multifactorial inheritance/common diseases Flashcards
what is the multifactorial mechanism of disease?
combo of genetics and environment
why do some traits “run in the family” but exhibit no defined inheritance pattern?
could be autosomal dominant with variable expression/reduced penetrance or the influences of multiple genes and their environment
what are “polygenic” traits?
combo of multiple genes
what are the characteristics of “continuous” traits?
distributed in a bell-curve
caused by the combined action of many genes
do not follow mendelian patterns
what is the additive model?
states that each gene adds an incremental amount to the phenotype
(more genes involved = increased # phenotypes observed)
what is the threshold model typically applied to?
birth defects
what does the threshold model follow?
the threshold of liability: for multifactorial dz, there is a threshold of liability that must be crossed before the dz is expressed
what increases the recurrence risk in multifactorial traits? (4)
- increasing severity
- increased # of affected family members
- at risk child is member of the more frequently affected sex
- proband is a member of the less frequently affected sex
what decreases the recurrence risk in multifactorial traits? (1)
decreasing degree of relatedness
what are 2 conditions that follow the threshold model?
pyloric stenosis and neural tube defects
in pyloric stenosis, which affected sex is more likely to have affected offspring? which offspring are more likely to be affected?
since it is less common in females, an affected female is more likely to have affected offspring. male offspring are more likely to be affected than female offspring
which sex has higher rates of NTD?
females
what increases the risk for NTD the most?
having 2+ children already affected
what are susceptibility genes?
genes that predispose to a common disease but do NOT independently cause the disease to occur
characterize monogenic, multifactorial and infectious diseases
monogenic- mostly genes
multifactorial- 50/50 genes and environment
infectious- mostly environment
