An international survey of patients with tetrahydrobiopterin deficiencies presenting with hyperphenylalaninaemia

Abstract

The present study summarizes clinical and biochemical findings, current treatment strategies and follow-up in patients with tetrahydrobiopterin (BH₄) deficiencies. We analyzed the clinical, biochemical and treatment data of 626 patients with BH₄ deficiencies [355 with 6-pyruvoyl-tetrahydropterin synthase (PTPS), 217 with dihydropteridine reductase (DHPR), 31 with autosomal recessive GTP cyclohydrolase I (GTPCH), and 23 with pterin-4a-carbinolamine dehydratase (PCD) deficiencies] from the BIODEF Database. Patients with autosomal dominant GTPCH and SR deficiencies will not be discussed in detail. Up to 57 % of neonates with BH₄ deficiencies are already clinically symptomatic. During infancy and childhood, the predominant symptoms are muscular hypotonia, mental retardation and age-dependent movement disorders, including dystonia. The laboratory diagnosis of BH₄ deficiency is based on a positive newborn screening (NBS) for phenylketonuria (PKU), characteristic profiles of urinary or dried blood spot pterins (biopterin, neopterin, and primapterin), and the measurement of DHPR activity in blood. Some patients with autosomal recessive GTPCH deficiency and all with sepiapterin reductase deficiency may be diagnosed late due to normal blood phenylalanine in NBS. L-dopa, 5-hydroxytryptophan, and BH₄ are supplemented in PTPS and GTPCH-deficient patients, whereas L-dopa, 5-hydroxytryptophan, folinic acid and diet are used in DHPR-deficient patients. Medication doses vary widely among patients, and our understanding of the effects of dopamine agonists and monoamine catabolism inhibitors are limited. BH₄ deficiencies are a group of treatable pediatric neurotransmitter disorders that are characterized by motor dysfunction, mental retardation, impaired muscle tone, movement disorders and epileptic seizures. Although the outcomes of BH₄ deficiencies are highly variable, early diagnosis and treatment result in improved outcomes.