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Powerpoint Presentation: Phenylketonuria
Word Document: Phenylketonuria Fact Sheet

Powerpoint Presentation: Cystic Fibrocis

Evolution Index

The origins of life
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Antibiotic Resistance
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Palaeontology : The study of fossils
The C-14 Decay Curve
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Topic Chapters Index

References

Cystic fibrosis data base

Cystic Fibrocis (CF) Fact Sheet

Symptoms

  • Incorrect folding of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein results in its destruction.
  • The cell membranes in epithelial cells of lungs, pancreas, colon and urinogenital tract lack chloride ion pores.
  • Chloride and sodium imbalance results.
  • Excessively salty sweat.
  • Mucus secretion becomes thick and viscous. It cannot easily be cleared.
  • Chronic lung congestion
  • Pancreatic obstruction
  • Liver damage and diabetes common amongst patients.
  • Median survival 19 years.

Tests

  • Fetal proteins tested by amniocentesis
  • Sodium ion concentrations in sweat.
  • Carriers tested using DNA probes for mutant allele.

Treatment

  • Physiotherapy helps reduce lung congestion
  • Pancreatic extracts can help digestive problems
  • Gene therapy being developed.

Frequency

1 in 2500 births in N Europe. One person in 25 is heterozygous (carrier).

Cause

  • A single mutant recessive allele of the CFTR gene 90%
  • Caused by a deletion on the codon of position 508 (amino acid phenylalanine).
  • About 400 mutations of this gene are known.
  • The CFTR gene is located on chromosome 7

Evolution

  • The high frequency of heterozygotes in N Europe suggests a selective advantage.
  • Some geneticists suggest it can protect against fluid and salt loss by diarrhaea caused by infection of the digestive system (eg cholera).
  • Salt loss in sweat by CF carriers did not give them the advantage in hot climates.
  • So CF frequency increased in temperate climates not in the tropics.

 

EVOLUTION

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Phenylketonuria (PKU) Fact Sheet

The normal metabolism of Phenylalanine (pathways a and b) and the abmornal metobolism in Phenylketonuric subjects (pathway c)

 

PKU

 

*Agents, thought to be responsible for mental retardation, which accumulate in phenylketonuric subjects (PKU). These are broken down into ketone bodies which appear in the urine.

Other symptoms include skin lesions.

 

Test

Ferric chloride + urine of new born baby

arrow

Green colour in the presence of ketone bodies

 

Treatment

A strictly controlled phenylalanine free diet up to the age of about 14 years old.

As phenylalanine is itself an essential amino acid small doses must be supplied.

After this age the growth and development of the brain is not affected by high levels of phenylalanine in the body.

 

Frequency

1 in 10 000 in Caucasians of NW Europe

 

Causes

  1. A single mutant recessive allele of the Phenylalanine Hydroxylase (PAH) gene. This results in the inability to produce the enzyme.Locus : Long arm of Chromosome 12.

  2. Dietary excess of plant proteins which results in the exhaustion of a protein cofactor (pterin) needed by the enzyme.

 

Evolution

Heterozygotes (carriers) are thought to be less susceptible to toxins produced by the moulds Aspergillus and Penecillium.

These grow on foods in damp wet climates (eg NW Europe). Heterozygous women show lower spontaneous abortion rates.

 

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