The SPR gene helps your body make tetrahydrobiopterin, a helper molecule needed to produce the brain chemicals dopamine and serotonin. If the gene does not work properly, levels of these chemicals can drop, and pathogenic variants can cause sepiapterin reductase deficiency. People with this condition may have movement problems, low muscle tone, developmental delay, sleep or mood changes, and episodes of forced upward eye movement.
What is a gene?
Genes are sections of DNA that carry instructions your cells use to make molecules or regulate processes in the body. Some genes hold the directions for producing proteins, the parts of cells that do the work. Other genes mainly help control when certain processes happen, where they happen, and how strongly they occur. Together, genes influence how the body develops and works, and they can also shape how you respond to food, stress, or medications. More information on this topic is available in the LearnHub.
Overview
SPRGene function
What if the gene works
The SPR gene helps your body make tetrahydrobiopterin, a helper molecule needed to produce dopamine and serotonin. This supports normal movement, mood, and brain function.
Risk
What if the gene does not work
Variants in the SPR gene can reduce brain chemical production and cause sepiapterin reductase deficiency. Many people develop dystonia, low muscle tone, and developmental delay, with milder or more severe variants often shaping onset and symptom range.
Treatment
What does that mean for your treatment
Pathogenic variants in the SPR gene often point to treatment with low dose levodopa plus carbidopa or benserazide, which can markedly improve movement symptoms. Some people also benefit from 5-hydroxytryptophan to support serotonin levels. Treatment usually starts carefully because levodopa can cause involuntary movements or behavior changes if the dose is too high.
Conditions associated with SPR
Gene function
What if the gene works
Your cells use the SPR gene to make tetrahydrobiopterin, often called BH4. This small helper molecule supports several everyday chemical reactions, especially in the brain, blood vessels, and protein handling. Understanding SPR gene function helps explain how the body makes key brain signals and keeps routine cell processes running.
The SPR gene helps your cells complete the last step of making tetrahydrobiopterin, also called BH4. BH4 is a helper molecule that other enzymes need for routine body functions.
BH4 made with help from the SPR gene supports enzymes that produce dopamine and serotonin, which are important brain messengers. This supports everyday nerve signaling throughout the brain and body.
BH4 also supports enzymes that make nitric oxide, a signal used for blood vessel relaxation and cell communication. This contributes to steady control of circulation from moment to moment.
BH4 is also used by an enzyme that processes phenylalanine, an amino acid from food. Through this pathway, the SPR gene supports normal handling of protein building blocks.
What is a variant?
A genetic variant is a minor difference in a gene’s DNA sequence. These differences are common and help shape normal human variation, including differences in appearance, metabolism, and the way the body responds to environmental influences. Many variants do not have any noticeable effect and are simply part of natural genetic diversity. In some cases, though, a variant can change how a gene works more substantially and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the SPR gene can change the shape or stability of the sepiapterin reductase protein, so cells make less of it or it works less well. In plain terms, this is how SPR gene variants affect enzyme activity and lower production of tetrahydrobiopterin, a helper molecule needed to make dopamine and serotonin. Milder variants may leave some activity, while more severe variants can nearly shut it down, which often relates to earlier or more noticeable symptoms.
How variants are linked to conditions
Pathogenic variants in the SPR gene are linked to sepiapterin reductase deficiency, a rare inherited condition that often starts in infancy or childhood. People with this diagnosis may have low muscle tone, movement difficulties, developmental delay, or episodes of unusual eye movements. Some are first labeled as having dopa responsive dystonia because walking, stiffness, or abnormal postures can be part of the picture.
A variant is not necessarily a diagnosis
Gene variants are a normal feature of human biology and are common throughout the general population. Most do not have a direct effect on health and simply reflect natural human diversity. For many genes, carrying a variant associated with a condition suggests a possible link rather than a definite diagnosis, especially when several genes and environmental factors also play a part. In some cases, though, a single well-characterized variant in a particular gene can be enough to confirm a diagnosis.
Are there things that can increase or change my risk?
For SPR, the chance of having the related condition is mainly shaped by inheritance, especially if both parents carry a harmful SPR variant. There is not broadly confirmed evidence that lifestyle or environmental factors meaningfully change this risk, so anyone worried about personal or family risk should speak with a doctor or genetic counselor.
Inheritance of SPR variants
Variants in the SPR gene are inherited in an autosomal recessive pattern. This means a child usually needs to inherit 2 altered copies of the SPR gene, 1 from each parent, to have SPR-related disease. Parents who each carry 1 variant are often unaffected carriers, and with each pregnancy they have a 25% chance of having an affected child, a 50% chance of having a child who is a carrier, and a 25% chance of having a child who inherits neither variant. Sons and daughters are affected at the same rate because the SPR gene is on a non-sex chromosome.
What does my SPR result mean for my family?
For families, an SPR result is most often relevant in a recessive condition, which means parents are often healthy carriers and brothers or sisters may also be affected or be carriers. Close relatives may want to learn whether the same gene change runs in the family, especially if there are movement problems, low muscle tone, or developmental concerns in childhood. The chance for relatives depends on the exact result found in your family.
Genetic information
Genetic testing
How you find out about variants
To look for changes in the SPR gene, doctors use SPR genetic testing on a blood sample, cheek swab, or saliva sample. A lab reads the gene's DNA sequence to check for variants, which can help confirm or rule out an inherited condition when results are interpreted alongside symptoms and family history.
When should I consider getting a genetic test?
You might consider SPR genetic testing if there are unexplained movement symptoms starting in childhood, such as muscle stiffness, low muscle tone, trouble walking, or developmental delay, especially if similar problems run in the family. Testing can help confirm a rare inherited condition linked to the SPR gene.
A genetic result is only one part of your health story
Genetic results can be informative, but how much they explain depends on the condition and on the specific type of variant. How the body works over time is also shaped by factors such as lifestyle, environment, age, and medical history. For some conditions, especially those influenced by many genes, genetic information provides context rather than certainty and is best understood along with other parts of care. In other situations, a genetic result may offer a clear answer. In areas like medication response, genetic results can also help put individual experiences into perspective.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how people respond to medicines. This helps explain why the same medication may work well for one person, have little effect in another, or cause more side effects in someone else. Small differences in genes can change how the body breaks down a drug, moves it through the body, or responds to it at its target, and these differences are common.
What is Pharmacogenetics?
Pharmacogenetics focuses on how differences in a person’s genes affect the way they respond to medicines. By examining links between genes and drugs, it helps explain why the same treatment can have different effects in different people. With many medications, genes influence both how powerfully a drug works and how the body handles it. Understanding this can support treatment choices that are more informed and more tailored to the individual. More detailed information on this topic is available in the LearnHub.
Drugs influenced by the SPR gene
When should I seek medical advice?
There is not yet a widely accepted role for this gene in guiding everyday medicine choices. Questions about side effects, new symptoms, or how a treatment may affect you are best discussed with your doctor. SPR has mainly been studied in a rare inherited condition that affects certain brain chemicals, where treatment decisions are based on the condition itself rather than on a standard gene-based prescribing guideline.