Transcript Genetic Diseases vs Common Diseases

Genetic and Common Diseases
What’s the Difference?
What’s Inherited?
 A widespread misconception is that traits due to dominant
alleles are the most common in the population. While this is
sometimes true, it is not always the case. For example, the
allele for Huntington’s Disease is dominant, while the allele
for not developing this disorder is recessive. At most, only 1
in 20,000 people will get Huntington’s; most people have
two recessive, normal alleles.
Gene Interactions
 While a few traits are due to only one gene (and its alleles),
most genetic traits are the product of interactions between
several genes. When more than one gene influences a trait,
the inheritance pattern is not easily predictable. The
predictable patterns referred to as dominant and recessive
apply only to single gene traits.
Rare Genetic Disorders & Common
Disorders
 The prevalence of rare genetic disorders caused by a single
gene such as cystic fibrosis is 1 in 10,000 and the prevalence
of more common diseases such as heart disease is 1 in
 Other genetic disorders include Down Syndrome, Crohn’s
Disease, Hemophilia, Muscular Dystrophe.
 Do common diseases like heart disease, arthritis, diabetes,
autism, ADHD or colon cancer have a genetic component?
Multifactorial Diseases
 Most common diseases do have a genetic component and
tend to run in families.
 However, common diseases differ from rare genetic disorders
in that they are usually not caused by defects in a single gene.
Rather, they result from the combined effects of multiple
genes and environmental factors. Thus, they are called
multifactorial diseases
Common Diseases = Many Genes
 Because more than one gene is involved in most common
diseases, the inheritance of a common disease is not
predictable.
 Information found in a family health history and recorded on
a pedigree is used to estimate an individual’s genetic risk
(low, medium, or high) of developing a common disease.
Common Disease vs. Genetic Disease
 The chance of a common disease being passed from a
grandfather to a grandchild, for example, isn’t high because
the chance of all the contributing genes being passed through
the generations isn’t great.
 The chance of a genetic disease (Williams’ Syndrome, for
example) being passed along is higher because it’s due to one
single gene.