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SAMHD1
SAM and HD domain containing deoxynucleoside triphosphate triphosphohydrolase 1
SAMHD1 is located on the long (q) arm of chromosome 20, at band 20q11.23. Arm ratio per GRCh38 - banding schematic.
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Overview
SAMHD1 encodes SAM and HD domain containing deoxynucleoside triphosphate triphosphohydrolase 1, an enzyme located on chromosome 20. This protein functions as a cellular gatekeeper, controlling the levels of deoxynucleoside triphosphates (dNTPs) that cells need for DNA synthesis and repair. The enzyme's regulatory activity is particularly important in immune cells, where it helps limit viral infections by restricting the nucleotide supply that viruses require for replication.
Pathogenic variants in SAMHD1 are associated with Aicardi-Goutières syndrome, a neurological condition that can cause severe brain dysfunction and immune system abnormalities. The gene is included on multiple NHS Genomic Medicine Service panels focused on neurogenetics, reflecting its clinical relevance in inherited white matter disorders and childhood-onset neurological conditions.
What the gene does
The SAMHD1 protein acts as a triphosphohydrolase enzyme, cleaving deoxynucleoside triphosphates into their component parts: a deoxynucleoside and a triphosphate molecule. This enzymatic activity regulates the size of the cellular dNTP pool, ensuring that cells maintain appropriate levels of these molecules for DNA replication and repair whilst preventing excessive accumulation that could support viral infections such as HIV.
Research suggests the enzyme also contributes to maintaining genomic stability through participation in DNA repair processes. By controlling nucleotide availability, SAMHD1 influences the fidelity of DNA synthesis and may help prevent mutations that arise from imbalanced nucleotide pools. The protein is particularly abundant in certain immune cell types, including dendritic cells and monocytes, where it was initially identified as an interferon-induced protein responding to immune signals.
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Chromosome location
SAMHD1 is located on the long arm of chromosome 20 at position 20q11.23. This chromosomal region contains genes involved in various cellular processes, and the SAMHD1 locus spans multiple exons encoding a 626-amino acid protein. The gene's position in the genome places it within a region that has been studied in the context of both neurological and immunological disorders.
Protein structure
The SAMHD1 protein comprises 626 amino acids organised into several functional regions. The N-terminal portion contains a disordered region spanning amino acids 1 to 36, followed by a SAM domain extending from amino acids 45 to 110. The SAM domain, short for sterile alpha motif, is a protein interaction module found in diverse signalling and regulatory proteins. The central portion of the protein contains an HD domain occupying amino acids 164 to 316, which provides the catalytic machinery responsible for the enzyme's triphosphohydrolase activity. The HD domain is named for conserved histidine and aspartate residues that coordinate metal ions essential for catalysis.
Key variants
Pathogenic variants in SAMHD1 typically disrupt the enzyme's ability to properly regulate dNTP levels or impair its role in DNA repair processes. These genetic changes can occur throughout the coding sequence and may affect either the catalytic activity of the HD domain or the protein's overall stability and regulation. The inheritance pattern associated with SAMHD1-related conditions can vary depending on the specific disorder and variant type.
No pathogenic or likely-pathogenic ClinVar variants recorded yet for this gene.
Associated conditions
SAMHD1 is primarily associated with Aicardi-Goutières syndrome, an inherited neurological disorder characterised by brain dysfunction, skin lesions, and immune system abnormalities. This condition typically follows an autosomal recessive pattern of inheritance. Research suggests that variants impairing SAMHD1 function lead to dysregulated nucleotide metabolism, which may trigger inappropriate immune responses and interfere with normal brain development. Affected individuals often present in early childhood with features that can include developmental regression, movement disorders, and calcification of brain tissue.
UK clinical status
SAMHD1 appears with green (high evidence) status on numerous NHS Genomic Medicine Service gene panels. These include panels for inherited white matter disorders, childhood onset dystonia and movement disorders, early onset epilepsy, intellectual disability, and intracerebral calcification disorders. The gene is also listed on panels for adult onset leukodystrophy, foetal anomalies, and primary immunodeficiency. This broad panel representation reflects the gene's relevance across paediatric neurology, metabolic medicine, and immunology services within the NHS.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What does the SAMHD1 enzyme do in cells?
The SAMHD1 enzyme breaks down deoxynucleoside triphosphates, the building blocks cells use to make DNA. By controlling the levels of these molecules, it helps regulate both normal DNA synthesis and the cell's ability to restrict viral infections that depend on the same building blocks.
How is SAMHD1 related to Aicardi-Goutières syndrome?
Pathogenic variants in SAMHD1 can cause Aicardi-Goutières syndrome, typically following an autosomal recessive inheritance pattern. When the enzyme does not function properly, dysregulated nucleotide metabolism may trigger abnormal immune responses and interfere with brain development, leading to the neurological and immunological features of the condition.
Why is SAMHD1 included on multiple NHS gene panels?
SAMHD1 appears on many NHS panels because variants in this gene can cause a range of neurological features including white matter abnormalities, movement disorders, epilepsy, and brain calcification. The gene's broad panel membership reflects its clinical relevance across multiple paediatric and adult neurology specialties.
References
- Livingston JH, Crow YJ. Neurologic Phenotypes Associated with Mutations in TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, ADAR1, and IFIH1: Aicardi-Goutières Syndrome and Beyond. Neuropediatrics. 2016. PMID: 27643693
- Kretschmer S, Wolf C, König N. SAMHD1 prevents autoimmunity by maintaining genome stability. Annals of the rheumatic diseases. 2015. PMID: 24445253
- Crow YJ, Chase DS, Lowenstein Schmidt J. Characterization of human disease phenotypes associated with mutations in TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, ADAR, and IFIH1. American journal of medical genetics. Part A. 2015. PMID: 25604658
- Crow YJ. Aicardi-Goutières syndrome. Handbook of clinical neurology. 2013. PMID: 23622384
- Franzolin E, Pontarin G, Rampazzo C. The deoxynucleotide triphosphohydrolase SAMHD1 is a major regulator of DNA precursor pools in mammalian cells. Proceedings of the National Academy of Sciences of the United States of America. 2013. PMID: 23858451
- Sze A, Olagnier D, Lin R. SAMHD1 host restriction factor: a link with innate immune sensing of retrovirus infection. Journal of molecular biology. 2013. PMID: 24161438
- Rice GI, Forte GM, Szynkiewicz M. Assessment of interferon-related biomarkers in Aicardi-Goutières syndrome associated with mutations in TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, and ADAR: a case-control study. The Lancet. Neurology. 2013. PMID: 24183309
- Dale RC, Gornall H, Singh-Grewal D. Familial Aicardi-Goutières syndrome due to SAMHD1 mutations is associated with chronic arthropathy and contractures. American journal of medical genetics. Part A. 2010. PMID: 20358604
- Rice GI, Bond J, Asipu A. Mutations involved in Aicardi-Goutières syndrome implicate SAMHD1 as regulator of the innate immune response. Nature genetics. 2009. PMID: 19525956
- Crow YJ, Rehwinkel J. Aicardi-Goutieres syndrome and related phenotypes: linking nucleic acid metabolism with autoimmunity. Human molecular genetics. 2009. PMID: 19808788
- Adam MP, Bick S, Mirzaa GM. Aicardi-Goutières Syndrome. 1993. PMID: 20301648