Racial variation in the O-acetylation phenotype of human colonic mucosa

Abstract

O-acetylated and non-O-acetylated sialoglycoproteins can be distinguished by the mPAS (mild periodic acid-Schiff) histochemical technique. Individual adults show one of three different patterns of staining of large intestinal mucosa: uniformly mPAS-positive, uniformly mPAS-negative, or mPAS-negative with scattered mPAS-positive crypts. To test our hypothesis that these variations are the result of a single autosomal gene (oat) polymorphism, we have studied the frequency of the three patterns of staining in a total of 435 adult colon specimens from six geographically separate populations: British, South African blacks, Icelanders, Japanese, Hong Kong Chinese, and Bahrainis. The distribution of the three types of staining fell into two groups. In Japanese and Chinese, uniformly mPAS-positive cases were much more frequent than uniformly mPAS-negative cases; this distribution differed significantly (χ 2 P<0.001) from that in non-Sine-Japanese, where the uniformly mPAS-positive phenotype was much less frequently found than the uniformly mPAS-negative phenotype. In neither of the groups did the frequency of the three phenotypes differ significantly from that predicted for a single gene polymorphism by the Hardy-Weinberg law. The variation in staining patterns between populations is consistent with variation in frequency of a single polymorphic autosomal gene (oat) controlling O-acetylation of sialic acid, probably by an O-acetyl transferase enzyme. Loss of function mutation in the high acetylator gene (oat a) in a colonic crypt stem cell in heterozygous individuals would account for the scattered discordant crypts. Gene frequencies for a variety of enzymes differ between the Sine-Japanese and non-Sine-Japanese races. This newly described gene polymorphism may be related to differential susceptibility to organisms binding specifically to either O-acetylated or non-O-acetylated sialoglycoproteins, or to differential enteric colonization by bacterial flora that vary in their relative secretion of sialidases and sialate O-acetyl esterases.