discontinuous multifactorial traits
Last reviewed 01/2018
Discontinuous multifactorial traits are dependent on the balance of gene interactions. Once a certain number of genes have become underactive, a threshold level is passed and the trait, usually a congenital malformation, will become evident. Beyond the threshold, the greater the frequency of underactive genes, the greater will be the severity of the trait.
The further the relationship of relatives from an affected individual, the lesser will be the proportion of underactive genes, and the lesser the probability that the threshold for trait manifestation will have been exceeded.
Some multifactorial traits show an overt sex bias. This is accounted for by a different threshold for disease appearance in only one sex. For example, pyloric stenosis affects 5 in 1000 males and only 1 in 1000 females.
Common examples of discontinuous multifactorial traits are:
- congenital malformations:
- cleft lip and palate
- congenital right heart disease
- neural tube defects
- pyloric stenosis
- common adult diseases:
- rheumatoid arthritis
- epilepsy
- peptic ulcer
- schizophrenia
- manic depression