BLM rs118203956: Understanding the blmAsh Carrier Variant
The variant rs118203956, often referred to as blmAsh, is a specific genetic alteration in the BLM gene. It is recognized as a pathogenic founder mutation associated with carrier status for Bloom syndrome, an autosomal recessive condition.
What each genotype means
Typical BLM gene profile
This genotype indicates that you do not carry the specific BLM gene mutation associated with Bloom syndrome. You do not have the increased risk of passing this specific condition to your children that is associated with this variant.
This is the most common genotype in all populations, including the Ashkenazi Jewish population.
Bloom syndrome carrier status
You carry one copy of the BLM gene mutation (c.2207_2212delinsTAGATTC, also known as blmAsh). As a carrier, you are generally healthy, but you have a 50% chance of passing this variant to each child; if your partner is also a carrier, there is a risk of having a child with Bloom syndrome.
Carried by approximately 1 in 111 individuals of Ashkenazi Jewish ancestry.
Bloom syndrome affected status
This genotype indicates the presence of two copies of the pathogenic BLM mutation. This is associated with Bloom syndrome, a condition characterized by genomic instability and increased cancer risk. Please consult with a medical geneticist or your healthcare provider to discuss clinical implications and management.
This genotype is extremely rare in the general population.
What is the rs118203956 Variant?
The variant rs118203956 is a complex genetic change involving the deletion of 6 nucleotides and the insertion of 7 nucleotides within the BLM gene. In scientific literature, this is frequently denoted as c.2207_2212delinsTAGATTC or simply as blmAsh. This specific mutation is located in exon 10 of the BLM gene. Because it causes a frameshift, it alters the reading frame of the genetic code, which typically leads to the production of a truncated, non-functional protein. This variant is well-documented in clinical genetics as a pathogenic mutation, meaning it is known to disrupt the normal function of the gene. It is primarily studied in the context of carrier screening, as individuals who inherit one copy of this variant are considered carriers of Bloom syndrome, while inheriting two copies is associated with the development of the condition itself.
The Role of the BLM Gene
The BLM gene provides the instructions for creating the Bloom syndrome protein, which belongs to a family of enzymes known as RecQ helicases. These proteins are often referred to as 'caretakers' of the genome because they play a critical role in maintaining genomic stability. Helicases function by unwinding DNA, a necessary step for DNA replication, repair, and recombination. When the BLM protein is absent or non-functional, cells struggle to repair DNA damage correctly, leading to increased chromosomal instability. This instability is a hallmark of Bloom syndrome, which is characterized by a significantly increased risk of early-onset cancers, growth deficiency, and immune system abnormalities. The protein's ability to ensure that DNA is copied and repaired accurately is essential for preventing the accumulation of mutations that can lead to malignancy.
Research and Clinical Significance
Research has firmly established rs118203956 as a founder mutation, meaning it is found at a higher frequency in specific populations due to historical demographic factors. It is the most common pathogenic variant identified in individuals of Ashkenazi Jewish descent who have Bloom syndrome. Clinical evidence from the Bloom Syndrome Registry and various genetic studies confirms that this variant is a primary cause of the condition in this population. While the evidence for its pathogenicity is strong, the clinical presentation of Bloom syndrome can vary. Carriers of a single copy of this variant are generally asymptomatic, though the long-term health implications for carriers, such as potential cancer risks, remain a subject of ongoing research. Because Bloom syndrome is an autosomal recessive disorder, it only manifests when an individual inherits two pathogenic variants—one from each parent.
Population Frequency
The frequency of the rs118203956 variant is notably higher in the Ashkenazi Jewish population compared to the general population. Studies have estimated the carrier frequency within this group to range from approximately 1 in 111 to 1 in 157, depending on the specific geographic cohort studied. While it is considered a founder mutation in Ashkenazi Jewish populations, it has also been identified in other groups, including Spanish-speaking families in the Americas. In the general population, the variant is extremely rare. Because of the increased carrier rate in Ashkenazi Jewish individuals, genetic counseling and carrier screening are often recommended for those of this ancestry who are planning a family, allowing them to understand their reproductive risks and options.
Managing Genetic Information
Understanding your status regarding the rs118203956 variant is primarily relevant for family planning and reproductive health. If you have received results indicating you are a carrier, it does not mean you have Bloom syndrome, but it does mean you have a 50% chance of passing the variant to your children. If both parents are carriers of a pathogenic BLM variant, there is a 25% chance for each pregnancy to result in a child with Bloom syndrome. This information should not be used for self-diagnosis or to make medical decisions without professional guidance. If you are concerned about your carrier status or family history, you should consult with a certified genetic counselor or a medical geneticist. They can provide context based on your specific results, discuss the implications for your family, and explain the available options for prenatal or preimplantation genetic testing.
How common is this variant?
The rs118203956 variant is a founder mutation in the Ashkenazi Jewish population with a carrier frequency estimated between 1:111 and 1:157, while remaining extremely rare in the general population.
Frequently asked questions
What is Bloom syndrome?
Bloom syndrome is a rare, inherited disorder characterized by short stature, a high-pitched voice, and a significantly increased risk of developing various types of cancer at an early age. It is caused by mutations in the BLM gene that lead to genomic instability.
Does being a carrier mean I will get sick?
No, being a carrier of a single copy of the rs118203956 variant typically does not cause symptoms of Bloom syndrome. Bloom syndrome is an autosomal recessive condition, meaning it generally only affects individuals who inherit two copies of a pathogenic variant.
Should I get tested for this variant?
Carrier screening is often recommended for individuals of Ashkenazi Jewish descent who are planning a family. You should discuss the benefits and limitations of genetic testing with a healthcare provider or a genetic counselor.
What should I do if I am a carrier?
If you are a carrier, it is recommended to speak with a genetic counselor to understand the implications for your reproductive health. They can help you understand the risks to future children and discuss options such as partner testing.
Sources & further reading
Educational information only, last refreshed 10/15/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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