BCKDHB rs28940875: Understanding Carrier Status
The rs28940875 variant in the BCKDHB gene is a genetic change associated with carrier status for maple syrup urine disease (MSUD) type 1B. It is primarily recognized for its presence within the Ashkenazi Jewish population.
What each genotype means
Typical risk profile
You have two copies of the standard allele and do not carry the c.827T>G (p.Arg276Gly) variant associated with maple syrup urine disease type 1B. Because this condition is inherited in an autosomal recessive manner, you are not considered a carrier for this specific founder variant. However, this test does not eliminate the possibility of rare, unexamined variants in this or related genes.
Carried by the vast majority of individuals across all major ancestry groups (greater than 99%).
Carrier status
You have one copy of the c.827T>G variant, making you an asymptomatic carrier of maple syrup urine disease type 1B. Carriers do not experience health complications because a single functioning allele provides adequate branched-chain alpha-keto acid dehydrogenase activity. If you are planning a family, reproductive counseling may be considered because having a biological child with this condition requires both parents to be carriers.
Identified in approximately 1 in 80 to 1 in 100 individuals of Ashkenazi Jewish heritage, but extremely rare in general global populations.
Maple syrup urine disease risk
You have two copies of the pathogenic c.827T>G alteration in the BCKDHB gene. In clinical literature, possessing two pathogenic copies typically causes maple syrup urine disease type 1B, a metabolic condition requiring strict dietary management of branched-chain amino acids. Clinical genetics evaluation and comprehensive confirmatory testing are recommended to evaluate diagnostic context and health implications.
Extremely rare across all populations, estimated at fewer than 1 in 30,000 to 1 in 40,000 individuals within Ashkenazi Jewish ancestry and virtually absent elsewhere.
What is the rs28940875 Variant?
The rs28940875 variant is a specific change in the DNA sequence of the BCKDHB gene, located on chromosome 6. In scientific literature, this variant is often identified by its protein-level change, p.Arg276Gly, which results from a nucleotide substitution of thymine (T) to guanine (G) at position 827 (c.827T>G). Genetic variants like this are essentially 'typos' in the genetic code that can alter the instructions for building proteins. Because humans carry two copies of every gene—one inherited from each parent—a person may have one copy with this variant and one typical copy, or two typical copies. This specific variant is categorized as a carrier variant, meaning that individuals who carry one copy of the altered gene typically do not exhibit the symptoms of the associated condition, as the other functional copy of the gene is usually sufficient to maintain normal biological processes.
The Role of the BCKDHB Gene
The BCKDHB gene provides instructions for making one part (the E1 beta subunit) of an enzyme complex called branched-chain alpha-ketoacid dehydrogenase (BCKD). This complex is essential for the body's ability to break down three specific amino acids: leucine, isoleucine, and valine. These amino acids are building blocks of proteins found in many foods. When the BCKD complex is functioning correctly, it processes these amino acids so they can be used for energy or other cellular functions. If the BCKDHB gene contains mutations that prevent the production of a functional E1 beta subunit, the BCKD complex cannot work properly. This leads to a dangerous buildup of these amino acids and their toxic byproducts in the body, which can cause severe neurological and physical health issues if left unmanaged. The gene is therefore critical for normal metabolic health.
Research and Clinical Associations
Research associates the BCKDHB gene with maple syrup urine disease (MSUD), a rare, autosomal recessive metabolic disorder. The name of the condition comes from the characteristic sweet, maple syrup-like odor of the urine in affected infants. While many different mutations in the BCKDHB gene can lead to MSUD, the evidence for specific variants like rs28940875 is often focused on their role as carrier markers in specific ancestral groups. Being a 'carrier' means an individual has one altered copy of the gene but does not have the disease. However, if two carriers have a child together, there is a statistical possibility that the child could inherit the altered copy from both parents, resulting in MSUD. The evidence strength for this specific variant as a primary driver of disease is considered limited compared to other well-documented pathogenic mutations, and it is primarily studied in the context of carrier screening programs.
Population Frequency and Ancestry
Genetic variants are not distributed equally across all human populations. The rs28940875 variant is notably observed in the Ashkenazi Jewish population. Studies have indicated that the carrier frequency for certain BCKDHB mutations in this group is approximately 1 in 80 to 1 in 100. This higher frequency is often attributed to a 'founder effect,' where a specific genetic variant becomes more common in a population due to the limited number of ancestors who carried the trait. Because this variant is more prevalent in individuals of Ashkenazi Jewish descent, it is frequently included in carrier screening panels designed for this community. It is important to note that population frequencies are statistical estimates and do not predict the health status of any single individual. Genetic testing is the only way to determine an individual's specific carrier status.
Managing Genetic Information
Understanding your carrier status for a variant like rs28940875 is a personal health decision. If you have received results indicating you are a carrier, it does not mean you have maple syrup urine disease, nor does it mean you will develop it. Carrier status is primarily relevant for family planning, as it provides information about the potential risk of passing a genetic condition to future children. If you are concerned about your results or your family history, the most appropriate step is to consult with a certified genetic counselor or a medical professional. They can help interpret what these findings mean in the context of your specific health history and provide guidance on reproductive options. You should never use genetic information to make medical decisions, such as changing your diet or starting supplements, without direct supervision from a qualified healthcare provider.
How common is this variant?
The rs28940875 variant is most commonly observed in the Ashkenazi Jewish population, with a carrier frequency estimated between 1 in 80 and 1 in 100.
Frequently asked questions
What is maple syrup urine disease?
Maple syrup urine disease is a rare, inherited metabolic disorder where the body cannot properly break down certain amino acids. This leads to a buildup of toxic substances that can cause serious health problems, including neurological damage, if not treated early.
Does being a carrier mean I have the disease?
No, being a carrier means you have one copy of the altered gene but do not have the disease yourself. Carriers are typically healthy and do not show symptoms of the condition.
What should I do if I am a carrier?
If you are a carrier, you may want to speak with a genetic counselor to understand the implications for your family planning. They can explain the risks and discuss options for testing your partner or future children.
Is this variant found in all populations?
This specific variant is most frequently associated with the Ashkenazi Jewish population. It is less common or rare in other ancestral groups.
Can I change my diet to fix this variant?
No, genetic variants cannot be changed by diet. If you have concerns about your metabolic health or carrier status, please consult a physician or a registered dietitian who specializes in metabolic disorders.
Sources & further reading
Educational information only, last refreshed 10/18/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Pathogenic missense mutation (p.Arg183Pro) in BCKDHB causing maple syrup urine disease type 1B.
Pathogenic BCKDHB missense variant (p.Arg183Pro) causative of Maple Syrup Urine Disease (MSUD) type 1B, common in expanded carrier panels.
A missense variant (c.548A>G, p.Asn183Ser) in BCKDHB causing classic Maple Syrup Urine Disease (MSUD) type 1B in homozygotes and defining Ashkenazi Jewish carrier status.
This variant in the BCKDHB gene is linked to Maple Syrup Urine Disease and is documented in clinical variant databases.