SMPD1 rs121908297: What Your Genotype Means
The rs121908297 variant is a specific single-nucleotide deletion within the SMPD1 gene. It is recognized as a pathogenic variant associated with carrier status for Niemann-Pick disease types A and B.
What each genotype means
Typical SMPD1 genotype
This genotype represents the absence of the specific c.996delC deletion in the SMPD1 gene. Individuals with this result do not carry this specific genetic change associated with Niemann-Pick disease type A or B.
This is the most common genotype observed in all global populations.
Carrier status for Niemann-Pick
This genotype indicates you carry one copy of the c.996delC deletion (also known as p.Phe333LeufsTer52) in the SMPD1 gene. Carriers typically do not show symptoms of Niemann-Pick disease, but they may have reduced acid sphingomyelinase enzyme activity compared to non-carriers. If you are planning a family, you may wish to discuss carrier screening options with a genetic counselor or your healthcare provider.
This variant is found at an allele frequency of approximately 0.008 in the Ashkenazi Jewish population, making it a known carrier-associated allele in that group.
Potential Niemann-Pick disease risk
This genotype indicates the presence of two copies of the c.996delC deletion in the SMPD1 gene. This variant is associated with severe deficiency of acid sphingomyelinase, which is the underlying cause of Niemann-Pick disease types A and B. Please consult with a medical geneticist or your primary care physician to discuss these results and their clinical implications.
This genotype is extremely rare in the general population.
Understanding the rs121908297 Variant
The variant rs121908297 is a genetic alteration located within the SMPD1 gene, which is situated on chromosome 11. Specifically, this variant is a single-nucleotide deletion, often referred to in scientific literature as c.996delC or by the legacy term fsP330. A deletion occurs when a single base pair is removed from the DNA sequence, which can disrupt the reading frame of the gene. This disruption typically leads to the production of a truncated or non-functional protein. Because this variant alters the fundamental instructions for building a protein, it is classified as a pathogenic variant in the context of recessive genetic conditions. Understanding such variants is a key component of modern genomic screening, as they provide insight into the underlying genetic architecture of inherited disorders.
The Role of the SMPD1 Gene
The SMPD1 gene provides the essential instructions for the body to produce an enzyme known as acid sphingomyelinase. This enzyme is primarily located within lysosomes, which are the recycling centers of the cell. Its main function is to break down a type of fat called sphingomyelin into ceramide. When the SMPD1 gene is defective, the acid sphingomyelinase enzyme cannot function properly, leading to the accumulation of sphingomyelin within cells. This buildup is toxic and interferes with normal cellular processes, particularly in the liver, spleen, and nervous system. Because this enzyme is critical for maintaining cellular health, mutations that significantly reduce or eliminate its activity are linked to Niemann-Pick disease, a group of lysosomal storage disorders that can have severe health consequences.
Clinical Associations and Evidence
Research has established a strong link between pathogenic variants in SMPD1 and Niemann-Pick disease types A and B. Niemann-Pick disease is a recessive condition, meaning an individual must typically inherit two copies of a pathogenic variant—one from each parent—to manifest the disease. The rs121908297 variant is specifically identified as a carrier-status marker. Carriers possess one copy of the variant and one functional copy of the gene, and they generally do not exhibit the severe symptoms associated with the disease. However, if two carriers have children, there is a statistical risk of passing on the condition. The evidence for this variant's role in disease pathology is well-documented in clinical genetics, though the clinical expression can vary based on the specific combination of mutations inherited.
Population Frequency and Ancestry
Genetic variants are not distributed equally across all human populations due to historical factors such as founder effects and genetic drift. The rs121908297 variant has been observed with a higher frequency in the Ashkenazi Jewish population, with an estimated allele frequency of approximately 0.008. This frequency is significant enough that it is often included in carrier screening panels for this specific ancestry. Because of the shared genetic history within this group, certain recessive conditions are more prevalent, making genetic counseling and screening valuable tools for family planning. It is important to note that while this variant is more common in specific groups, it can theoretically occur in other populations, and the presence of the variant does not imply a diagnosis of the disease itself.
Interpreting Your Genetic Information
Information regarding your carrier status for rs121908297 is intended for educational purposes and should not be used for self-diagnosis. If you have received results indicating you are a carrier for an SMPD1 variant, the most appropriate next step is to consult with a certified genetic counselor or a medical professional. They can help you understand the implications of your results, discuss the risks for your biological relatives, and explain the options for reproductive planning. Genetic testing results are complex and should always be interpreted within the context of your personal and family medical history. Never make changes to your health management or medical decisions based solely on a genetic report without professional guidance. A clinician can provide the necessary context to ensure you receive accurate and actionable information.
How common is this variant?
The rs121908297 variant has an estimated allele frequency of approximately 0.008 in the Ashkenazi Jewish population.
Frequently asked questions
What is Niemann-Pick disease?
Niemann-Pick disease is a group of inherited lysosomal storage disorders caused by the inability of the body to properly break down fats. This leads to the accumulation of harmful substances in various organs, including the liver, spleen, and brain.
Does being a carrier mean I have the disease?
No, being a carrier typically means you have one copy of a pathogenic variant and one functional copy of the gene. Carriers generally do not show symptoms of the disease but can pass the variant to their children.
Why is this variant more common in Ashkenazi Jewish populations?
This is due to a founder effect, where a small group of ancestors passed on specific genetic traits to a larger population over time. This historical phenomenon leads to a higher prevalence of certain recessive conditions within the group.
Should I be tested for SMPD1 variants?
Carrier screening is a personal decision often discussed during family planning. You should speak with a genetic counselor or your primary care physician to determine if testing is appropriate for your specific situation.
Sources & further reading
Educational information only, last refreshed 9/24/2026. Not medical advice — these associations describe population statistics, not individual predictions.
Curious what your genotype is for rs121908297?
Upload a raw DNA file from 23andMe, AncestryDNA, MyHeritage, or FamilyTreeDNA and see this variant — plus thousands more — interpreted in your full report.
Get my report — $29Related variants in SMPD1
Pathogenic missense variant (p.Arg498Leu) associated with Niemann-Pick disease types A and B.
Pathogenic missense variant (p.Leu304Pro) associated with Niemann-Pick disease types A and B.
Pathogenic substitution (p.Arg498Leu) in SMPD1 associated with Niemann-Pick disease type A/B.
Pathogenic missense variant in SMPD1 (p.Arg498Leu) causing severe infantile Niemann-Pick disease type A in homozygous or compound heterozygous individuals.
A missense variant (c.1493G>A, p.Arg498Leu) in acid sphingomyelinase conferring carrier status for Niemann-Pick disease types A and B.
Pathogenic missense variant (p.Arg498Leu) causing acid sphingomyelinase deficiency (Niemann-Pick disease type A/B).