Fanconi anemia (FA) is a rare genetic disease caused by mutations or alterations in one of seven different genes. The disease is an autosomal recessive condition, meaning that the genes are not located on the sex chromosomes and a mutated gene copy must be inherited from both parents in order for a person to be affected. Test results of cells from FA patients suggest that the genetic defects of FA reduce the cell's ability to repair damaged deoxyribonucleic acid (DNA), the primary chemical component of chromosomes. Five of the seven genes associated with FA have been isolated.
With only approximately 1000 cases documented in the literature, FA is a rare disease with varied frequency in different ethnic groups. It is particularly prevalent in the Ashkenazi Jewish population, where carriers are 1 in 89 persons, compared to an overall carrier frequency of 1 in 100 to 600. A carrier is a person unaffected by the disease who has one mutated and one normal gene in their genome. Both parents must be carriers in order to produce a child with FA.
Causes and symptoms
FA is caused by inheriting two abnormal copies of one of seven different genes, all thought to be involved in DNA repair. About 67% of children with FA are born with some sort of congenital defect. The problems seen include:
- short stature
- abnormalities of the thumb or arm
- other skeletal abnormalities such as of the hip or ribs
- kidney malformations
- skin discoloration
- small eyes or head
- mental retardation
- low birth weight and failure to thrive
- abnormalities of the digestive system
- heart defects
The defining characteristic of FA is progressive pancytopenia, a gradual reduction of the cellular components of the blood. A reduction in red blood cells is typically noted first, then white blood cells, and finally, platelets. Complete bone marrow failure in FA patients is usually seen between the ages of three and twelve, with a median of seven.
Later in life, FA patients have delayed sexual maturity and an increased probability of developing cancer. For FA patients surviving into adulthood, 50% develop leukemia (a malignancy of the white blood cells) and/or myelodysplastic syndrome (MDS, a pre-leukemic state). Persons with FA also have an elevated chance of developing squamous cell cancers (originating in the outer layer of the skin), particularly gynecological cancers (for females); head, neck and throat cancers; gastrointestinal cancers; and liver cancers.
Diagnosis can be made upon the appearance of the characteristic congenital defects, but is more common upon development of aplastic anemia (when the bone marrow fails to produce normal numbers of blood cells).
FA is usually treated by pediatricians, hematologists, and, if a bone marrow transplant (BMT) is performed, a specialized teams of physicians, nurses, and medical assistants who are experienced in BMT.
Clinical staging, treatments, and prognosis
There is no clinical staging system for FA.
BMT and androgen therapy are two long-term non-experimental treatments for FA. BMT involves the suppression of the patient's own marrow and replacement with stem cells of the donor. The effectiveness of BMT is highly dependent on the existence of a donor that is closely matched to the patient. For sibling match (full match) transplants, the two-year survival rate is about 80%, compared to about 37% for less than a full match. The difference is due the prevalence of graft-versus-host disease (GVHD), where the recipient's body rejects the donor cells. The use of T-cell (a type of immune cell) depletion before transplantation and the drug fludarabine have significantly reduced the occurrence of GVHD. BMT does not alter the tendency of FA patients to develop other malignancies later in life, however.
Androgen therapy involves the administration of male hormones to stimulate the production of blood cells. Most FA patients respond for at least a time to this therapy. The cell increase lasts a few years at most, however, and the hormones have serious side effects, including masculinization of female patients and liver disease.
Growth factor therapy and gene therapy are two treatments being tested in clinical trials. Two growth factors—granulocyte/macrophage colony stimulating factor (GM-CSF) and granulocyte colony stimulating factor (G-CSF)—were shown to increase blood cell production. Patients with low neutrophil counts particularly benefit from this treatment.
A clinical trial for gene therapy of FA patients is ongoing. The normal copy of the mutated gene is introduced into the patient's own bone marrow stem cells using a viral vector. When the virus infects the stem cells, the normal FANC gene is integrated into the stem cell's DNA. This therapy will, theoretically, correct the defect in the stem cells and prevent their premature death, curing the aplastic anemia seen in FA patients. As with BMT, however, this gene therapy will not reduce the development of other cancers in FA patients.
The only known method of prevention of this disease is prenatal diagnosis and termination of pregnancies for affected embryos. Preimplantation genetic diagnosis, where one or two cells are tested from in vitro fertilized embryos, is also available. This method avoids the need for abortion, but carries more risk.
Because FA can be present without any outward symptoms, it is essential that any potential sibling donor for BMT be carefully tested for the disease using white blood cell exposure to DNA damaging agents or direct examination of their FANC gene copies before the transplant.
Frohnmeyer, Lynn, and Dave Frohnmeyer. Fanconi Anemia: A Handbook for Families and Their Physicians. Eugene, Oregon: Fanconi Anemia Research Fund, Inc., 2000.
de Winter, J.P., et al. "The Fanconi anemia protein FANCF forms a nuclear complex with FANCA, FANCC and FANCG." Human Molecular Genetics 9 (November 2000): 2665-74.
Garcia-Higuera, I., et al. "Interaction of the Fanconi anemia proteins and BRCA1 in a common pathway." Molecular Cell 7 (February 2001): 249-62.
Fanconi Anemia Research Fund, Inc. 1801 Willamette St., Suite 200, Eugene, OR 97401. (800) 828-4891. <www.fanconi.org>.
Online Mendelian Inheritance in Man (OMIM). John Hopkins University, Baltimore, MD. MIM Nos. 602956, 603467, 227645, 227646, 227650. April 2001. 25 June 2001 <http://www.ncbi.nlm.nih.gov/omim/>.
Michelle Johnson, M.S., J.D.
—A disease in which the bone marrow stops producing all three types of cells of the blood: red blood cells, white blood cells, and platelets.
—A drug that inhibits a blood cell's ability to produce DNA, eliminating native cells from FA patients so they can undergo BMT.
—A disease where the bone marrow stops producing healthy blood cells and the cells that are produced function poorly. This syndrome sometimes develops into leukemia.
—A type of white blood cells important in the defense of the body against infection.