| ALKAPTONURIA — Inborn metabolic defect by single gene | Blackening of urine on exposure to air & mild arthritis due to deposition of black pigment in the cartilage of ear or nose. | Absence of homogentisate oxidase enzyme which oxidized homogentisic acid into carbon dioxide and water.In the absence of enzyme homogentisic acid or alkapton accumulate & excreted in urine and form black pigment by reacting with oxygen. |
| PHENYLKETONURIA—-Recessive inherited disease Homozygous individual are affected while heterozygous are carrier.The child is born normal but within 6 months he develops the symptoms. | It causes excessive mental retardation in children also result in hypopigmentation of skin and eczema. | Absence of enzyme phenylalanine hydroxilase hence amini acid phenylalanine do not convert into tyrosine hence phenylalanine accumulate In tissues & some changes into phenylpyruvic acid. Later excreted in urine and the former and its metabolites damage the brain tissue. |
