We recently completely elucidated the molecular basis of genetic polym
orphism in human deoxyribonuclease I and found it to be controlled by
four codominant alleles, DNASE11, *2, *3 and *4. In this paper we des
cribe a novel DNase I-genotyping system that could be used directly on
DNA samples using the polymerase chain reaction (PCR) based on the th
ree nucleotide substitutions underlying the protein polymorphism. The
system consists of three independent reactions. Since the substitution
s neither suppress nor create any known enzyme recognition site in the
DNase I gene, two separate mismatched PCR followed by XhoI digestion
methods were introduced to discriminate between the DNASE11 (or *3) a
nd the DNASE12 (or *4) alleles, and to detect the DNASE1*4 allele. An
amplification refractory mutation system was employed to detect DNASE
13. A 100% correlation was found between the results of this genotypi
ng method and those obtained by phenotyping using conventional isoelec
tric focusing. The high sensitivity and specificity of this genotyping
method allows us to survey DNase I-polymorphism in small DNA samples.