A Case of Suspected Hyperphenylalaninemia at Newborn Screening by Tandem Mass Spectrometry during Total Parenteral Nutrition

Abstract

Phenylketonuria (PKU) is a rare autosomal recessive condition affecting about 1 in 10,000 people in the Europe, with a higher rate in some countries, like Ireland and Italy. In Italy, newborn screening (NBS) by MS/MS allows the diagnostic suspicion of PKU and its variants (Hyperphenylalaninemia (HPA), Tetrahydrobiopterin (BH4) synthesis deficiency, and Tetrahydrobiopterin (BH4) recycling deficiency) through the quantification of Phenylalanine (Phe) and the Phenylalanine/Tyrosine (Phe/Tyr) ratio in dried blood Spot (DBS) samples. Here, we report a case of an HPA whose suspicion was possible with expanded NBS, even if the normal-weight newborn was in total parenteral nutrition (TPN). It is known that TPN may present metabolic alterations, mainly for amino acids at NBS in MS/MS, frequently causing false positives. Actually, TPN is considered a special protocol in NBS, requiring several sample collections. In particular, a DBS sample is required before TPN, at basal time point (48 h after birth) and 72 h after the end of the procedure. In the case we report, even if the first DBS sample (before TPN) resulted negative, the repeated NBS tests revealed increased levels of Phe and dramatically high Phe/Tyr ratio. Thus, the newborn was recalled, and the NBS test was repeated several times before that HPA suspicion was confirmed by other specific biochemical tests. This case highlights the importance of Phe/Tyr ratio, only detectable by MS/MS analysis, in supporting the diagnostic suspicion during amino acids administration in the neonatal period.

Timing of Newborn Blood Collection Alters Metabolic Disease Screening Performance

“…In contrast to the other covariates studied, TPN was associated with different metabolic patterns in relation to AaBC, and particularly for blood sampling before 24 h ( Figures 2D,H,L,P ). While these differences could be caused directly by TPN, there may also be other confounding factors related to TPN such as preterm birth or an unknown disease status ( 33 ). We only included term infants (37–41 weeks) with a normal birth weight (2,500 g to 4,000 g) in the TPN analysis based on our finding of a smaller fraction of newborns with TPN amongst term infants (0.45%) compared to preterm infants (12.13%).…”

Partial Biotinidase Deficiency Revealed Imbalances in Acylcarnitines Profile at Tandem Mass Spectrometry Newborn Screening

“…In Italy, BTD deficiency is one of the disorders incorporated in the nationwide screening program that also includes testing for disorders of amino acid metabolism, urea cycle metabolism, organic acid metabolism, and for defects of fatty acid oxidation, galactosemia, cystic fibrosis, and congenital hypothyroidism. Nowadays, it is well known that metabolic findings and imbalances revealed at NBS may be influenced not only by the genome, but also by other factors such as partial enzyme deficiencies, treatments, nutritional deficiency, prematurity, and maternal defects [ 15 , 16 , 17 ]. In fact, in screening newborns for BTD deficiency, both profound and partial variants can be detected [ 1 , 18 ].…”

A False-Positive Case of Methylmalonic Aciduria by Tandem Mass Spectrometry Newborn Screening Dependent on Maternal Malnutrition in Pregnancy

“…In agreement with laboratory collection protocol, samples for NBS are collected at 48-72 h after birth by heel-pricking blood specimen onto Ahlstrom 226 filter paper provided by PerkinElmer. Details of NBS by a flow injection-tandem mass spectrometry analysis (FIA-MS/MS) for the detection of 36 IEMs [9] as well as information on second-tier analysis for the determination of mma, mca, and hcy by LC-MS/MS are fully described in Supplementary Materials and specifically reported in Figure S1 and in Tables S3-S6.…”

“…Figure 1 shows the workflow of the second-tier testing strategy in the management of C3 alterations. In recent years, the application of MS/MS to NBS for the expansion of the IEMs panel has strongly changed the scenario: leading to significant advantages in terms of diagnosis and treatment of these metabolic disorders, but also bringing out a number of "side effects" [9]. In detecting newborns with classical OAs in a pre-symptomatic or early symptomatic period, MS/MS NBS may point out other conditions as unintended consequences: partial enzyme deficiency, maternal defects, nutritional deficiency, drugs, prematurity, and a sick neonate [4].…”