Mutation case study : Cystic Fibrosis

Cystic fibrosis is a severe, genetically determined disease that involves both the lungs and the gastrointestinal tract. It occurs in about one in every two thousand births among white children and at a far lower rate in asian and black children. There are now more than 500 different mutations known to cause the disease. These mutations occur in a huge gene (>6000 nucleotides) on chromosome 7 that encodes a protein of 1480 amino acids called the cystic fibrosis transmembrane conductance regulator (CFTR). This protein transports chloride ions out of cells. People with cystic fibrosis must inherit two mutant genes to develop the disease but these mutations need not be the same. This disease results from a number of different mutations in the CFTR gene. The most commonly observed mutations that have been observed include deletion of a codon resulting in the deletion of the amino acid phenylalanine at position 508, a missense mutation resulting in an aspartic acid being substituted for a glutamic acid at position 551, a nonsense mutation at position 542 resulting in a stop codon instead of one that codes for glycine and hence a truncated protein and mutations at the splice sites of intron 8.