Autosomal dominant GTP cyclohydrolase I deficiency

A genetic disorder affecting neurotransmitter synthesis

Autosomal dominant GTP cyclohydrolase I deficiency is a rare genetic disorder that affects the production of certain neurotransmitters in the brain. It is characterized by a deficiency in the enzyme GTP cyclohydrolase I, which is crucial for the synthesis of tetrahydrobiopterin (BH4), a cofactor necessary for the production of dopamine, serotonin, and other neurotransmitters.

Pathophysiology

Pattern of cerebrospinal fluid metabolites for Autosomal dominant GTP cyclohydrolase I deficiency

The disorder is caused by mutations in the GCH1 gene, which encodes the enzyme GTP cyclohydrolase I. This enzyme is the first and rate-limiting step in the biosynthesis of tetrahydrobiopterin. BH4 is essential for the hydroxylation of phenylalanine, tyrosine, and tryptophan, which are precursors to neurotransmitters such as dopamine and serotonin. A deficiency in BH4 leads to reduced levels of these neurotransmitters, resulting in the clinical manifestations of the disorder.

Clinical Features

The clinical presentation of autosomal dominant GTP cyclohydrolase I deficiency can vary widely among affected individuals. Common symptoms include:

• Dystonia: Involuntary muscle contractions that cause repetitive movements or abnormal postures.
• Parkinsonism: Symptoms similar to Parkinson's disease, such as tremor, rigidity, and bradykinesia.
• Developmental delay: Delays in reaching developmental milestones.
• Intellectual disability: Varying degrees of cognitive impairment.

Diagnosis

Diagnosis of this condition is based on clinical evaluation, biochemical testing, and genetic analysis. Measurement of neurotransmitter metabolites in the cerebrospinal fluid (CSF) can reveal low levels of homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), which are indicative of dopamine and serotonin deficiencies, respectively. Genetic testing can confirm mutations in the GCH1 gene.

Treatment

Treatment typically involves supplementation with levodopa, a precursor to dopamine, which can help alleviate some of the motor symptoms. In some cases, supplementation with 5-hydroxytryptophan (5-HTP) and folinic acid may also be beneficial. Regular monitoring and adjustment of treatment regimens are necessary to manage symptoms effectively.

Prognosis

The prognosis for individuals with autosomal dominant GTP cyclohydrolase I deficiency varies depending on the severity of the symptoms and the effectiveness of treatment. Early diagnosis and intervention can improve outcomes and quality of life for affected individuals.

Related pages

• GTP cyclohydrolase I
• Tetrahydrobiopterin
• Dopamine
• Serotonin
• Dystonia