Journal of Immunogenetics (1982) 9, 367-370.

A N E W F A S T V A R I A N T ( B P * P 0 8 ) O F T H E BF POLYMORPHISM

C . D A V R I N C H E , ~ C . R I V A T , ~ L . RIVAT-PER AN,^ M . H. C A Z E S ~ A N D A . C H A V E N T R E ~

uInstitut National de la Sante' et de la Recherche Mkdicale Bois-Guillaume, France

bInstitut National des Etudes Dbmographiques, Paris, France

(Received 6 May 1982)

S U M M A R Y

A new variant in the BF polymorphism was found in one individual from an isolate (Dogons) of Mali. I t might correspond to the expression of a new allele BF*FO8 with haemolytic activity.

I N T R O D U C T I O N

Genetic polymorphism of the B component of the alternative pathway of the human complement system was first described by Alper et al. (1972). An increasing interest in BF polymorphism study has arisen since a close linkage between the BF locus and HLA loci was found by Allen (1974). Up till now, BF polymorphism analysis among several populations has shown the existence of twelve electrophoretically-distinguishable allele products from which two, BF*S and BF*F, are the most frequent; two less common,, BF*S07 and BF*FI, and some further nine variants much rarer: *S045, *S030, *S025, *F055, *F065, *F085, *F155 (reviewed by Mauff et al., 1978), and more recently, *F129 (Larsen et al., 1981) and *F075 (Dykes et af., 1981). Under the investigation of BF typing in a Negroid population from Mali, we report here the description of a novel variant that might agree with the expression of a new allele BF*F08.

M A T E R I A L S A N D M E T H O D S

Serum samples came from a Dogon population living in the Boni rounding off Mali. Located at the North-Eastern end of the ethnical settling area, they are composed of 4000 individuals distributed on four mountainous massifs, 15 to 30 kilometers away from each other, and constitute an isolated group. Gathering of the genealogies from the whoie population has corroborated a very marked endogamy inside the group. Marriages are contracted essentially in the inside of each massif, although a moderate exchange of women between massifs was observed.

All the 457 samples of blood were taken from among the four massifs. The new variant carrier individual was from the Tabi massif, the most populated of the four.

The determination of BF phenotypes was investigated as described by Teisberg (1970) with additional slight modifications as previously reported (Davrinche et al., 198 1).

Chemin de la Breteque, 76230 Bois-Guillaume, France. Correspondence: Dr Christian Davrinche, Institut National de la Sante et de la Recherche Medicale 543,

0305-18 1 1/82/1200-0367$02.00 0 1982 Blackwell Scientific Publications

367

368 C. Davrinche et al. Individual serum samples, from which we suspected the existence of a new migrating band, were sent for identification to the International Reference Laboratory (Dr Mauff, Cologne). Functional activity of the new variant band was determined by the same laboratory using a haemolytic detection gel following isofocusing as described (Mauff, 1977).

Alleles at the B component locus (BF) were designated according to the terminology established at the meeting for an ‘International System for Human Gene Nomenclature’ in 1979 (Shows et al., 1979).

RESULTS A N D D I S C U S S I O N

The distribution of BF phenotypes in Dogons is presented in Table 1 with associated allele frequencies. Expected values from the Hardy-Weindberg law for each phenotype are in agreement with those observed (x’ = 12.8, df = 9, P > 0.10). On a large extent, the usual observation of a BF*F allele frequency higher than BF*S is confirmed as a characteristic of Negroid populations in reverse order to Caucasoid and Mongoloid ones (Benkmann el al., 1980). Previous studies among Negroid populations have revealed allele frequency values from 0.688 in Nigeria (Larsen et al., 1981) to 0.597 in Niger (Davrinche et al., 1981) for the BF*F allele. Our finding of 0.640 is in the range of previous works. As a rule, it appears that the BF*FI allele is more frequent than the *SO7 one in Negroid people. Some nine, much rarer variants have been described all over the world, from which five: *F155 (Mauff et al., 1975); *F055 (Hauptmann et al., 1976); *SO45 (Hauptmann et al., 1977); *SO25 (Scherz et af., Pausch et al., 1979); *F075 (Dykes et af., 1981) were amongst Caucasoid populations, and four others: *F065, *F085. *SO3 (Mauff el al., 1976); *F129 (Larsen et al., 198 1) amongst Negroid populations of Africa. Once more, the present study of a Negroid group from Mali has shown one individual carrying a new variant band measured as *F078 It_ 002 (1 s, n = 9) by the International Reference Laboratory and designated *F08 (Fig. 1) for the reason raised in the report on B allotype nomenclature (Mauff et al., 1978) about a limited discrimination of 0.05 for the designation of variants.

TABLE 1. Distribution of BF phenotypes in Dogons (Mali)

Observed Calculated

Phenotype n YO n % Gene frequencies

BFS BFF BFFS BFFFl BFFlS BFF 1 BFFlSO7 BFSSO7 BFFS07 BFS07

Total

39 184 184 23 10 4 1 2

10 0

457

8.53 40.26 40.26 5.03 2.19 0.87 0.22 0.44 2.19 0.00

100~00

41.13 187.19 175.49 26.9 1 12.61 0.97 0.59 3.84 8.19 0.09

457.00

9.00 BF*S =0.300 40.96 BF*F =0.640 38.40 BF*FZ ~ 0 . 0 4 6 5.89 BF*S07= 0.014 2.76 0.21 Hardy- Weindberg law 0.13 x 2 = 12.8 df=Y 0.84 P > 0.10 1.79 0.02

100,oo

BFSFO8 1

A new variant in the BFpolymorphism 369

FIG. 1. Irnmunofixation electrophoresis showing the BFSF08 phenotype.

The propositus was typed as BFSF08 and haemolytic activity of the *F08 corresponding band has been found within the normal ranges. Except for one of them, the BF*F055 allele (Mauff el al., 1980), a positive haemolytic activity has been found for all the other rare allotypes.

The genetic basis of this new *FO8 electrophoretic variant has not been demonstrated because family studies have not yet been possible. No molecular significance has been proposed yet for BF genetic variability, even for easily accessible allotypes such as BF*S, BF*F, BF*S07 and BF*FI. Further difficulties arise for the study of rare allotypes due to the fact that they are always expressed in a single dose by carrying individuals. Nevertheless, BF polymorphism usefulness is more and more evident in anthropological studies.

A C K N O W L E D G M E N T S

This work was supported by INSERM (Grant 80.10.38) and the University of Rouen.

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