Hi dear, the susceptibility to certain disease could be really reached through the study of single nucleotide polymorphisms (SNPs) known to affect the biological function of certain genes.  I think that reading this attachment may help you in understanding the point of your enquiry. 

Waiting for reply,

Thanks

Article IL-18 gene polymorphisms in aphthous stomatitis vs. Behcet's...

To label any particular disease to be genetically inherited, there should be sequence of evaluation, only at the end we can locate the factor that is making patient genetically susceptible.

1. There should be familial pattern of disease (may not be in all patients)

2. inheritence pattern of the disease should be found out (homogenous/heterogenous/etc)

3. linkage disequilibrium

4. determine the particular set of nucleotides that are transmissible and are responsible for the observed phenotype.

5. Locate the particular SNP (single nucleotide, the polymorphism of which is associated with the presence of concerned phetotype)

Even after this one may not be 100% sure whether the SNP that has been found is the real culprit itself or it is so close to the real culprit that it is transferred along with it in all gene multiplications.

Another setback could be in chronic multifactorial disease, there could be more than 1SNP that would show a combined effect. 

In this regard, i've coined a new concept of "susceptible profile" as against "susceptible gene" . A susceptible profile is where several relatively common high-risk polymorphism could be inherited by an individual giving him a cumulative high-susceptibility profile.

http://www.ijdr.in/article.asp?issn=0970-9290;year=2014;volume=25;issue=1;spage=133;epage=133;aulast=Agrawal

 Thank you. 

 Thank you.