title: Impact of neonatal protein metabolism and nutrition on screening for phenylketonuria.
abstract: OBJECTIVE
  Early blood phenylalanine (Phe) elevation after birth enables screening for and anticipation of the diagnosis of phenylketonuria. The differential impact of factors involved in this phenomenon, however, has not been elucidated. To solve this question, phenotype, genotype, dietary Phe intake, timing of blood collection, and Phe metabolism were retrospectively analyzed in 21 phenylketonuria newborns and prospectively in 1.
  
  
  METHODS
  Patients were assigned to 1 of 4 classes of phenylalanine hydroxylase (PAH) deficiency (severe, moderate, mild, and benign) on the basis of their Phe tolerance. Phe ingested, tolerated, and released from endogenous catabolism was assessed.
  
  
  RESULTS
  From birth to screening test, the amount of Phe tolerated ranged from 704 to 1620 mg, according to the class of PAH deficiency. The amount of Phe ingested ranged only from 204 to 405 mg, whereas the endogenous Phe breakdown ranged from 812 to 1534 mg, resulting in a rate of Phe catabolism ranging from 262 to 341 mg/day, regardless of the class of PAH deficiency.
  
  
  CONCLUSIONS
  The high rate of protein catabolism is the main determinant of neonatal hyperphenylalaninemia. It is sufficient to turn to positive the screening test in severe and moderate PAH deficiency. In mild and benign PAH deficiency, the outcome of screening procedures can be substantially altered by the concurrence of genetic and peristaltic factors. These results imply that the value of blood Phe at the screening test is not fully predictive of the phenylketonuria phenotype, and strengthen concerns regarding the reliability of early screening procedures.
authors.affiliation: Department of Pediatrics, University of Torino, Italy. alberto.ponzone@unito.it
authors.forename: Alberto
authors.initials: A
authors.lastname: Ponzone
authors.forename: Marco
authors.initials: M
authors.lastname: Spada
authors.forename: Luca
authors.initials: L
authors.lastname: Roasio
authors.forename: Francesco
authors.initials: F
authors.lastname: Porta
authors.forename: Alessandro
authors.initials: A
authors.lastname: Mussa
authors.forename: Silvio
authors.initials: S
authors.lastname: Ferraris
mesh_terms: D000293:Adolescent; D015415:Biomarkers / Q000097:blood; D002648:Child; D002675:Child, Preschool; D003937:Diagnosis, Differential; D005260:Female; D005838:Genotype; D006801:Humans; D007227:Infant Nutritional Physiological Phenomena; D007231:Infant, Newborn; D008297:Male; D008403:Mass Screening; D009154:Mutation; D010641:Phenotype; D010649:Phenylalanine / Q000097:blood*; D010651:Phenylalanine Hydroxylase / Q000172:deficiency*; D010661:Phenylketonurias / Q000175:diagnosis* / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D011237:Predictive Value of Tests; D011506:Proteins / Q000378:metabolism*; D012189:Retrospective Studies
chemical_list: D015415:Biomarkers; D011506:Proteins; D010649:Phenylalanine; D010651:Phenylalanine Hydroxylase