Mail Address: Comparative
Molecular Sciences Bldg 21, James Cook University,
Townsville, 4811, Queensland, Australia
Telephone: 61-7-4781 6265 Fax: 61-7-4781 6078
AN EXERCISE IN CALCULATING DISEASE SUSCEPTIBILITY
2. Identify the incidence of type 1 diabetes in the general community of that country, estimating the incidence for that year from the figures published in Onkamo et al.
3. Convert the incidence figure from Onkamo et al from per 100,000 to percent by dividing by 1,000, and from per year to life time risk by multiplying by 30.
4. Use the GeneRiskCalc Excel spreadsheet to calculate the heritability for type 1 diabetes in the country and year for the primary research manuscript provided.
5. Repeat the calculation using Falconer's tables. Brief instructions are provided below. The Baxter manuscript contains a more detailed description of the procedure.
6. Is there a difference in the heritability calculated using the two methods? Why?
7. Use the figure for
heritability obtained from the GeneRiskCalc Excel spreadsheet, and the
population incidence obtained above to calculate the risk of developing
type 1 diabetes for the following:
a) Child of a patient with type 1 diabetes
b) Sibling of a patient with type 1 diabetes
c) Child of a patient with schizophrenia
d) Grandchild of a patient with type 1 diabetes
e) Child of a patient with type 2 diabetes
f) Identical twin of a patient with type 1 diabetes
8. Bring all results to the synthesis session.
Calculating Heritability using Falconer's Appendix:
|Step 1:||Determine the incidences of the trait in the general population, and in a select group of relatives of patients, for which the distance of the relationship is know, e.g. identical twins, siblings, grand children etc.|
|Step 2:||Express each incidence of the trait in terms of the threshold distance from the mean, x (in standard deviations), from the table in Appendix A of Falconer.|
xg is x for the general population
xr is x for the relatives,
Calculate the difference,
|Step 4:||Determine a, the mean deviation of liability of affected individuals in the general population from the mean liability of the general population, (in standard deviations) from the table in Appendix A of Falconer|
|Step 5:||Calculate the Regression Coefficient,
b = (xg-xr)/a
|Step 6:||Calculate heritability, h2
h2 = b/r