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Electrospray tandem mass spectrometry for newborn screening

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Methods
Research
Implications
Limitations
Safety
Future research
Author information
Bibliography

Methods
  • General: Mass spectrometry (MS) is an analytical technique used for measuring the molecular mass of a sample using a mass spectrometer. Molecular mass is the mass of a molecule relative to the mass of a standard atom. A mass spectrometer creates charged particles called ions from molecules and analyzes those ions to provide information about the molecular weight/mass of the compound and its chemical structure. A mass spectrometer is divided into three areas, namely the ionization source, the analyzer, and the detector.
  • A tandem mass spectrometer is an instrument used in MS that has more than one analyzer, in practice usually two. The two analyzers are separated by a fragmentation chamber/collision cell into which an inert gas (e.g., argon, xenon) is admitted to collide with the selected sample ions and bring about their breakdown (fragmentation). The fragmented ions are passed through the two analyzers, which may be of the same or of different types. The most common combinations being: quadrupole-quadrupole or quadrupole-time-of-flight analyzers, which are explained below. The major steps involved in electrospray tandem mass spectrometry are described below.
  • First mass spectrometer: The first step involves the introduction of the sample into the ionization source of the first mass spectrometer. Electrospray ionization (ESI) is a technique in MS used to produce ions because ions are easier to manipulate than neutral molecules, thereby facilitating the identification of the target molecule/analyte in the sample. In ESI, the sample solution containing the analyte is dissolved in a large amount of solvent that flows through a source chamber to form droplets. The droplets carry charge and highly charged analyte molecules are formed when the solvent in the solution vaporizes.
  • Mass analyzer: The ions then move into the analyzer region of the first mass spectrometer where the ions are separated and weighed according to their mass-to-charge ratios. The mass-to-charge ratio is the physical quantity that may be calculated by dividing the charge of the substance/analyte by the mass of the same substance. There are a number of mass analyzers available and some of them include time-of-flight (TOF) analyzers, quadrupoles, etc. TOF analyzers use an electric field to filter ions based on their mass-to-charge ratio. The quadrupole mass analyzer consists of four circular rods that are parallel to each other and facilitate the filtering of sample ions based on their mass-to-charge ratio.
  • Collision cell chamber: The ions produced and analyzed in the first mass spectrometer then enter the collision cell chamber. The ions are broken into smaller pieces using an inert gas (e.g. argon, xenon), which collides with the selected sample ions and brings about their fragmentation to sort out the ions needed by the researchers for the diagnosis of disease.
  • Second mass spectrometer: The sorted or selected ions are then introduced into the second mass spectrometer for further analysis. The selected analyte is separated based on its mass-to-charge ratios, which is similar to the process of analysis in the first mass spectrometer.
  • Detector: The detector in the mass spectrometer monitors the ion current and amplifies (increases) it. There are many types of detectors and most of them produce an electronic signal when struck by an ion. The signal is transmitted to the data system (computer programs) and is stored in the form of mass spectra. A mass spectrum is commonly presented as a vertical bar graph, wherein each bar represents an ion having a specific mass-to-charge ratio (m/z) and the amount of the ion is indicated by the length of the bar. The m/z value of an ion is equivalent to mass itself because most of the ions formed in the mass spectrometer have a single charge. Hence, this method facilitates the accurate identification of the target molecule. Thus, MS/MS helps to identify the compound that is responsible for causing a disorder in newborns and assists in the early identification of the disorder allowing the treatment to begin at an early stage for better treatment outcomes.

Research
  • Electrospray tandem mass spectrometry (MS/MS) may assist in diagnosing several metabolic disorders. Several studies are being conducted to improve MS/MS as well as detect more metabolic disorders in newborns using MS/MS. Some of the studies are described below.
  • Methylmalonic and propionic aciduria: Both of these diseases are types of organic aciduria, which is a group of metabolic disorders that interferes with the normal amino acid metabolism, leading to a buildup of acids in abnormal amounts. This causes damage to many organs, especially the central nervous system. Methylmalonic and propionic aciduria have been found due to the decreased function of enzymes, methylmalonyl-CoA mutase and propionyl-CoA carboxylase, respectively. The screening of newborns with electrospray tandem mass spectrometry (MS/MS) may decrease the incidence of deaths thanks to early detection and the treatment of diseases in affected children.
  • Peroxisomal disorders: Peroxisomal disorders are a group of metabolic diseases that have defective peroxisomes, which is an organelle (a specialized organ within a cell) that helps in cell function such as the oxidation of fatty acids. The identification of fatty acids (hexacosanoic acid) is the basis for the detection of these disorders; hence, researchers have used MS/MS along with ultra performance liquid chromatography (UPLC) to detect these disorders. UPLC is a type of analytical technique used in a laboratory to separate, identify, and quantify (count) compounds. The degree of separation is increased by forcing a solvent under pressure through a densely packed adsorbent/absorptive material. Initial results of the studies show promise; however, further research is required to examine the benefits and drawbacks of the combined technique.
  • Tyrosinemia type 1: Tyrosinemia is a type of genetic disorder wherein an elevated level of the amino acid tyrosine is found in the blood due to the decreased amount of the enzyme fumarylacetoacetate hydrolase. Symptoms usually appear in the first few months of life and include failure to gain weight or grow at the expected rate (failure to thrive) and may lead to liver and kidney failure. Researchers have conducted studies using MS/MS and UPLC to identify this disorder by determining the level of succinylacetone, a metabolite elevated in tyrosinemia type 1.

