This test analyzes the BLM gene, associated with Bloom syndrome. This rare, inherited condition is characterized by short stature, a skin rash that develops after sun exposure, infertility, and an increased risk of malignancy.
Genetic testing of this gene may confirm a diagnosis and help guide treatment and management decisions. Identification of a disease-causing variant would also guide testing and diagnosis of at-risk relatives. This test is specifically designed for heritable germline mutations and is not appropriate for the detection of somatic mutations in tumor tissue.
Bloom syndrome (BLM)
Bloom syndrome is a rare, inherited condition characterized by short stature, a skin rash that develops after sun exposure, infertility, and an increased risk of malignancy.
Affected individuals typically present with severe pre- and postnatal growth deficiency and sparse subcutaneous fat throughout infancy and childhood. Most are less than the 97th percentile, when compared to the general population for both height and weight, and are rarely taller than five feet as adults. Other characteristic features include a high-pitched voice, learning disabilities, and distinctive facial features, such as a long and narrow face, retrognathia, and prominent nose and ears. Those affected with Bloom syndrome also have an increased risk of diabetes, chronic obstructive pulmonary disease (COPD), gastroesophageal reflux, and mild immune system dysfunction. Adult males with Bloom syndrome are infertile due to lack of sperm production; adult women have reduced fertility and experience menopause unusually early.
Upon sun exposure, those with Bloom syndrome develop a red rash over the nose and cheeks in a butterfly-shaped pattern. A skin rash can also appear on other areas typically exposed to the sun, such as the back of the hands and the forearms. Telangiectases often appear within the rash and can also occur in the eyes. Other skin features include hypopigmentation or hyperpigmentation on areas of skin protected from sun exposure.
Bloom syndrome is associated with an increased risk of cancer. Cancer types are diverse and include, but are not limited to, various carcinomas, lymphomas, and leukemia. Cancers typically occur earlier in life compared to the general population, and more than one cancer type may develop in the same individual.
Due to the rarity of Bloom syndrome, the specific lifetime risk of developing BLM-related tumors is unknown. See the table below for the incidence of various malignancies among 205 affected individuals, as collected from the Bloom’s Syndrome Registry from 1954 to 2012.
|Cancer type||Age range at diagnosis (years)||Number||Percent|
|Lower enteric tract||16-49||30||14.6%|
|Upper entero/respiratory tract||25-48||22||10.7%|
|Genitalia and urinary tract||<1-43||17||8%|
|Lower respiratory tract||26-40||9||4.3%|
|Acute lymphoblastic leukemia||5-40||12||5.8%|
|Acute myelogenous leukemia||2-47||25||12.2%|
|Connective tissue (sarcoma)||4-30||4||2%|
|Central nervous system (brain)||3||1||0.5%|
|Primary site unidentified, metastatic||28-33||3||1.5%|
Analysis of the BLM gene identifies pathogenic variants in 90% of affected individuals.
Bloom syndrome is inherited in an autosomal recessive pattern.
Bloom syndrome is overall a rare condition; however, the carrier frequency among the Ashkenazi Jewish population in New York City and Israel is approximately 1%.
Analysis of the BLM gene may be considered in individuals with the following:
Invitae is a College of American Pathologists (CAP)-accredited and Clinical Laboratory Improvement Amendments (CLIA)-certified clinical diagnostic laboratory performing full-gene sequencing and deletion/duplication analysis using next-generation sequencing technology (NGS).
Our sequence analysis covers clinically important regions of each gene, including coding exons, +/- 10 base pairs of adjacent intronic sequence, and select noncoding variants. Our assay provides a Q30 quality-adjusted mean coverage depth of 350x (50x minimum, or supplemented with additional analysis). Variants classified as pathogenic or likely pathogenic are confirmed with orthogonal methods, except individual variants that have high quality scores and previously validated in at least ten unrelated samples.
Our analysis detects most intragenic deletions and duplications at single exon resolution. However, in rare situations, single-exon copy number events may not be analyzed due to inherent sequence properties or isolated reduction in data quality. If you are requesting the detection of a specific single-exon copy number variation, please contact Client Services before placing your order.
|Gene||Transcript reference||Sequencing analysis||Deletion/Duplication analysis|