• Register
  • Login
  • Bookmark this page!
Skip Navigation LinksHome Page    >    Tests during the pregnancy    >    Indirect testing for genetic markers in a family that has one or several patients - when there are a number of different genes that can each cause the disease - the gene, or most of the genes not having been located / identified / mapped - multifactorial diseases
 
 
Pregnancy links...
Health links...
Genetics links...
Medical links...
Autism links...
Other links...
 

Indirect testing for genetic markers in a family that has one or several patients - when there are a number of different genes that can each cause the disease - the gene, or most of the genes not having been located / identified / mapped - multifactorial diseases


Ths is not a direct test, but a comparative one, which is called linkage analysis. In genetic linkage studies, alleles of each of the genes being tested (an allele is one member of the pair of genes at a given disease locus) are compared between the patients and the healthy family members. The allele that is present only in the patients but in none of the healthy family members - i.e. the -shared allele- of these patients - is the one in which the mutation responsible for the disease is located. If the -shared allele- is found, it will be possible to test other family members without identifying the mutation itself, and prenatal testing by amniocentesis or chorionic villus sampling can be carried out. This is done by looking for the -shared allele- in the DNA of the affected individuals in the family.

Because the location of the disease-causing gene, or most of the genes, has yet to be identified, the test cannot be completed. There are a number of genes that can each cause the disease, and in different families, different genes in different combinations will result in the disease-s being expressed, so the problem is even more severe. In addition, the inheritance pattern of the disease and the specific contribution of each gene to its expression have not yet been adequately elucidated. Another factor that compounds the issue is what effect if any the environment has.

However, in very large families with a large number of patients an attempt can be made to locate the genes.

This can be done by performing a comparative test for each of the regions in the genome (or candidate areas).

Only in the locus containing the gene responsible for the disease will there be complete correlation between the genotype and the phenotype - in other words, the -shared allele- will be found in all the patients, but in none of the healthy relatives.

In the other loci, complete genotype-phenotype correlation will not be found.

The test requires comparison of a number of affected and healthy members of the same family. The test is only reliable if DNA from several affected individuals in the family is already available, or if it can be obtained from a blood sample. The cooperation of the family members is required - they must be examined by a physician in order to ascertain whether they have signs of the disease, and must agree to give a blood sample. The more candidate genes there are the more complex and difficult it is to perform the test, as a new gene must in fact be identified.
 
Haven't found what you're looking for? Search for it here:   
Comments (0)





Leave a Comment
Name
Email (will not be published)
Website (optional)
Subject
Your Comment

Line and paragraph breaks are automatic.

Please type the characters you see in the picture:


All content Copyright © 2009-2011, Genetics of Pregnancy Encyclopedia Corporation. All rights reserved.