**5. Treatment options**

Currently, there are numbers of available therapeutic approaches that aim in a substrate and downstream products restoration balance (**Figure 11**). One of the

#### **Figure 12.**

*Removal of toxic ammonia. In urea cycle disorders ammonia cannot be converted to urea, but alternatively can be converted to glutamine and glycine. Ammonia scavengers phenylbutyrate and sodium benzoate react with glutamine and glycine and consequently remove excess of ammonia. Phenylglutamine and hippurate are excreted in urine.*

approaches in this direction is to reduce substrate accumulation by dietary restrictions. Nutritional therapies restrict offending amino acid or often total protein consumption through provision and monitoring of all essential components to meet dietary requirements. For example, special medical foods for PKU affected individuals have a very negligible amount of phenylalanine, but supplement the total protein required for the normal growth, development and nutritional status. Another example is MSUD nutritional management that restricts intake of the branch chain amino acids [41], but supplies the majority of the protein required in the standard diet.

Amino acids disorders are often manifested by the accumulation of toxic downstream metabolites. For example, urea acid disorders are characterized by life-threatening hyperammonemia (ammonia accumulation). Toxic metabolites removal treatment aims at reducing production or increasing excretion of these metabolites. To reduce hyperammonemia, sodium benzoate and phenylbutyrate are used to increased ammonia excretion (**Figure 12**) and to bypass the urea cycle metabolic block [42, 43]. Another example is an approach to reduce the production of succinylacetone, a neurological toxin that accumulates in tyrosinaemia I. Nitisinone (NTBC) treatment blocks a formation of fumarylacetoacetate and its subsequent conversion to the succinylacetone [44, 45].

If as a result of mutation, a specific enzyme still retains its residual activity, it can be stimulated by a co-factor or a co-factor precursor supplementation. This concept applies in treating tetrahydrobiopterin deficiency (**Figure 2**) [46, 47], remethylation defects (**Figure 4**) [48] and cystathionine beta-synthase deficiency (**Figure 4**) [10]. In some amino acids disorders, even partial metabolic block prevents from synthesizing an essential downstream metabolite to meet metabolic requirements. In these cases, essential product supplementation is required. For example, as a part of urea cycle disorders management, l-arginine and l-citrulline are administered [43]. This helps to reduce excessive protein catabolism, due to the low arginine levels.

#### **6. Conclusion**

In conclusion, amino acids disorders are a group of inborn errors of metabolism with highly variable clinical and biochemical presentations. Clinical manifestation often comprises severe neurological symptoms, growth and developmental delays. Most of the amino acids disorders related conditions are included in the newborn screening program to facilitate early diagnosis and early disease treatment. The analysis of physiological amino acids levels is a key tool in the diagnosis and clinical management of inborn errors of amino acids metabolism. A small subset of amino acids is analyzed in newborn screening by tandem mass spectrometry and leads to the detection of affected neonates even when they do not have a symptomatic disease manifestation. A more comprehensive, quantitative amino acids analysis covers analysis of nearly 40 amino acids. Prior to the analysis and results interpretation, pre-analytical variables such as a fasting status and medication treatments should be taken into account in order to avoid false reported findings. A most common sample preparation method for the quantitative amino acids analysis is acidification of specimen with a known small volume of concentrated acid, such as sulfosalicylic acid to precipitate proteins and large molecules, followed by centrifugation, leaving the water-soluble amino acids in the supernatant for the analysis. A variety of analytical methods have been developed over the past 60 years, and scientists have made significant achievements in the fields of derivatization, chromatography and mass spectrometry, however, the ion exchange chromatography method still

**129**

**Author details**

the field [50, 51].

Yana Sandlers

provided the original work is properly cited.

Cleveland State University, Cleveland, OH, USA

\*Address all correspondence to: y.sandlers@csuohio.edu

*Amino Acids Profiling for the Diagnosis of Metabolic Disorders*

remains the gold standard technique in the field. It is expected that more advanced techniques will be developed targeting important clinical laboratories requirements such as reduced samples pretreatment, linearity over the large concentration range for over the 40 amino acids, increased automation, high sensitivity, shorter run time and improved specificity. These methodological improvements will facilitate the diagnostic process and therapy monitoring for amino acids disorders. The field is also expending to the more exploratory platforms such as a whole-genome sequencing and untargeted metabolomics. Although these modalities have some restrictions in clinical settings [1, 49], they facilitate novel genes identification, novel biomarkers discovery and disease associations and thus strongly advancing

The major treatment goal for amino acids disorders is to normalize imbalance between the substrate and its downstream products and to avoid accumulation of the toxic substances. At the same time, nutritional management must meet basic dietary requirements for growth and normal development. Even though for many amino acids disorders current treatments do not offer a cure, they significantly improve the quality of life. It is expected over the upcoming years, that methodological advances will lead to a greater understanding of the IEM and in particular amino acids related disorders which will help further to improve disease outcomes.

