BLM gene

BLM gene

The BLM gene encodes a protein that is involved in stabilizing DNA during replication. When this protein is absent or non-functional, it can lead to chromosomal breaks and rearrangements which contribute to the development cancer, immunodeficiency, and other symptoms.

The BLM gene has typically been associated with Bloom syndrome when inherited from both parents. However, there is limited evidence showing if individuals who carry only one mutation in the BLM gene are actually at an increased risk for any cancers.

Bloom syndrome

Each person has two copies of the BLM gene, one inherited from each parent. The BLM gene is most well known for the condition caused by having mutations in both copies of the BLM gene: Bloom Syndrome. People with Bloom Syndrome tend to have short stature, have prominent facial features such as nose and ears, sensitivity to the sun, infertility, and an increased risk of cancers. While individuals with a single pathogenic BLM variant do not have Bloom syndrome, there is evidence they may have an increased risk of colon cancer.

Bloom syndrome is inherited in an autosomal recessive manner.  Therefore, to have bloom syndrome a defective copy of the BLM gene must be received from both the mother and the father.  However, those who are heterozygous for the BLM gene, meaning they have only one defected copy and are carriers for the disease, are thought to have an increased risk for colorectal cancer.  It is recommended that these individuals  should speak with their doctors about having more frequent colonoscopies.

The BLM gene is very important in making a protein that plays a crucial role in DNA replication. When there is a mutation in the BLM gene, the protein is unable to function properly.  This results in a much higher rate of mistakes in DNA replication, causing an increased amount of mutations that prevent cells from being able to function normally.   Sometimes, these abnormalities allow cells to divide in an unconstrained way, leading to cancer.

Screening for individuals with only one BLM mutation:

Because of the unclear risk of colon cancer associated with being BLM carrier, follow general population guidelines, unless more screening is indicated based on personal and family history.

Because of the unclear risk of breast cancer associated with being BLM carrier, follow general population guidelines, unless more screening is indicated based on personal and family history.

Resources

https://ghr.nlm.nih.gov/condition/bloom-syndrome#inheritance

https://www.nccn.org/professionals/physician_gls/pdf/genetics_colon.pdf