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.{{Cite journal |last1=Roy |first1=Alec |last2=Rylander |first2=Gunnar |last3=Sarchiapone |first3=Marco |date=December 1997 |title=Genetics of Suicide.: Family Studies and Molecular Genetics |journal=Annals of the New York Academy of Sciences |language=en |volume=836 |issue=1 Neurobiology |pages=135–157 |doi=10.1111/j.1749-6632.1997.tb52358.x |pmid=9616797 |s2cid=29415906 |issn=0077-8923}}{{Cite journal |last1=Hopper |first1=John L. |last2=Bishop |first2=D. Timothy |last3=Easton |first3=Douglas F. |date=October 2005 |title=Population-based family studies in genetic epidemiology |journal=Lancet |volume=366 |issue=9494 |pages=1397–1406 |doi=10.1016/S0140-6736(05)67570-8 |issn=1474-547X |pmid=16226618|s2cid=6434807 }} 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.{{Cite journal |last1=Nestadt |first1=Gerald |last2=Samuels |first2=Jack |last3=Riddle |first3=Mark |last4=Bienvenu |first4=O. Joseph |last5=Liang |first5=Kung-Yee |last6=LaBuda |first6=Michele |last7=Walkup |first7=John |last8=Grados |first8=Marco |last9=Hoehn-Saric |first9=Rudolf |date=2000-04-01 |title=A Family Study of Obsessive-compulsive Disorder |journal=Archives of General Psychiatry |language=en |volume=57 |issue=4 |pages=358–63 |doi=10.1001/archpsyc.57.4.358 |pmid=10768697 |issn=0003-990X|doi-access=free }}

Types

There are three main types of family studies in genetics:

Those aimed at measuring the extent of familial aggregation for a trait
Familial aggregation is the practice of combing multiple data sets of different traits and/or characteristics in a family. {{Cite web|title=familial aggregation|url=https://medical-dictionary.thefreedictionary.com/familial+aggregation|access-date=2021-11-05|website=TheFreeDictionary.com}}
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.{{Cite journal|last1=Matthews|first1=Abigail G.|last2=Finkelstein|first2=Dianne M.|last3=Betensky|first3=Rebecca A.|date=2008-10-30|title=Analysis of familial aggregation studies with complex ascertainment schemes|journal=Statistics in Medicine|volume=27|issue=24|pages=5076–5092|doi=10.1002/sim.3327|issn=0277-6715|pmc=2562890|pmid=18618413}}
Linkage studies aimed at identifying specific genetic loci that have a moderate to large effect on risk
Genetic linkage occurs when two genes on a DNA sequence on the same chromosome are inherited together. {{Cite web|title=linkage {{!}} Learn Science at Scitable|url=https://www.nature.com/scitable/definition/linkage-51/|access-date=2021-11-05|website=www.nature.com|language=en}}
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. {{Cite web|date=2016-09-21|title=3.10: Genetic Linkage|url=https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_Introductory_Biology_(CK-12)/03%3A_Genetics/3.10%3A_Genetic_Linkage|access-date=2021-11-05|website=Biology LibreTexts|language=en}}
Association studies aimed at detecting loci with relatively small effects on risk.{{Cite encyclopedia |chapter=Family Studies in Genetics |encyclopedia=Encyclopedia of Epidemiology |publisher=SAGE Publications, Inc. |location=Thousand Oaks |chapter-url=http://methods.sagepub.com/reference/encyc-of-epidemiology/n153.xml |date=2008 |doi=10.4135/9781412953948.n153 |isbn=9781412928168 }}
Locus (loci plural) is the physical location and position of a gene or genetic marker on the chromosome. {{Cite web|title=Locus|url=https://www.genome.gov/genetics-glossary/Locus|access-date=2021-11-05|website=Genome.gov|language=en}}
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. {{Cite journal|last1=Ezkurdia|first1=Iakes|last2=Juan|first2=David|last3=Rodriguez|first3=Jose Manuel|last4=Frankish|first4=Adam|last5=Diekhans|first5=Mark|last6=Harrow|first6=Jennifer|last7=Vazquez|first7=Jesus|last8=Valencia|first8=Alfonso|last9=Tress|first9=Michael L.|date=2014-11-15|title=Multiple evidence strands suggest that there may be as few as 19 000 human protein-coding genes|journal=Human Molecular Genetics|volume=23|issue=22|pages=5866–5878|doi=10.1093/hmg/ddu309|issn=0964-6906|pmc=4204768|pmid=24939910}}

References

Category:Genetic epidemiology