Notes on Bloom's Syndrome
Rahul's Noteblog
Notes on Genetics
Notes on Bloom's Syndrome
Principles
• Inbreeding
• Genetic drift
• Ethnic variation in allelic frequencies
• Population screening
Major Phenotypic Features
Age of onset: Infancy through adulthood
Reddish skin on face, aggravated by sunlight
Respiratory tract and ear infections
High pitched voice
There may be mental retardation
History
Originally discovered by dermatologist Dr. David Bloom in 1954, Bloom's syndrome is an autosomal disorder caused by a mutation on chromosome 15. Therefore, the disease is present since infancy and leads into adulthood. This disease is relatively common among Ashkenazi Jews where at least 1 in 110 persons would be a career. Symptoms are not visible in careers. Currently, however, the disease has been seen in other ethnic groups like American Indians, Ethiopian, Turkish and others.
Molecular Basis
According to laboratory tests, the defective gene has been located on chromosome 15. There may be abnormal chromosomal reorganization and breakage.
Phenotype(s)
Affected individuals are overly short (about 5 feet tall) but may mature normally. They may have a prominent nose and a narrow face. Facial skin is reddish in color and may get worse in sunlight. There is noticeable butterfly rash on face, especially on the nose-bridge, cheeks, lower lips and lower eyelids. This skin problem may be worse in some individuals compared to others. Individuals are more prone to ear and respiratory infections, cancer and leukemia, and diabetes. There may be infertility problems in both the affected sexes. Death may occur sometime after age 27.
Pathogenesis
Patients with Bloom's syndrome have abnormal sister chromatid exchanges. Various theories have been put forward. One states that there may be a defect in DNA Ligase I that causes metabolic defects in Bloom's syndrome, particularly, heat sensitivity, cancer and other phenotypes. If this theory is true, some suggested that there should also be a mutation on chromosome 19. It has also been suggested that Bloom's syndromes also involves the over production of superoxide radical anion, and this causes inefficient removal of peroxide from Bloom's syndrome cells accounting for the defects.
Inheritance Risk/Disease Management
Bloom's syndrome is an automomal recessive disorder, that is, if both parents are careers, they have a 1 in 4 chance of having a child with the disease. There is no treatment for the disease. It is best advised o follow-up regularly with physicians and have medical tests in order to detect early signs of cancer and/or other disease during its treatable phases.
References
Bloom's Syndrome article at mazornet.com
Article at About.com
Bloom's Syndrome article at NIH.gov
Additional Readings:
Basic Genetics
1. Single-Gene Disorders
2. Population Genetics
3. Genetic Disease Transmission Probability
4. What is Cytogenetics?
5. Notes on Bloom's Syndrome
6. Introduction to Human Chromosomes
7. Life Cycle of Somatic Cells
Related Topics
1. Genetic and Developmental Disorders
2. Genetic Code, Mutations, and Translation
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