ADA polymorphisms and asthma: a study in the Chinese Han population.

We have studied a sample of 120 asthmatic patients and 116 healthy control subjects from the Chinese Han population. Three polymorphic sites: ADA(1), ADA(2), and ADA(6), within the ADA gene have been examined. The proportion of carriers of *2 allele at locus ADA(1) is drastically reduced in asthmatics as compared to controls. There is an epistatic interaction of ADA(2) on the ADA(1) site characterized by a suppressive effect by the *2 allele of ADA(2) on the protective effect exerted by the *2 allele of ADA(1) site on susceptibility to asthma. Our data suggest the presence of some DNA sequences influencing the susceptibility to asthma are located in the area between ADA(1) and ADA(2) sites.