Implications
  • General: Electrospray tandem mass spectrometry (MS/MS) may assist in detecting metabolic disorders during the neonatal period (first 28 days of life) that previously were diagnosed only after symptoms developed later in life. MS/MS is a technique or type of mass spectrometry (MS) used for measuring the molecular mass of a sample; it helps to identify the chemical composition of a compound present in the sample. MS/MS has been used for several years in children suspected of having inborn errors of metabolism (IEM) using just a single blood drop. IEM include a large group of genetic diseases characterized by illnesses that occur when the body is unable to process fats (lipids), proteins, sugars (carbohydrates), or nucleic acids properly.
  • Generally, in metabolic disorders, specific enzymes that facilitate the breakdown of amino acids or that are needed for converting fat to energy do not work or are absent. This prevents a compound from breaking down/being metabolized and thus it accumulates in the blood and tissues of the body. The accumulated compound is toxic or poisonous, causing damage to different organs of the body. MS/MS detects the levels of this toxic compound and helps in the diagnosis of disorders.
  • In newborns, MS/MS enables medical professionals to count the number of many compounds, such as acylcarnitines and amino acids, in a single process. Carnitine is an ammonium compound that has a key role in the transportation system of fats in and out of the mitochondria, the cell's energy factory. In humans, carnitines are synthesized in the liver, kidney, and brain and actively transported to other areas of the body. It is called as an acylcarnitine when a fat molecule is attached to a carnitine. An acylcarnitine is known or determined by the size of the fat molecule attached to it. The acylcarnitine is classified as a short, medium, or long chain of fats. For example, in a metabolic disorder called medium chain acylCoA dehydrogenase deficiency (MCADD), the fat attached to carnitine is a medium-sized eight-carbon fatty acid known as octanoylcarnitine.
  • MS/MS helps to screen newborns with inborn errors of metabolism (IEM) in the categories of fatty acid oxidation disorders, organic acidemias, and aminoacidopathies, which are explained below. All these categories of diseases, which are known to cause sudden death in infancy, may be prevented or treated effectively by the early identification of these diseases by MS/MS.
  • Aminoacidopathies: Aminoacidopathies are a type of inborn error of metabolism (IEM) where there is an enzyme defect that inhibits the body's ability to metabolize certain proteins (amino acid).
  • Fatty acid oxidation disorders: Fatty acid oxidation disorder is a genetic metabolic deficiency wherein the body is unable to breakdown (oxidize) fatty acids to make energy because an enzyme involved in the process is either absent or is nonfunctional.
  • Maple syrup urine disease (MSUD): MSUD is a disease caused by the defective metabolism of amino acids such as leucine, isoleucine, and valine due to low levels of an enzyme called branched-chain alpha-keto acid dehydrogenase (BCKD) in the blood. This results in amino acids being present in the blood and urine in high concentrations. Some signs of the disease include feeding difficulties, physical and mental retardation, and a urine odor similar to that of maple syrup. Neonatal death is also common.
  • Medium chain acylCoA dehydrogenase deficiency (MCADD): MCADD is diagnosed based on an elevated level of the fat attached to carnitine known as octanoylcarnitine. It is one of the most common fatty acid oxidation disorders, presenting as acute episodes triggered by prolonged fasting for more than 12-16 hours, with hypoglycemia (reduced blood sugar level), vomiting, and fatigue or weariness. This may progress to seizures, coma, or even sudden death and usually presents before the age of three years.
  • Organic acidemia: Organic acidemia, also known as organic aciduria, is a group of metabolic disorders that interferes with the normal amino acid metabolism, leading to the buildup of acids in abnormal amounts. This causes damage to many organs, especially the central nervous system. One of the examples of this disorder is explained below.
  • Phenylketonuria (PKU): Newborns with PKU lack the enzyme phenylalanine hydroxylase that converts the amino acid phenylalanine to tyrosine. If left untreated, this leads to excessive buildup of phenylalanine and its breakdown products in the blood that are toxic to the brain, causing brain damage and progressive mental retardation.
  • Sudden infant death syndrome (SIDS): SIDS is the sudden and unexplained death of an infant younger than one year of age. It may strike without warning, usually in a seemingly healthy infant. It is a leading cause of death among infants who are one month to one year old; it claims the lives of about 2,500 infants each year in the United States. It is most common, however, between the ages of two and four months. Although multiple factors may be involved, some studies have suggested that fatty acid metabolism disorders may be responsible for cases of sudden and unexpected death in infancy.
  • Advantage of MS/MS: Due to the large increase in the number of inherited metabolic disorders detectable in the newborn period, MS/MS screening improves the possibility of early detection of disorders before the initiation of symptoms and helps to start the treatment while the infant is still healthy. MS/MS also assists in defining the range of clinical diseases related to these disorders and thereby may reduce deaths due to these disorders in the affected children. MS/MS also provides rapid results (within one to two minutes), and therefore may be used to screen large numbers of samples in newborn screening programs.

