THE HDC GENE
LOCATION
Each cell in the human body contains a full set of unique chromosomes made up of DNA. Each cell nucleus carries 46 chromosomes that create 23 pairs. When stretched end to end, all of these chromosomes would equate to 2 meters of DNA [1]. Genes are segments of DNA that encode for particular proteins that function within the cell. The Hdc gene contains 24, 080 bases and is located on chromosome 15, refer to Figure 1. The correct notation for the location of the Hdc gene is 15q21.2 [2].
MUTATION ASSOCIATED WITH TOURETTE SYNDROME
Researchers at Yale University have recently shown that a mutation within the Hdc gene is associated with the cause of Tourette Syndrome. This mutation, W317X, is a base pair substitution of guanine to an alanine (G-to-A) at the 317th amino acid position. This substitution is predicted to result in a change from the wild-type, or "normal type" tryptophan codon to a stop codon [3]. The Hdc gene without the W317X mutation usually codes for histidine decarboxylase which assists in the conversion of histidine to histamine. The W317X mutation introduces a stop codon which codes for a truncated protein making the production of a viable histidine decarboxylase enzyme impossible.
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INHERITANCE
Many diseases can be caused by mutations in a single gene. There is more than one pattern that these genetic diseases can be inherited, depending on the affected gene. If the gene is on an X chromosome, the inheritance is called X-linked, while non-sex chromosomes pass on genes through autosomal inheritance [4].
In the case of Tourette Syndrome, inheritance isn't as clear as other diseases. Tourette Syndrome reoccurs in family generations but other genetic and environmental factors can also influence the onset of the disease, and not just the newly discovered W317X mutation. However, Tourette's was previously thought to be inherited through an autosomal dominant pattern. Autosomal refers to which chromosome Hdc is located on while dominant refers to the number of copies needed to display symptoms. Only one copy of the mutation is needed in the case of a dominant inheritance pattern [5]. Below is an example of this pattern of inheritance.
In the case of Tourette Syndrome, inheritance isn't as clear as other diseases. Tourette Syndrome reoccurs in family generations but other genetic and environmental factors can also influence the onset of the disease, and not just the newly discovered W317X mutation. However, Tourette's was previously thought to be inherited through an autosomal dominant pattern. Autosomal refers to which chromosome Hdc is located on while dominant refers to the number of copies needed to display symptoms. Only one copy of the mutation is needed in the case of a dominant inheritance pattern [5]. Below is an example of this pattern of inheritance.
REFERENCES
1 "Chromosomes" National Human Genome Research Institute. Retrieved 20 Feb 2014 http://www.genome.gov/26524120
2 "HDC Gene" GeneCards: The Human Gene Compendium. Retrieved 20 Feb 2014 http://www.genecards.org/cgi-bin/carddisp.pl?gene=HDC
3 "L-Histidine Decarboxylase and Tourette's Syndrome" NIH Public Access: Author Manuscript Retrieved. 20 Feb 2014 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2894694/figure/F2/
4 "Patterns of Inheritance" Genetics Home Reference: Your Guide to Understanding Genetic Conditions. Retrieved 20 Feb 2014 http://ghr.nlm.nih.gov/
5 "Tourette Syndrome" Genetics Home Reference. Retrieved 20 Feb 2014 http://ghr.nlm.nih.gov/condition/tourette-syndrome#genes
1 "Chromosomes" National Human Genome Research Institute. Retrieved 20 Feb 2014 http://www.genome.gov/26524120
2 "HDC Gene" GeneCards: The Human Gene Compendium. Retrieved 20 Feb 2014 http://www.genecards.org/cgi-bin/carddisp.pl?gene=HDC
3 "L-Histidine Decarboxylase and Tourette's Syndrome" NIH Public Access: Author Manuscript Retrieved. 20 Feb 2014 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2894694/figure/F2/
4 "Patterns of Inheritance" Genetics Home Reference: Your Guide to Understanding Genetic Conditions. Retrieved 20 Feb 2014 http://ghr.nlm.nih.gov/
5 "Tourette Syndrome" Genetics Home Reference. Retrieved 20 Feb 2014 http://ghr.nlm.nih.gov/condition/tourette-syndrome#genes
University of Wisconsin – Madison
Spring 2014 Genetics 564 |
TOURETTE SYNDROME |