Commentary: What degree of hyperphenylalaninaemia requires treatment?

In Silico Structural Protein Evaluation of the Phenylalanine Hydroxylase p.(Tyr77His) Variant Associated with Benign Hyperphenylalaninemia as Identified through Mexican Newborn Screening

Hyperphenylalaninemia (HPA), which includes phenylketonuria (PKU), is a genetic autosomal recessive disorder arising from a deficiency in the enzyme named phenylalanine hydroxylase (PAH). Affected patients can experience severe and irreversible neurological impairments when phenylalanine (Phe) blood concentration exceeds 360 μmol/L (6 mg/dL). Here, we describe a female HPA patient who was born in Mexico to Cuban non-consanguineous parents and identified by newborn screening, and who bears the previously unreported PAH NM_000277.3(PAH):c.[229T>C];[1222C>T] or p.[Tyr77His];[Arg408Trp] genotype. At diagnosis, the patient showed a Phe blood level of 321 μmol/L (5.3 mg/dL), indicative of mild HPA. Neither of the PAH variants found in this patient had been previously reported in the mutational PAH spectrum of the Mexican population. The c.229T>C or p.(Tyr77His) PAH variant was previously related to mild HPA in the Swedish population. Our in silico structural analysis and molecular docking showed that mutated His 77 residue is located in the allosteric site of PAH at the interface of the two monomers. The PDBsum in silico tool predicted that this variant would cause minimal structural disturbance of the protein interface in the presence of Phe at the allosteric site. Docking studies revealed that these structural changes might be attenuated by the allosteric effect of Phe. Given the classic PKU phenotype conditioned by the "Celtic" or c.[1222C>T] or p.(Arg408Trp) PAH variant, which is the second variant in this patient, we propose that p.(Tyr77His) has a hypomorphic feature that could explain her mild HPA phenotype. Our results show the importance of following up on cases detected by NBS and the value of genetic studies and in silico tools that aid in the establishment of correct therapeutic strategies.

Different Viewpoints: International Perspectives on Newborn Screening

Newborn blood-spot screening to detect potentially treatable disorders is widely practiced across the globe. However, there are great variations in practice, both in terms of disorders covered, screening technologies, disease definition, information provision, parental informed consent, and storage and disposal of residual specimens, partly reflecting the degree to which screening is the subject of explicit legislation (and thus public and media pressure) or is embedded in a general health care system and managed at an executive level. It is generally accepted that disorders to be screened for should comply with the ten Wilson and Jungner criteria, but the way that compliance is assessed ranges from broadly-based opinion surveys to detailed analysis of quantitative data. Consequently, even countries with comparable levels of economic development and health care show large differences in the number of disorders screened for. There are several areas on which there are no generally accepted guidelines: how should parents be informed about screening and to what extent should they be encouraged to regard screening as an option to choose to refuse? Is DNA mutation analysis acceptable as part of a screening protocol? How soon should the blood samples be destroyed once screening has been completed? As technology advances and the potential scope of screening expands at both the metabolite and genome level, challenging policy issues will have to be faced.