Phenylketonuria

Definition

Phenylketonuria (PKU) is an inherited metabolic disorder caused by a deficiency in the enzyme phenylalanine hydroxylase, which is responsible for breaking down the amino acid phenylalanine. This leads to the accumulation of phenylalanine in the body, which can be toxic to the brain and cause intellectual disability if left untreated.

5 Must Know Facts For Your Next Test

1. Phenylketonuria is an autosomal recessive genetic disorder, meaning that an individual must inherit two copies of the defective gene, one from each parent, to develop the condition.
2. Early diagnosis and treatment through a specialized diet low in phenylalanine can prevent the severe neurological complications associated with untreated PKU.
3. Individuals with PKU must follow a strict diet for life, as even small amounts of phenylalanine can be harmful to their brain development and cognitive function.
4. PKU is more common in certain ethnic groups, such as those of European descent, with an incidence of approximately 1 in 10,000 to 15,000 newborns.
5. Newborn screening for PKU is mandatory in many countries, allowing for early intervention and the prevention of intellectual disability.

Review Questions

• Explain the role of the enzyme phenylalanine hydroxylase in the context of phenylketonuria.
  • The enzyme phenylalanine hydroxylase is responsible for breaking down the amino acid phenylalanine in the body. In individuals with phenylketonuria, this enzyme is deficient or absent, leading to the accumulation of phenylalanine. The buildup of phenylalanine can be toxic to the brain, particularly during critical periods of development, and can cause intellectual disability if left untreated.
• Describe the inheritance pattern of phenylketonuria and its implications for affected individuals and their families.
  • Phenylketonuria is an autosomal recessive genetic disorder, meaning that an individual must inherit two copies of the defective gene, one from each parent, to develop the condition. This has important implications for affected individuals and their families, as both parents must be carriers of the defective gene in order for a child to be born with PKU. If both parents are carriers, there is a 25% chance with each pregnancy that the child will have PKU, a 50% chance that the child will be a carrier, and a 25% chance that the child will not have the disorder.
• Analyze the importance of early diagnosis and treatment in the management of phenylketonuria, and how this relates to patterns of inheritance.
  • Early diagnosis and treatment are crucial in the management of phenylketonuria, as they can prevent the severe neurological complications associated with the disorder. Newborn screening programs, which are mandatory in many countries, allow for the early identification of infants with PKU, enabling them to be placed on a specialized diet low in phenylalanine before any irreversible brain damage occurs. This is particularly important given the autosomal recessive inheritance pattern of PKU, as affected individuals must inherit two copies of the defective gene. By implementing early intervention strategies, the patterns of inheritance can be effectively managed, and the negative impacts of the disorder can be mitigated.

Related terms

Amino Acid: The building blocks of proteins, essential for growth, repair, and maintenance of the body's cells and tissues.

Enzyme: A protein that acts as a catalyst, speeding up chemical reactions in the body without being consumed in the process.

Metabolic Disorder: A condition that affects the body's ability to convert food into energy, leading to an accumulation of harmful substances or a deficiency of essential substances.