> Bloom Syndrome

• Symptoms & Characteristics
• Treatment
• How Common Is It?
• Genetics & Inheritance
• Genetic Testing
• Support & More Information
• Alternative Names

Last Reviewed May 28, 2009

Symptoms & Characteristics

Bloom syndrome is a genetic condition that causes abnormalities such as breaks and rearrangements in an affected person's chromosomes. Common characteristics and symptoms may include:

• small stature

• high-pitched voice

• distinct facial features (such as a long, narrow face; small lower jaw; and prominent ears and nose)

• reddening of skin in response to sun exposure - especially on the face (in the form of a butterfly-shaped rash), arms and hands

• learning problems

• mental retardation

• diabetes

• chronic lung problems

• compromised immune system - may lead to recurrent pneumonia and ear infections

• fertility problems (males are infertile; females experience early menopause)

Chromosome instability in Bloom syndrome results in a high risk of cancer in affected people. People with Bloom syndrome develop the full range of cancers found in the general population, but the cancers arise unusually early in life. Affected individuals may be first diagnosed with cancer at about 25 years old.

Treatment

There is no cure for Bloom syndrome. Early diagnosis, routine surveillance and treatment may help to manage some of the symptoms and sometimes prevent related problems. Lifespan may be shortened by cancer.

How Common Is It?

Bloom syndrome is generally considered rare.

• Bloom syndrome is more common in people of Ashkenazi (central and eastern European) Jewish ancestry, as about 1 in 48,000 people are affected. Overall, about 1/4 of all people with Bloom syndrome are of Ashkenazi Jewish descent.

Genetics & Inheritance

Bloom syndrome is caused by mutations in a gene called BLM on the chromosome 15 at the location q26.1.

• The BLM gene provides instructions for producing a protein called the Bloom (BLM) syndrome protein. When a cell prepares to divide to form two cells, the chromosomes are duplicated (replicated) so that each new cell will get a complete set of chromosomes. The replication process involves unwinding the DNA so that it can be copied. The BLM protein is important in maintaining the stability of the DNA during this process.

• Mutations in the BLM gene can cause errors in this copying process during replication. As a result, people with Bloom syndrome have a higher frequency of chromosome breakage and rearrangement than unaffected people. This increase in chromosome breakage and rearrangement leads to the signs and symptoms of Bloom syndrome.

We all have two copies of the BLM gene - one from each parent. In Bloom syndrome, it is necessary to have two mutations, one in each gene copy, to be affected. This is called autosomal recessive inheritance.

• Both parents of an affected person are always both obligate carriers (each have only one mutation). Two carriers have a 25% chance with each pregnancy to have an affected child, but do not have symptoms themselves.

• Without a family history, the chance to be a carrier is determined by a person's ethnic background. For example, 1 in 100 people of Ashkenazi Jewish ancestry are carriers of Bloom syndrome.

There are other genetic conditions that have characteristics that overlap with Bloom syndrome. Some of these conditions include Fanconi Anemia, Russell-Silver syndrome, and Cockayne syndrome.

A genetic consultation with a trained genetic professional is important for a complete evaluation, accurate diagnosis, as well as discussion of the benefits and limitations of testing and recurrence risk.

Genetic Testing

Clinical genetic testing for Bloom syndrome can be broken down into two categories: diagnostic testing and carrier testing.

• Diagnostic testing may be used to confirm or rule out a diagnosis in a person suspected to have the disorder. Alternatively, special testing called sister chromatid exchange (SCE) testing may also be used confirm or rule out a diagnosis. SCE testing looks for an abnormally high number of exchanges of genetic material between identical chromosome arms (called sister chromatids) during cell replication when exposed to a chemical agent. SCE testing cannot identify DNA mutations.

• Carrier testing is typically offered after a clinical diagnosis and/or mutations have already been identified in an affected family member(s). Carrier testing is also available for people of high risk ethnic groups.

Carrier testing for the Ashkenazi-specific mutation that causes Bloom syndrome is available online (over the internet). This testing is available individually or as part of an Ashkenazi Jewish panel. Go to the Tests tab to link to the best providers, compare providers and read provider reviews.

Diagnostic testing and carrier testing for people who are not of Ashkenazi Jewish ancestry is available through an in person genetic consultation for people who are considered at risk. Use our find a genetic professional directory to locate a trained genetic professional in your area.

• A medical geneticist can also be found at the American College of Medical Genetics website.

• A genetic counselor can also be found at the National Society of Genetic Counselors website.

Support & More Information

More information can be found at:

• Genetics Home Reference

Support can be found at:

• MAGIC Foundation for Children's Growth

Alternative Names

• Bloom-Torre-Machacek Syndrome