**4. Diagnosis of amino acids related disorders**

The initial diagnosis of amino acids disorders is based on clinical presentation and biochemical findings such as abnormal levels of specific amino acids (**Tables 1–6**) or accumulation of the downstream metabolites in biological fluids, however, these characteristics are very heterogenic and often nonspecific. The most common clinical indications for the quantitative amino acid analysis in neonates and pediatric patients are coma, lethargy, seizures and vomiting, unexplained developmental delay and siblings with similar symptoms. Plasma amino acids analysis is also ordered as a conformational test to follow up abnormal newborn screening results. Hyperammonemia is characteristic to the most urea cycle disorders (**Table 3**) and therefore is another

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**Figure 12.**

*excreted in urine.*

*Amino Acids Profiling for the Diagnosis of Metabolic Disorders*

strong indication for plasma amino acids analysis. Additional general biochemical indicators of follow up quantitative amino acids analysis are ketosis (high blood and urine ketones), acidosis (blood pH below 7.35) and lactic acidemia (high lactate excretion), alkalosis (blood pH above 7.45), polyuria, polydipsia (extreme thirstiness), and dehydration. Amino acids analysis is also an important tool in the diagnosis of muscle and liver diseases, neurological disorders, renal failure, autism spectrum disorders and nutritional disturbances. Interpretation of amino acids profile is not just based on the abnormal level of a single amino acid, but rather involves pattern recognition, diagnostic ratios (**Tables 1** and **2**) and correlation to the patient's clinical history. It is recommended to confirm the diagnosis by molecular analysis or *in vitro*

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

*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* 

enzymatic assay (usually skin or tissue biopsy sample or blood cells).

**5. Treatment options**

**Figure 11.**

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

*Treatment strategies in amino acids disorders.*

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

**Figure 11.** *Treatment strategies in amino acids disorders.*

*Biochemical Testing - Clinical correlation and Diagnosis*

scans in the single analysis.

*Sulfur amino acids and their disulfides.*

analysis.

**Figure 10.**

limitations.

**4. Diagnosis of amino acids related disorders**

collision cell (*m*/*z* 119). For glycine and arginine, the most intensive signal corresponds to the loss of 56 and 161 Da, respectively. All these specific losses or transitions can be detected by different and highly specific tandem mass spectrometer's

The main limitation of the FIA-MS/MS is inability to differentiate amino acids that share the same *m*/*z* such as leucine/isoleucine and hydroxyproline (butylated derivatives *m*/*z* 188), alanine/sarcosine (butylated derivatives *m*/*z* 146) and in a more extended profiles glutamine/lysine (butylated derivatives *m*/*z* 186), proline/ asparagine (butylated derivatives *m*/*z* 172). Also, FIA-MS/MS is not applicable for cysteine and homocysteine analysis since these amino acids are not stable and react to form cystine and homocystine (**Figure 10**). During the ionization process, cystine and homocystine produce double charged molecules and it complicates the

Due to the high sensitivity and selectivity, there are more mass spectrometrybased techniques are available for the amino acids analysis, although because of extensive sample preparation or limited number of amino acids covered, these methods are not widely used in clinical laboratories. Gas chromatography mass spectrometry (GCMS) [36], capillary electrophoresis mass spectrometry (CEMS) [37], ion pairing (IP)-LC-MS/MS, HILIC-LC-mass spectrometry [38] and two column LC-MS/MS methods [39], ion pairing (IP)-LC-HRMS (TOF) [40] can be successfully applied for the physiological amino acids analysis although with some

The initial diagnosis of amino acids disorders is based on clinical presentation and biochemical findings such as abnormal levels of specific amino acids (**Tables 1–6**) or accumulation of the downstream metabolites in biological fluids, however, these characteristics are very heterogenic and often nonspecific. The most common clinical indications for the quantitative amino acid analysis in neonates and pediatric patients are coma, lethargy, seizures and vomiting, unexplained developmental delay and siblings with similar symptoms. Plasma amino acids analysis is also ordered as a conformational test to follow up abnormal newborn screening results. Hyperammonemia is characteristic to the most urea cycle disorders (**Table 3**) and therefore is another

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strong indication for plasma amino acids analysis. Additional general biochemical indicators of follow up quantitative amino acids analysis are ketosis (high blood and urine ketones), acidosis (blood pH below 7.35) and lactic acidemia (high lactate excretion), alkalosis (blood pH above 7.45), polyuria, polydipsia (extreme thirstiness), and dehydration. Amino acids analysis is also an important tool in the diagnosis of muscle and liver diseases, neurological disorders, renal failure, autism spectrum disorders and nutritional disturbances. Interpretation of amino acids profile is not just based on the abnormal level of a single amino acid, but rather involves pattern recognition, diagnostic ratios (**Tables 1** and **2**) and correlation to the patient's clinical history. It is recommended to confirm the diagnosis by molecular analysis or *in vitro* enzymatic assay (usually skin or tissue biopsy sample or blood cells).