*DOI: http://dx.doi.org/10.5772/intechopen.84672*

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

#### *Amino Acids Profiling for the Diagnosis of Metabolic Disorders DOI: http://dx.doi.org/10.5772/intechopen.84672*

*Biochemical Testing - Clinical correlation and Diagnosis*

subsequent conversion to the succinylacetone [44, 45].

the standard diet.

low arginine levels.

**6. Conclusion**

approaches in this direction is to reduce substrate accumulation by dietary restrictions. Nutritional therapies restrict offending amino acid or often total protein consumption through provision and monitoring of all essential components to meet dietary requirements. For example, special medical foods for PKU affected individuals have a very negligible amount of phenylalanine, but supplement the total protein required for the normal growth, development and nutritional status. Another example is MSUD nutritional management that restricts intake of the branch chain amino acids [41], but supplies the majority of the protein required in

Amino acids disorders are often manifested by the accumulation of toxic downstream metabolites. For example, urea acid disorders are characterized by life-threatening hyperammonemia (ammonia accumulation). Toxic metabolites removal treatment aims at reducing production or increasing excretion of these metabolites. To reduce hyperammonemia, sodium benzoate and phenylbutyrate are used to increased ammonia excretion (**Figure 12**) and to bypass the urea cycle metabolic block [42, 43]. Another example is an approach to reduce the production of succinylacetone, a neurological toxin that accumulates in tyrosinaemia I. Nitisinone (NTBC) treatment blocks a formation of fumarylacetoacetate and its

If as a result of mutation, a specific enzyme still retains its residual activity, it can be stimulated by a co-factor or a co-factor precursor supplementation. This concept applies in treating tetrahydrobiopterin deficiency (**Figure 2**) [46, 47], remethylation defects (**Figure 4**) [48] and cystathionine beta-synthase deficiency (**Figure 4**) [10]. In some amino acids disorders, even partial metabolic block prevents from synthesizing an essential downstream metabolite to meet metabolic requirements. In these cases, essential product supplementation is required. For example, as a part of urea cycle disorders management, l-arginine and l-citrulline are administered [43]. This helps to reduce excessive protein catabolism, due to the

In conclusion, amino acids disorders are a group of inborn errors of metabolism with highly variable clinical and biochemical presentations. Clinical manifestation often comprises severe neurological symptoms, growth and developmental delays. Most of the amino acids disorders related conditions are included in the newborn screening program to facilitate early diagnosis and early disease treatment. The analysis of physiological amino acids levels is a key tool in the diagnosis and clinical management of inborn errors of amino acids metabolism. A small subset of amino acids is analyzed in newborn screening by tandem mass spectrometry and leads to the detection of affected neonates even when they do not have a symptomatic disease manifestation. A more comprehensive, quantitative amino acids analysis covers analysis of nearly 40 amino acids. Prior to the analysis and results interpretation, pre-analytical variables such as a fasting status and medication treatments should be taken into account in order to avoid false reported findings. A most common sample preparation method for the quantitative amino acids analysis is acidification of specimen with a known small volume of concentrated acid, such as sulfosalicylic acid to precipitate proteins and large molecules, followed by centrifugation, leaving the water-soluble amino acids in the supernatant for the analysis. A variety of analytical methods have been developed over the past 60 years, and scientists have made significant achievements in the fields of derivatization, chromatography and mass spectrometry, however, the ion exchange chromatography method still

**128**

remains the gold standard technique in the field. It is expected that more advanced techniques will be developed targeting important clinical laboratories requirements such as reduced samples pretreatment, linearity over the large concentration range for over the 40 amino acids, increased automation, high sensitivity, shorter run time and improved specificity. These methodological improvements will facilitate the diagnostic process and therapy monitoring for amino acids disorders. The field is also expending to the more exploratory platforms such as a whole-genome sequencing and untargeted metabolomics. Although these modalities have some restrictions in clinical settings [1, 49], they facilitate novel genes identification, novel biomarkers discovery and disease associations and thus strongly advancing the field [50, 51].

The major treatment goal for amino acids disorders is to normalize imbalance between the substrate and its downstream products and to avoid accumulation of the toxic substances. At the same time, nutritional management must meet basic dietary requirements for growth and normal development. Even though for many amino acids disorders current treatments do not offer a cure, they significantly improve the quality of life. It is expected over the upcoming years, that methodological advances will lead to a greater understanding of the IEM and in particular amino acids related disorders which will help further to improve disease outcomes.
