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C1-51 Multifactorial Inheritance And Common Diseases
Genetics Stuff
5
Biology
Professional
10/09/2010
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Term




Multifactorial inheritance, disease types:

 

 Definition

1.Certain congenital malformations: CL(P),   NTD, CHD, pyloric stenosis, etc.

2. “Common diseases,” usually of adult onset:

     ischaemic heart disease, hypertension, manic depression, schizophrenia, Alzheimer disease, etc. Also HLA-related autoimmune diseases: type I diabetes, rheumatoid arthritis, etc.
Term




Heritability

 Definition

is based on the variance of the trait in the population studied, and is symbolized as H2 or h2.

H2 and h2 are numbers that vary between 0 and 1.

H2 =  Vg / Vt     

 
Term




The threshold model for malformations 

 Definition

•A set of polygenes and environmental factors contribute to the developmental process (closure of the neural tube or of the palatal shelves, etc.)
•The malformation occurs when a sufficient number of mutant polygenic alleles and harmful environmental factors reach a threshold.
Term



Multifactorial inheritance in congenital malformations; summary

 Definition

•Threshold rates are determined empirically for each disease.
•Occurrence risks vary with populations.
•Recurrence risk is higher when:

   - the proband is more severely affected

   - the proband is of the seldom affected sex 

   - more than one family member is affected

   - there is a consanguineous marriage
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