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Genetic Variation
heritable vs. somatic
Germ-line (heritable)
Somatic
Origin: transmission from parents (+ de novo at conception)
Typically present in every cell (Exception: ‘mosaicism’)
Constitutes ‘heritability’ of traits and diseases
Origin: mutation event in DNA of a single cell
Present in selected cells; in tissues through clonal expansion
Basis for most cancers
Endometriosis is ‘heritable’
Main evidence:
– 5-7-fold increased risk in sisters and mothers of women with vs. without endometriosis:
(Simpson 1980; Lamb 1986; Coxhead 1993; Moen 1993)
– Twin study of 854 genetically identical/493 non-identical twin sisters: increased disease rate in identical twins (Treloar, 1999)
– Large genealogical database Iceland comparing 750 women with endometriosis with sets of matched controls (Stefansson 2002)
Heritability = 50%
= the proportion of disease risk in the population that is due to genetic factors
Does not distinguish between possible endometriosis subtypes! Does not translate to individual risk to the patient!
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