Cystic Fibrosis and the CFTR Gene

Study Notes

The CFTR gene encodes for the CFTR protein, which contains 1480 amino acids and acts as a chloride channel across the cell membrane.
The CFTR gene is located at 7q31.2, has a size of 189,000 bp, and consists of 27 exons.
Over 1000 mutations (point and frameshift) have been identified in the CFTR gene, with approximately 70% of them corresponding to a specific deletion of 3 base pairs (CTT) at exon 11, known as the ΔF508 mutation.
The ΔF508 mutation results in the loss of a phenylalanine residue in the CFTR protein, causing misfolding and preventing its integration into the cell membrane.

PCR amplification can be used to detect mutations, such as the ΔF508 mutation, by checking the size of the PCR product using gel electrophoresis.
Southern blotting can be used to investigate larger segments of DNA within and around a gene, including the detection of partial gene inversions and triplet repeat disorders.

Haemophilia A is caused by mutations in the F8 gene, which encodes clotting factor VIII of the blood clotting cascade.
The F8 gene is located at Xq28 and has 26 exons spanning 187 kb of DNA.
A gene inversion involving 500 kb of DNA can occur, disrupting the F8 gene and causing the disease.
Southern blotting can be used to detect this inversion by checking the size of the DNA fragment of the F8 gene.

Triplet repeat disorders include Myotonic Dystrophy, Huntington's disease, Fragile X syndrome, and others.
These disorders are characterized by an expansion of triplet repeats in the DNA, leading to disease symptoms.
The number of repeats can vary between diseases, and an increase in repeats can lead to worsening symptoms across generations.

Myotonic Dystrophy is the most common heritable neuromuscular disorder, causing progressive weakness and myotonia.
The disease is caused by a triplet repeat expansion of CTG (dynamic mutation) in the 3' UTR of the myotonin gene at 19q13.3.
The normal number of CTG repeats is 5-37, while affected individuals have CTG repeats from 50 to many thousand (full mutation).

Array CGH is used to scan the entire genome for any copy number change (deletion or duplication) involving sequences of a few kb or longer.
This technique is used to screen for sub-microscopic chromosomal deletions for which the location cannot be deduced from the patient's phenotype.
Array CGH cannot detect balanced chromosomal rearrangements or inversions.