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Related Concept Videos

Mutations01:39

Mutations

Overview
Mutations01:39

Mutations

Overview
Nonsense-mediated mRNA Decay02:27

Nonsense-mediated mRNA Decay

The Upf proteins that carry out nonsense-mediated decay (NMD) are found in all eukaryotic organisms, including humans. Each protein has an individual role, but they need to work in collaboration. Upf1 is an ATP-dependent RNA helicase that unwinds the RNA helix. Because Upf1 can unwind any RNA, Upf2 and Upf3 are required to help Upf1 discriminate between nonsense and normal mRNAs.
Usually, Upf3 binds to an Exon Junction Complex (EJC) at mRNA splice sites. If a ribosome fully translates the mRNA,...
Mutations01:35

Mutations

Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. Mutations can be characterized in a number of different ways: whether and how they alter the amino acid sequence of the protein, whether they occur over a small or large area of DNA, and whether they occur in somatic cells or germline cells.
Chromosomal Alterations Are Large-Scale Mutations
While point mutations are changes in a single nucleotide in...
Nonsense-mediated mRNA Decay02:27

Nonsense-mediated mRNA Decay

The Upf proteins that carry out nonsense-mediated decay (NMD) are found in all eukaryotic organisms, including humans. Each protein has an individual role, but they need to work in collaboration. Upf1 is an ATP-dependent RNA helicase that unwinds the RNA helix. Because Upf1 can unwind any RNA, Upf2 and Upf3 are required to help Upf1 discriminate between nonsense and normal mRNAs.
Usually, Upf3 binds to an Exon Junction Complex (EJC) at mRNA splice sites. If a ribosome fully translates the mRNA,...
Inborn Errors of Metabolism01:20

Inborn Errors of Metabolism

Phenylketonuria (PKU) is a protein metabolism disorder characterized by high blood levels of the amino acid phenylalanine. This results from a mutation in the gene responsible for phenylalanine hydroxylase, an enzyme that converts phenylalanine into tyrosine. When this enzyme is deficient, phenylalanine builds up in the blood, leading to symptoms such as vomiting, rashes, seizures, growth deficiency, and severe mental retardation. An early diagnosis and a diet restricting phenylalanine intake...

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A Strategy to Identify de Novo Mutations in Common Disorders such as Autism and Schizophrenia
05:51

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Published on: June 15, 2011

Nonsense mutation causing steroid 21-hydroxylase deficiency.

H Globerman1, M Amor, K L Parker

  • 1Division of Pediatric Endocrinology, Cornell University Medical College, New York 10021.

The Journal of Clinical Investigation
|July 1, 1988
PubMed
Summary

A mutation in the CYP21B gene causes a severe form of congenital adrenal hyperplasia by creating a premature stop codon. This genetic defect leads to a nonfunctional enzyme and reduced mRNA levels, impacting steroid 21-hydroxylase activity.

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Area of Science:

  • Genetics
  • Endocrinology
  • Molecular Biology

Background:

  • Congenital adrenal hyperplasia (CAH) is a group of genetic disorders affecting the adrenal glands.
  • Steroid 21-hydroxylase deficiency is the most common cause of CAH, leading to impaired cortisol and aldosterone synthesis.
  • The severe "salt-wasting" form of CAH results from near-complete or complete deficiency of 21-hydroxylase activity.

Purpose of the Study:

  • To identify and characterize mutations in the CYP21B gene associated with the salt-wasting form of CAH.
  • To investigate the functional consequences of a specific CYP21B mutation on enzyme activity and gene expression.
  • To determine the frequency of this mutation in patients with 21-hydroxylase deficiency.

Main Methods:

  • DNA sequencing of the CYP21B gene from a patient with salt-wasting CAH.
  • Site-directed mutagenesis to introduce the identified mutation into the CYP21B gene.
  • Transfection of the mutant and wild-type CYP21B genes into mouse Y1 adrenal cells.
  • Analysis of mRNA levels using hybridization with specific oligonucleotide probes.

Main Results:

  • A mutation changing codon 318 from glutamine (CAG) to a premature stop codon (TAG) was identified in the CYP21B gene.
  • This nonsense mutation is predicted to cause a completely nonfunctional steroid 21-hydroxylase enzyme due to premature translation termination.
  • Transfection studies showed decreased mRNA levels for the mutant CYP21B gene compared to the normal gene.
  • The identified mutation was present in 3 out of 20 unrelated patients with 21-hydroxylase deficiency alleles.

Conclusions:

  • The nonsense mutation at codon 318 in the CYP21B gene is a significant cause of severe congenital adrenal hyperplasia due to steroid 21-hydroxylase deficiency.
  • This mutation leads to a nonfunctional enzyme and reduced gene expression, consistent with the severe phenotype.
  • The presence of this mutation in the CYP21A pseudogene suggests a potential gene conversion event contributing to its occurrence in the functional CYP21B gene.