Monitoring of Phenylalanine Levels in Patients with Phenylketonuria Using Dried Blood Spots: a Comparison of Two Methods

Abstract Phenylketonuria (PKU) is caused by deficient activity of phenylalanine hydroxylase (PAH), responsible for the conversion of phenylalanine (Phe) to tyrosine (Tyr). Monitoring of patients with PKU requires the measurement of Phe in plasma using high-performance liquid chromatography (HPLC) or in dried blood spots (DBS) using different techniques to adjust treatment strategy. The objective of this study was to evaluate Phe levels in DBS measured by two different methods and compare them with Phe levels measured in plasma by HPLC. We analyzed 89 blood samples from 47 PKU patients by two different methods: fluorometric method developed in-house (method A) and the commercially available PerkinElmer® Neonatal Phenylalanine Kit (method B) and in plasma by HPLC. The mean Phe levels by method A, method B, and HPLC were 430.4±39.9μmol/L, 439.3±35.4μmol/L, and 442.2±41.6μmol/L, respectively. The correlation values between HPLC and methods A and B were 0.990 and 0.974, respectively (p < 0.001 for both). Our data suggest that methods A and B are useful alternatives for monitoring Phe levels in patients with PKU, with method A being in closer agreement with the reference standard (HPLC).

A terapia de reposição enzimática pode mudar a frequência de intervenções médicas na mucopolissacaridose tipo I? Um estudo retrospectivo e exploratório / Can enzyme replacement therapy change the frequency of medical interventions in mucopolysaccharidosis type I? An exploratory retrospective study

Introdução: A mucopolissacaridose tipo I (MPS I) é uma doença lisossômica (DL) para a qual está disponível a terapia de reposição enzimática (TRE) com laronidase. Objetivo: caracterizar o efeito da TRE em pacientes com MPS I avaliados por um único centro de referências para DL a partir da análise da frequência de intervenções médicas. Métodos: Estudo retrospectivo e exploratório com comparações pré e pós-intervenção. O número/ano/paciente de consultas, medicamentos usados, internações, cirurgias e exames realizados, foi obtido por meio de revisão de prontuário médico. Essas variáveis foram, então, comparadas entre dois períodos: pré-TRE e pós-TRE. Resultados: Nove pacientes (graves=3, atenuados=6) foram incluídos no estudo. A mediana de idade de início da TRE foi 9 anos e a mediana de duração da TRE foi 4 anos. Em média, os pacientes realizaram 90% das infusões previstas para o período. Somente o número de cirurgias/ano/paciente foi dependente do tempo de doença (p=0,0004) e da gravidade do fenótipo (p=0,014). Com relação às comparações pré e pós-TRE, as variáveis que apresentaram diferença significativa (média do número/ano/paciente) foram: exames (pré-TRE=10,2±2,7; pós-TRE=22,5±2,1; p=0,005) e internações (pré-TRE=0,05±0,04; pós-TRE=0,30±0,11; p=0,013). Conclusão: Nossos dados sugerem que a TRE não alterou a história natural da MPS I em relação aos desfechos analisados. Este achado pode ser devido à idade relativamente avançada de início do tratamento no nosso centro.

Background: Mucopolysaccharidosis type I (MPSI) is a lysosomal disorder (LSD) which can be treated with enzyme replacement therapy (ERT) with laronidase. Aim: To describe the effect of ERT on MPSI patients evaluated at a single referral center for LSD by assessing the frequency of medical interventions. Methods: An exploratory, retrospective study with pre- and post-intervention assessments. We reviewed medical records to collect data on the number of medical appointments/year/patient, medications used, hospital admissions, surgeries, and exams performed. These variables were then compared between the pre- and the post-ERT periods.Results: Nine patients (severe=3; attenuated=6) were included in the study.The median age for the start of ERT was 9 years, and the median time on ERT was 4 years. On average, patients received 90% of the infusions predicted for the study period. Only the number of surgeries/year/patient was found to be dependent on length of disease (p=0.0004) and on severity of phenotype (p=0.014). Regarding pre- and post-ERT comparisons, there was a significant difference (mean number/year/patient in exams (pre-ERT, 10.2±2.7; post-ERT, 22.5±2.1; p=0.005) and hospital admissions (pre-ERT, 0.05±0.04; post-ERT, 0.30±0.11; p=0.013). Conclusion: Our data suggest ERT didn’t alter the natural history of MPSI the outcomes assessed in this study. This may be due to the relatively advanced age of patients when they started treatment at our Center.