Medical Genetics 2.1 Phenylketonuria, PKU Phenylketonuria is one of the commonest inherited disorders-occurring in approximately 1 in 10,000 babies born in theu s. it occurs in babies who inherit two mutant genes for the enzyme phenylalanine hydroxylase(PAh). This enzyme normally breaks down molecules of the amino acid phenylalanine that are in excess of the body,'s needs for protein synthesis
Medical Genetics 2.1 Phenylketonuria，PKU Phenylketonuria is one of the commonest inherited disorders - occurring in approximately 1 in 10,000 babies born in the U. S. It occurs in babies who inherit two mutant genes for the enzyme phenylalanine hydroxylase (PAH). This enzyme normally breaks down molecules of the amino acid phenylalanine that are in excess of the body's needs for protein synthesis
Medical Genetics Phenylalanine Phenylpyruvic acid Phenylketonuria Phenylalanine block hydroxylase rosine 3, 4-dihydroxyphenylalanine (DOPA) Melanin pigments Ty rosine Co2+H2o- transaminase Citric acid cycle p-hydroxyphenylpyruvic acid Fumaric+T- Acetoacetic id acid p-hydroxyphenylpyruvic Fumarylacetoacetic acid acid oxidase Homogentisic acid oxidase Homogentisic acid 2, 5-dihydroxyphenylacetic acid Maleylacetoacetic acid Phenyl ketonuria lug Cummings 1997)
Medical Genetics
Medical Genetics Because we inherit two copies of the gene for the enzyme, both must be defective to produce the disease. A laboratory test that measures how quickly an injection of phenylalanine is removed from the blood can distinguish a person who has one pku gene from a person who ha las none but the person with one is perfectly healthy because the unmutated allele produces enough of the enzyme However, these heterozygous individuals are carriers of the disease
Medical Genetics Because we inherit two copies of the gene for the enzyme, both must be defective to produce the disease. A laboratory test that measures how quickly an injection of phenylalanine is removed from the blood can distinguish a person who has one PKU gene from a person who has none, but the person with one is perfectly healthy because the unmutated allele produces enough of the enzyme. However, these heterozygous individuals are "carriers" of the disease
Medical Genetics The phenylalanine tolerance test: A short time after administering a measured amount of phenylalanine to the subject, the concentration of phenylalanine in the blood plasma is measured
Medical Genetics The phenylalanine tolerance test: A short time after administering a measured amount of phenylalanine to the subject, the concentration of phenylalanine in the blood plasma is measured
Medical Genetics The level is usually substantially higher in people who carry one pku gene(even though they show no signs of disease than in individuals who are homozygous for the unmutated gene. Both parents must be heterozygous (i.e. must be carriers" of the trait to produce a child with pkU. the chance of their doing so is 1 in 4 卜 oNna homozygotes Heterozygotes Plasma phenylalanine level
Medical Genetics The level is usually substantially higher in people who carry one PKU gene (even though they show no signs of disease) than in individuals who are homozygous for the unmutated gene. Both parents must be heterozygous (i.e., must be "carriers" of the trait) to produce a child with PKU. The chance of their doing so is 1 in 4