α-N-acetyl-D-glucosaminidase (NAG) activities were evaluated on serum samples from 67 persons in a large black family. These data were analyzed in conjunction with those from 126 previously tested unrelated blacks. After log(e) transformation, admixture analysis indicated a significantly better fit (P < .01) of a mixture of 2 normal distributions for NAG activity versus a single normal distribution. Segregation analysis using the transmission probability model of Elston and Stewart demonstrated that a genetic model fits the data better than the random 'environmental' model. Thus, the existence of a major gene is suggested in the family, although the possibility of polygenic or other familial effects cannot be ruled out. These results confirm the existence of a polymorphism for NAG reported earlier in a series of White half-sib twin families. However, the estimates of the means of the three genotypes (AA, AA', A'A') appear to differ in the two racial groups. Thus, the data suggest either a racial polygenic effect and/or different alleles segregating in the two populations. In fact, thermal stability data suggest that at least two alleles are structurally distinct. Linkage analysis of the pedigree with 20 marker loci gave no clear indication of linkage. A lod score of 1.44 was found at 0 recombination with orosomucoid (ORM).
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