Thirteen years experience with selective screening for disorders in purine and pyrimidine metabolism.

Purine and pyrimidine disorders represent a heterogeneous group with variable clinical symptoms and low prevalence rate. In the last thirteen years, we have studied urine/plasma specimens from about 1600 patients and we have identified 35 patients: eight patients with adenylosuccinate lyase deficiency, eight patients with hypoxanthine-guanine phosphoribosyltransferase deficiency, one patient with purine nucleoside phosphorylase deficiency, ten patients with xanthine dehydrogenase deficiency, six patients with molybdenum cofactor deficiency and two patients with dihydropyrimidine dehydrogenase deficiency. Despite low incidence of these diseases, our findings highlight the importance of including the purine and pyrimidine analysis in the selective screening for inborn errors of metabolism in specialized laboratories, where amino acid and organic acid disorders are simultaneously investigated.

[Tetrahydrobiopterin therapy for hyperphenylalaninemia due to phenylalanine hydroxylase deficiency. When and how?]. / Tratamiento de la hiperfenilalaninemia por déficit de fenilalanina hidroxilasa con tetrahidrobiopterina. Cuándo y cómo?

INTRODUCTION: Some patients with hyperphenylalaninemia due to phenylalanine hydroxylase deficiency respond with a variable decrease in plasma phenylalanine levels after oral tetrahydrobiopterin (BH4) administration and are then able to tolerate higher dietary phenylalanine intake or even to discontinue a phenylalanine-restricted diet. BH4-sensitive patients are usually identified by means of a BH4 loading test, but consensus on the methodology of this test and the interpretation of its results is lacking. Consequently, a simple tool to identify which patients are likely candidates for this treatment and how they will progress in the long-term is required. MATERIAL AND METHODS: A combined oral BH4 loading test with phenylalanine (100 mg/kg) and BH4 (20 mg/kg) was performed in 20 patients with hyperphenylalaninemia under dietary phenylalanine restriction. RESULTS: Independently of the genotype, the result was positive in all the 9 patients whose maximum phenylalanine level at diagnosis was below 815 nmol/ml. Currently, they are under treatment with tetrahydrobiopterin doses of 7-15 mg/kg/day. All these patients have been able to increase their oral phenylalanine intake. Six are currently following a normal diet and the remaining three are close to reaching this goal. None of the patients with a maximum phenylalanine level at diagnosis higher than 938 nmol/ml responded to the BH4 loading test. CONCLUSIONS: The maximum phenylalanine level at diagnosis seems to be a simple and reliable method to predict response to BH4 treatment. A high percentage of BH4-sensitive patients are able to discontinue a phenylalanine-restricted diet after long-term tetrahydrobiopterin treatment.

Tratamiento de la hiperfenilalaninemia por déficit de fenilalanina hidroxilasa con tetrahidrobiopterina. ¿Cuándo y cómo? / Tetrahydrobiopterin therapy for hyperphenylalaninemia due to phenylalanine hydroxylase deficiency. When and how?

Introducción: Algunos pacientes afectados de hiperfenilalaninemia por déficit de fenilalanina hidroxilasa responden con un descenso variable de las concentraciones plasmáticas de fenilalanina, a la administración por vía oral de tetrahidrobiopterina (BH4), de tal modo que pueden liberalizar o incluso abandonar la dieta con ingesta limitada de fenilalanina. Habitualmente, la identificación de los pacientes sensibles a BH4 se realiza mediante el test de sobrecarga con BH4, pero no existe acuerdo unánime con relación a su metodología e interpretación de los resultados. Desde esta perspectiva, es importante disponer de una herramienta que nos ayude a identificar del modo más sencillo posible a los pacientes tributarios de este tipo de tratamiento y conocer cuál es su evolución a largo plazo. Material y métodos: Se ha practicado el test de sobrecarga combinado de fenilalanina (100 mg/kg) y BH4 (20 mg/kg) en 20 pacientes con hiperfenilalaninemia sometidos a dieta limitada en fenilalanina. Resultados: Con independencia de su genotipo, la respuesta al test fue positiva en los 9 pacientes cuyo máximo nivel de fenilalanina al diagnóstico fue menor de 815 nmol/ml. Todos están en tratamiento con dosis de BH4 entre 7 y 15 mg/kg/día y en todos los casos ha sido posible aumentar notablemente la ingesta diaria de fenilalanina. En este momento 6 están con dieta libre, y los otros muy cerca de alcanzar este objetivo. Ninguno de los pacientes con un nivel de fenilalanina máximo al diagnóstico de más de 938 nmol/ml ha respondido al test de sobrecarga. Conclusiones: El nivel máximo de fenilalanina en el momento del diagnóstico, parece ser un método sencillo y fiable para predecir la respuesta al tratamiento con BH4. En los pacientes respondedores, el tratamiento continuado con BH4 permite la eliminación de la dieta limitada en fenilalanina en un alto porcentaje de casos

Introduction: Some patients with hyperphenylalaninemia due to phenylalanine hydroxylase deficiency respond with a variable decrease in plasma phenylalanine levels after oral tetrahydrobiopterin (BH4) administration and are then able to tolerate higher dietary phenylalanine intake or even to discontinue a phenylalanine-restricted diet. BH4-sensitive patients are usually identified by means of a BH4 loading test, but consensus on the methodology of this test and the interpretation of its results is lacking. Consequently, a simple tool to identify which patients are likely candidates for this treatment and how they will progress in the long-term is required. Material and methods: A combined oral BH4 loading test with phenylalanine (100 mg/kg) and BH4 (20 mg/kg) was performed in 20 patients with hyperphenylalaninemia under dietary phenylalanine restriction. Results: Independently of the genotype, the result was positive in all the 9 patients whose maximum phenylalanine level at diagnosis was below 815 nmol/ml. Currently, they are under treatment with tetrahydrobiopterin doses of 7-15 mg/kg/day. All these patients have been able to increase their oral phenylalanine intake. Six are currently following a normal diet and the remaining three are close to reaching this goal. None of the patients with a maximum phenylalanine level at diagnosis higher than 938 nmol/ml responded to the BH4 loading test. Conclusions: The maximum phenylalanine level at diagnosis seems to be a simple and reliable method to predict response to BH4 treatment. A high percentage of BH4-sensitive patients are able to discontinue a phenylalanine-restricted diet after long-term tetrahydrobiopterin treatment