[High association between properdin factors BfF1 and HLA-B 18 in a Portuguese family (author's transl)].

The HLA and the Bf systems were studied as part of a family investigation carried out in Portugal. In four generations the rare phenotype BfF1 could be determined four times and the BfF1S phenotype six times, HLA-B18 being simultaneously positive in all cases. Since the frequencies of the individual factors F1 and B18 do not differ essentially from those obtained in Central Europe and no inbreeding situation was present, the high-grade linkage disequilibrium between F1 and B18 may also be presumed for the Portuguese population. Neither among the F1/B18 homozygous nor among the heterozygous subjects could one discern any morbid state (e.g., insulin-dependent diabetes mellitus) from which an association with the F1/B18 haplotype could be deduced. Finally, the rarity of Bf factors, such as F1 and S0.7, is discussed from the standpoint of selection vs. mutation.