The present study reports an analysis of genetic differentiation among 14 Sardinian villages located mainly in the center of the island. Chi-square tests show significant genetic heterogeneity among villages, and analyses by F- and R- statistics indicate an essentially random pattern of differentiation for all alleles. Using the kinship methods of Morton, a matrix, R, with elements rij describing the correlations between the gene frequencies of villages i and j is obtained. Use of Malécot's formula relating the rij to the geographic distances between villages shows a rapid decline of kinship with increasing distance but reveals essentially no relationship for distances over 40 km. Rotation of a two-dimensional reduction of the kinship matrix to maximum congruence with the geographic distances indicates that about 25% of the genetic distances can be accounted for by the geographic location of the villages. Isolation due in part to cultural factors, genetic drift, and special local or regional patterns of villages associations appear to be involved in the pattern of genetic variation.

The frequency of carriers of the P(a)and P(c) alleles of the gene for acid phosphatase in the erythrocyte is significantly higher in male subjects deficient in glucose-6-phosphate dehydrogenase and having hemolytic clinical favism than it is in the general population. This observation seems to indicate that alleles (P(a) and P(c)) of a gene polymorphic in all human populations affect the fitness of the involved phenotypes in special genotypic and nongenotypic conditions.

The frequency of PC allele for acid phosphatase in fourteen Sardinian villages correlates positively with the altitude and negatively with past malarial morbidity and GdMed prevalence. The susceptibility towards hemolytic favism in Sardinian males with G6PD deficiency is dependent on the erythrocyte acid phosphatase and thalassemia phenotypes. Thalassemia trait exerts a protective action only in subjects carrying PA allele for acid phosphatase. The data suggest that the gradient for malaria morbidity directly or indirectly, through interactions with thalassemia and G6PD polymorphisms, mediated by the habit of eating Vecia faba, may have had a significant role in determining the heterogeneous distribution of acid phosphatase polymorphism in Sardinia. Besides malaria, other environmental factors related with altitude seem to have been very important in shaping the present pattern of distribution of both acid phosphatase and G6PD polymorphisms in Sardinia.

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