Segregation and linkage analysis of α‐N‐acetyl‐D‐glucosaminidase (NAG) levels in a black family

Alpha-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 [Vance et al, 1980]. After loge transformation, admixture analysis indicated a significantly better fit (P less than .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 [1971] 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 [Vance et al, 1980]. 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 [Vance et al, 1981a] 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).