During process of digestion, proteins are broken down in into amino acids. Mainly the proteins contain 22 standard amino acids and several non-standard amino acids. We possess synthetic pathways for only 11 amino acids out of 22 standard amino acids. The remaining ones must be obtained from diet and hence they are referred to as essential amino acids. During day to day protein turnover most of amino acids used in protein synthesis were not from food but obtained through endogenous protein breakdown. The amino acid degradation occurs in Liver, Muscles and Kidneys. The liver being the major site of degradation while for some specific ones Muscles and Kidneys are the sites. During the amino acid degradation the nitrogen is removed from the carbon skeleton and transferred to the alpha-ketoglutarate which results into Glutamate. The carbon skeletons are converted into intermediates of mainstream carbon oxidation pathways via specific adapter pathways. Surplus nitrogen is removed from glutamate, and excreted in urea. In the degradation process, the amino acids are converted into the intermediates of the citric acid cycle to pyruvate which in turn can serve as precursors for gluconeogenesis, can be referred as glucogenic amino acids. Those amino acids which yield acetoacetate are termed as ketogenic.1 Phenylketonuria (PKU) is a metabolic disorder occurring since birth which results into decreased metabolism of the amino acid phenylalanine.2 It is observed that the untreated, PKU can develop intellectual disability, seizures, behavioral problems, and mental disorders.3 It may also result in a musty smell and lighter skin. A baby born to a mother who has poorly treated PKU may have heart problems, a small head, and low birth weight.2 Present review study will compare the prevalence of disease in the countries with special focus to India.

Keywords: Amino acids; Phenylketonuria (PKU); Metabolism; Phenylalanine.