Tandem Mass Spectrometry.

Methods used for detection and results

Analytical Techniques for Screening There are many analytical techniques usable for semi-quantitative and quantitative analysis from dry blood spots of the levels of phenylalanine (Schulze et al., 2002). In the expanded and the introduction of the newborn screening, MS/MS (tandem mass spectrometry) is used by the majority of screening laboratories for the amino acids analysis which includes acylcarnitine and phenylalanine species. Bacterial Inhibition Test On agar plate, bacterial growth has had the inhibition through a specific chemical’s (‘inhibitor’) action in the middle of the plate on a small disc. Any compound, which is structurally related, such as metabolite or amino acid (phenylalanine) will be completing the inhibitor or would initiate the bacterial growth. Result Around the punch, the growth zone will be in proportion to the phenylalanine amount such as the blood concentration is brought to the platter with dry blood punch. Tandem Mass Spectrometry The introduction of MS/MS to the screening laboratories of newborn was done in late 1990s. Results The phenylalanine measurement to tyrosine ratio differentiates between the cases and false positives of HPA/PKU. Newborn Screening for PKU For elevated phenylalanine levels follow up, a detailed algorithm for PKU’s newborn screening can be depicted in figure below.

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The FACT and ACT sheet have been followed by this algorithm that American College of Medicine developed (American Academy of Pediatrics, 1996). Any elevated level of phenylalanine found in the sample of newborn screening must be subject to following by the second sample, either whole blood sample or a dry blood filter card. The former is advantageous in terms of all amino acids’ accurate analysis and is preferred when there is significant elevation (e.g. above 3 mg/dl) of the first phenylalanine. The elevation of phenylalanine in critically ill and/or preterm infants is because of TPN (total parental nutrition) and/or catabolism. These circumstances lead to analysis of all amino acids in whole blood in fasted state or to follow a brief period without TPN.

Just before delivery or during the life’s first days of infants, the mothers are given antibiotics that do not affect the PKU’s screening results unless there is use of bacterial inhibition test. In neonates, elevated phenylalanine levels are secondary to HPA or PKU and also observable in biopterin metabolism, which is the less frequent disorders (Longo, 2009). In At-Risk Populations, Screening for PKU Besides PKU of newborn screening, a number of studies have indicated that PKU’s relatively high prevalence in mentally retarded, the adults and children unscreened previously (Sempere et al., 2010). Results The PKU’s prevalence of adults who are mentally retarded in an unselected population in Spain has been 0.3%. In Iran, a similar research has recognized a prevalence of 2.1% (Sempere et al., 2010).

Principle of method

The screening of the disorders having to follow criteria has been developed by Wilson and Jungner in 1968 as an initiative by WHO on the practice and principles of disease screening (Wilson and Jungner, 1968). The early detection of the disease and its treatment is basically very simple. The path, however, in relation to its successful achievement (to bring undetected disease previously on one hand, and to avoid the harming the people who do not need treatment on the other hand) is not very simple although at times it is apparently deceptively easy. Even today, these principles have validity, albeit their adaptation has been with the modern newborn screening requirements.

The disorders such as PKU, being screened must have reasonable frequency and they must constitute considerable problem of public health. The course of natural disease must be understood and intervention or treatment form should exist altering the course of natural disease benefitting the patients affected. The specific and sensitive screening test is obvious, readily applicable to dry blood spots of neonates in large number. This has been the newborn screening’s prerequisite for any disorder such as PKU. PKU, in many ways, has led the way and in fulfilling all criteria has been the first disorder, excepting the countries where there is low PKU incidences, such as Japan and Finland (Aoki et al., 2007).

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References

  • American Academy of Pediatrics (1996) ‘Committee on Genetics: Newborn screening fact sheets’, Pediatrics, 98:473–501.
  • Aoki, K., Ohwada, M. and Kitagawa, T. (2007) ‘Long-term follow-up study of patients with phenylketonuria detected by the newborn screening programme in Japan’, J Inherit Metab Dis, 30:608
  • Longo, N. (2009) ‘Disorders of biopterin metabolism’, J Inherit Metab Dis, 32:333–342.
  • Schulze, A., Mayatepek, E. and Hoffmann, G. F. (2002) ‘Evaluation of 6-year application of the enzymatic colorimetric phenylalanine assay in the setting of neonatal screening for phenylketonuria’, Clin Chim Acta, 317:27–37. Sempere, A., Arias, A., Farre, G., et al. (2010) ‘Study of inborn errors of metabolism in urine from patients with unexplained mental retardation’, J Inherit Metab Dis, 33:1–7. Wilson, J. M. G. and Jungner, G. (1968) Principles of Screening for Disease, Geneva, World Health Organization.

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