the body’s immune system attacks its own tissues and organs.9 Inflammation caused by lupus can affect many different body systems— including joints, skin, kidneys, blood cells, brain, heart, and lungs. It’s a difficult disease to diagnose, largely because its symptoms often mimic those of other ailments. The most common signs of lupus are fatigue, fever, joint pain or stiffness, a butterfly-shaped rash on the face covering the cheeks and bridge of the nose, skin lesions that may get worse when exposed to the sun, fingers and toes that turn white or blue when exposed to cold, shortness of breath, chest pain, dry eyes, headaches, confusion, and memory loss. Though most people with lupus have mild cases characterized by episodes—called flares—when signs and symptoms worsen and then improve or disappear for a while, the inflammation that is a hallmark of the disease can lead to more serious complications such as kidney failure, stroke, cardiovascular disease, and even death. Lupus likely results from a combination of genetics and environment.9
Hereditary ATTR (hATTR) amyloidosis is caused by a mutation or change in the TTR gene. This gene change affects the function of a protein called transthyretin (TTR). But when there is a genetic mutation of the TTR gene, it can lead to changes that cause the TTR protein to take on an abnormal shape.10 This abnormality causes the protein to clump together and deposit in the nervous, cardiac, or digestive systems, leading to serious symptoms of the disease such as numbness and tingling in the hands and feet, symptoms of heart failure, and problems with digestion.11 African Americans are one population that is at an increased risk of carrying a genetic mutation associated with disease. It is estimated that about 4% of African Americans may have a common type of mutation in the TTR gene, called the Val122Ile mutation.5 hATTR amyloidosis is passed from parent to child in an autosomal dominant fashion. Everyone gets two copies of the TTR gene, one inherited from each parent. When one parent carries an autosomal dominant mutation, each child has a 50 percent chance of inheriting that mutation. However, inheriting the TTR gene with a mutation does not necessarily mean that he or she will develop hATTR amyloidosis.12
During Black History Month, Black Health Matters, in partnership with Alnylam Pharmaceuticals, will focus on hATTR amyloidosis in its “Understanding hATTR Amyloidosis” series. For more information and resources about hATTR amyloidosis, visit Alnylam’s hATTRbridge.com.
3 National Institute of Health. “Annual Report on the Rare Diseases and Conditions Research Activities of the National Institutes of Health FY 2000 – National Center on Minority Health and Health Disparities (NCMHD) – Office of Rare Diseases.” Genetic and Rare Diseases Information Center, U.S. Department of Health and Human Services, 27 Jan. 2005, https://rarediseases.info.nih.gov/asp/html/reports/fy2000/ncmhd.html. Accessed February 2020.
4 Ando et al. Orphanet J Rare Dis. 2013;8:31.
5 Mayo Clinic Staff. “Thalassemia.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 22 Nov. 2019, www.mayoclinic.org/diseases-conditions/thalassemia/symptoms-causes/syc-20354995. Accessed February 2020.
6 National Institutes of Health. “Why are some genetic conditions more common in particular ethnic groups?” U.S. National Library of Medicine. 11 Feb 2020, https://ghr.nlm.nih.gov/primer/inheritance/ethnicgroup. Accessed February 2020.
7 Mayo Clinic Staff. “Sickle Cell Anemia.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 30 Jan. 2020, www.mayoclinic.org/diseases-conditions/sickle-cell-anemia/symptoms-causes/syc-20355876. Accessed February 2020.
8 American Lung Association. “Learn About Sarcoidosis” American Lunch Association. 2 Oct 2019, www.lung.org/lung-health-and-diseases/lung-disease-lookup/sarcoidosis/learn-about-sarcoidosis.html. Accessed February 2020.
10 Adams D, Coelho T, Obici L, et al. Neurology. 2015;85(8):675-682.
11 Shin et al. Mt Sinai J Med. 2012;79(6):733-748.
12 National Institutes of Health: Department of Health and Human Services. Genetics Home Reference. Transthyretin amyloidosis. 11 Feb 2020, https://ghr.nlm.nih.gov/condition/transthyretin-amyloidosis. Accessed February 2020.