PRNP rs28936675: Understanding the D178N Variant
The rs28936675 variant, commonly known as the D178N mutation, is a rare genetic change in the PRNP gene. It is primarily associated with the development of Fatal Familial Insomnia (FFI), a rare, inherited neurodegenerative condition.
What each genotype means
Typical prion protein sequence
You carry two copies of the standard cytosine allele encoding aspartic acid at position 178 of the PRNP gene. This is the common non-pathogenic genotype and is not associated with fatal familial insomnia or familial Creutzfeldt-Jakob disease. No elevated genetic risk for inherited prion disease is conferred by this site.
Found in greater than 99.99% of individuals across all major global ancestries.
Prion disease susceptibility allele carrier
You have one copy of the pathogenic thymine allele encoding the Asp178Asn (D178N) missense alteration in PRNP. Published research demonstrates that this variant follows an autosomal dominant inheritance pattern and causes fatal familial insomnia when in cis with methionine at codon 129, or familial Creutzfeldt-Jakob disease when coupled with valine at codon 129. Because clinical manifestations depend on haplotype configuration and genetic penetrance, individuals with this genotype should discuss findings with a medical geneticist or clinical neurologist.
Extremely rare globally, occurring in fewer than 1 in 100,000 individuals in population databases such as gnomAD.
Homozygous pathogenic variant
You carry two copies of the pathogenic thymine allele corresponding to the Asp178Asn (D178N) substitution in PRNP. Homozygosity for this rare pathogenic prion mutation has rarely or never been documented in living population cohorts and is linked to severe inherited neurodegenerative prion disease risk. Formal genetic counseling and neurological consultation are strongly recommended to evaluate family history and diagnostic context.
Virtually non-existent in healthy population reference databases such as gnomAD.
What is the rs28936675 Variant?
The rs28936675 variant is a single nucleotide polymorphism (SNP) located within the PRNP gene on chromosome 20. In scientific literature, this specific change is frequently referred to as the D178N mutation, which stands for an amino acid substitution where aspartic acid (D) is replaced by asparagine (N) at position 178 of the prion protein. This variant does not occur in isolation regarding its clinical impact; it is known to cosegregate with a specific polymorphism at codon 129 of the same gene. The presence of methionine at codon 129 on the same allele as the D178N mutation is a critical factor in the manifestation of the associated condition. Because this variant is extremely rare in the general population, it is typically identified through specialized genetic testing in families with a history of specific neurological symptoms.
The Role of the PRNP Gene
The PRNP gene provides the biological instructions for producing the prion protein (PrP). While the exact physiological function of this protein remains a subject of ongoing research, it is known to be expressed in the brain and various other tissues throughout the body. Scientists have proposed that the prion protein may play roles in cellular signaling, copper binding, and protecting cells against oxidative stress. Under normal conditions, the protein exists in a healthy, functional form. However, mutations in the PRNP gene can lead to the production of misfolded proteins. These abnormal proteins can accumulate in the brain, potentially leading to neurodegenerative disorders. The D178N variant is one of several known mutations in this gene that can alter the structure and stability of the prion protein, contributing to the development of rare, inherited prion diseases.
Research and Clinical Associations
Research has established a strong link between the D178N mutation and Fatal Familial Insomnia (FFI). FFI is a rare, autosomal-dominant neurodegenerative disease characterized by progressive, untreatable insomnia, autonomic dysfunction, and motor coordination issues. The clinical presentation of FFI is often linked to selective atrophy in the thalamus, a region of the brain involved in sleep regulation. It is important to note that there is significant clinical heterogeneity associated with this variant. While the D178N mutation is a primary driver, the specific phenotype can sometimes overlap with other prion diseases, such as Creutzfeldt-Jakob disease. Studies indicate that the presence of methionine at codon 129 is a key modifier in the expression of the disease. Because FFI is exceptionally rare, the evidence base is derived primarily from case studies and family-based research rather than large-scale population screenings.
Population Frequency
The rs28936675 variant is extremely rare in the global population, with a frequency reported as less than 0.00005 in major databases like gnomAD. Due to its rarity, it is not considered a common polymorphism found in the general public.
Navigating Genetic Information
Understanding genetic variants like rs28936675 requires careful interpretation. This variant is associated with a serious, rare condition, and its presence does not automatically imply a specific clinical outcome for every individual. Genetic testing for such rare variants is typically conducted in a clinical setting, often following genetic counseling, to help families understand the implications of their results. If you have concerns about your genetic health or family history, it is essential to consult with a qualified healthcare provider or a genetic counselor. They can provide context based on your personal medical history and guide you through the appropriate diagnostic steps. Never use genetic information to make independent medical decisions or diagnoses; always rely on professional clinical evaluation to interpret the significance of any genetic finding.
How common is this variant?
The rs28936675 variant is extremely rare worldwide, with a frequency of less than 0.00005 in gnomAD.
Frequently asked questions
What is Fatal Familial Insomnia?
Fatal Familial Insomnia is a rare, inherited neurodegenerative disease that causes progressive, untreatable insomnia and autonomic dysfunction. It is caused by specific mutations in the PRNP gene.
Is the D178N mutation common?
No, the D178N mutation is extremely rare in the general population. It is typically only identified in families with a known history of specific prion diseases.
Does having this variant mean I will get sick?
Genetic variants like D178N are associated with specific conditions, but clinical expression can be complex. You should discuss any genetic findings with a medical professional or genetic counselor to understand your specific risk.
How is this variant inherited?
The D178N mutation follows an autosomal-dominant inheritance pattern. This means that an individual only needs to inherit one copy of the mutated gene from one parent to be at risk.
Sources & further reading
Educational information only, last refreshed 10/10/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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