Huntingtons Disease Nontraditional Inheritance
DNA, the chemical that makes up our genes, contains a "code" of three letter words known as "codons" or "trinucleotide repeats." Many genes normally contain a trinucleotide repeat, which is present several times. When the number of repeats increases to a larger than normal number of copies, the DNA is altered, and the gene may not function correctly or at all ("Trinucleotide repeats: fragile-x," 2008).
Huntington’s Disease (HD) is an autosomal dominant pattern of inheritance. Males and females are equally likely to inherit the mutant gene. The change in the gene takes place when the gene is passed from parent to child. Nontraditional inheritance plays a role in the development of HD when symptoms appear at an earlier age with each generation. The mutant genes repeat more times than the usual number in normal copies of these genes. It is not clear what causes a trinucleotide repeat to multiply into more copies than it should in a gene. Sometimes, a person may have more than the usual number of copies, but not enough to alter the function of the gene” ("Trinucleotide repeats: fragile-x," 2008).
The higher numbers of repeats in each copy of the HD gene, the earlier the symptoms appear ("Huntington 's disease," 2009). This is evident in the pedigree beginning with Martha and Horace. Martha died ten years after symptoms of HD appeared and her son, Allen also died ten years after his diagnosis. Martha’s symptoms appeared at 55 years of age, her son Allen’s symptoms appeared at 50 years of age and his children’s symptoms appeared between the ages of 37-40.
If the mutant HD gene is inherited from the father, the chance of the number of repeats is greater than if inherited from the mother. Either the number of times a repeat can change during transmission can expand or contract, thereby changing the way and age in which HD presents itself. The risk for developing HD for the members of the fifth generation (unborn children of Joseph and Becky) are 50/50 because even
Huntington’s Disease (HD) is an autosomal dominant pattern of inheritance. Males and females are equally likely to inherit the mutant gene. The change in the gene takes place when the gene is passed from parent to child. Nontraditional inheritance plays a role in the development of HD when symptoms appear at an earlier age with each generation. The mutant genes repeat more times than the usual number in normal copies of these genes. It is not clear what causes a trinucleotide repeat to multiply into more copies than it should in a gene. Sometimes, a person may have more than the usual number of copies, but not enough to alter the function of the gene” ("Trinucleotide repeats: fragile-x," 2008).
The higher numbers of repeats in each copy of the HD gene, the earlier the symptoms appear ("Huntington 's disease," 2009). This is evident in the pedigree beginning with Martha and Horace. Martha died ten years after symptoms of HD appeared and her son, Allen also died ten years after his diagnosis. Martha’s symptoms appeared at 55 years of age, her son Allen’s symptoms appeared at 50 years of age and his children’s symptoms appeared between the ages of 37-40.
If the mutant HD gene is inherited from the father, the chance of the number of repeats is greater than if inherited from the mother. Either the number of times a repeat can change during transmission can expand or contract, thereby changing the way and age in which HD presents itself. The risk for developing HD for the members of the fifth generation (unborn children of Joseph and Becky) are 50/50 because even
References: Huntington 's disease. (2009, June 24). Retrieved from http://www.chp.edu/CHP/P02155 Trinucleotide repeats: fragile-x syndrome. (2008, February 08). Retrieved from http://www.chp.edu/CHP/P02155