Pathogenic variants (disease-causing) in the BLM gene may increase the risk for colon cancer, but additional data is needed to confirm this.
Pathogenic variants in BLM exhibit autosomal dominant inheritance. This means there is a 50% chance the condition can be passed from generation-to-generation. First degree relatives (parents, siblings, children) have a 50% chance to have the same pathogenic variant whereas second degree relatives (grandparents, aunts/uncles, nieces/nephews, half-siblings) have a 25% chance. More distant relatives have lower chances of having the same pathogenic variant when one is identified in the family.
In addition, when an individual inherits pathogenic variants in both copies of the BLM gene, it can cause a rare childhood-onset condition called Bloom syndrome. Bloom syndrome is condition characterized by short stature, sun-sensitive skin changes, immune deficiency (problems with the immune system), and a markedly increased risk of many types of cancer, including leukemias, lymphomas, and gastrointestinal cancers. Individuals with Bloom syndrome often develop cancer at younger ages than the general population. Bloom syndrome exhibits autosomal recessive inheritance. This means that both parents must be have a single pathogenic variant in the BLM gene to have a 25% chance to have a child with the condition. Approximately 1 in 100 Ashkenazi Jewish individuals are carriers for Bloom syndrome.
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Written December 2025
