Clinical Chemistry 1: Amino Acids and Proteins Lecture

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Questions and Answers

What are the high levels of phenylalanine and some of its metabolites associated with in patients with PKU?

significant brain problems

What is the characteristic odor of the urine in patients with PKU?

musty

What can be the result of toxic effects of phenylalanine or its metabolic byproducts in the brain?

mental retardation and microcephaly

What are the phenylalanine levels in patients with non-PKU mild hyperphenylalaninemia?

180-600 μmol/L Signup and view all the answers

What can be avoided if the disease is detected at birth and the infant is maintained on a diet containing low levels of phenylalanine?

brain damage Signup and view all the answers

What is the deficiency in the enzymes needed for the synthesis of tetrahydrobiopterin associated with in PKU cases?

hyperphenylalaninemia Signup and view all the answers

What is the goal of PKU treatment in terms of maintaining the blood level of phenylalanine?

2-10 mg/dL or 120-160 μmol/L Signup and view all the answers

What is the first drug to manage PKU?

Kuvan (sapropterin dihydrochloride) Signup and view all the answers

What test allows for the early detection and implementation of treatment for PKU?

newborn screening test Signup and view all the answers

What color does the urine turn when treated with ferric chloride in the urine test for PKU?

permanent bluegreen Signup and view all the answers

What is the estimated occurrence of phenylketonuria (PKU)?

1 in every 15,000 births Signup and view all the answers

What causes phenylketonuria (PKU)?

Phenylalanine hydroxylase (PAH) deficiency Signup and view all the answers

What is the consequence of phenylalanine hydroxylase (PAH) deficiency?

Disruption in the normal conversion of phenylalanine to tyrosine Signup and view all the answers

What are the phenylalanine levels in newborns with untreated classic PKU?

Greater than 1,200 μmol/L Signup and view all the answers

What is the normal phenylalanine level in newborns?

Less than 120 μmol/L Signup and view all the answers

What is the problem in aminoacidopathies?

An enzyme defect that inhibits the body’s ability to metabolize certain amino acids Signup and view all the answers

Where do abnormalities exist in aminoacidopathies?

In the activity of a specific enzyme in the metabolic pathway or in the membrane transport system for amino acids Signup and view all the answers

Name some disorders covered in aminoacidopathies.

Phenylketonuria (PKU), tyrosinemia, alkaptonuria, maple syrup urine disease (MSUD), isovaleric acidemia, homocystinuria, citrullinemia, arginosuccinic aciduria, and cystinuria Signup and view all the answers

What is the consequence of untreated classic PKU in terms of phenylalanine levels?

As high as 1,200 μmol/L Signup and view all the answers

What is the problem in phenylketonuria (PKU) due to the deficiency of the enzyme phenylalanine hydroxylase?

Disruption in the normal conversion of phenylalanine to tyrosine Signup and view all the answers

Study Notes

Phenylketonuria (PKU) Overview

High phenylalanine and its metabolites are associated with neurological damage and developmental disabilities in PKU patients.
Characteristic urine odor in PKU patients is a musty or mousy smell due to excess phenylacetate.
Toxic effects of phenylalanine or its metabolic byproducts can lead to intellectual disabilities and impaired brain development.
Non-PKU mild hyperphenylalaninemia typically presents with phenylalanine levels between 2-6 mg/dL.

Early Detection and Management

Early diagnosis at birth and a low-phenylalanine diet can prevent severe intellectual disabilities and neurological damage.
Enzyme deficiencies in tetrahydrobiopterin synthesis can be associated with more severe cases of PKU.
PKU treatment aims to maintain blood phenylalanine levels generally below 6 mg/dL to prevent toxicity.

Treatment and Diagnosis

The first drug approved for managing PKU is sapropterin dihydrochloride, which enhances phenylalanine metabolism.
Newborn screening tests, such as the heel prick test, allow for early detection and treatment of PKU.
Urine treated with ferric chloride turns green, indicating the presence of phenylketones, which is critical for diagnosing PKU.

Incidence and Genetic Factors

Phenylketonuria is estimated to occur in 1 in 10,000 to 1 in 15,000 live births.
PKU is caused by mutations in the gene coding for phenylalanine hydroxylase (PAH), leading to enzyme deficiency.
PAH deficiency results in an inability to convert phenylalanine to tyrosine, resulting in phenylalanine accumulation.

Phenylalanine Levels and Consequences

Newborns with untreated classic PKU can exhibit phenylalanine levels exceeding 20 mg/dL, causing severe effects.
Normal phenylalanine levels in newborns are typically less than 2 mg/dL.
Aminoacidopathies involve metabolic disorders caused by defects in amino acid metabolism, leading to toxicity.

Disorders and Consequences

Common disorders in aminoacidopathies include maple syrup urine disease and cystinuria, which stem from similar metabolic issues.
Untreated classic PKU leads to progressive mental impairment and potentially severe cognitive deficits due to sustained high phenylalanine levels.
The primary issue in PKU arises from phenylalanine hydroxylase deficiency, highlighting the need for lifelong dietary management.

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Description

Test your knowledge on amino acid analysis, aminoacidopathies, and protein structure and classification with this quiz based on the lecture by Prof. Gail Ann Parel-Pascual. Explore topics like phenylketonuria, tyrosinemia, alkaptonuria, and more.