Family study

In genetic epidemiology, family studies are studies of whether a disease or trait "runs in a family". In other words, they are studies aimed at detecting the presence or absence of familial aggregation for the disease or trait, in which having a family history is associated with greater risk. The family research design can also be used to estimate penetrance for a given genotype, to conduct genetic association studies, and to study potential modifiers of an individual's genetic risk.^[1][2] If a family study shows that a trait is familial, this is a necessary, but not sufficient, criterion for it to be established as genetically influenced.^[3]

Types

There are three main types of family studies in genetics:

1. Those aimed at measuring the extent of familial aggregation for a trait
   1. Familial aggregation is the practice of combing multiple data sets of different traits and/or characteristics in a family. ^[4]
   2. Family history of disease is collected in case studies, which seeks if a certain disease of one family member increases the risk of that disease being passed down to others. This could be related to either genes or environmental factors.^[5]
2. Linkage studies aimed at identifying specific genetic loci that have a moderate to large effect on risk
   1. Genetic linkage occurs when two genes on a DNA sequence on the same chromosome are inherited together. ^[6]
   2. This can occur with sex linked genes with the X or Y chromosome. Although it is more common to be inherited from the X chromosome because the Y chromosome has less genes attached. ^[7]
3. Association studies aimed at detecting loci with relatively small effects on risk.^[8]
   1. Locus (loci plural) is the physical location and position of a gene or genetic marker on the chromosome. ^[9]
   2. Chromosomes carry genetic information across all of it, each gene having its specific location and position. There are 40,000 to 100,000  protein coding genes across human chromosomes. ^[10]