SMPD1 rs121907936: What Your Genotype Means
The rs121907936 variant in the SMPD1 gene is a missense mutation, also known as p.Arg498Leu or R496L, that results in an amino acid change in the acid sphingomyelinase enzyme. It is recognized as a pathogenic variant associated with Niemann-Pick disease types A and B, particularly within the Ashkenazi Jewish population.
What each genotype means
Typical risk profile
You have two functional copies of the SMPD1 gene at this position. You do not carry the pathogenic p.Arg498Leu (R496L) founder variant associated with acid sphingomyelinase deficiency. While this result significantly reduces the likelihood of being a carrier for Niemann-Pick disease types A and B, it does not completely rule out carrier status for other rare variants across the SMPD1 gene.
Found in greater than 99% of individuals across global populations, including non-Ashkenazi and most Ashkenazi Jewish individuals.
Niemann-Pick disease carrier
You carry one copy of the pathogenic p.Arg498Leu missense mutation (historically called R496L, c.1493G>T) in the SMPD1 gene. Carriers are generally asymptomatic and do not develop Niemann-Pick disease, though population studies note mild statistical variations in sphingomyelin metabolism and an exploratory association with Parkinson's disease risk. If your reproductive partner is also a carrier of an SMPD1 pathogenic variant, each child has a 25% risk of inheriting Niemann-Pick disease types A or B.
Carried by approximately 1 in 90 individuals of Ashkenazi Jewish ancestry, but extremely rare in other world populations.
Acid sphingomyelinase deficiency risk
You have inherited two copies of the severe p.Arg498Leu mutation in SMPD1. In clinical literature, biallelic inheritance of this variant results in profound acid sphingomyelinase deficiency, typically presenting as infantile neurodegenerative Niemann-Pick disease type A. This is a severe clinical profile that warrants detailed genetic and specialist evaluation.
Extremely rare globally, estimated at less than 1 in 32,000 live births in Ashkenazi Jewish populations and virtually absent in other groups.
Understanding the Variant
The variant rs121907936, often referred to in scientific literature as p.Arg498Leu or R496L, is a specific change in the DNA sequence of the SMPD1 gene. In this mutation, the amino acid arginine is replaced by leucine at position 498 of the protein. This change occurs within the coding region of the gene, which provides the blueprint for the acid sphingomyelinase enzyme. Because this is a missense mutation, it alters the structure of the resulting protein, which can impact its ability to function correctly within the cell. This variant is categorized as pathogenic or likely pathogenic in clinical databases, meaning it is known to contribute to specific genetic conditions when inherited in certain patterns.
The Role of the SMPD1 Gene
The SMPD1 gene is responsible for producing an enzyme called acid sphingomyelinase. This enzyme is located in lysosomes, which are the cell's recycling centers. Its primary job is to break down a type of fat called sphingomyelin into smaller components that the cell can reuse. When the SMPD1 gene contains mutations that significantly reduce or abolish the activity of this enzyme, sphingomyelin cannot be properly broken down. This leads to the accumulation of fat within cells, which can cause damage to various organs, including the liver, spleen, and lungs. In severe cases, such as Niemann-Pick disease type A, this accumulation also leads to significant neurological impairment in early childhood.
Research and Clinical Associations
Research has established a strong link between rs121907936 and Niemann-Pick disease types A and B. These are autosomal recessive disorders, meaning an individual typically needs to inherit two copies of a pathogenic variant—one from each parent—to manifest the disease. In the Ashkenazi Jewish population, this specific variant is one of several common mutations that account for a significant portion of Niemann-Pick disease cases. While the evidence for its pathogenicity in this context is well-documented, the clinical severity can vary depending on the specific combination of mutations an individual carries. It is important to note that while some studies have investigated potential links between SMPD1 variants and other conditions like Parkinson's disease, the evidence for such associations remains limited or inconclusive.
Population Frequency
The frequency of the rs121907936 variant varies significantly across different ancestral groups. It is most notably observed in individuals of Ashkenazi Jewish descent, where it is estimated to be a carrier variant in approximately 1 in 100 people. Because it is a recessive condition, being a carrier—having only one copy of the variant—generally does not result in the symptoms of Niemann-Pick disease. However, the higher carrier frequency in this specific population makes it a common focus for genetic screening programs. In the general global population, the variant is much rarer, and its presence is not as widespread as it is within specific founder populations.
Interpreting Your Results
If you have received information about your status for rs121907936, it is essential to understand that this is not a medical diagnosis. Genetic testing results should always be interpreted by a qualified healthcare professional or a genetic counselor who can place the findings in the context of your personal and family medical history. If you are a carrier, you may wish to discuss reproductive options or family planning with a specialist. Never make changes to your health management or medication based solely on a genetic report without consulting your clinician. This information is intended for educational purposes to help you understand the science behind your genetic data.
How common is this variant?
The carrier frequency for this variant is approximately 1 in 100 in the Ashkenazi Jewish population, while it is significantly rarer in the general global 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 called sphingomyelin. This leads to the accumulation of these fats in cells, causing damage to organs like the liver, spleen, and brain.
Does having one copy of this variant mean I have the disease?
No, Niemann-Pick disease is an autosomal recessive condition. This means that typically, an individual must inherit two copies of a pathogenic variant—one from each parent—to develop the disease.
Should I be tested for this variant?
Genetic carrier screening is often recommended for individuals of Ashkenazi Jewish descent who are planning a family. You should discuss the benefits and limitations of such testing with a genetic counselor or your primary care physician.
Is there a cure for Niemann-Pick disease?
Currently, there is no cure for Niemann-Pick disease, and treatment focuses on managing symptoms and providing supportive care. Research into enzyme replacement therapies and other interventions is ongoing.
Sources & further reading
Educational information only, last refreshed 10/27/2026. Not medical advice — these associations describe population statistics, not individual predictions.
Curious what your genotype is for rs121907936?
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.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.
Single-nucleotide deletion (c.996delC) leading to acid sphingomyelinase deficiency.
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).