Meyahealth
HomeGeneticsConditionSepiapterin reductase deficiency
Back to Condition
Sepiapterin reductase deficiency
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Sepiapterin reductase deficiency

Sepiapterin reductase deficiency is a rare genetic disorder that disrupts neurotransmitter production, leading to progressive movement problems and cognitive symptoms.

Overview

Sepiapterin reductase deficiency is characterized by movement abnormalities, most notably dystonia (involuntary, sustained muscle contractions). Symptoms typically worsen over time and often fluctuate in severity throughout the day.

Symptoms

  • Movement disorders: Muscle stiffness (spasticity), tremors, problems with coordination and balance (ataxia), and involuntary jerking movements (chorea).
  • Oculogyric crises: Episodes involving abnormal rotation of the eyeballs, extreme irritability, pain, and muscle spasms, particularly in the head and neck.
  • Developmental and neurological signs: Delayed motor skill development, intellectual disability, seizures, excessive sleeping, and mood swings.
  • Physical characteristics: Some individuals may have an unusually small head size (microcephaly).

Causes

The condition is caused by mutations in the SPR gene, which provides instructions for making the sepiapterin reductase enzyme. This enzyme is essential for the final step in producing tetrahydrobiopterin (BH4). BH4 is a necessary cofactor for the production of neurotransmitters, specifically dopamine and serotonin, in the brain.

When SPR gene mutations occur, the resulting lack of BH4 in the brain leads to a significant reduction in dopamine and serotonin. Because dopamine is required for smooth physical movement and serotonin regulates mood, sleep, and emotion, their deficiency results in the movement and cognitive symptoms associated with the disorder.

Inheritance

This condition is inherited in an autosomal recessive pattern, meaning both copies of the gene in each cell must have mutations for the disorder to occur. Parents of an affected individual each carry one copy of the mutated gene but typically do not display symptoms.

Frequently Asked Questions

Symptoms display marked diurnal fluctuation because the body naturally depletes its critically low reserves of dopamine as daily physical and cognitive demands continue. By late afternoon or evening, muscle stiffness, tremors, and fatigue become more pronounced. Families and caregivers can manage this by scheduling physical therapy, demanding school tasks, and heavy exertion for the morning, building structured rest periods into the afternoon, and aligning medication timing with daily peak activities.
Because routine newborn metabolic screenings and blood amino acid tests are typically normal, definitive diagnosis requires a lumbar puncture to analyze cerebrospinal fluid (CSF) neurotransmitter metabolites. The characteristic CSF pattern reveals low levels of homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), alongside elevated total biopterin and sepiapterin. The diagnosis is confirmed through targeted molecular genetic testing demonstrating pathogenic variants in the SPR gene.
Medical therapy centers on replenishing depleted dopamine and serotonin pathways. Patients are treated with low-dose levodopa paired with a decarboxylase inhibitor (carbidopa), alongside 5-hydroxytryptophan (5-HTP) to restore serotonin levels. Some individuals also benefit from tetrahydrobiopterin (BH4) supplementation or monoamine oxidase inhibitors like selegiline. Dosages are titrated gradually to prevent medication-induced dyskinesias and gastrointestinal side effects.
Oculogyric crises—episodes of involuntary upward eye deviation accompanied by neck posturing, pain, and severe agitation—are often triggered by physiological stress, illness, fatigue, or wearing off of medication doses. Keeping a strict medication schedule for levodopa and 5-HTP minimizes these episodes. For acute, severe episodes, neurologists may recommend rescue doses of anticholinergic medications such as trihexyphenidyl or short-acting benzodiazepines in a quiet, dark environment.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

Meyahealth

Ⓒ 2026. All rights reserved by MEYA

About UsTerms & PolicyFAQ