Limitations
  • The diseases screened using tandem mass spectrometry (MS/MS) are rather rare and vary in clinical severity. Also, the screening's clinical utility or usefulness and cost-effectiveness have not yet been fully established. Hence, further careful data collection regarding the sensitivity of MS/MS screening and outcomes of patients in whom disorders are detected is required.
  • The cost of MS/MS itself is expensive and may be impractical to use in many countries for mass screening programs. Also, tandem mass spectrometry requires experts (trained personnel) to perform the analyses and interpret the large amount of clinical data produced from the analysis of a blood sample. Hence, to get accurate results, people have to be trained, which again increases cost and time.
  • MS/MS is a useful tool to detect specific metabolic conditions through newborn screening. False negative and false positive results, however, do occur. Close coordination between the laboratories performing the screening is needed to determine screening parameters and to adjust cut-off levels to reduce false-positive and false-negative results. A false positive is a positive test result in spite of the true absence of a disease/disorder and a false negative is a negative test result in spite of the true presence of a disease/disorder.

Safety




Future research
  • General: Tandem mass spectrometry (MS/MS) is a powerful tool that expands newborn screening for many diseases. Along with other types of mass spectrometry, it may be used to analyze other treatable disorders or to improve existing tests so that more accurate and more comprehensive tests may be available in future. This may lead to the further development of new therapies along with the improvement of existing treatments, which may benefit future generations.
  • Maple syrup urine disease (MSUD): Researchers are conducting studies analyzing the results of newborn screening with electrospray tandem mass spectrometry for inborn errors of metabolism, such as MSUD. MSUD is a disorder due to low levels of an enzyme called branched-chain alpha-keto acid dehydrogenase (BCKD) in the blood. They have found that newborns with the intermediate form of MSUD cannot be diagnosed with this method, thus suggesting that partial enzyme deficiencies may not be detected using MS/MS. Hence, further research is required to improve MS/MS detection of mild or intermediate forms of metabolic disorders.

Author information
  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Bibliography
  1. Al-Dirbashi OY, Rashed MS, Jacob M, et al. Improved method to determine succinylacetone in dried blood spots for diagnosis of tyrosinemia type 1 using UPLC-MS/MS. Biomed Chromatogr. 2008 Jul 23;doi 10.1002/bmc.1049.
  2. Al-Dirbashi OY, Santa T, Rashed MS, et al. Rapid UPLC-MS/MS method for routine analysis of plasma pristanic, phytanic, and very long chain fatty acid markers of peroxisomal disorders. J Lipid Res. 2008 Aug;49(8):1855-62.
  3. Bhattacharya K, Khalili V, Wiley V, et al. Newborn screening may fail to identify intermediate forms of maple syrup urine disease. J Inherit Metab Dis. 2006 Aug;29(4):586.
  4. Centers for Disease Control and Prevention. . Accessed September 2, 2008.
  5. Copeland S. A review of newborn screening in the era of tandem mass spectrometry: what's new for the pediatric neurologist? Semin Pediatr Neurol. 2008 Sep;15(3):110-6.
  6. Deodato F, Boenzi S, Santorelli FM, et al. Methylmalonic and propionic aciduria. Am J Med Genet C Semin Med Genet. 2006 May 15;142C(2):104-12.
  7. Genetics Home Reference. . Accessed September 2, 2008.
  8. Marsden D. Expanded newborn screening by tandem mass spectrometry: the Massachusetts and New England experience. Southeast Asian J Trop Med Public Health. 2003;34 Suppl 3:111-4.
  9. Natural Standard: The Authority on Integrative Medicine. . Copyright © 2009.
  10. Opdal SH, Rognum TO. The sudden infant death syndrome gene: does it exist? Pediatrics. 2004 Oct;114(4):e506-12.

Copyright © 2011 Natural Standard (www.naturalstandard.com)


The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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