Causes


 * Contents:**
 * 1) Overview of Huntington's Disease
 * 2) History of Huntington's Disease
 * 3) __**Causes of Huntington's Disease**__
 * 4) Symptoms of Huntington's Disease
 * 5) Spread of Huntington's Disease
 * 6) Diagnosis of Huntington's Disease
 * 7) Treatment of Huntington's Disease
 * 8) Prevention of Huntington's Disease
 * 9) Huntington's Disease statistics
 * 10) Bibliography

=**Causes** **of Huntington's Disease**= The end of a Huntington's disease gene has the codon "CAG" (cytosine-adenine-guanine). The codon "CAG" codes for the amino acid glutamine. Normally, there are less than 40 glutamine amino acids in a row, and a protein called huntingtin (Htt) is made. But if there are more than 40 glutamine amino acids, mHtt - a mutated version of Htt - will be formed. When mHtt molecules build up in brain cells, they die in certain parts of the brain. Huntington's disease is passed down from one generation to the next. The mutated gene is passed from one generation to the next; thus, if the parent is a carrier of the mutated gene, their children stand a 50% chance of either inheriting the disease or escaping from it altogether (Philips). Only one affected gene is needed from each parent for the child to inherit Huntington's disease. If a person inherits that mutated gene, the gene will start to become active in the body, destroying brain cells in the body's central nervous system (Philips).

This disease is caused by the **__Insertion mutation__**.

Insertion and Deletion (Indels)
Extra base pairs may be added (**insertions**) or removed (**deletions**) from the DNA of a gene. The number can range from one to thousands. Collectively, these mutations are called **indels**. Indels involving one or two base pairs (or multiples thereof) can have devastating consequences to the gene because translation of the gene is "frameshifted". This figure shows how by **shifting the reading frame** one nucleotide to the right, the same sequence of nucleotides encodes a different sequence of amino acids. The mRNA is translated in new groups of three nucleotides and the protein specified by these new codons will be worthless.

Frameshifts often create new **STOP** codons and thus generate nonsense mutations. Perhaps that is just as well as the protein would probably be too garbled anyway to be useful to the cell. (source?)

Symptoms-->