Family study explained

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]

Notes and References

1. Roy . Alec . Rylander . Gunnar . Sarchiapone . Marco . December 1997 . Genetics of Suicide.: Family Studies and Molecular Genetics . Annals of the New York Academy of Sciences . en . 836 . 1 Neurobiology . 135–157 . 10.1111/j.1749-6632.1997.tb52358.x . 9616797 . 29415906 . 0077-8923.
2. Hopper . John L. . Bishop . D. Timothy . Easton . Douglas F. . October 2005 . Population-based family studies in genetic epidemiology . Lancet . 366 . 9494 . 1397–1406 . 10.1016/S0140-6736(05)67570-8 . 1474-547X . 16226618. 6434807 .
3. Nestadt . Gerald . Samuels . Jack . Riddle . Mark . Bienvenu . O. Joseph . Liang . Kung-Yee . LaBuda . Michele . Walkup . John . Grados . Marco . Hoehn-Saric . Rudolf . 2000-04-01 . A Family Study of Obsessive-compulsive Disorder . Archives of General Psychiatry . en . 57 . 4 . 358–63 . 10.1001/archpsyc.57.4.358 . 10768697 . 0003-990X. free .
4. Web site: familial aggregation. 2021-11-05. TheFreeDictionary.com.
5. Matthews. Abigail G.. Finkelstein. Dianne M.. Betensky. Rebecca A.. 2008-10-30. Analysis of familial aggregation studies with complex ascertainment schemes. Statistics in Medicine. 27. 24. 5076–5092. 10.1002/sim.3327. 0277-6715. 2562890. 18618413.
6. Web site: linkage Learn Science at Scitable. 2021-11-05. www.nature.com. en.
7. Web site: 2016-09-21. 3.10: Genetic Linkage. 2021-11-05. Biology LibreTexts. en.
8. Encyclopedia: Family Studies in Genetics . Encyclopedia of Epidemiology . SAGE Publications, Inc. . Thousand Oaks . http://methods.sagepub.com/reference/encyc-of-epidemiology/n153.xml . 2008 . 10.4135/9781412953948.n153 . 9781412928168 .
9. Web site: Locus. 2021-11-05. Genome.gov. en.
10. Ezkurdia. Iakes. Juan. David. Rodriguez. Jose Manuel. Frankish. Adam. Diekhans. Mark. Harrow. Jennifer. Vazquez. Jesus. Valencia. Alfonso. Tress. Michael L.. 2014-11-15. Multiple evidence strands suggest that there may be as few as 19 000 human protein-coding genes. Human Molecular Genetics. 23. 22. 5866–5878. 10.1093/hmg/ddu309. 0964-6906. 4204768. 24939910.