To provide an overview of the available clinical data on the natural history and treatment outcomes of BH4 deficiencies, focusing on unresolved problems in clinical monitoring and potential predictive markers of outcomes.
Approach:
Systematic Review: A systematic review based on PRISMA guidelines was conducted, including follow-up and outcome studies on BH4 deficiencies from the first description of the diseases to 31 October 2025.
Key Findings:
BH4 deficiencies can occur with or without hyperphenylalaninemia (HPA), impacting diagnosis and treatment follow-up.
Neurodevelopmental impairment and movement disorders are core symptoms across BH4 deficiency conditions.
Best clinical outcomes are associated with autosomal dominant guanosine triphosphate cyclohydrolase I deficiency (AD-GTPCHd).
Prognosis for recessive conditions varies with treatment timing and severity of metabolic derangement.
Neurocognitive, psychiatric, and sleep disorders are often underestimated in affected individuals.
Interpretation:
Clinical follow-up aims to prevent symptoms in early-diagnosed patients and restore function in those diagnosed after symptom onset. Monitoring of various biomarkers and imaging is crucial for managing these conditions effectively.
Limitations:
Current data primarily comes from retrospective observational studies.
Standardized measures are used in only a few studies, limiting comparability.
Conclusion:
Future clinical studies should adopt standardized tools for assessing neurological and behavioral impairments, considering patient age.
