[medhahegde]

Homocystinuria is another metabolic disorder and is associated with the metabolism of the amino acid methionine. It is caused by the deficiency of the enzyme Cystathionine-β-synthase (or CBS) that is essential to metabolize homocysteine. This disorder causes a variety of symptoms that includes decreased vision and CNS (central nervous system) abnormalities. The disorder is inherited as autosomal recessive. Homocystinuria exemplify the hereditary metabolic defect described by the build-up of homocysteine in the blood serum and its elevated excretion in the urine. Newborns show up to be normal and the early symptoms are unclear.

Alkaptonuria is a rare metabolic condition due to the defect in the metabolism of the amino acids phenylalanine and tyrosine. It is an inherited disorder in which an individual’s urine changes from dark brown to black colour when it is exposed to air. The disorder results due to the faulty enzyme homogentisate 1,2- dioxygenase which is involved in the breakdown of the amino acid tyrosine. As a consequence homogentistic acid and alkapton (oxide of homogentistic acid) build-up in the blood and get expelled in the urine in huge amounts. The presence of homogentistic acid in excess causes harm to the cartilage and also causes kidney stones. Defect in the HGD gene results in alkaptonuria.

Phenylketonuria (PKU) is one of the most typical metabolic disorders of protein. The disorder is due to the non functional enzyme called phenylalanine hydroxylase (PAH). This enzyme is essential in the metabolism of phenylalanine to tyrosine. Therefore, as a result, the amino acid phenylalanine builds-up in the blood and gets converted to a phenylketone (phenylpyruvate) which gets excreted in the urine. The disorder is inherited in an autosomal recessive manner. If the disorder is untreated it results in the symptoms such as Eczema, Lethargy, Hyperactivity, Seizures and Intellectual disability. The newborn screening for the disorder is usually performed in most of the nations.